TITLE: The effects of pre-exercise vibration stimulation on the exercise-induced
muscle damage

  ABSTRACT:
[Purpose] To investigate the effects of pre-induced muscle damage vibration stimulation
on the pressure-pain threshold and muscle-fatigue-related metabolites of exercise-induced
muscle damage. [Subjects and Methods] Thirty healthy, adult male subjects were randomly
assigned to the pre-induced muscle damage vibration stimulation group, post-induced muscle
damage vibration stimulation group, or control group (n=10 per group). To investigate the
effects of pre-induced muscle damage vibration stimulation, changes in the pressure-pain
threshold (lb), creatine kinase level (U/L), and lactate dehydrogenase level (U/L) were
measured and analyzed at baseline and at 24 hours, 48 hours, and 72 hours after exercise.
[Results] The pressure-pain thresholds and concentrations of creatine kinase and lactate
dehydrogenase varied significantly in each group and during each measurement period. There
were interactions between the measurement periods and groups, and results of the post-hoc
test showed that the pre-induced muscle damage vibration stimulation group had the highest
efficacy among the groups. [Conclusion] Pre-induced muscle damage vibration stimulation is
more effective than post-induced muscle damage vibration stimulation for preventing muscle
damage.

BODY.INTRODUCTION:
Exercise-induced muscle damage (EIMD) is caused by eccentric contraction or excessive
overload, which requires large changes in muscle length1). EIMD secretes the intracellular proteins of muscle cells such as
creatine kinase (CK), lactate dehydrogenase (LDH), and myoglobin into the blood. In
addition, metabolites such as lactic acid and potassium are temporarily produced in the
contracted muscle, which can cause fatigue, pain, and a decrease or loss in muscular
performance and exercise regulation ability due to inappropriate blood and oxygen supply to
the muscles2, 3). Delayed onset muscle soreness is first felt 24 hours after
exercise, and it peaks within 24–72 hours after exercise. The soreness gradually decreases
and disappears after 5–7 days3).  Physical therapy interventions such as stretching4), ultrasound treatment5), and micro-current treatment6) are used to treat symptoms of EIMD. Recently, vibration stimulation,
which is a type of mechanical stimulation, has emerged as a new treatment method7). Lebedev and Peliakov have suggested the
possibility that vibrations may elicit excitatory inflow through muscle spindle-motoneurons
connections in the overall motoneuron inflow8). Koh et al. reported that a significant change in the pressure-pain
threshold (PPT) was observed when 10 minutes of a 20-Hz vibration stimulus was applied after
the onset of delayed muscle soreness9).
Song et al. reported that a significant decrease in muscular pain was observed when 10
minutes of a 20-Hz vibration stimulus was applied on biceps with muscle damage for 4
days10). In addition, Kim reported that
the levels of CK and LDH in the quadriceps and biceps femoris decreased in the group that
received 1-minute long vibration stimulation at 30 Hz after exercise compared to the control
group11). As shown in previous studies,
the positive effects of vibration stimulation have mostly been investigated for improving
the symptoms after EIMD. However, there is a lack of studies on using pre-induced muscle
damage vibration stimulation to prevent EIMD. Therefore, the present study aimed to
investigate the effects of local pre-induced muscle damage vibration stimulation for
preventing muscle damage.

BODY.SUBJECTS AND METHODS:
All 30 participants in this study were healthy, male adults in their 20s with an average
weight of 66.6 kg and an average height of 174.5 cm. Participants were all right hand
dominant with no recent or previous history of a neck disorder requiring medical
intervention, and absent signs of physical dysfunction in a clinical examination of the
neck. Participants were excluded from the study if they reported any current shoulder
disorders. This study received approval from the Cheongju University's Research and Ethics
Committee. All participants received verbal and written information about the study and
signed a consent form. Participants were randomly assigned to the pre-induced muscle damage
vibration stimulation group (group I), post-induced muscle damage vibration stimulation
group (group II), or non-intervention group (control group) (n=10 per group). The PPT and
blood muscle-related fatigue metabolite levels were measured before EIMD. These variables
were measured again at 24 hours, 48 hours, and 72 hours after a vibration stimulus was
applied in the same conditions used in the control group. EIMD was measured by using weight
equivalent to 60% of one repetition maximum, which was lifted and lowered in the 0–135°
range of motion of the elbow joint while participants' bodies and shoulders were in a fixed
position. The weight-bearing arms were slowly lowered at the same pace (8 seconds according
to a metronome), and an assistant helped lift them. Five sets of 15 repetitions were
performed with a 60-second break in between sets12). A 60-Hz vibrator (AT-1000, AT System, Seongnam-si, Korea) was used
to apply the vibration stimulus to the middle of the biceps muscle for 5 minutes during a
relaxed state by the same therapist13). To
determine the PPT before and after EIMD, we used a digital pressure algometer (Algometer TM
Commander, J-TECH Medical, Salt Lake City, UT, USA). The measuring electrodes were
vertically placed 5, 9, and 13 cm from the muscular body, and then force was applied. The
amount of applied pressure increased linearly, and participants were instructed to notify
the therapist when they felt pain. The amount of pressure exerted when pain was felt was
measured. The measurements were repeated three times, and an average value was calculated.
The measurement locations were clearly marked with an oil-based marker. The measurements
were assessed again at pre-exercise and at 24 hours, 48 hours, and 72 hours after vibration
stimulation was applied. High measurement values indicated a low PPT14).  Participants' blood samples were collected at pre-exercise and at 24 hours, 48 hours, and
72 hours after vibration stimulation was applied to determine the CK and LDH levels. Blood
samples were obtained after fasting, and participants were instructed to have their blood
drawn at their designated time with an error margin of ± 1 hour10).  Windows SPSS 18.0 (SPSS, Inc., Chicago, IL, USA) was used for data analysis, and one-way
analysis of variance (ANOVA) was conducted to test for homogeneity. Differences in the
variables among each group were tested using repeated-measure ANOVA. The Tukey method was
used to perform the post-hoc test, and the statistical significance was set to
p<0.05.

BODY.RESULTS:
Changes in the PPT with vibration stimulation before or after EIMD showed significant
differences (p<0.001) and significant interactions (p<0.01) between the application
times and groups. Results of the post-hoc test showed that the pre-induced muscle damage
vibration stimulation group had the highest PPT (Table
1Table 1.Comparison of changes in the pressure-pain threshold among the groups
(n=10)M ± SD (lb)PrePost-24hPost-48hPost-72hCON35.0 ± 2.616.8 ± 2.615.5 ± 2.115.6 ± 3.1Exp-I†31.3 ± 6.320.4 ± 7.527.6 ± 6.827.6 ± 5.1Exp-II36.4 ± 9.919.0 ± 7.817.4 ± 5.012.8 ± 6.7†p<0.01, Comparison among the groups. Exp-I: Vibration stimulus before EIMD of biceps brachii. Exp-II: Vibration stimulus after EIMD of biceps brachii ).  Changes in the CK levels with vibration stimulation before or after EIMD showed significant
differences between the application times and groups (p<0.01), and significant
interactions between the application times and groups (p<0.001). Results of the post-hoc
test showed that the pre-induced muscle damage vibration stimulation group had the lowest CK
level (Table 2Table 2.Comparison of changes in the creatine kinase level among the groups
(n=10)M ± SD (U/L)PrePost-24hPost-48hPost-72hCON147.6 ± 12.1140.5 ± 8.2433.3 ± 8.0131.6 ± 7.3Exp-I†141.0 ± 4.2131.7 ± 3.9130.7 ± 4.6128.1 ± 3.7Exp-II139.0 ± 5.0136.8 ± 3.1135.4 ± 2.0133.1 ± 1.7†p<0.001, Comparison among the groups).  Changes in the LDH levels with vibration stimulation before or after EIMD showed
significant differences (p<0.001) and significant interactions (p<0.001) between the
application times and groups. Results of the post-hoc test showed that the pre-induced
muscle damage vibration stimulation group had the lowest LDH level (Table 3Table 3.Comparison of changes in the lactate dehydrogenase level among the groups
(n=10)M ± SD (U/L)PrePost-24hPost-48hPost-72hCON392.3 ± 41.4609.0 ± 56.7890.0 ± 51.42,034.1 ± 207.4Exp-I†383.7 ± 113.0417.2 ± 65.9365.1 ± 54.9345.3 ± 54.5Exp-II377.4 ± 37.1384.9 ± 99.6360.1 ± 43.1430.5 ± 65.1†p<0.001, Comparison among the groups).

BODY.DISCUSSION:
Vibration stimulation is a treatment method that directly stimulates the human body and
induces exercise-like effects on desired locations15). Bakhtiary et al.16) reported that vibration stimulation was very effective for muscle
damage recovery, and it could be used in athletes and the public who require a fast
recovery. Aminian-Far reported that 5 minutes of pre-induced muscle damage vibration
stimulation of the lower limbs significantly reduced the delayed muscle soreness-pain
threshold in healthy adults compared to those in the control group17). In the present study, the pre-induced muscle damage
vibration stimulation group showed a relatively higher PPT than the other groups, which
coincided with the results from previous studies. Saijo et al.18) reported that vibration stimulation induced pain relief
and topical anesthesia based on gate control theory. Additionally, McHugh19) reported that vibration stimulation
increased the activity and tension of the muscle, which helped prevent damage caused by
injuries or contraction. Therefore, it can be inferred that vibration stimulation of the
muscle decreases muscle injuries, EIMD, and pain.  The CK and LDH levels are used as indicators of cell membrane damage, tissue necrosis, and
muscle cell damage caused by high-intensity exercise. In addition, CK and LDH are enzymes
that aid in regulating the balance between catabolism and anabolism of carbohydrates, which
means they represent energy metabolism20, 21). Changes in the CK and LDH levels in the
current study showed that the pre-induced muscle damage vibration stimulation group
displayed the lowest CK level, whereas LDH levels in the pre-induced muscle damage vibration
stimulation group and post-induced muscle damage vibration stimulation group were lower than
those in the control group. Bakhtiary et al.16) studied 25 non-athletes who ran on a treadmill after 50 Hz of
vibration stimulation was applied to the lower limbs, and they reported that the CK level
was relatively lower in the experimental group than in the control group. Imtiyaz et
al.7) conducted a study in which 5
minutes of 50 Hz of vibration stimulation was applied to healthy women after EIMD was
induced; they also reported that the CK and LDH levels were significantly reduced after 48
hours of stimulation.  Based on these results, we infer that vibration stimulation improved muscle recovery from
fatigue by quickly removing lactic acid in the blood22). Hazell et al. reported that arterial pressure, blood flow, and the
superficial skin temperature significantly increase around the location of vibration
stimulation23). Similarly, Butterfield
et al. reported that the increased blood flow improved permeability of the cell membrane and
removed inflammatory agents such as prostaglandin, bradykinin, and histamine24), which improved exercise-induced fatigue
and muscle damage25). These results
indicate that vibration stimulation on the biceps after EIMD affects the PPT and CK and LDH
levels. We determined that pre-induced muscle damage vibration stimulation is more effective
than post-EIMD vibration stimulation for preventing muscle damage.

Question: Compared to post-exercise vibration stimulation  what was the result of pre-exercise vibration stimulation on reduce muscle damage.?
Evidence: Changes in the PPT with vibration stimulation before or after EIMD showed significant
differences (p<0.001) and significant interactions (p<0.01) between the application
times and groups. 
Answer: significantly increased