Perceptual, metabolic, and neuromuscular responses to 10, 20, and 30% velocity loss thresholds during the barbell back-squat.

Introduction: This study compared the effects of 10, 20, and 30% velocity loss (VL) thresholds on differential ratings of perceived exertion (dRPE), lactate, and countermovement jump height (CMJ) during, immediately post-, and 24 hours post-five sets of the barbell back-squat.
Methods: In a randomised-crossover design, 15 resistance-trained males completed five sets of the back-squat with an initial mean concentric velocity of 0.70±0.01 m·s-1 and a set termination threshold of either 10% (0.63m·s-1), 20% (0.56m·s-1), or 30% (0.49m·s-1) VL. External load was manipulated throughout each session to ensure the first repetition of sets 2-5 was 0.70±0.06 m·s-1. Participants provided fingertip lactate at the completion of each set, while CMJ was collected pre-, post-, and 24 hours post-exercise. dRPE for the legs and lungs was provided at the completion of the 5th set. Three minutes rest was provided between sets, while barbell velocity was assessed during exercise to guide set termination.
Results: Peak lactate responses in the 30% condition were likely (effect size ±90confidence interval: 1.45±2.29) and almost certainly (4.56±1.66) greater when compared to the 20% and 10%, respectively. In the 10, 20, and 30% conditions, CMJ height was reduced by 11.3% (±2.4), 14.0% (±3.3), and 20.0% (±3.4), immediately post-exercise. Additionally, dRPE (mean (±SD)) of the legs and lungs were, 10%: 27±12 and 20±9; 20%: 53±16 and 50±17; and 30%: 65±18 and 65±17. At 24 hours post-training, CMJ performance was, 10%: +0.7% (±2.4); 20%: -0.6% (±2.0); and 30%: -2.7% (±2.7).
Conclusion: Different VL thresholds during the back-squat cause varying perceptual, metabolic, and neuromuscular responses. The use of 30% VL thresholds can cause substantially greater metabolic responses and potentially attenuate neuromuscular function at 24 hours post-training. Alternatively, a 10% VL can mitigate perceived exertion and changes in metabolic responses. These findings should be considered during the planning of velocity-based resistance training programmes.

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