Background: Blood flow restriction (BFR) during low-intensity endurance exercise has been proposed as an effective strategy to induce neuromuscular and perceptual stress with reduced mechanical load. However, the acute effects of different BFR pressures, particularly at or above arterial occlusion pressure (AOP), on neuromuscular activation, perceptual responses, and performance remain unclear. Aim: To investigate the acute effects of increasing BFR pressures on electromyographic activity, perceptual responses, and maximal power output during low-intensity interval swim ergometer exercise. Materials and Methods: Eleven trained swimmers completed five interval training sessions at lactate threshold intensity under different BFR conditions applied to the upper limbs: 0%, 80%, 100%, 120%, and 140% of AOP. Surface electromyography (EMG) was recorded from the triceps brachii and latissimus dorsi, and root mean square (RMS) values were analyzed. Perceptual responses included rating of perceived exertion (RPE) and pain (VAS). Maximal power (PMAX) was assessed pre- and post-exercise using a 5-second maximal effort test on a swim ergometer. Results: Increasing BFR pressure significantly elevated perceptual responses. RPE was higher in all BFR conditions compared to control, with the greatest values observed at 140% AOP. Pain perception increased progressively with pressure, with 100%, 120%, and 140% AOP showing significantly higher values than lower pressures. EMG results demonstrated a reduction in triceps brachii RMS during the second set at 100%, 120%, and 140% AOP, while latissimus dorsi activity remained unchanged across conditions. No significant differences were observed in maximal power output either within or between conditions. Conclusions: Higher BFR pressures increase perceptual strain and reduce neuromuscular activation in the occluded muscle without impairing maximal power output. Among the tested conditions, 100% AOP appears to provide a balance between neuromuscular stress and tolerability, while supramaximal pressures further increase discomfort without additional performance impairment.
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