THE EFFECTS OF CAFFEINE INGESTION ON
MUSCLE CRAMP THRESHOLD FREQUENCY

A Thesis
Submitted to the Graduate Facultyof theNorth Dakota State Universityof Agriculture and Applied Science

By
Max Marvin Pagel

In Partial Fulfillment
for the Degree of
MASTER OF SCIENCE

Major Program:
Advanced Athletic Training

May 2014

Fargo, North Dakota

North Dakota State University
Graduate School
Title

The Effects of Caffeine Ingestion on Muscle Cramp Threshold Frequency
By

Max Marvin Pagel
The Supervisory Committee certifies that this disquisition complies with North Dakota State
University’s regulations and meets the accepted standards for the degree of
MASTER OF SCIENCE

SUPERVISORY COMMITTEE:

Dr. Pamela Hansen
Chair

Dr. Yeong Rhee
Dr. James Deal
Dr. Donald Miller

Approved:

05-28-2014

Dr. Margaret Fitzgerald

Date

Department Chair

ABSTRACT

Context: The effects of caffeine on muscle cramp threshold frequency were investigated.
Objective: To determine the effect of caffeine on muscle cramp threshold frequency. Design:
Randomized Trial. Experimental Design Setting: Institutional Research Laboratory.
Participants: 11 males, 6 females. Intervention: Each subject ingested different caffeine doses
over three testing days. Main Outcome Measures: Muscle cramp threshold frequency,
hemoglobin, hematocrit, plasma sodium concentration, plasma potassium concentration, plasma
chloride concentration, and osmolality were recorded. Results: There was a significant
difference between baseline and post ingestion threshold frequency as well as significant
differences between 0 mg to 500 mg and 250 mg to 500 mg. Hemoglobin, plasma potassium
concentration, and osmolality were significantly different from pre to post ingestion.
Conclusions: There was a significant difference from pre to post muscle cramp thresholdfrequency. Hemoglobin, plasma potassium concentration, and osmolality were significantly
different pre to post ingestion. The significance of these findings requires further study.

iii

ACKNOWLEDGMENTS

To Dr. Pamela Hansen, for helping me with this thesis every step of the way and to myfamily and friends for believing in me and telling me that I still looked handsome even though
my hairline kept diminishing over these past two years.

iv

TABLE OF CONTENTS
ABSTRACT…………………………………………………………………………………..iii
ACKNOWLEDGMENTS………….………………………………………………………... iv
LIST OF TABLES…………………………………………..……………………………….vii
INRODUCTION........................................................................................................................ 1
Research Question......................................................................................................... 2
Assumptions................................................................................................................... 2
Limitations..................................................................................................................... 3
Inclusion Criteria........................................................................................................... 3
Significance of Study...................................................................................................... 4
Definition of Terms........................................................................................................ 4
LITERATURE REVIEW.......................................................................................................... 6
Caffeine.......................................................................................................................... 6
Physiological Effects of Caffeine................................................................................... 7
Caffeine Effects on Aerobic Performance and Anaerobic Performance………........... 9
Muscle Cramps: Dehydration Theory…………………………………………......... 14
Muscle Cramps: Muscle Fatigue Theory .................................................................... 16
Prevention of EAMC………………………………………………………………… 19
Caffeine and Muscular Functions relating to EAMC……………………….............. 20
Summary……………………………………………………………………………...24
METHODS.............................................................................................................................. 25
Experimental Design.................................................................................................... 25
Subjects........................................................................................................................ 25v

Procedures................................................................................................................... 26
Instrumentation............................................................................................................ 28
Muscle Stimulation...........................................................................................28
Urine Analysis.................................................................................................. 29
Blood Analysis..................................................................................................29
Statistical Analysis.......................................................................................................30
MANUSCRIPT. THE EFFECTS OF CAFFEINE INGESTION ON MUSCLE CRAMP
THRESHOLD FREQUENCY………………………………………………………………. 31
Introduction..................................................................................................................31
Methods........................................................................................................................ 32
Participants...................................................................................................... 32
Instruments....................................................................................................... 33
Muscle Stimulation................................................................................... 33
Urine Analysis..........................................................................................33
Blood Analysis.......................................................................................... 34
Procedures....................................................................................................... 35
Statistical Analysis........................................................................................... 38
Results.......................................................................................................................... 38
Discussion.................................................................................................................... 41
Conclusion................................................................................................................... 44
References…………………………………………………………..………………...45
REFERENCES........................................................................................................................ 48
APPENDIX. IRB APPROVAL…………………………………………………..…............. 54vi

LIST OF TABLES
Table

Page

1. Urine Specific Gravity Specifications Prior to Intervention……………….………...... 37
2. Mean and Standard Deviations of Dependent Variables…………………………………… 40
3. ANOVA Dependent Variable Results ……………………………………….………...40
4. Caffeine Dose and Post Muscle Cramp Threshold Frequency Comparison…………...41vii

INTRODUCTION
Caffeine is the most widely consumed substance for recreational and ergogenic purposes.
Eighty-four to ninety-one percent of men and women between the ages of 18-35 consume, on
average, 238 mg per day.1 Caffeine is normally consumed in beverages such as coffee (71%), tea(16%), and soft drinks (12%).1 Soda and coffee caffeine content varies as soda contains 20-55
mg of caffeine (12 oz.)2 and coffee can contain up to 80-120 mg of caffeine (8 oz.).2 Daily
caffeine consumption varies, but has been reported to be as high as 600 mg per day.1
Caffeine ingestion causes several physiological effects such as stimulating the central andperipheral nervous systems. Caffeine has been shown to cause ergogenic effects by ingesting 23 mg/kg.3 Consuming caffeine prior to exercise improves endurance in trained cyclists,4 but
appears to have negligible effects on anaerobic performance (e.g., strength and power).5 While
ingested at rest, urine production increases,6 however when caffeine is ingested prior to exercise
or during exercise, urine production is unaffected.7,8,9 The neurological effects of caffeine is also
well documented.10,11,12 Caffeine ingestion stimulates the sympathetic nervous system,13 which
may increase resting metabolic rate and internal heat storage, leading to higher core bodytemperatures and sweat rates.13 Moreover, caffeine ingestion increases spinal excitability (i.e.
Hoffman reflex)11 and motor unit self-sustaining firing rates.12
Exercise-associated muscle cramps (EAMC) are a common injury affecting recreationaland competitive athletes.14 EAMC are thought to be caused by dehydration/electrolyte
imbalances15 and changes in neuromuscular control.16 The dehydration and electrolyte imbalance
theory proposes EAMC occur when select motor nerves become hyperexcitable due to fluid andelectrolyte losses incurred during exercise.15 The neuromuscular control theory states that EAMC

1

occur because of fatigue-induced changes to muscle spindles and golgi tendon organs whichalters alpha motor neuron activity.16
Since EAMC are unpredictable, scientists induce them in laboratory settings. Crampthreshold frequency (TF) is the minimal amount of electrical stimulation needed to elicit amuscle cramp.17 Scientists have used TF as a quantitative indicator of cramp risk.18 Individuals
with a self-reported history of muscle cramping have a lower TF than those who self-report nohistory of cramping.19 Therefore, cramp TF may be useful as a clinical tool to identify
individuals at risk of cramping and develop treatment and prevention strategies.
Because caffeine may cause diuresis13 and excitation of the peripheral nervous system,10,
11, 12

ingesting it may increase cramp risk. No scientific data exist on the effect of caffeine on

cramp TF. The purpose of this study is to determine if caffeine ingestion decreases cramp TF
and increases the likelihood of EAMC occurring in physically active individuals. This study also
determined if caffeine ingestion causes dehydration 1-hour post ingestion by looking at pre andpost blood analysis of hemoglobin, hematocrit, plasma sodium concentration, plasma potassium
concentration, plasma chloride concentration, and osmolality.
Research Question
1. Did ingesting either 0 mg (placebo), 250 mg, or 500 mg of caffeine decrease cramp TF?
Assumptions
1. An electrically induced muscle cramp (EIMC) of the flexor hallucis brevis is similar to
all EIMCs induced through the body.
2. An EIMC of the flexor hallucis brevis is the same as an EAMC of the flexor hallucis
brevis.

2

3. Caffeine consumed in a pill is the same as caffeine ingested in beverages (e.g. Red Bull,
coffee).
Limitations
1. Individuals likely consumed caffeine in beverages (e.g. energy drinks, coffee) rather thanin pills.
2. Caffeine ingestion was not specific to subject’s body mass (mg vs. mg/kg).
3. The study looked at the effects of caffeine on cramp TF at rest and not during physicalactivity.
4. Subjects self-reported a history of not having any neurological, neuromuscular,
cardiovascular, or thermoregulatory disorders especially cardiomyopathy, heartarrhythmia, heart murmur, high blood pressure, high cholesterol, and a history of heartdisease in their immediate family.
Inclusion Criteria
1. Subjects self-reported not having any neurological, neuromuscular, cardiovascular, or
thermoregulatory disorders especially cardiomyopathy, heart arrhythmia, heart murmur,
high blood pressure, high cholesterol, and a history of heart disease in their immediatefamily.
2. Male and female subjects were between the ages of 18-35.
3. Subjects were excluded if they had injured or had surgery in their dominant lower limb
within the last 12 months preceding data collection.
4. Subjects had self-reported a history of cramping within the 6 months preceding datacollection.
5. Subjects were excluded if they smoke tobacco products.
3

6. Subjects were excluded if their body mass index is ≥30 kg/m2.
7. Female subjects were excluded if they are currently taking oral contraceptives.
8. Female subjects were tested during the follicular phase of their menstrual cycle.
9. Subjects were excluded if they exercise vigorously (≥60% VO2R)22 for more than 5 days
per week.
10. Subjects avoided caffeine ingestion three days prior to data collection.
Significance of Study
This study was significant as recent literature had looked at the effects of caffeine
ingestion in physically active individuals competing in heat-stressed environments,6,7, 8
dehydration,4 and normal physiological functions.4,13 However, there is no current literature
discussing the possibilities of increased risks of EAMC following caffeine ingestion.
Definition of Terms
Caffeine (1,3,7-trimethylxanthine): common ingredient found in tea, cocoa. Acts as anergogenic aid.21
Body mass index (BMI): a number calculated from a person's weight and height indicating thepercentage of body fat. BMI= body mass (lbs.) x 703/ height (in.).2
Hoffman (H-Reflex): a monosynaptic reflex consistently obtained in normal adults only byelectrically stimulating the tibial nerve, generally in the popliteal fossa, while recordingfrom the gastrocnemius-soleus muscle group.10
Hypohydration: the state of water output exceeding water intake, resulting in a body water
deficit.21

4

Electrolyte: minerals in blood and other body fluids that carry an electric charge and affects
water volume, blood pH, muscle function, and other bodily functions.21
Euhydration: the state of being hydrated. Urine specific gravity less than or equal to 1.012.20
Glomerular filtration rate: the rate at which renal function occurs to process water absorption andexcretion.21
Golgi tendon organ: a proprioceptor located in muscle tendons that provide information aboutchanges in muscle tension.21
Muscle spindle: a proprioceptor located within muscles that provide information about changes
in muscle length.21
Sympathetic nervous system: originates in the thoracic regions of the spinal cord; opposes
physiological effects of the parasympathetic system: reduces digestive secretions; speeds
the heart; contracts blood vessels.21

5

LITERATURE REVIEWThe purpose of this study determined if caffeine ingestion decreased cramp thresholdfrequency and increased the likelihood of exercise associated muscle cramps occurring inathletes and physically active individuals. The following research question was addressed during
this study: Did ingesting 0mg (placebo), 250mg or 500 mg of caffeine decrease cramp TF?
This literature review discussed the prevalence of caffeine usage and associated factors
leading to muscle cramps. Specific emphasis was placed on the athletic population and thosethat live an active lifestyle. The following key areas regarding caffeine and muscle cramping
were discussed: Caffeine, Physiological Effects of Caffeine, Caffeine and Aerobic Performanceor Anaerobic Performance, Dehydration Theory, Muscular Fatigue Theory, Prevention of
EAMC, and Caffeine and Muscular Functions relating to EAMC.
Caffeine
Caffeine is widely used and found in natural sources such as coffee beans, tea leaves,kola nuts, bissy nuts, cacao beans, guarana, and mate.1 These natural sources of caffeine areadded to foods, beverages, herbal supplements, and medications.1 Besides food, beverages
containing caffeine are considered the gold standard of caffeine consumption.1 Soft drink
consumption in 18-35 year olds increased 11 gal/year to 49 gal/year and coffee consumption has
decreased from 16 gal/year to 9 gal/year since 2002.1 This is due to an increase of specialty
coffee, caffeinated water, and energy drink production.
Consumption is not only popular among adults (ages 18-65 years old), but children as
well. Among children, ages 2-11 years old, data showed that 36 % (5,765/15,716) consume
beverages or food containing caffeine.1 Tea and soft drink consumption was higher (mean=4.8
mg/daily, 8.0 mg/daily) in children, ages 2-5, than flavored dairy products and sweetened grains6(mean=1.0mg/daily, 1.1 mg/daily).1 Children, ages 6-11, consumed tea and soft drinks at higher
rates (mean=6.1 mg/daily, 14.7 mg/daily) compared to flavored dairy products and sweetened
grains (mean=1.7 mg/daily, 1.5 mg/daily).1 Caffeine consumption is also popular among college
age athletes (ages 18-22).1 Athletes widely consume caffeine prior to competition in regards toincreasing their focus and performance (i.e. endurance, aerobic capacity).11 In a study showing
caffeine ingestion prior to competition, 89 % of females (1,073/15,716) and 91% males(1,135/15,716) consumed either food or beverages containing caffeine.1 Coffee ingestion within
the 18-34 age group was popular (mean=111.5 mg/daily), but as age increases coffee
consumption increases (ages 35-54; mean=260.9 mg/daily).1
Widely considered for its use for increasing focus and energy, caffeine is a popularergogenic aid across the world.23 Data shows that 82-95 % of adults in the United Kingdom and
Denmark consume caffeine.23 Caffeine consumption was reported in more than 40% British
athletes in order to enhance performance.4 Research collected on Ironman World Triathlon
Championship participants showed that 89% of the athletes competing planned on using caffeine
prior to competition.23
Energy drinks and supplements that contain caffeine is popular among college-aged
individuals.1 Energy drink production reaches annual global sales near several billion dollars.24
Among the total sales, adolescents, young adults, and college-aged individuals are the top
consumer.24 American adolescents, young adults, and college-aged individuals account for 30%of the total population that consumes energy drinks.23
Physiological Effects of Caffeine
The main physiological effects of caffeine are diuresis, ergogenic aid, lipolysis, andsecondary electrolyte excretion at rest. While there are physiological effects at rest, caffeine has
7shown little to no physiological changes while exercising.7 The main physiological action ofcaffeine at rest is it acts as a diuretic.7 Diuresis is the act of increased fluid loss throughincreased urine output.7 Athletes should refrain from caffeine during exercise due to the diuretic
effect, especially in hot environments which can increase dehydration status through increased
fluid loss.7
The process of diuresis influences the kidney’s glomerular filtration rate.7 Caffeine
increases blood flow to the kidneys causing a greater glomerular filtration rate.7 Glomerular
filtration rate increases urine production.8 Grandjean et al. observed no differences in urine
volume over a 24-hour urine collection.9 Even though participants consumed various doses ofwater, caffeinated and carbonated beverages there were no significant differences between thethree groups (water, caffeinated beverages, carbonated beverages) and its effect on urine output.9
However, Millard-Stafford et al. states that consuming a caffeinated sports drink while
exercising in hot environments does not affect urine output.9 Millard-Stafford et al. studied 16
cyclists completing submaximal cycling at 60-75% VO2 max for 120 min.9 Participants were
given a placebo, carbohydrate-electrolyte, or caffeinated carbohydrate-electrolyte beverage on 3
different trials.9 The caffeinated carbohydrate-electrolyte beverage maintained hydration as wellas the carbohydrate-electrolyte beverage with no change in sweat and urine production.9
Researchers have concluded that performing submaximal prolonged exercise show no effect onurine production with consumption of a caffeinated sports drink.9
The purpose of using caffeine as an ergogenic aid has shown improvements in endurance
performance.9 The use of caffeine in endurance activities such as cycling, running, andswimming has improved overall aerobic capacity times.4 Endurance athletes are frequent usersof caffeine pre-exercise and during exercise.4 Caffeine stimulates lipolysis, the breakdown and8mobilization of free fatty acids (FFA).10 FFA utilization delays usage of muscle glycogenstores.10 Sparing muscle glycogen stores can increase performance by delaying the onset of
fatigue during prolonged endurance activities.10
Electrolyte excretion at rest is present with caffeine ingestion even though limited
research exsists.7 The diuretic effects increase urine production and results in excretion of
sodium, chloride, and potassium.7 The electrolytes are excreted due to decreased reabsorption by
the nephrons located within the kidneys.7 Del Coso et al. observed no significant change incyclists exercising in hot-dry environment.7 Seven endurance trained cyclists performed
submaximal cycling for 120 min. at 63 % of VO2 max.7 Each cyclist hydrated during exercise
by completing each trail of either hydrating 97% of total sweat loss with water, an 6%
carbohydrate-electrolyte solution, no replacement of total sweat loss, or combing the threetreatments over different testing intervals with 6 mg/kg of body mass of caffeine.7 The results
showed increased urine excretion and sweat electrolyte loss, but not enough to cause
dehydration.7
Caffeine Effects on Aerobic Performance and Anaerobic PerformanceCaffeine ingestion acts as a stimulant of the central and peripheral nervous systems byincreasing focus and attention by retaining natural energy stores (fatty free acid, carbohydrates,
etc.26 Though this is true, caffeine’s effects on performance while exercising are limited.
Limited scientific data have shown what occurs within the central and peripheral nervous
systems with caffeine ingestion during exercise.26 However, there is evidence that states
improved performance during prolonged exercise.26
As previously noted, caffeine ingestion stimulates the lipolysis.25 Lipolysis is the processof chemically breaking down lipids into FFA.25 FFA can then be utilized as energy while at rest9

or exercising.25 During exercise, FFA is utilized towards energy expenditure and spare muscle
glycogen.25 When muscle glycogen stores are depleted, fatigue and exhaustion is evident in theparticipant. Decreased time to fatigue results in spare FFA and sparing of muscle glycogenstores.25
Caffeine’s emphasis towards endurance performance proves its effectiveness as anergogenic aid.26 Lockwood et al. looked at this theory in 38 sedentary men. The men
participating were randomly assigned to Group A (exercise and energy drink) or Group B(energy drink only).26 Each participant was to drink one energy drink (12 fluid oz.) (Celsius,
Celsius, Inc., Delray Beach, Florida) for 70 days.26 Guidelines for the exercise protocol
performed by Group A were established by the standards set by the American College of Sports
Medicine (ACSM).26 Each participant completed resistance training two days per week andaerobic training 3 days per week. Body fat percentage, cardiovascular function, and strength
measures were assessed.26
The participants in Group A had significant improvements compared to Group B. Body
fat percentage showed a significant difference (p<0.05) between Group A and Group B (-2.50kg, -2.12%; +0.57 kg, +0.29% respectively).26 Cardiovascular measures improved for Group B(p=0.001) while Group A improved significantly (p≤0.010) from baseline.26 Strength measuresassessing 1-rep max in bench press and leg press improved significantly for both groups A(+11.64% and 8.14% respectively; p<0.001) and B (+9.54% and +10.72% respectively;
p=0.001).26
Walsh and his colleagues further examined the point by investigating caffeine andendurance.23 Though FFA concentration was not analyzed, the amount of work performed by
the participants was assessed.23 Work was assessed by the amount of time until exhaustion while10performing a VO2 max test.23 Fifteen subjects (9 men, 6 women) participated in a randomized
study. Each participant completed a 5 min. warm-up followed by running on the treadmill at aself-selected speed. Every 2 minutes, the inclination increases 2% while maintaining the speed.23
Caffeine ingestion at pre-exercise showed a significant difference in performance over time.
Participants consuming the energy drink supplement were able to run 12.5% longer thanparticipants that consumed the non-caffeinated beverage.23 Visual analog scales (VAS) were
established focusing on focus, energy, and fatigue.23 Participants ingesting the energy
supplement pre-exercise reported greater focus (p=0.031), energy (p=0.016), and less fatigue(p=0.005) than the non-caffeinated beverage.23 Significant differences were also shown at 10
minutes during exercise with greater focus (p=0.026) and energy (p=0.004).23 There were no
significant differences between the control and treatment groups post exercise.23
Further studies have concluded caffeine ingestion prior to exercise can improveendurance.27,28 Ivy et al. and Rutherford et al. observed cyclists over prolonged exercise bouts.2728

In both trials, cyclists that consumed caffeine (Red Bull) showed some to significant

improvements (p<.01; p>0.05).27-28 More importantly, both studies provided facts of FFA
utilization over time.27-28 Cyclists ingesting caffeine prior to exercise showed greater fatty acidoxidation, leading to increased performance.27-28 Two studies looking at the effects mentioned
above indicated that caffeine ingestion prior to exercise improves aerobic activity such as
endurance.1,13 However, caffeine ingestion prior to anaerobic conditioning shows minor to noeffects on increasing strength and power.5
The effects of caffeine ingestion on anaerobic performance are still unclear. Studies
showed that caffeine ingestion is indicative towards muscular endurance, but no correlation wasmade between caffeine ingestion and muscular force.29 Caffeine dosages varied amongst studies
11

testing for anaerobic performance.29 This research concludes that muscular endurance and focus
improves, but no cause and effect relationship between caffeine ingestion and muscular measures(e.g. peak torque, strength, power, force).24
Two studies trying to prove a theorem behind caffeine ingestion and anaerobic
performance involved 12 strength-trained males and 12 strength-trained males with 4 strengthtrained females, respectively.5,29 Both studies looked at caffeine ingestion and power measure
output while performing the Wingate cycle test and bench press repetition test.5,29 All
participants either consumed commercially available energy drinks (Red Bull, Redline Extreme)or a placebo, 60 minutes and 10 minutes pre-exercise respectively.5,29 After caffeine ingestion,
Wingate cycle test and bench press repetition test were initiated. Significant evidence wasfound, but nothing to correlate caffeine ingestion to muscular power.5,29 Red Bull ingestion
showed an increase in the number of repetitions performed (34 ± 9; placebo: 32± 8).5,29 There
was no effect on post Red Bull ingestion on peak or average power (peak power: 701± 124
watts) placebo: 700± 132 W, average power: 479± 74 W; placebo: 471± 74 W).5,29 Redline
Extreme ingestion increased focus among those consuming the beverage (3.8± 0.5) compared toplacebo (3.3± 0.7).5,29 However, there were no improvements to anaerobic power measures.5,29
Many biomechanical functions have been tested to determine cause and effect of caffeine
ingestion and anaerobic performance measures. Primary biomechanical functions scientists havelooked at include catecholamine levels and potassium.30 Catecholamine stimulates adrenaline
secretion and caffeine consumption increases adrenaline.30 Increased adrenaline levels increase
glycolytic flux, which can lead to improved endurance.30 Nonetheless, limited studies haveshown no increase in glycolytic flux when adrenaline and catecholamine levels were increased.30

12

Potassium plays a role in the excitation-contraction coupling series in muscle.30 Na+/K+
pumps are essential for depolarization of muscle cells.30 During muscle contractions, K+ diffuses
into the extracellular space creating a more negative environment.30 Caffeine has been known tostimulate K+ transport in skeletal muscle by increasing Na+/K+ ATPase activity.30 However,
little research has been done to compare K+ levels during anaerobe activity following caffeine
ingestion.30
Two physiological effects of caffeine not proven while exercising anaerobically areadenosine antagonism and pain perception.30 First, caffeine stimulates the central nervous
system primarily through adenosine receptor antagonism.30 Adenosine is regulated throughadenine nucleotide breakdown, which increases during exercise.30 Adenosine has been shown to
reduce pain perception, induce sleep, reduce arousal, and act as a neuromodulator.30 However,caffeine can inhibit the effects of adenosine.30
Adenosine receptors (A1, A2a, A2b, A3 respond to different stimuli.30 Inhibitory effects
primarily affect A1 receptors and excitatory effects primarily affect A2 receptors.30 Caffeine cancross the blood-brain barrier through simple diffusion and acts as an adenosine inhibitor.30 A1
and A2a receptors are primarily affected through caffeine ingestion as they contain more levels of
adenosine compared to A2b and A3 receptors.30 Thus leading to decreased pain perception while
maintaining motor unit firing rates.30 This is yet to be proven while exercising anaerobically.30
Second, pain perception. The logic behind pain perception is it would play a role inanaerobic performance.30 Pain perception influences motor unit recruitment by decreasing firing
rates.30 Adenosine has been shown to cause muscle pain in healthy and unhealthy subjects.30
Caffeine binds on to adenosine receptors and inhibits the acts of adenosine.30 Through simple

13

logic though unproven, caffeine’s inhibitory effects on adenosine can reduce pain perception andmaintain good motor unit recruitment.30
Caffeine is an ingredient available in over-the-counter medication such as headache
medication.30 One of caffeine’s main roles is inhibiting adenosine by binding on adenosine
receptors.30 This is a leading hypothesis in finding a correlation between caffeine and anaerobic
performance.30 Inhibition of pain signals as experienced in exercise and post-exercise, athletes
and physically-active individuals should see improvements in performance, however adenosine
pre and post caffeine ingestion levels and adenosine pre and post injury with caffeine ingestion
has few to very minimal data sources to support this premise.30
Muscle Cramps: Dehydration Theory
Exercise associated muscle cramps (EAMC) can affect healthy individuals that have noserious medical condition.31 The underlying cause of EAMC is unknown; however, there are twotheories that might help explain it: the dehydration theory and the muscular fatigue theory.15,16,31
Clinical and perceptual diagnoses of EAMC through years have been related to dehydration andelectrolyte imbalances.15,16,31 Global corporations (e.g. Gatorade, Powerade) market products
based on the premise of maintaining hydration through carbohydrate-electrolyte ingestion inhopes of decreasing chances of EAMC occurring. Proprietors in sport marketing focus ondeveloping new beverages to maintain hydration and reduce cramp risks. For years athletic
trainers and athletes have believed that EAMC occur due to electrolyte imbalances leading toclinical practices that include sport drink, pickle juice, and banana ingestion.31
According to the dehydration theory the human body does not store enough water during
exercise.31 Athletes and active individuals begin to lose water and do not consume enough waterto restore water losses.31 Water losses increase fluid and electrolyte depletion causing
14

desensitization of nerve terminals.31 Sensitization of select nerve terminals increase mechanicalpressure on motor nerve endings, resulting in an EAMC.31
Exercising in hot, humid conditions exacerbate these effects.31 EAMC and dehydration
theory data inflict cause and effect with increased fluid losses and prevalence of EAMC.31
Research has reported that 95% (87/92) of cramping occurs in hot months.31 Athletesparticipating in football were more at risk due to environmental conditions that could inquire aheat –related illness.31 Case studies and observational studies involving athletes and workers
developing EAMC were either competing or working in hot, humid environments.31
High sweat rates accompany the dehydration theory. Sodium and chloride are two mainelectrolytes lost in sweat.15 A sodium and chloride deficit occurs when an individual partakes inprolonged exercise when sodium and chloride losses are greater than salt intake.15 A 20-30%
estimated sweat loss of the Na+ pool has been seen with severe muscle cramping.15
Compensation occurs from increased plasma volume losses. Water from the interstitialspace of the body shifts to the intravascular space.15 As sweat rates continue, the interstitial fluid
becomes more contracted.15 As the interstitial compartment becomes more contracted,
neuromuscular junctions can become hyperexcitable by mechanical deformation.15 Increased
levels of acetylcholine, electrolytes, and exercise-related metabolites could trigger nerve fibers tofire or cause an end-plate current and postsynaptic potential.15 As water levels increase in theintravascular space, nerve terminals and post-synaptic membranes can be affected, prompting
cramping in various muscle fibers and bundles.15
Athletes and active individuals can develop EAMC; however, hot, humid conditions is
not the only climate prevalent in EAMC.31 Marathon runners (18%, 15/82) still develop EAMC
when competing in ambient, cool temperatures (10-12°C; 50-54°F).31 The notion of developing
15

EAMC from hot, humid environments is limitless as athletes can develop EAMC in cooltemperatures.31
Plasma and blood volume losses in those with EAMC and without EAMC had shown nosignificant difference.31 A study looking at sweat rates, sodium, and fluid losses in athletes with
EAMC and without EAMC showed no significant differences.31 Concluding the same study,
body weight losses between athletes with EAMC and without EAMC had shown significant
difference.31
More significantly, carbohydrate-electrolyte ingestion shows no difference in fluidbalance.31 The dehydration theory focuses on increased fluid and electrolyte losses.
Carbohydrate-electrolyte ingestion should restore fluid and electrolyte losses reproduced throughexercise. However, when athletes consumed carbohydrate-electrolyte beverages, 69% (9/13)
still developed EAMC post ingestion.31 EAMC and the dehydration theory has its points, but nological evidence to state that increased fluid and electrolyte losses cause EAMC.15,16,31
Muscle Cramps: Muscle Fatigue Theory
Muscle fatigue and EAMC is a well hypothesized and critical link for pathology of
EAMC. Muscle fatigue during times of fluid and electrolyte imbalances result from prolonged
exercise.15,16,31 A study investigating 1383 marathon runners were asked about the prevalence of
EAMC.16 The majority of the runners (60%, 830/1383) stated they were experiencing muscle
fatigue prior to episodes of EAMC.16 Of the 1383 runners, 26 % (536/1383) stated they had ahistory of EAMC.16 Altered muscular function leads to the next available hypothesis for EAMC.
EAMC during muscle fatigue are caused by an increased excitatory response in muscle
spindles and a decrease inhibitory response in Golgi tendon organs (GTO).15 This response leads
to abnormal alpha (α) motor neuron control and activity.15 The neural control of detecting
16

muscle tension by the GTO is disrupted and muscle contractions are unlimited.15 The afferent
activity of the muscle spindles enhances excitatory activity by causing involuntary muscle
contractions.15 The inhibitory effects of the GTO opposing an increase in excitatory activity bymuscle spindles are limited.15
Already shortened muscles while exercising are more vulnerable to muscle cramps.15
Neuromotor end-plate depolarization and GTO inhibitory activity are disrupted, especially in the
shortened position.15 Stretching can help relieve EAMC. Stretching causes tension in themuscle tendon activating the GTO, thus the inhibitory effects of the alpha motor neuron
increases creating the balance between inhibitory and excitatory activity.15,16,31
A multi-analysis looking at EAMC and muscular fatigue was done in normal college
students. One hundred fifteen college students performed maximal muscle contractions at restand during exercise.16 Eighteen percent (21/115) sustained muscle cramps prior to exercise and
26% (30/115) sustained muscle cramps after a 20-30 minute workout.16 The muscle cramps
endured in this study were tested by electromyography and were easily relieved with stretching.16
The conclusions from this study showed that muscle cramps could be caused by increased anddecreased activity originating in the central nervous system.16
Muscle fatigue has more direct cause and effect correlation with EAMC.15,16,31 A study
looked at 13 healthy men focused on EAMC and muscle fatigue. Each male participant
completed an exercise protocol designed to fatigue the gastrocnemius.16 Each participant
ingested 1.0 to 1.5 L per hour of fluids containing carbohydrates and electrolytes prior to
exercise.16 After a mean of 15 minutes, the mean sweat rate was 2.0 L per hour and mean total
fluid loss was 500 mL.16 Significant episodes of EAMC were experienced by all participants,
but sweat rate and sodium losses were not high enough to cause dehydration.16
17

Muscle fatigue and EAMC have been well documented in animal research.16,31 Though
animal research does not reflect on human purposes, it has been shown that EAMC can becaused by muscle fatigue. Muscle fatigue in animals was shown by disrupting the functional
ability of peripheral muscle receptors.16 Increased firing rate of the muscle spindle’s type Ia andII afferent was present.16 Also, a decrease in the type IIb afferent activity from the GTO waspresent.16 Therefore, a combination of the increased muscle spindle activity and decreased GTO
activity could be present during prolonged exercise.16 Results from this would be sustained αmotor neuron activity and possible EAMC.16
EAMC and muscle fatigue has more premises behind the occurrence of muscle
cramps.15,16,31 Though these premises occur, scientific data while exercising have yet to be
proven to correlate EAMC and muscle fatigue.15,16,31 Muscle injury and muscle damage fromexercise can result in a spasm causing involuntary muscle contractions.16 Decreased signals
from pain or pressure receptors could alter neuromuscular control through central nervous
system output.16 Muscle spindles and GTO would be the recipients of those alteredneuromuscular changes.16
Not only has dehydration and prevalence of EAMC been studied by amount of electrolyte
levels after exercise, but as well as total body weight loss and muscle re-education. Weight loss
levels near 3 % hypohydration and near 5 % hypohydration have shown no effect on EAMC
threshold frequency from pre to post threshold frequency.32,33 Through these total body water
losses, it is also concluded that electrolytes prevalent in sweat and perspiration lost during
exercise has shown no effect on those with a self-reported history of EAMC during prolonged
exercise.34,35,36,37 Finally, a case study looked at the effect of muscle re-education by properly
training and eliciting the correct firing sequence.38 The patient suffered from bilateral episodes18

of EAMC in his gastrocnemius during prolonged training for triatholons.38 The patientunderwent initial electrolyte replacement therapy via enhanced diet and continued to have boutsof EAMC. The patient began physical therapy focusing on strengthening his core, with emphasison his glute and pelvic girdle muscles.38 After three months of therapy, the patient began to train
and never had one episode of EAMC occur while obtaining personal record times.38
Muscular fatigue and EAMC are more prevalent than EAMC and dehydration. EAMC
has occurred in many athletes and workers, but the evidence comes from case studies, clinicalobservations, and a case-control study.16,31 Studies focusing on EAMC show that while working
in hot, humid environments, cramp risks increase.16,31 The observations were not tested andscientific data are irrelevant for a majority of this theory.
Evidence supporting muscle fatigue theory was reported in humans inducing muscle
cramps. Spinal reflex activity measuring type I, type IIa, and type IIb afferents in animals
provides significant data.16,31 Field studies measuring electromyography were recorded inhumans during and after fatiguing exercise that induced muscle cramps.16 While there are morethings to be resolved, muscle fatigue and EAMC acts as the main physiological response of
EAMC in comparison to dehydration and electrolyte imbalances.15,16,31
Prevention of EAMC
Treatment and prevention methods of EAMC contain aspects from both theories.
Ingesting fluids high in electrolytes is a common practice for treatment of EAMC.31 Many sport
drinks do not contain the necessary amount of electrolytes in order to replace the electrolyte
losses through sweat.31 The National Athletic Trainers Association (NATA) recommends adding
0.3-0.7 g/L of sodium to your drink in order to reduce the occurrence of muscle cramps.39
Further recommendations is adding one-quarter teaspoon of salt to 500 cc of water.40
19Ingesting fluids for immediate treatment for cramps have been misconceived. Mustard,
pickle juice, bananas, dextrose have been used for immediate treatment for EAMC.40 However,ingesting these substances have not shown to alleviate EAMC.21 It has been shown that fluids
and electrolytes are not absorbed immediately.31 Even hypotonic fluids have been shown to beabsorbed into the circulatory system after 13 minutes.31 Beyond increasing carbohydrateelectrolyte ingestion, stretching is a common mode of treating EAMC. Stretching is an effective
remedy for treating EAMC and is one the more widely used practices in treating EAMC.31,40
Common practices are available to prevent occurrence of EAMC. Acclimation toenvironmental temperatures compliments the dehydration theory.40 Ingesting at least one liter of
fluids (e.g. water, sports drink) prior to competition prompts proper absorption of fluids andavailability of electrolytes and nutrients for any chance of EAMC.31 During competition,
consumption of powder and gel supplements may boost depleted electrolytes stores and reducethe chance of EAMC.40
Performing exercises targeting the neuromuscular system compliments the muscularfatigue theory. Exercises activating the muscle spindles and GTO receptors can be implemented
to reduce muscular fatigue.31 Plyometric exercises implemented into an athlete’s regimen elicit
adaptations in muscle spindle and GTO receptor firing sequences controlling the neuromuscularsystem.31 Endurance training also serves a purpose in neuromuscular control by increasingplasma volume and extracellular fluid during exercise.31 Therefore, increasing endurance andplyometric training can delay neuromuscular fatigue.31
Caffeine and Muscular Functions relating to EAMC
Caffeine and prevalence of muscle cramps have not been shown to elicit neuromuscularchanges after ingestion. However, a case study regarding abundant use of caffeine on a daily
20basis eventually led to frequent cramping episodes.41 The patient from the following caseingested caffeinated pills (Finimal) six to seven times a day, four cups of coffee, and two cups oftea daily.41 Upon ingestion of beverages and pills, the patient smoked 10 cigarettes daily.41
The patient had recurrent muscle cramps at night. Reflecting on the patient’s use of
caffeine, scientists performed a double-blind study prescribing varying doses of caffeine to thepatient. Through one week of testing, the patient reported back to the scientist. Patient’svulnerability of muscle cramping increased when the dosage exceeded 600 mg.41 Below 600 mg
of caffeine, the occurrence of cramping dispersed to no episodes of cramping.41
Caffeine and neuromuscular patterns provide a greater insight on possible eventsoccurring between caffeine ingestion and EAMC. Scientists have found some key points onneuromuscular patterns following caffeine ingestion. Even though research around caffeine
ingestion and EAMC are limited, caffeine ingestion and neuromuscular patterns explain somepossible points of what could occur with caffeine and EAMC. One theory that can be made is
the Hoffman Reflex or H-reflex.
The H-reflex is an electrically induced reflex that is similar to an mechanically induced
spinal stretch reflex.42 The difference between the H-reflex and a spinal stretch reflex is the Hreflex bypasses the muscle spindle allowing assessment of monosynaptic reflex activity
occurring in the spinal cord.42 The H-reflex is an estimate of alpha motor neuron excitability
when presynaptic inhibition and intrinsic excitability of the alpha motor neurons are constant.42
The H-reflex is a tool to assess the nervous system during application of many neurologicalconditions.42
The H-reflex has been known to decrease in amplitude post exercise.10 Scientists havefound that the H-reflex remains at the same amplitude, but the state anxiety after exercise
21

increases post caffeine ingestion.10 State anxiety is described as the amount of tension within themuscle assessed by the H-reflex post exercise.10 Motl and Dishman observed 16 participants
cycling at 60% of VO2Peak.10 H-reflex and state anxiety were assessed before and one hour post
caffeine ingestion as well as 10 minutes and 30 minutes post cycling. No changes in theamplitude of the H-reflex was shown, but state anxiety increased after caffeine consumption.10
The clinical application of the H-reflex can relate to sport-specific conditions. H-reflex
measurements can assess the excitability actions occurring within the spinal cord. Assessing thisby using the H-reflex can associate excitability levels and muscular fatigue. Walton, Kalmar,
and Cafarelli11 noted this action between caffeine and H-reflex. Seven subjects were either given
caffeine (6 mg/kg) or placebo-filled capsules.11 Assessments by stimulating the tibial nerve weremade pre-ingestion and one hour post-ingestion. Excitatory function of the spinal cord increased
43±17% (P<0.05) showing increased excitability following caffeine ingestion.11
H-reflex and caffeine ingestion is documented, as well as caffeine ingestion and skeletal
muscle function. Caffeine’s effect on adenosine and the sarcoplasmic reticulum questions itsrole in human skeletal muscle. Caffeine inhibits the actions of adenosine increasing excitatoryneurotransmitter release by lowering the threshold for neuronal activity.11 Caffeine also increases
calcium permeability within the sarcoplasmic reticulum allowing the contraction mechanism to
be readily available.43
These observations are well documented and proven to occur in human skeletal muscle.
Walton, Kalmar, and Cafarelli12 observed this change in humans. Their main premise wasobserving self-sustained firing (SSF) in human motor units.12 SSF is the continued firing of a
motor neuron following a recruitment by a synaptic excitation during a constant, maybe
decreasing, level of synaptic drive.1222Caffeine’s inhibition effects on adenosine causes other neurologic processes.12 Serotonin
and noradrenaline increase following adenosine inhibition.12 Serotonin and noradrenaline
facilitate as neurotransmitters allowing plateau potentials in SSF to occur.12 By ingesting
caffeine, increases should be show during SSF function in motor units.12
Stimulation of the tibialis anterior motor units performed by Walton et al.12 provided
clarity in this premise. Two hundred-fourteen trials among seven male participants showed anincrease in SSF (P<0.05).12 The caffeine group had a significantly higher SSF (87.0±5.8%) thanthe placebo group (64.6±9.7%).12 Although this showed the effects of caffeine on SSF, further
research needs to be conducted to conclude this fact between SSF and caffeine ingestion.
Effects of caffeine ingestion on neuromuscular function have mixed results. While thereis evidence to point to caffeine ingestion causing effects on neuromuscular function, Kalmar44
shows that there is something greater to the concept of caffeine ingestion and neuromuscularfunction. Kalmar notes that the effects of caffeine has some general points on neurologicalmodulation, but there is no empirical evidence stating the effects of caffeine on neuromuscularfunction.44 The effects of caffeine at the spinal and supraspinal level have been noted in somestudies, but no direct cause and effect relationship between caffeine and neuromuscular function
exists at the time of this research, but limited research has been done since 2005.44
Research purposing a relationship between caffeine ingestion and neuromuscularfunction is slightly outdated (1999), but provides a good insight on what can occur. Kalmar andCafarelli45 induced electrical stimulation of the tibial nerve following caffeine ingestion (6mg/kg).45 Maximum voluntary contraction of the knee extensors and maximal H-reflexes of thesoleus were assessed.45 Maximum voluntary contraction increased 3.50±1.01% (P<0.01), but nochange in H-reflex amplitude was shown.45 Therefore, caffeine increased excitatory responses at23

the supraspinal level.45 The effect of the caffeine did not reach the spinal level, which could
dismay the fact that the caffeine had any role at all in causing altering neuromuscular function.45
Summary
EAMC is prevalent among all populations, especially athletes and individuals living anactive lifestyle. Many athletes and active individuals consume caffeine on a regular basis inefforts to increase mood, focus, alertness, and possibly performance. Caffeine is shown toincrease endurance during prolonged exercise, however no conclusive evidence states acorrelation between caffeine and improvements in anaerobic performance (e.g. strength, power,
torque). Physiological aspects of caffeine ingestion at normal doses include diuresis, increased
thermoregulatory function, and possibly altered neuromuscular alteration. Therefore, EAMC
should be more prevalent and the likelihood should increase during exercise. Furthermore, moreevidence of caffeine usage prior to exercising needs to be concluded.

24

METHODS
The purpose of this study determined if caffeine ingestion decreased cramp thresholdfrequency and increased the likelihood of exercise associated muscle cramps occurring inathletes and physically active individuals. The following research question was addressed during
this study: Did ingesting 0 mg (placebo), 250 mg or 500 mg of caffeine decrease cramp TF?
Experimental Design
A 2x3 factorial crossover design guided data collection. The order of treatments wererandomized and counterbalanced with a Latin square. The dependent variable was flexor hallucis
brevis cramp threshold frequency (TF). Threshold frequency was measure in hertz. The
independent variable was caffeine dosage (0 mg, 250 mg, and 500 mg). Caffeine consisted of apowder and was inserted into an ingestible capsule. Hematocrit, hemoglobin, plasma sodium
concentration, plasma potassium concentration, plasma chloride concentration, and osmolality
were identified and analyzed for any change in hydration status prior to and post-caffeine
ingestion respectively.
Subjects
A convenience sample of 11 male and 6 female participants detecting a significant
difference in caffeine ingestion and EAMC (P<0.05) with a self-reported history of muscle
cramping within the last six months prior to data collection was recruited by word of mouth andsocial media advertisement. Exclusion criteria for subject’s participation consisted of 1) injury or
surgery to the dominant limb within the last 12 months; 2) any neurologic, cardiovascular, orneuromuscular condition/disease; or 3) not between the ages of 18-35. All subjects provided awritten informed consent and the study was reviewed and approved by the North Dakota State
University Institutional Review Board prior to data collection.
25

Procedures
Participants reported to the Research Lab (BBF 14) and were instructed to maintain theircurrent diet, water intake, and refrain from strenuous exercise for the next 24 hours. A baseline
TF was established with each subject on the first day. The participant was informed by readingand providing a written informed consent and fill out the health history questionnaire prior tobaseline testing. Concluding the health questionnaire the subject was given a detailed brochureon what they can and can’t consume for the next 72 hours. The brochure listed foods andbeverages that contained caffeine or caffeine substitutes.
The participant laid supine on the table. Preparation of the participant’s dominant lower
limb occurred once their weight had been taken. Dominant lower limb selection was done byasking the participant if they were to kick a ball, what leg would they use to kick the ball. To
determine the exact location of the flexor hallucis brevis, participant was asked to dorsiflex the
1st ray. The co-investigator marked the joint space in between the distal phalanx and metatarsalof the 1st ray, the joint space of the 1st metatarsal, and the 1st cuneiform. Hair was removed
around the tibial tuberosity depending on the participant. Then the following areas were debrided
using fine sandpaper: 1) tibial tuberosity, 2) medial plantar aspect of the mid 1st metatarsal, and3) medial malleolous. Isopropyl alcohol was applied to the same areas following debridement of
the fine sandpaper. The 1st metatarsal was dorsiflexed and 2- 8mm Ag-AgCl electrodes (Biopac
Systems, Inc.) over the flexor hallucis brevis was applied. Inter-between electrodes was be 2 cm.
The co-investigator located the tibial pulse and applied a mark for tibial nerve. The coinvestigator began the stimulation of the tibial nerve to find a strong, yet proper contraction. The
flexor hallucis brevis contraction should not be felt in the heel by the participant. The coinvestigator also noted the involuntary flexion of the big toe. A dispersive electrode was applied26

to the lateral malleolous while the stimulating electrode was applied along the medial malleolous
to stimulate the tibial nerve. While trying to identify the tibial nerve, the area was stimulated 2-4
times with a 1-ms electrical stimulus to determine the exact location of the tibial nerve. Once
located, the stimulating electrode was re-applied with tape to secure the correct location and thedispersive electrode was secured with an elastic wrap.
The participant was advised of types of sensations and would receive electricalstimulation beginning at 80-V trains at 2 second bursts per minute. Each participant began with 4
Hz. Each participant increased the electrical stimulation they receive by 2 Hz from the previous
stimulation. Over a 2 second period, the participant received 8 electrical bursts. If the participant
did not cramp after the bout of stimulation, the participant rested for one minute. This processcontinued until a muscle cramp occurred.
A muscle cramp must meet the following criteria: 1) involuntary contraction of the flexor
hallucis brevis immediately after electrical stimulation resulting in great toe flexion and 2) the
participant states they are having a cramp. Cramp TF was recorded at baseline and after eachcaffeine ingestion trial. Each participant was asked to perform this task over three testing days
with 48 hours in between each testing session. Each day included dosages of caffeine (0 mg, 250
mg, 500 mg) administered in random order and was ingested one hour prior to the stimulation
bouts. On each testing day, the participant was asked to empty their bladder and provide the coinvestigator a collected urine sample. Subjects with a urine specific gravity of 1.020 or less canbe determined as euhydrated and begin the equilibration stage. If the urine sample was greaterthan 1.020, the participants would ingest 3 mL/kg of water and rest for 30 minutes to allow water
absorption. Urine specific gravity was re-assessed until the participants had reached aeuhydrated state.
27

Following urine analysis, the subject laid supine to begin the equilibration stage for 30
minutes. This would allow the body’s internal fluid compartments to balance and provide aproper blood sample. After 30 minutes, a venous catheter was inserted in the subject’s forearmvein and a 5 mL sample was drawn. The subject picked a number out of a hat which included
either a 1, 2, 3, 4, 5, or 6. The number correlates with the sequence relating to the dosage orderbalanced via Latin Square and ingested by subject over the three testing days.
Once the first blood draw had been performed and the subject’s dose sequenceestablished, the subject was given their first dose. The subject would either ingest 0 mg, 250 mg,
or 500 mg of caffeine depending on their selected dose sequence. Caffeine doses were blinded
for all participants and ingested one hour prior to the stimulation bouts. After 1 hour, a second
blood sample was drawn and a urine sample collected if subject needed to empty their bladder.
The subject then began the stimulation bout. The results were recorded following the subject’s
maximal cramp threshold frequency. The subject did this over a course of three days and wascompensated following their last testing day.
Instrumentation
Muscle Stimulation
An 8 mm Ag-AgCl shielded active electrode and an 8 cm2 dispersive electrode wereapplied to the foot of each participant.46 The muscle action potential of the flexor hallucis brevis
was collected using the MP150 analog-to-digital data acquisition system with AcqKnowledge
software (version 3.7.3; Biopac Systems Inc.).46 Signals were amplified using the TEL 100C
(Biopac Systems, Inc.) with a gain set to 5000 from disposable, long-term recording electrodes
with a center-to-center interelectrode distance of 2 cm.46 The EMG signals were sampled at2000 Hz.1 The total EMG recording consisted of 1 second of resting activity, 2 seconds of28

stimulation, and 12 seconds of post stimulus activity (cramping).46 The train (bouts ofstimulation) of the electrical stimuli were delivered to the tibial nerve by a Grass S88 stimulator
and SIU5 Stimulation Isolation Unit (Astro-Med, Inc., West Warwick, RI).1
Urine Analysis
Urine specific gravity was measured with a handheld refractometer (SUR-Ne; Atago
USA Inc., Bellevue, WA). A specific gravity less than or equal to 1.020 indicated subject’s stateof euhydration.20 If specific gravity was greater than 1.020, the subject would continue tohydrate on testing day until their specific gravity was less than or equal to 1.020.
Blood Analysis
Hematocrit, hemoglobin, plasma sodium concentration, plasma potassium concentration,
plasma chloride concentration, and osmolality were measured by conducting venipuncture of
subject’s antecubital region. The subject’s antecubital region was sterilized with alcohol andone, single-use, 20-gauge venous catheter (BD, Sandy, UT) was inserted into a superficial
forearm vein. The catheter was attached to a 3-way stopcock (Tyco Healthcare Group LP,
Mansfield, VA) with extension tubing (B. Braun Medical Inc., Bethlehem, PA). A 5 mL blood
sample was drawn. Four mL of whole blood was drawn into a 6 mL lithium heparin vacutainer(BD, Franklin Lakes, NJ) and chilled in a crushed-ice bath until the last blood sample wasdrawn. To measure hematocrit, about 1 mL from the 5 mL sample of whole blood was drawn
into heperanized microcapillary tubes and centrifuged at 3000 rpm for 5 minutes (IEC MicroMB; IEC, Needham Heights, MA). The final hematocrit was read using a microcapillary reader(IEC 2201; Damon/IEC, Needham Heights, MA). Hemoglobin was measured by mixing 20 µLof whole blood with 5 mL of cyanmethemoglobin reagent. The sample was read with a standard

29

spectrophotometer at 540 nm (iMark; Biord, Hercules, CA). Hemoglobin and hematocrit were
sampled and measured for each time for reliable measures.
The remaining 4 mL of whole blood was centrifuged at 3000 rpm for 15 minutes at 3°C(5804; Eppendorf North America Inc., New York, NY) and plasma was drawn from the red
blood cells. Plasma osmolality was determined with freezing point depression osmometry (3D3;
Advanced Instruments Inc., Norwood, MA). Plasma electrolyte concentrations were measured
two times using an ion-sensitive electrode system (NOVA 16; NOVA Biomedical, Waltham,MA).
Statistical Analysis
Means and standard deviations were calculated and used for statistical analysis with thefactors being time and dose. A two-way analysis of variance (ANOVA) was used to determine
the effect of caffeine dosages on cramp threshold frequency, pre and post hemoglobin,
hematocrit, plasma sodium concentration, plasma potassium concentration, plasma chloride
concentration, and osmolality. If significant F-values were noted through two-way analysis ofvariance, Tukey-Kramer post hoc tests and one-way analysis of variance (ANOVA) for eachdose were used to identify significant differences between baseline muscle cramp TF and post
caffeine ingestion muscle cramp TF as well as pre and post hemoglobin, hematocrit, plasma
sodium concentration, plasma potassium concentration, plasma chloride concentration, andosmolality. The α-level was set at 0.05 (SPSS: 20th edition; Pearson Education Inc., Upper
Saddle River, NJ).

30

MANUSCRIPT. THE EFFECTS OF CAFFEINE INGESTION ON MUSCLE CRAMP
THRESHOLD FREQUENCY

Introduction
Caffeine is the most widely consumed substance for recreational and ergogenic purposes.
Eighty-four to 91 percent of men and women between the ages of 18-35 consume, on average,
238 mg of caffeine per day.1 Caffeine is normally consumed in beverages such as coffee (71%),tea (16%), and soft drinks (12%).1 The caffeine in soda and coffee varies as soda contains 20-55
mg of caffeine (12 oz.)2 and coffee contains up to 80-120 mg of caffeine (8 oz.).2 Daily caffeine
consumption varies, but it has been reported to be as high as 600 mg per day in adults ages 1835.1
Caffeine ingestion causes several physiological effects such as stimulating the central andperipheral nervous systems. Caffeine has been shown to cause ergogenic effects ingesting 2-3
mg/kg.3 Consuming caffeine prior to exercise improved endurance in trained cyclists,4 but it
appeared to have negligible effects on anaerobic performance (e.g., strength and power).5 Wheningested at rest, urine production increased;6 however, when caffeine was ingested prior to
exercise or during exercise, urine production was unaffected.7,8,9 The neurological effects ofcaffeine are also well documented.10,11,12 Caffeine ingestion stimulates the sympathetic nervous
system,13 which may increase resting metabolic rate and internal heat storage, leading to higher
core body temperatures and sweat rates.13 Moreover, caffeine ingestion increases spinal
excitability (i.e. Hoffman reflex)11 and motor unit self-sustaining firing rates.12
Exercise associated muscle cramps (EAMC) are a common injury affecting recreationaland competitive athletes.14 EAMC are thought to be caused by dehydration/electrolyte
imbalances15 and changes in neuromuscular control.16 The dehydration and electrolyte imbalance31theory proposes EAMC occur when select motor nerves become hyperexcitable due to fluid andelectrolyte losses incurred during exercise.15 The neuromuscular control theory states that EAMC
occur because of fatigue induced changes to muscle spindles and golgi tendon organs whichalters alpha motor neuron activity.16
Since EAMC are unpredictable, researchers induce them in laboratory settings. Crampthreshold frequency (TF) is the minimal amount of electrical stimulation needed to elicit amuscle cramp17 and is used as a quantitative indicator of cramp risk.18 Individuals with a selfreported history of muscle cramping have a lower TF than those who self-report no history ofcramping.19 Therefore, cramp TF may be useful as a clinical tool to identify individuals at risk ofcramping and develop treatment and prevention strategies. Because caffeine may cause diuresis13
and excitation of the peripheral nervous system,10, 11, 12 ingesting it may increase cramp risk. No
scientific data exist on the effect of caffeine on cramp TF.
The purpose of this study determined if caffeine ingestion decreased cramp thresholdfrequency and increased the likelihood of exercise associated muscle cramps occurring inphysically active individuals. This study also determined if caffeine ingestion causes
dehydration 1-hour post ingestion by looking at pre and post blood analysis of hemoglobin,
hematocrit, plasma sodium concentration, plasma potassium concentration, plasma chloride
concentration, and osmolality. The following research question was addressed: Did ingesting
either 0 mg (placebo), 250 mg, or 500 mg of caffeine decrease cramp TF?
Methods
Participants
A convenience sample of 11 male and 6 female healthy, physically active participants(females; age: 22.16 ± 2.32 years, height: 166.37 ± 9.32 cm, weight: 64.86 ± 15.82 kg, males;32age: 22.72 ± 4.05 years, height: 178.49 ± 9.30 cm, weight: 84.95 ± 12.67 kg) with a self-reported
history of muscle cramping within the last six months prior to data collection was recruited byword of mouth and social media advertisement. Exclusion criteria for subject’s participationconsisted of 1) injury or surgery to the dominant limb within the last 12 months; 2) any
neurologic, cardiovascular, or neuromuscular condition/disease; or 3) not between the ages of
18-35. All subjects signed an informed consent and our study was approved by the Institutional
Review Board prior to data collection.
Instruments
Muscle Stimulation
An 8 mm Ag-AgCl shielded active electrode and an 8 cm2 dispersive electrode wereapplied to the dominant foot of each participant.20 The muscle action potential of the flexor
hallucis brevis was collected using the MP150 analog-to-digital data acquisition system with
AcqKnowledge software (version 3.7.3; Biopac Systems Inc.).20 Signals were amplified using the
TEL 100C (Biopac Systems, Inc.) with a gain set to 5000 from disposable, long-term recording
electrodes with a center-to-center interelectrode distance of 2 cm.20 The EMG signals were
sampled at 2000 Hz.1 The total EMG recording consisted of 1 second of resting activity, 2seconds of stimulation, and 12 seconds of post stimulus activity (cramping).20 The train (bouts ofstimulation) of the electrical stimuli was delivered to the tibial nerve by a Grass S88 stimulator
and SIU5 Stimulation Isolation Unit (Astro-Med, Inc., West Warwick, RI).1
Urine Analysis
Urine specific gravity was measured with a handheld refractometer (SUR-Ne; Atago
USA Inc., Bellevue, WA). A specific gravity less than or equal to 1.020 indicated the subject’s

33

state of euhydration. If specific gravity was greater than 1.020, the subject would continue tohydrate on testing day until their specific gravity was less than or equal to 1.020.
Blood Analysis
Hematocrit, hemoglobin, plasma sodium concentration, plasma potassium concentration,
plasma chloride concentration, and osmolality were measured by conducting venipuncture of
subject’s antecubital region. The subject’s antecubital region was sterilized with alcohol andone, single-use, 20-gauge venous catheter (BD, Sandy, UT) was inserted into a superficial
forearm vein. The catheter was attached to a 3-way stopcock (Tyco Healthcare Group LP,
Mansfield, VA) with an extension tubing (B. Braun Medical Inc., Bethlehem, PA). A 5 mL
blood sample was drawn. Four mL of whole blood was drawn into a 6 mL lithium heparinvacutainer (BD, Franklin Lakes, NJ) and chilled in a crushed ice bath. To measure hematocrit,
approximately 1 mL from the 5 mL sample of whole blood was drawn into heparinized
microcapillary tubes and centrifuged at 3000 rpm for 5 minutes (IEC Micro-MB; IEC, Needham
Heights, MA). The final hematocrit was read using a microcapillary reader (IEC 2201;
Damon/IEC, Needham Heights, MA). Hemoglobin was measured by mixing 20 µL of whole
blood with 5 mL of cyanmethemoglobin reagent. The sample was read with a standard
spectrophotometer at 540 nm (iMark; Biorad, Hercules, CA). Hemoglobin and hematocrit was
sampled and measured twice each time for reliability.
The remaining 4 mL of whole blood was centrifuged at 3000 rpm for 15 minutes at 3°C(5804; Eppendorf North America Inc., New York, NY) and plasma was drawn from theseparated red blood cells. Plasma osmolality was determined with freezing point depression
osmometry (3D3; Advanced Instruments Inc., Norwood, MA). Plasma electrolyte

34

concentrations were measured two times for each sample using an ion-sensitive electrode system(NOVA 16; NOVA Biomedical, Waltham, MA).
Procedures
Participants reported to the Research Lab and were instructed to maintain their current
diet, water intake, and refrain from strenuous exercise for the next 24 hours. A baseline TF wasestablished with each subject on the first day. The participants were informed of the testingprocedures and signed an informed consent and filled out the health history questionnaire. Next
the subject was given a detailed brochure on what they could and couldn’t consume for the next
72 hours. The brochure listed foods and beverages that contained caffeine and caffeine
substitutes.
To determine baseline muscle cramp TF the participant laid supine on the table.
Preparation of the participant’s dominant lower limb occurred once their height and weight had
been taken. To determine the exact location of the flexor hallucis brevis on the subjects dominate
leg, participants were asked to dorsiflex the 1st ray. The joint space between the distal phalanx
and metatarsal of the 1st ray, the joint space of the 1st metatarsal, and the 1st cuneiform weremarked for electrode placement. If necessary, hair was removed around the tibial tuberosity andthe following areas were debrided using fine sandpaper: 1) tibial tuberosity, 2) medial plantar
aspect of the mid 1st metatarsal, and 3) medial malleolous. Isopropyl alcohol was applied to thesame areas following debridement of the fine sandpaper. The 1st metatarsal was dorsiflexed and2- 8mm Ag-AgCl electrodes (Biopac Systems, Inc.) were applied over the flexor hallucis brevis.
Inter-between distance for the electrodes was 2 cm.
The tibial pulse was located and marked to identify the tibial nerve. Stimulation bursts tothe tibial nerve were used to identify a strong, yet proper contraction of the flexor hallucis brevis.
35While trying to identify the tibial nerve, the area was stimulated 2 to 4 times with a 1-ms
electrical stimulus to determine the exact location of the tibial nerve. A dispersive electrode wasapplied to the lateral malleolous while the stimulating electrode was applied along the medial
malleolous to stimulate the tibial nerve. Once located, the stimulating electrode was re-appliedwith tape to secure the correct location and the dispersive electrode was secured with an elastic
wrap.
The participants were advised of the various types of sensations and received electricalstimulation beginning at 80-V trains at 2 second bursts per minute. Each participant began with 4
Hz. The participant’s amount of electrical stimulation increased by 2 Hz with each unsuccessful
bout that provided no sign of a muscle cramp. Over a two-second period, the participant received
eight electrical bursts. If the participant did not cramp after the bout of stimulation, theparticipant rested one minute. The process continued until the muscle cramp occurred.
A muscle cramp met the following criteria: 1) involuntary contraction of the flexor
hallucis brevis immediately after electrical stimulation resulting in great toe flexion and 2) the
participant stated they had a cramp. Cramp TF was recorded at baseline (day 1) and after eachcaffeine ingestion trial (days 2, 3, 4). On the first caffeine ingestion trial, the participant picked anumber out of a hat which included 1, 2, 3, 4, 5, or 6. The number correlated with a sequence
relating to the dosage order balanced via Latin Square and ingested by the participant over thethree testing days. Each participant ingested 0 mg (placebo), 250 mg, and 500 mg of caffeine
and performed this process over the three caffeine ingestion days with 48 hours between eachsession. Caffeine doses were blinded for all participants and ingested one hour prior to thestimulation bouts.

36On each testing day, the participant was asked to empty their bladder and provide a urine
sample. Participants with a urine specific gravity of 1.020 or less were determined as euhydrated
and began the equilibration stage. If the urine sample was greater than 1.020, the participants
ingested 3 mL/kg of water and rested for 30 minutes to allow water absorption. Urine specificgravity was re-assessed until the participants reached a euhydrated state. Table 1 shows
specifications on each subject’s urine specific gravity for each testing days.
Table 1. Urine Specific Gravity Specifications Prior to Intervention.
Urine Specific
Gravity(Subjects)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

0 mg Caffeine(n=17)

250 mg Caffeine(n=17)

500 mg Caffeine(n=17)

1.008
1.010
1.012
1.009
1.005
1.019
1.015
1.020
1.017
1.018
1.012
1.014
1.020
1.011
1.019
1.020
1.010
*1.014 ± .004

1.009
1.010
1.012
1.013
1.020
1.007
1.020
1.005
1.020
1.020
1.019
1.020
1.017
1.018
1.020
1.013
1.009
*1.014 ± .005

1.009
1.012
1.010
1.011
1.011
1.017
1.016
1.020
1.015
1.017
1.020
1.020
1.011
1.018
1.020
1.020
1.011
*1.015 ± .004

*Values are Means ± SD

Following urine analysis, the participants laid supine and began the equilibration stage
for 30 minutes. This allowed the body’s internal fluid compartments to balance and provide aproper blood sample. After 30 minutes, a venous catheter was inserted in the subject’s forearmvein and 5 mL of blood was drawn.
37

Once the first blood draw had been performed and the participant’s dose sequenceestablished, the participant was given his/her first dose. The participant either ingested 0 mg,
250 mg, or 500 mg of caffeine depending on their selected dose sequence. The participant
ingested the dosage immediately and continued to lay supine for one hour. After one hour, asecond blood sample was drawn followed by the muscle stimulation bout. The results wererecorded following the participant’s maximal cramp threshold frequency. The participant
repeated this procedure over the course of three testing days and was compensated on their last
testing day.
Statistical Analysis
Means and standard deviations were calculated and used for statistical analysis with thefactors being time and dose. A two-way analysis of variance (ANOVA) was used to determine
the effect of caffeine dosages on cramp threshold frequency, pre and post hemoglobin,
hematocrit, plasma sodium concentration, plasma potassium concentration, plasma chloride
concentration, and osmolality. If significant F-values were noted through two-way analysis ofvariance, Tukey-Kramer post hoc tests and one-way analysis of variance for each dose were used
to identify significant differences between baseline muscle cramp TF and post caffeine ingestion
muscle cramp TF as well as pre and post hemoglobin, hematocrit, plasma sodium concentration,
plasma potassium concentration, plasma chloride concentration, and osmolality. The α-level was
set at 0.05 (SPSS: 20th edition; Pearson Education Inc., Upper Saddle River, NJ).
Results
Ingesting 0 mg, 250 mg or 500 mg of caffeine increased muscle cramp thresholdfrequency. Means and standard deviations for all dependent variables are found in Table 2;
results of ANOVA’s for caffeine dose are found in Table 3. For muscle cramp threshold
38

frequency, a significant time by dose interaction was found. Follow-up analysis showed that, ateach dosage level, post-test threshold frequency was significantly higher than baseline. In
addition, when post-test cramp threshold was compared across the three dosages, there was asignificant difference from 0 mg to 500 mg and 250 mg to 500 mg. There was no significant
difference found between 0 mg and 250 mg with post-test cramp threshold frequency (see Table
4).
For hemoglobin, plasma potassium concentration, and osmolality, a significant main
effect was also found for time. Hemoglobin, plasma sodium concentration, and osmolality
showed significant increases from pre to post caffeine ingestion for all three doses, with the
exception of hemoglobin decreasing from pre to post caffeine ingestion at 0 mg. No effect fordose or for the interaction of dose and time was found. Finally, no significant effects of any typewere found for hematocrit, plasma chloride concentration, or plasma sodium concentration.

39

Table 2. Mean and Standard Deviations of Dependent Variables.
Pre Ingestion
0 mg
250 mg
500 mg
Hb (g/dl)
16.14 ± .67
16.11 ± .74
16.14 ± .56
Hct (%)
43.04 ± 1.26
42.98 ± 1.75
43.42 ± 1.86
[Na] (mmol/l)
138.56 ± 3.29
139.85 ± 2.80
139.09 ± 1.82
[K] (mmol/l)
3.68 ± .29
3.7 ± .40
3.64 ± .30[Cl] (mmol/l)
104.97 ± 2.28
105.21 ± 2.64
105.82 ± 1.89
OsM (mOsm/kg H2O)
286.35 ± 5.98
288.82 ± 2.29
288 ± 2.55
Baseline Muscle CTF
15.65 ± 4.19
(Hz)
Post Ingestion
Muscle CTF (Hz)16 ± 4.84
17.41 ± 6.11
19.41 ± 6.43
Hb (g/dl)
16.26 ± .56
16.35 ± .59
16.38 ± .63
Hct (%)
43.21 ± 1.40
43.45 ± 1.43
44.04 ± 1.58
[Na] (mmol/l)
138.59 ± 2.31
139.53 ± 2.76
139.09 ± 1.96
[K] (mmol/l)
3.76 ± .21
3.78 ± .36
3.78 ± .27[Cl] (mmol/l)
105.65 ± 2.12
105.35 ± 2.52
106.09 ± 1.91
OsM (mOsm/kg H2O)
288.41 ± 2.09
289.35 ± 3.08
289 ± 3.52
*Values are Means ± SD (n=17)*CTF, cramp threshold frequency; Hb, hemoglobin; Hct, hematocrit, [Na], plasma sodium
concentration; [K], plasma potassium concentration; [Cl], plasma chloride concentration; OsM,
osmolality
Table 3. ANOVA Dependent Variable Results.
Variables
Caffeine Dose Pre to Post Ingestion Dose from Pre to Post Ingestion
Muscle CTF
F2,15=.016
F1,16=.068
F2,15=.016
Hb
F2,15=.906
F1,16=.001
F2,15=.692
HctF2,15=.246
F1,16=.091
F2,15=.610[Na]
F2,15=.415
F1,16=.349
F2,15=.100[K]
F2,15=.904
F1,16=.007
F2,15=.417[Cl]F2,15=.196
F1,16=.113
F2,15=.426
OsM
F2,15=.247
F1,16=.044
F2,15=.682*α value=.05*CTF, cramp threshold frequency; Hb, hemoglobin; Hct, hematocrit, [Na], plasma sodium
concentration; [K], plasma potassium concentration; [Cl], plasma chloride concentration; OsM,
osmolality

40

Table 4. Caffeine Dose and Post Muscle Cramp Threshold Frequency Comparison.
Paired Sample
Comparisonsof Caffeine Dosages
Pair 10 mg – 250 mg
Pair 2 250 mg – 500 mg
Pair 3500 mg – 0 mg

95% ConfidenceInterval of the
Difference-3.55538.73185-3.88912-.11088
1.237545.58599tdf

Sig. (2tailed)-1.396-2.244
3.327

16
16
16

.182
.039
.004

Discussion
There is no current literature regarding the effects of caffeine on muscle cramp thresholdfrequency or the effects of caffeine on muscle cramping. Our study looked at the effect of
caffeine ingestion and dosage on cramp threshold frequency. We found a significant increase formuscle cramp threshold frequency for each dose as well from pre to post ingestion.
Hemoglobin, plasma potassium concentration, and osmolality showed significant differencesfrom pre to post ingestion, but no significant effects for caffeine dose. These differences may be
due to any change in body position. If the participant moved during the hour following caffeine
ingestion, fluid compartments would rapidly shift from the intracellular space to the extracellularspace resulting in significant increases in hemoglobin, plasma potassium, and osmolality. We
measured hemoglobin, hematocrit, plasma sodium concentration, plasma potassium
concentration, plasma chloride concentration, and osmolality as they are precursors to anindividual’s hydration status. Any change would indicate either dehydration or euhydration
status of the individual.
Muscle cramping revolves around two theories: the dehydration theory and the muscle
fatigue theory. According to the dehydration theory the human body does not store enoughwater during exercise.21 Water losses increase fluid and electrolyte depletion causing
desensitization of nerve terminals.21 Desensitization of select nerve terminals increase41

mechanical pressure on motor nerve endings, resulting in exercise associated muscle cramps(EAMC).21 Our study looked at participants who were euhydrated (≤ 1.020) prior to ingesting
caffeine on each testing day. Testing for euhydration controlled the outcome of any event
relating to the dehydration theory and limiting any change in muscle cramp threshold frequency
due to dehydration.
The muscle fatigue theory states that muscle fatigue is caused by an increased excitatory
response in muscle spindles and a decreased inhibitory response in Golgi tendon organs (GTO).15
This response leads to abnormal alpha (α) motor neuron control and activity.15 The neuralcontrol of detecting muscle tension by the GTO is disrupted and muscle contractions are
unlimited.15 The afferent activity of the muscle spindles enhances excitatory activity by causing
involuntary muscle contractions.15 The inhibitory effects of the GTO opposing an increase inexcitatory activity by muscle spindles are limited.15
Even though our study did not assess urine analysis post caffeine ingestion, our study
assumes that dehydration does not have a significant effect on the participant’s muscle cramp
threshold frequency. From pre ingestion to post ingestion of caffeine, muscle cramp thresholdfrequency should decrease from baseline threshold frequency to post caffeine ingestion thresholdfrequency. The results from our study showed significant differences for dose pre ingestion topost ingestion, with cramp threshold frequency increasing over baseline for all three doses.
The relationship between caffeine ingestion and increased cramp threshold frequency
maybe related to caffeine’s effect on the functional capacity of the muscle. The effect of
caffeine on adenosine and the sarcoplasmic reticulum dictates the role of neurotransmitters innormal skeletal muscle. Caffeine inhibits the actions of adenosine increasing excitatoryneurotransmitter release by lowering the threshold for neuronal activity.11 Also observed in42skeletal muscle relating to caffeine ingestion is self-sustained firing (SSF) in human motor
units.12 SSF is the continued firing of a motor neuron following a recruitment by a synaptic
excitation during a constant, maybe decreasing, level of synaptic drive.12 However, this does not
explain the increase in muscle cramp threshold frequency in our study.
There are three premises describing how cramp threshold frequency increased following
caffeine ingestion in our study. The first premise is pain perception was altered following
caffeine ingestion. One study showed plasma b-endorphin concentrations nearly doubled during
a two-hour cycling session when consuming caffeine with no significant increase in participants
selected for the placebo group.22 Exercise associated muscle cramps and electrically induced
muscle cramps can be painful and cause discomfort for the individual. As caffeine dosage
increased, so did the cramp threshold frequency. On many occasions, participants in this study
stated they were not feeling a muscle cramp, but showed involuntary flexion of the great toe.
They finally realized they were indeed having a muscle cramp when their great toe was stretchedallowing the great toe to relax.
The second premise is the effect of caffeine on adenosine. Caffeine resembles adenosine
and binds onto adenosine receptors. Adenosine inhibits stimulating events provided through theautonomic nervous system, primarily the sympathetic nervous system. Once caffeine binds toadenosine receptors, adenosine can no longer bind to these receptors allowing the individual’s
overall perception increase such as mood, alertness, focus, and energy levels. As caffeine dosage
increases, the perception of muscle tension increases due to the flight or fight response. Throughthis reaction, the muscle is already available causing the effects of the caffeine to override theelectrical stimulation.

43

The final premise is related to the individuals that participated in the study. Eachindividual was advised to refrain from moving and allow the muscle cramp to occur. A normal
physical reaction during a muscle cramp event is to relieve the cramp by stretching the great toe.
Many individuals tried to follow the recommendation, but had to receive an extra bout of
stimulation if they did indeed try to alleviate their muscle cramp.
The clinical relevance of this study supports the view that caffeine did not contribute tocausing cramps in active individuals. In the meantime, healthcare professionals should continue
to advise physically active individuals to hydrate with uncaffeinated beverages following
rehydration periods. Future research is needed in this area to conclude the effects of caffeine on
muscle cramp threshold frequency.
Conclusion
There was a statistically significant difference from pre to post muscle cramp thresholdfrequency when subjects ingested caffeine doses of 0mg (placebo), 250mg, and 500mg.
Hemoglobin, plasma potassium concentration, and osmolality were statistically significantly
different from pre to post ingestion. Even though cramp thresholds were not lowered by thecaffeine ingestion, healthcare professionals should continue to monitor patient’s caffeine intake
and modify with more suitable hydration sources. Along with hydration maintenance, further
research needs to be done with caffeine and its effect on muscle cramp threshold frequency.
Looking at the effects of caffeine on various neurotransmitters, caffeine’s effect on cramp
threshold frequency following physical activity, different modes of caffeine and the effect it has
on cramp threshold frequency is recommended for further research. Additionally, further
research investigating pre cramp threshold frequency test prior to ingesting caffeine along withperforming a post cramp threshold frequency test is needed.
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47

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48

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53

APPENDIX. IRB APPROVAL

54