The Potential of a Low Oxygen Environmental Chamber as an Aid to Exercise Training to Improve Metabolic Health

Obesity is a major global health issue and a primary risk factor for metabolic-related disorders. While physical inactivity is one of the main contributors to obesity, it is a modifiable risk factor with exercise training as an established, non-pharmacological treatment to prevent the onset of metabolic-related disorders, including obesity. Exposure to hypoxia via normobaric hypoxia (simulated altitude via reduced inspired oxygen fraction), termed hypoxic conditioning, in combination with exercise has been increasingly shown in the last decade to enhance blood glucose regulation and decrease body mass index, providing a feasible strategy to treat obesity.

Nonetheless, findings from studies investigating the potential for a hypoxic environment to augment the exercise training response and subsequent metabolic health are equivocal. Notably, there is a paucity of information regarding the optimal combination of exercise variables and hypoxic load (i.e. level of hypoxia) to enable an individualized and safe practice of exercising in a hypoxic environment.

In the present randomized, single-blind, cross-over study, the investigators will investigate the effects of single-bout of exercise under normoxia (FiO2, 20.9%), moderate (FiO2, 16.5%) and high normobaric hypoxic conditions (FiO2, 14.8%) (60-min cycling session at 90% LT) on 2h OGTT and 24h-glucose level in individuals with overweight. The investigators hypothesize that exercise in combination with hypoxia improves glucose homeostasis in individuals with overweight.

In the present randomized, single-blind, cross-over study, participants will be exposed to normobaric 1) normoxia (oxygen level 20.9%), 2) moderate hypoxia (oxygen level 16.5%) and 3) high hypoxia (oxygen level 14.8%) 1) during exercise (60 minutes on a cycle ergometer) at 90% LT. Participants will be randomly assigned to each condition (computer-generated randomization plan), separated by a washout period (5-7 days). To accomplish this, participants will exercise in an environmental chamber in which oxygen concentration of the ambient air and, as such, oxygen levels can be closely controlled and monitored. Participants will cycle for 60 minutes at a 90% lactate threshold (LT), determined by an LT test.

Visit 1 (Screening and consent):

Introduction to the research team and tour of the facility. Complete and sign the Adult Pre-Exercise Screening System form. Complete and sign the consent information form.

Visit 2:

Body composition screening using bioimpedance analysis (Inbody 770, Cerritos, CA, USA) Blood pressure screening. Lactate threshold test-participants will be riding a Velotron cycle ergometer (Racermate, Seattle, USA) with an initial load of 50 Watts. The load increased progressively in 15 Watts increments every 4 minutes, with participants maintaining a constant pedal frequency (cadence \~90 rpm) until reaching LT.

Visit 3:

Baseline oral glucose tolerance test (OGTT)-Participants will be consumed 75 grams of glucose dissolved in water (Glucolin glucose powder) and blood samples will be collected to determine baseline glucose and insulin level.

Visit 4:

Attachment of Continuous Glucose Monitor (CGM) (FreeStyle Libre, Abbott Diabetes Care, Witney, UK) will be placed on the back of the upper arm as recommended by the manufacturer.

Visit 5:

Pre-exercise blood sampling-to determine plasma glucose, insulin and circulatory factors.

Participants will be 60 minutes of cycling bouts at 90% of LT under simulated altitude exposure (normoxia or two hypoxic conditions) in the environmental chamber.

Post-exercise blood sampling-2 hours OGTT will be performed immediately following each experimental trial to determine glucose homeostasis and circulatory factors.

Visit 6:

Post-exercise 24 hours blood sampling-to determine glucose homeostasis and circulatory factors.

Removal of CGM

Eligibility Criteria:
Inclusion Criteria:

* BMI is between 25-29 kg/m²
* Sedentary (physical activity \<150 min/week)
* No known heart or metabolic diseases (such as Type 2 diabetes)
* Not currently taking any prescribed medication
* No reported musculoskeletal injuries recently
* Not exposed to hypoxia \>1000 m prior to the study

Exclusion Criteria:

* Impaired glucose tolerance (2 hour glucose: \>7.8 - 11.1 mmol/L)
* Type 2 diabetes mellitus
* Obstructive sleep apnea
* Chronic obstructive pulmonary disease