Acute Effects of a Multi-Ingredient Preworkout Supplement on Peak Torque and Muscle Excitation During an Isokinetic Fatigue Protocol

The primary purpose of this study was to examine the acute effects of a multi-ingredient preworkout supplement (MIPS) on isometric, concentric, and eccentric peak torque and electromyographic (EMG) responses of the leg extensors during a fatiguing isokinetic protocol. Thirteen male subjects (mean age ± SD = 22.9 ± 2.2 years) were assigned in crossover fashion to ingest an MIPS or placebo before an isokinetic protocol that consisted of 30 maximal, concentric and eccentric muscle actions with EMG signals recorded from the vastus lateralis, rectus femoris, and vastus medialis muscles. Immediately before (PRE) and after (POST) the isokinetic fatigue protocol, subjects were assessed for isometric peak torque. The MIPS condition resulted in greater isometric (205 ± 48 vs. 185 ± 44 N·m, <i>p</i> = 0.04) and concentric (121 ± 34 vs. 103 ± 27 N·m, <i>p</i> = 0.015) torque values versus placebo (collapsed across time). For eccentric peak torque as well as EMG amplitude and frequency values, there were no significant (<i>p</i> > 0.05) interactions or main effects for each condition. These findings indicated that acute ingestion of the MIPS enhanced isometric and concentric peak torque of the leg extensors, which was not explained by changes in the EMG signal.