The Effects of Fatigue-Induced Velocity Loss on Performance and Neuromuscular Responses During Leg Extension Repetitions Performed With Maximal Intended Velocity

ABSTRACT: Pioske, JS, Arnett, JE, Roberts, TD, Ortega, DG, Schmidt, RJ, and Housh, TJ. The effects of fatigue-induced velocity loss on performance and neuromuscular responses during leg extension repetitions performed with maximal intended velocity. J Strength Cond Res XX(X): 000-000, 2026-Strength and power adaptations are dependent on the magnitude of the physiological stimulus during resistance exercise. Therefore, the present study examined the changes in velocity, force, power, and acute neuromuscular responses of the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) during maximal intended velocity (MIV) leg extension repetitions at velocity losses (VLoss) of 5, 15, and 25%. Twelve men (age: 21.67 ± 2.00 years) performed MIV unilateral leg extensions to failure at 40% 1RM with their nondominant leg. Mean and peak values for velocity, force, and power were recorded with a linear transducer, whereas surface electromyographic amplitude (EMG AMP) and mean power frequency (EMG MPF) values were assessed from the RF, VL, and VM. Repeated measures ANOVAs with Bonferroni-corrected post-hoc comparisons (α = 0.0083) revealed that mean and peak values for velocity and power (-5.9 to -42.3%), and peak values for force (-5.8 to -20.2%) decreased at all VLoss repetitions, whereas mean force decreased at 15% (-0.6%) and 25%VLoss (-0.9%) repetitions. EMG MPF decreased for the RF at all VLoss repetitions, whereas the VM and VL decreased at 15% and 25%VLoss, and 25%VLoss, respectively. EMG AMP increased for all 3 muscles at 15% and 25%VLoss. These findings suggested muscle-specific differences in the development of peripheral fatigue and possible intermuscular motor unit synchronization to maintain the MIV effort. It is recommended to use peak instead of mean VLoss to monitor the fatigue-induced decreases in force and power because peak values more closely tracked the fatigue-induced decreases in EMG MPF during MIV leg extensions.