Wingate performance and surface EMG frequency variables are not affected by caffeine ingestion

Area of Science:

• Exercise Physiology
• Sports Science
• Neuromuscular Function

Background:

• The ergogenic effect of caffeine on high-intensity exercise remains debated, with proposed mechanisms involving central nervous system stimulation and motor-unit excitation.
• Surface electromyography (EMG) frequency measures are used to assess motor-unit excitation non-invasively.
• Understanding caffeine's impact on neuromuscular function is crucial for optimizing athletic performance.

Purpose of the Study:

• To investigate the effects of caffeine ingestion on power output and surface EMG frequency variables during short-term, high-intensity cycling.
• To determine if caffeine alters central or peripheral neuromuscular drive during fatiguing exercise.

Main Methods:

• Eighteen recreationally active males completed a 30-second Wingate test (WG) under both placebo (PL) and caffeine (CAFF; 5 mg/kg) conditions, separated by a week.
• Subjects abstained from caffeine for 48 hours prior to each trial.
• Power output (peak power, minimum power, power decline) and surface EMG (vastus lateralis and gastrocnemius muscles) were recorded and analyzed for integrated EMG (IEMG), mean power frequency (MNPF), and median power frequency (MDPF).

Main Results:

• Caffeine ingestion did not significantly affect peak power, minimum power, or the percentage decline in power compared to placebo.
• Both caffeine and placebo trials showed significant decreases in MNPF and MDPF over time, indicating fatigue-related changes in motor-unit firing rates.
• No significant differences in IEMG changes or EMG signal amplitude decline were observed between caffeine and placebo groups, suggesting caffeine did not alter overall neuromuscular drive.

Conclusions:

• Caffeine (5 mg/kg) does not enhance power output during a 30-second high-intensity cycling bout.
• Caffeine does not appear to influence neuromuscular drive or the frequency characteristics of the EMG signal during this type of exercise.
• Fatigue mechanisms during the Wingate test likely involve peripheral factors, particularly in the gastrocnemius muscle, rather than central neural drive alterations.