Effect of Exercise and Heat Stress on Acute Cardiometabolic Adaptations in Healthy Young Adults

Description

Experimental procedures:

Participants will visit the lab on seven occasions. Participants will be required to practice regular exercise and dietary habits that can be easily replicated in the 24 hours prior to every laboratory visit. Exercise and dietary patterns will be documented during the first visit and thereafter the participants will be reminded of these practices and instructed to match them as closely as possible in the 24 hours leading up to all subsequent visits. Participants will only be instructed to avoid heavy exercise in the 12 hours prior to testing sessions. On the first visit, participants will be introduced into the lab, where the investigators will give oral and written instruction detailing the procedures and associated risks related to participating. Details of the experimental visits are outlined below:

Familiarization Visit (1 hour):

* Familiarization and fitness test
* Lactate threshold and maximal aerobic power test on an upright cycle ergometer.

Experimental visit #1 (6 hours):

* Control exercise, heated exercise or control rest
* Rectal or esophageal thermistor will be inserted.
* Venous cannula will be inserted by trained phlebotomist (Chloe Gustafson, Dr Travis Gibbons).
* Cycling exercise for 90 minutes at 90% of lactate threshold with 2 pedestal fans to maximize heat loss and prevent core temperature increase to <1 ̊ C.
* 2.5 hours of resting recovery in semi-supine position.
* Vascular assessment.
* Glucose tolerance test (blood will be sampled for glucose and insulin 15, 30, 60 and 120 minutes after consuming a mixed macronutrient meal)
* Rectal thermistor and venous cannula will be removed and participant will leave.

Experimental visit #2 (6 hours):

* Control exercise, heated exercise or control rest
* Complete identical procedures as experimental visit #2 with the following exceptions:
* Cycling exercise for 90 minutes at 90% of lactate threshold.
* No fans will be used to maximal heat gain.
* Participants will wear a water impermeable jacket, pants and gloves, and wear a winter hat (beanie).
* Core temperature will be allowed to rise naturally but exercise will stop if core temperature reaches 40 ̊ C.

Experimental visit #3 (6 hours):

* Control exercise, heated exercise or control rest
* Complete identical procedures as experimental visit #2 with the following exceptions:
* Participant will rest comfortably in the semi-supine position for 90 minutes.

Follow-up assessments after experimental visits 1, 2, and 3 (1 hour):

* Rectal or esophageal thermistor will be inserted.
* Participant will lie comfortably for 10 minutes.
* Arterial stiffness assessment will be performed (3 minutes)
* A venous blood sample will be collected.
* Participant will complete 5-minute blood volume assessment via carbon monoxide rebreathing technique.
* A final blood draw will be performed.