Cryo Pack Cooling After Exercise-induced Hyperthermia

This study will consist of three study visits:

Visit 1: Baseline and VO2max Testing Visit 2-3: Trial 1 and 2.

Visit 1: Baseline and VO2max Testing

Participants who are approved to participate will be scheduled for a baseline and VO2max testing day. Upon arrival to the lab, subjects will provide a urine sample in a clean urine cup. Urine specific gravity and urine color will be assessed. Nude body mass will be also be recorded. Privacy will be afforded for each participant while obtaining body mass measures by taking measurements with the participant alone in a private room behind a solid, closed door, and the research reading the scale outside of the room. Participants will only be permitted to continue to the VO2max test if the euhydrated criteria of a urine specific gravity (USG) ≤1.025 is met. If the participant arrives with a USG between 1.020 and 1.025, the subject will be asked to drink 500 mL of water to ensure proper hydration status. Height will be measured with a tape measure on Visit 1. Percent body fat will be calculated using a 3-site evaluation of skin fold thickness using skin fold calipers on one of the three baseline days. A researcher will use appropriate grasping technique to measure skin fold thickness on the chest, abdomen, and thigh. This will take less than ~5 minutes to complete. This information will be used to describe the subject demographics. Participants will also be asked to complete a maximal oxygen uptake (VO2max) test on a treadmill in a thermoneutral environment. This test will provide aerobic fitness levels of the participants.

Visit 2-3: Trials 1 and 2

This is a randomized, counter-balanced, cross over design. Participant numbers will be randomly assigned and trials will be ordered with a random number generator and assigned to a participant number. These orders will be counterbalanced between participants to ensure that there is not an order effect, and each participant will complete both trials as part of the study. Participants will be allowed to make-up trial visits if they are sick, suffer an injury or do not meet hydration requirements. Participants will be asked if they have a current illness or taking medications to determine whether they can complete the exercise trial. The participant's visit will be rescheduled if they have a fever, current illness or taking medications that influence body temperature.

Cooling Intervention:

1. Ice Pack Cooling

2. Commercially Available Ice Pack

The exercise protocol, performance testing, cognitive testing, and recovery portions of this study will be conducted in a climatic chamber with ambient temperature approximately 30-40°C and relative humidity at approximately 30-70%.

Upon arrival to the lab, participants will be asked to indicate if they have consumed alcohol or caffeine in the last 24 hours. They will not be asked to specify exactly what they have consumed, but if they provide a positive indication, their trial will be rescheduled for another day. Participants will provide a small urine sample in a clean urine cup, and a nude body mass will be measured. Upon arrival to the lab, hydration status will be assessed by urine specific gravity, nude body mass and urine color. Participants will only be permitted to continue to the exercise trial if the euhydrated criteria of a urine specific gravity (USG) ≤ 1.025 is met. If the participant arrives with a USG between 1.020 and 1.025, the subject will be asked to drink 500 mL of water to ensure proper hydration status. Participants will be given instructions at the prior visit about how to obtain desired hydration status for the upcoming trial. Key study personnel will insert an esophageal probe to measure esophageal temperature. Participants will then insert a rectal probe and wear a heart rate monitor strap. Additionally, participants will wear 4-site skin temperature sensors. The participants will also be asked to complete a subjective sleep questionnaire upon arriving to the lab. All perceptual measures, cognitive performance measures and physical performance tests will be administered to determine a baseline value at the beginning of each trial.

All participants will undergo a treadmill protocol involving approximately 90 minutes of jogging or walking. Cognitive and physical performance tests will be administered at various time points throughout the trial.

After exercise, participants will be cooled by either 5 cryothermic ice packs or 5 commercially available ice packs. Participants will be cooled for approximately 30 mins. All participants will be laying supine during cooling.

Cryothermic Cooling and Commercially Available Ice Pack Placement

Storage and Preparation:

Ice packs will be stored in a cooler at approximately 34°F for at least 6 hours prior to use and kept as dry as possible (35°F to 70°F). Ideally, Ice packs will be kept in tray or basket above ice or frozen gel packs, not in contact with the method of cooling the cooler. Refrigerator may be acceptable for storage before cooler use as well, but prefer cooler for real situations in field.

For cryo cooling elements: the cryo cooling packs will be shaken quickly and vigorously (10 seconds) and placed on subject (subject will be supine).

For commercially available ice pack: ice packs will be placed on subject (subject will be supine).

All ice packs will be placed on the following body segments:

- 1 ice pack on neck covering both carotid Triangle regions

- 2 ice packs in axilla region

- 2 ice packs in groin region

Cryo Cooling Elements and commercially available ice packs will be discarded after use.