The goal of this clinical trial is to evaluate the effectiveness of topical menthol as a cooling method during exercise in a hot air environment in healthy adult recreational runners aged 18 to 45 years.

The main questions it aims to answer are:

What is the difference in thermal sensation between the topical menthol gel application and a placebo during exercise? How does the application of topical menthol affect body temperature, heart rate, and physical performance compared to a placebo? Researchers will compare a 4% Menthol gel to a placebo gel in a cross-over design to see if the menthol gel improves thermal sensation, regulates body temperature, and enhances physical performance and comfort.

Participants will:

1. Undergo a screening process including a medical history review, physical examination, resting ECG, blood sugar test, and a Bleep fitness test.
2. Participate in two separate running activities at an athletic field, separated by a wash-out period of 7 days + 1 day.Have the assigned gel (menthol or placebo) applied to their neck, front upper arms, and front upper legs while running (specifically between kilometers 2.5 and 2.8).
3. Complete pre-run and post-run assessments measuring weight, skin and tympanic temperature, heart rate, vertical jump height, running duration, perceived exertion (RPE), thermal sensation, and comfort.

Inclusion Criteria:

• Adults, 18 - 45 years old
• Have a personal best 10-kilometer run time of under one hour (which will be confirmed during the screening of prospective Subjects through history taking) in the last 6 months.
• Doing running training at least 3 times/week for the past 1 year
• Have a level of heart-lung endurance or VO2max that is at least included in the average criteria (known through examination: Bleep test)
• Meets Subject screening criteria by answering "No" to all questions on the Physical Activity Readiness Questionnaire (PAR-Q) questionnaire.
• Have normal resting ECG and normal GDS results on screening of prospective Subjects.
• At the time of the study, the body temperature was within the normal range

Exclusion Criteria:

• Pregnant and/or breastfeeding women
• Have had a musculoskeletal injury in the last three months and still have symptoms or complaints
• Are experiencing acute infectious disorders, such as gastrointestinal, respiratory infections
• During treatment for chronic diseases (e.g. high blood pressure or hypertension, diabetes or diabetes mellitus, heart disease)
• Have a history of hypersensitivity or allergy to menthol or skin-applied products (especially gel-based products)
• Has a history of cold allergy
• Have a positive COVID-19 test result at the time of screening.