Acute Responses to Different Velocity-Loss Thresholds During Squat Training With and Without Blood-Flow Restriction

To compare the acute effects on mechanical, metabolic, neuromuscular, and muscle contractile responses to different velocity-loss (VL) thresholds (20% and 40%) under distinct blood-flow conditions (free [FF] vs restricted [BFR]) in full squat (SQ). Twenty strength-trained men performed 4 SQ protocols with 60% 1-repetition maximum that differed in the VL within the set and in the blood-flow condition (FF20: FF with 20% VL; FF40: FF with 40% VL; BFR20: BFR with 20% VL; and BFR40: BFR with 40% VL). The level of BFR was 50% of the arterial occlusion pressure. Before and after the SQ protocols, the following tests were performed: (1) tensiomyography, (2) blood lactate, (3) countermovement jump, (4) maximal voluntary isometric SQ contraction, and (5) performance with the load that elicited a 1 m·s-1 at baseline measurements in SQ. No "BFR × VL" interactions were observed. BFR protocols resulted in fewer repetitions and lower increases in lactate concentration than FF protocols. The 40% VL protocols completed more repetitions but resulted in lower mechanical performance and electromyography median frequency during the exercise than the 20% VL protocols. At postexercise, the 40% VL protocols also experienced greater blood lactate concentrations, higher alterations in tensiomyography-derived variables, and accentuated impairments in SQ and countermovement-jump performances. The 20% VL protocols showed an increased electromyography median frequency at postexercise maximal voluntary isometric contraction. Despite BFR-accelerated fatigue development during exercise, a given VL magnitude induced similar impairments in the distinct performance indicators assessed, regardless of the blood-flow condition.