The Influence of Menthol Gel During Exercise With Heat

Study Overview
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Brief Summary
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The purpose of this study is to examine the human thermoregulatory impact of applying a commercially available menthol gel (BioFreeze) to the skin prior to moderate intensity walking under heated conditions. Experimental Visits will consist of 30 min of treadmill walking at a moderate pace (3.5 mph, 5% grade) under hot conditions (38°C, 60%RH) and will be randomized and counterbalanced for BioFreeze or a hypoallergenic gel (control) application. Gels 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 BioFreeze and control trials will be separated by a 7-14 day washout period.

Detailed Description
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3 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 BioFreeze, and body composition (hydrostatic weigh, bioelectrical impedance). Visits 2 and 3 will be separated by 7-14 days, randomized, and counterbalanced for experimental (BioFreeze) 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 BioFreeze using a gloved hand from shoulder to wrist and mid thigh to ankle (areas outside of the clothing). A hypoallergenic cream 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. VISIT 1 Visit 1 will take approximately 1 hour. Informed consent will be given. Participants will then complete the physical activity readiness questionnaire (PARQ) to be cleared for physical activity. Participants will have a small amount of the BioFreeze 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. This initial skin reaction test is not a part of the research protocol. Those without a reaction 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). 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 in a temperate environment. Immediately after, a researcher with gloved hands will topically apply BioFreeze 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.

Official Title
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The Influence of Topical Menthol Gel on Thermoregulatory and Perceptual Outcomes During Exercise Within the Heat

Conditions
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Acute Exercise, Heat Exposure

Intervention / Treatment
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* Other: Hot environment
* Biological: Menthol Gel
* Biological: Control Gel
* Other: Exercise


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: 19-45 years of age cleared for physical activity via the 2022 physical activity readiness questionnaire (PARQ) no self-reported adverse reactions to menthol based gels Exclusion Criteria: outside 19-45 years of age not cleared for physical activity via the 2022 physical activity readiness questionnaire (PARQ) self-report or signs of sensitivity to menthol gels pregnant breast feeding

Ages Eligible for Study
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Minimum Age: 19 Years
Maximum Age: 45 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Non-Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: Each Subject acts as their own control in a repeated measures design
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Menthol gel application<br>Menthol gel will be applied to the skin prior to exercise in the heat | Other: Hot environment<br>* 38°C, 60% relative humidity<br>Biological: Menthol Gel<br>* application of 5% menthol gel from shoulder to wrist and mid thigh to ankle<br>Other: Exercise<br>* treadmill walking 3.5 mph at 5% grade<br>|
| Placebo Comparator: Hypoallergenic gel application<br>A hypoallergenic gel will be applied to the skin prior to exercise in the heat | Other: Hot environment<br>* 38°C, 60% relative humidity<br>Biological: Control Gel<br>* application of hypoallergenic gel from shoulder to wrist and mid thigh to ankle<br>Other: Exercise<br>* treadmill walking 3.5 mph at 5% grade<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Skin Blood Flow | Laser Doppler measurement of skin blood flow | 10 minutes into exercise bout | 
| Skin Blood Flow | Laser Doppler measurement of skin blood flow | 20 minutes into exercise bout | 
| Skin Blood Flow | Laser Doppler measurement of skin blood flow | 30 minutes into exercise bout | 
| Galvanic Skin Response | measurement of skin conductance | throughout the 30 minute exercise bout | 
| Sweat Composition | Sodium and Potassium concentrations in collected sweat | final 10 minutes of exercise bout | 
| Sweat Rate | Difference in Nude body weight from pre to post exercise | immediately after the intervention | 
| Thermal Perception | scale of thermal comfort developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) | throughout the 30 minute exercise bout | 
| Average Skin Temperature | average measurements from chest, forearm, and calf thermistors | throughout the 30 minute exercise bout | 
| Core Temperature | measured with rectal thermistor | throughout the 30 minute exercise bout | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Skin Surface Area | calculated as: square root of the product of; weight in kg times height in cm divided by 3600 | pre-exercise bout | 
| Body Fat | Hydrostatic Weight calculation of Body Fat, or bioelectrical impedance analysis | baseline, pre-intervention | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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heat exposure, menthol, exercise