The Influence of Topical Capsaicin on Thermoregulatory and Perceptual Outcomes During Exercise Within the Heat
Phase: PHASE4
Conditions: Acute Exercise, Heat Exposure
Sponsor: University of Nebraska

Study Protocol and Statistical Analysis Plan 
 
Title: The Influence of Topical Capsaicin on Thermoregulatory and Perceptual Outcomes During Exercise 
Within the Heat   
 
NCT05298202 
Unique Protocol ID: 0192-22-FB 
Date: 25 May 2022 
 
 
 

Abstract 
The purpose of this study is to examine the human thermoregulatory impact of applying a commercially 
available capsaicin cream to the skin prior to moderate intensity walking under heated conditions. Eligible 
participants will be aged 19-45 years, have no previously known adverse reactions to capsaicin (active 
ingredient) based upon a self-report, no adverse reactions to capsaicin as determined through application to a 
small forearm area, and cleared for physical activity via the 2022 Physical Activity Readiness Questionnaire 
(PARQ). There will be a total of 3 experimental visits to the laboratory. Visit 1 will test for adverse capsaicin 
reaction by applying a small amount of cream to the forearm (~2 x 2 in). Anthropometric and body composition 
data will also be collected at this time. Visits 2 and 3 will consist of 30 min of treadmill walking at a moderate 
pace (3.5 mph, 5% grade) under hot conditions (38°C, 60%RH). Visits 2 and 3 will be randomized and 
counterbalanced for capsaicin or a hypoallergenic cream (control) application. Creams will be applied to areas 
commonly exposed during outdoor activity in warm conditions (shoulder to wrist, mid-thigh to ankle). 
Accordingly, participants will wear shorts and a tank top shirt during exercise. Core temperature, skin 
temperature, galvanic skin response, laser doppler blood flow, and heart rate will be continuously recorded 
throughout the exercise bout via an integrated analog to digital converter. Sweat will be collected during 
exercise using commercially available absorbent patches. Thermal sensation will be assessed throughout 
exercise via the ASHRAE thermal sensation Likert scale (cold to hot). Lastly, nude body weight will be recorded 
pre and post exercise for sweat rate determination. The capsaicin and control trials will be separated by a 7-14 
day washout period. There will be no follow up visits. 
 
Purpose and Rationale 
The purpose of this study is to examine the impact of applying a capsaicin-based cream to the skin on 
human thermoregulation and thermal perception during exercise in the heat. The capsaicin chemical 
compound is found in many hot sauces, making it strongly associated with feelings of heat and pain. 
Topical capsaicin receptors can invoke a tingling sensation that can be perceived as heat. The capsaicin 
receptor is a part of a family of membrane proteins called transient receptor potential (TRP) channels 
[1]. TRPs allow for the perception of environmental stimuli and act as sensory mediators. The capsaicin 
receptor in our body, also known as vanilloid receptor one, is a TRPV1 channel. Besides activation of the 
TRPV1 channel by capsaicin, it is also activated by ambient noxious heat [1,3]. Capsaicin activated TRPV1 
receptors lead to vasodilation of the skin [1]. This vasodilation is vital to the cooling of the body, as it 
gets rid of excess heat, aiding in thermoregulation. This can be contradictory to the perceived heat since 
it aids in cooling. It was first discovered that TRPV1 plays a role in thermoregulation when it was found 
that capsaicin has hypothermic action that can lower core temperature significantly in multiple species, 
including humans [2]. This evidence supported that TRPV1 has profound effects on maintaining 
homeostasis of internal body temperature.  
 
If topical capsaicin provokes vasodilation, then the question remains as to why it is not more commonly 
used by humans in hot environments. This could be because of the previously referenced negative 
feelings of capsaicin. Currently, topical capsaicin creams are marketed as an analgesic, commonly aimed 
at those experiencing arthritic pains; yet this is not their full physiological potential. There is a 
physiological conflict between the perceived hot sensation of capsaicin compared to the observed 
physiological effects. It is currently unknown if over-the-counter capsaicin creams can aid in 
performance during exercise in the heat, or if the perceived burning sensation would hinder 

performance. This requires further investigation into the effects that topical capsaicin may have on 
exercise performance in the heat. 
 
Participants 
12-15 subjects, aged 19 to 45, will be needed to complete the study. Keeping the age range of 19-45 ensures 
that the participants will be of consenting age and cleared for physical activity participation. 
 
Research Plan 
Three experimental visits to the laboratory will be conducted. All visits will take place at the University 
of Nebraska at Omaha, Exercise Physiology Laboratory. Visit 1 will consist of the physical activity 
readiness questionnaire (PARQ), adverse reaction to Rugby Capsaicin Cream (0.025%), and body 
composition (hydrostatic weigh, bioelectrical impedance). Visits 2 and 3 will be separated by 7-14 days, 
randomized, and counterbalanced for experimental (capsaicin) and control (hypoallergenic cream) trials. 
Both the experimental and control visits will follow the same protocol.  
 
Participants will arrive following an overnight fast state while also refraining from strenuous activity, 
alcohol consumption, tobacco use, and recreational drugs for the previous 24 hour period. During these 
visit researchers will apply Rugby capsaicin cream using a gloved hand from shoulder to wrist and mid-
thigh to ankle (areas outside of the clothing). A hypoallergenic cream (Remedy Essentials Unscented 
Moisturizing Body Lotion, Medline Industries inc.) will be applied during the control visit.  
Exercise will consist of 30 min of moderate intensity treadmill walking (3.5 mph at 5% grade) within a 
heated temperature/humidity-controlled chamber (38°C, 60% relative humidity).  
Participants will be weighed before, and after completion of the exercise calculate sweat rate. Prior to 
the exercise session, participants will sit for 5 min in an ambient room temperature environment as a 
baseline. During baseline and during the exercise core temperature, skin temperature, laser doppler 
blood flow, galvanic skin response, and heart rate will be collected continuously. Sweat patches will be 
adhered to the forehead during exercise at minute 10 for collection of sweat composition over the next 
10-20 minutes.  
Thermal perception using the ASHRAE scale (cold to hot) will be assessed pre and during exercise.  
 
EXPERIMENTAL VISIT 1  
Visit 1 will take approximately 1 hour. Participants will then complete the physical activity readiness 
questionnaire (PARQ) to be cleared for physical activity. Participants will have a small amount of the 
capsaicin cream and control cream applied to a small area of the forearm (~2 x 2 in) to test for any 
adverse reaction over a period of 15 minutes. Those without a reaction will have height, weight, and 
body fat composition measured. Then, resting blood pressure and heart rate will be taken. Those 
without a reaction, and a resting blood pressure lower than 140/90, will have height, weight, and body 
fat composition measured. Height and weight will be measured using a medical scale and stadiometer, 
respectively. Body fat will be assessed with hydrostatic weighing using an electronic load cell-based 
system (Exertech, Dresbach, MN) correcting for residual lung volume or via a bio- electrical impedance 
analyzer (InBodyUSA, Cerritos, CA).  
 
EXPERIMENTAL VISITS 2 AND 3  
Visits 2 and 3 will take approximately 2 hours each. Upon arrival at the lab, a nude body  weight will be 
collected with the subject in a private room. While still in the room, subjects will self-insert a rectal 

thermistor 12-15 cm beyond the anal sphincter and don a chest strap heart rate monitor. After dressing 
in their exercise clothing, subjects will exit the private room so that chest, forearm, and calf thermistors 
can be adhered to the skin with tape.  
Laser doppler flow (forearm and or/finger) will be adhered with tape and galvanic skin response (fingers) 
will be adhered using Velcro straps to the skin. Measuring instruments will be recorded using an 
integrated digital to analog converter (ADInstruments, Colorado Springs, CO).  
 
Following instrumentation, subjects will sit for 5 minutes as a baseline for all recordings in a temperate 
environment. Immediately after, a researcher with gloved hands will topically apply capsaicin or the 
control hypoallergenic cream from the shoulder to wrist and mid-thigh to ankle. Subjects will then enter 
the heat chamber (38°C, 60% relative humidity) and immediately begin a 30-minute walk on a treadmill 
(3.5 mph, 5% grade). Subjects will be intermittently asked to hold their arm steady for laser doppler flow 
collection (10, 20, 30 minutes). Subjects will also briefly pause at minute 10 in order to adhere an 
absorbent patch to their forehead for sweat collection over the following 10-20 minutes. Thermal 
perception using the ASHRAE scale (cold to hot) will be assessed pre and during exercise. After 30 
minutes of walking, subjects will exit the chamber for removal of all skin and finger sensors. Subjects will 
then re-enter the private room, remove their own rectal thermistor with gloved hands, and then a final 
nude body weight will be recorded after toweling off.  
The rectal thermistor will measure core temperature. The heart rate monitor will measure the beats of the 
heart. Skin thermistors will measure the temperature of the skin surfaces. Laser doppler flow measure the 
relative units of blood flow velocity. Galvanic skin response measures skin conductivity changes as individuals 
begin to sweat. Sweat is collected for assessment of sweat composition. Thermal perception is assessed for 
individual perception surrounding the temperature of the ambient environment. Nude body weight is 
measured to calculate sweat rate. 
 
Statistical Analysis 
Recruitment 
Previous exercise research suggests that the difference in response of matched pairs is normally distributed 
with a standard deviation of 0.86. If the true difference of the mean response of matched pairs is 0.75, we will 
need to complete 12 experimental trials for each condition to be able to reject the null hypothesis that this 
response difference is zero with a power of 0.8. The Type I error probability associated with this test of the null 
hypothesis is 0.05. 
Interventions 
A repeated measures two-way ANOVA (Time x condition) will be used for the dependent variables. If the F-ratio 
values are found to be significant, a Fisher's Least Significant Difference post hoc analysis will be conducted. A 
type I error probability of < 5% will be considered significant (p< 0.05). All data will be analyzed using a 
combination of Microsoft Excel and the Statistical Package for the Social Sciences (SPSS).