Postexercise Hot-Water Immersion on Exercise Performance in Hypoxia

Human performance is compromised at altitude due to a lower partial pressure of oxygen and subsequent reductions in the convective transport of oxygen to tissue. Long-term acclimation to attitude incurs physiological adaptations that result in a near return to sea-level performance; however, the time required (\~2 weeks) for such adaptations is often logistically challenging for athletes, military personnel or other individuals who reside at sea level. Recent research suggests that physiological acclimation to heat stress (i.e., heat acclimation) and altitude (i.e., hypoxia) share similar cellular adaptations, namely an up-regulation of Hypoxia-inducible factor 1 (HIF-1) and various heat shock proteins. Therefore, it is hypothesized that heat acclimation may provide physiological protection from reduced oxygen transport to the tissue and enhance performance at altitude. This cross-tolerance model is supported by traditional heat acclimation protocols (i.e., submaximal exercise in hot ambient temperature); however, it has not been tested with passive exposure to heat stress through post-exercise hot water immersion.

• Post-Exercise Hot Water Immersion (Other): Participants will cycle for 60 minutes at 50% of maximal oxygen uptake (VO2 max) followed by 30 minutes post-exercise hot water immersion (40oC) for 5 consecutive days.
• Control Group (Other): Participants will cycle for 60 minutes at 50% maximal oxygen uptake (VO2 max) for 5 consecutive days. There is no water immersion following the exercise.

Primary outcomes

• Time-Trial Performance in hypoxia conditions [30 minutes]: Results of a 16 km time-trial test conducted at an fraction of inspired oxygen (FiO2) of 0.14

Secondary outcomes

• Pulse oxygen saturation during exercise [30 minutes]: Capillary oxygen saturation measured on the earlobe throughout the time-trial tests using pulse oximetry.
• Skin temperature during exercise [90 minutes]: Skin temperature measured throughout the time trial-tests and exercise training intervention using temperature probes attached to the calf, thigh, chest and arm, from which weighted averages are calculated.
• Core temperature during exercise [90 minutes]: Core body temperature measured throughout the time-trial tests and exercise training interventions using a rectal temperature probe.
• Heart Rate during exercise [90 minutes]: Heart rate will be measured throughout the time trial tests and exercise training interventions using a wireless (Polar) heart rate chest strap.

Sex: All, ages: 18 Years to 50 Years, accepts healthy volunteers

Inclusion Criteria:

* Physically active (minimum of 90 minutes of moderate-intensity exercise per week)

Exclusion Criteria:

* Cardiovascular disease
* resident of >1500 m above sea-level in the past year;
* history of fainting

• Geoffrey L Hartley, PhD, Principal investigator, Nipissing University