Multi-Ingredient Pre-Workout Supplementation Does Not Influence Muscle Activation Following A Fatiguing Isokinetic Protocol

BACKGROUND: Multi-ingredient pre-workout supplements (MIPS) have been shown to enhance overall force retention and muscular endurance during prolonged or intermittent high-intensity exercises. Currently, however, the underlying mechanisms responsible for these neuromuscular benefits are poorly understood. PURPOSE: To examine the acute effects of a MIPS on muscle activation of the leg extensors during a fatiguing isokinetic protocol. METHODS: Twelve male subjects (mean age ± SD = 23.1 ± 2.2 years; body mass = 84.7 ± 9.0 kg; resistance training = 5.0 ± 3.4 hr·wk-1) visited the laboratory on three occasions. The first visit served as an orientation session to familiarize the subjects with testing procedures. For the second and third visits, subjects were randomly assigned to ingest one serving of the MIPS or placebo 30 minutes before completing a fatigue protocol on an isokinetic dynamometer that consisted of 60 maximal, alternating concentric and eccentric muscle actions of the leg extensors at 60°·s-1. Immediately before (PRE) and after (POST) the protocol, subjects were assessed for isometric peak torque at a 120° angle at the knee. Electromyographic (EMG) signals were recorded during the isometric muscle actions from the vastus medialis, rectus femoris, and vastus lateralis using wireless electrodes. Two-way (time: PRE and POST; condition: MIPS, placebo) repeated-measures analysis of variances (ANOVAs) and paired-samples t-tests were used to analyze normalized EMG amplitude (%) and isometric peak torque. RESULTS: There was no significant time x condition interaction (p = 0.316) for isometric peak torque, but there were main effects for condition (MIPS: 205 ± 48 N·m vs. placebo: 185 ± 44 N·m, p = 0.044) and time (PRE: 225 ± 53 N·m vs. POST: 165 ± 42 N·m, p < 0.001). For EMG amplitude, there were no significant (p > 0.05) interactions or main effects for condition, but there were main effects for time in all muscles (vastus medialis: POST = 145 ± 65% vs. PRE = 100 ± 0%, p = 0.036; rectus femoris: POST: 149 ± 62% vs. 100 ± 0%, p = 0.019; vastus lateralis: POST: 143 ± 52% vs. PRE: 100 ± 0%, p = 0.014). CONCLUSION: Our findings indicated acute MIPS supplementation had no effect on muscle activation as reflected by EMG amplitude, despite resulting in greater isometric peak torque before and after the fatigue protocol compared to placebo.