Sex-specific effects of fatiguing handgrip plus blood flow restriction on upper limb neuromuscular characteristics during a repetitive shoulder height task.

Blood flow restriction (BFR) aims to accelerate reperfusion post-effort and could provide benefits after shoulder fatiguing work. However, sex-specific effects of localized BFR on whole-limb features are unknown. Ten females and eleven males performed three 30-second repetitive pointing tasks (RPTs) (pre-fatigue, post-fatigue, and recovery). The fatiguing protocol was an intermittent submaximal handgrip task performed until failure to meet the target force (50% of maximum grip strength). Participants completed two sessions: without BFR and with 50% BFR applied to the upper arm during the handgrip task. Electromyography was recorded during the handgrip and each RPT. Muscle thickness (ultrasound), and arm circumferences were recorded after each RPT sequence. Time-to-fatigue was unaffected by condition or sex. Females exhibited greater forearm electromyography amplitude and greater decreases in flexor carpi radialis and brachioradialis median power frequency (MdPF). Post-fatigue, forearm circumference and muscle thickness increased significantly in both sexes. Females demonstrated greater forearm muscle thickness changes, while males showed more consistent increases in biceps brachii thickness under BFR. During the RPTs, males displayed significant increases in MdPF of middle deltoid and pectoralis major, while females showed persistent fatigue effects in forearm muscles. Results suggest that sex differences exist in whole-limb mechanisms of fatigue and BFR adaptations.