Muscle Contraction Force Conforms to Muscle Oxygenation during Constant Activation Voluntary Forearm Exercise

Thumbnail Image
Drouin, Patrick
Forbes, Stacey
Liu, Taylor
Lew, Lindsay
McGarity-Shipley, Ellen
Tschakovsky, Michael
Exercise , Oxygen delivery , Skeletal muscle
In electrically stimulated skeletal muscle, force production is downregulated when oxygen delivery is compromised and rapidly restored upon oxygen delivery restoration in the absence of cellular disturbance. Whether this “oxygen conforming” response of force occurs and is exercise intensity dependent during stable voluntary muscle activation in humans is unknown. In 12-participants (6-female), handgrip force, forearm muscle activation (electromyography; EMG), muscle oxygenation, and forearm blood flow (FBF) were measured during rhythmic handgrip exercise at forearm EMG achieving 50, 75 or 90% critical impulse (CI). 4-min of brachial artery compression to reduce FBF by ∼60% (Hypoperfusion) or sham compression (adjacent to artery; Control) was performed during exercise. Sham compression had no effect. Hypoperfusion rapidly reduced muscle oxygenation at all exercise intensities, resulting in contraction force per muscle activation (force/EMG) progressively declining over 4 min by ∼16% in 75 and 90% CI. No force/EMG decline occurred in 50% CI. Rapid restoration of muscle oxygenation post-compression was closely followed by force/EMG such that it was not different from Control within 30-sec for 90% CI and after 90-sec for 75% CI. Our findings reveal an oxygen conforming response does occur in voluntary exercising muscle in humans. Within the exercise modality and magnitude of fluctuation of oxygenation in this study, the oxygen conforming response appears to be exercise intensity dependent. Mechanisms responsible for this oxygen conforming response have implications for exercise tolerance and warrant investigation.