Muscle Reflex Inhibition in Hypoxic Exercise

The goal of this interventional study is to compare muscle reflex function under settings of normoxia (normal oxygen level), acute hypoxia (brief oxygen-lack) and chronic hypoxia (long-duration exposure to oxygen-lack).The main question is: Does the muscle reflex adapt to chronic hypoxia?Young, healthy participants will complete light-to-high intensity cycling exercise with and without suppression of the muscle reflex. Suppression of the muscle reflex will be via spinal administration of the opioid Fentanyl. In the control condition, saline will be administered into the spinal space. Participants will complete control (saline) and experimental (Fentanyl) exercise conditions at sea-level (Kelowna, BC, Canada) breathing room air and whilst breathing a lower fraction of oxygen (acute hypoxia). Thereafter, participants will complete the exercise test after living at high altitude (White Mountain, CA, USA) for 2 weeks whilst breathing room air (chronic hypoxia) and breathing a higher fraction of oxygen (restored normoxia).

Inclusion Criteria:aged 19 - 40 years oldnot taking medications (exception oral contraception)no history of cardiovascular, respiratory or neurological diseasemembers of the high altitude expedition to White Mountain in 2023Exclusion Criteria:post-menopausal or pregnantobesecurrent smokerstaking prescription medications that may affect responses to exerciseAll potential participants will be screened by a physician to identify co-morbidities