The Influence of Menthol Gel During Exercise With Heat
Condition: Acute Exercise; Heat Exposure
Study type: Interventional
Phase: Phase 4

Summary: 
      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: 
      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.
    

Intervention name(s): Hot environment; Menthol Gel; Control Gel; Exercise
Intervention type(s): Other; Biological; Biological; Other
Intervention description(s): 38°C, 60% relative humidity; application of 5% menthol gel from shoulder to wrist and mid thigh to ankle; application of hypoallergenic gel from shoulder to wrist and mid thigh to ankle; treadmill walking 3.5 mph at 5% grade
Intervention MeSH terms: Menthol
Allocation: Non-Randomized
Intervention model: Crossover Assignment
Intervention model description: Each Subject acts as their own control in a repeated measures design
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: heat exposure; menthol; exercise