Acetaminophen ingestion improves muscle activation and performance during a 3-min all-out cycling test

Purpose: Acute acetaminophen (ACT) ingestion has been shown to enhance cycling time-trial performance. The purpose of this study was to assess whether ACT ingestion enhances muscle activation and critical power (CP) during maximal cycling exercise. Methods: Sixteen active male participants completed two 3-min all-out tests against a fixed resistance on an electronically-braked cycle ergometer 60 minutes following ingestion of 1 g ACT or placebo (maltodextrin, PL). CP was estimated as the mean power output over the final 30 s of the test and W′ (the curvature constant of the power-duration relationship) was estimated as the work done above CP. The femoral nerve was stimulated every 30 s to measure membrane excitability (M-wave) and surface electromyography (EMGRMS) was recorded continuously to infer muscle activation. Results: Compared to PL, ACT ingestion increased CP (ACT: 297 ± 32 vs PL: 288 ± 31 W, P<0.001) and total work done (ACT: 66.4 ± 6.5 vs PL: 65.4 ± 6.4 kJ, P=0.03) without impacting Wˈ (ACT: 13.1 ± 2.9 vs PL: 13.6 ± 2.4 kJ, P=0.19) or the M-wave amplitude (P=0.66) during the 3-min all-out cycling test. Normalized EMG_RMS amplitude declined throughout the 3-min protocol in both PL and ACT conditions; however, the decline in EMG_RMS was attenuated in the ACT condition, with the EMG_RMS amplitude being greater compared to PL over the last 60 s of the test (P=0.04). Conclusion: These findings indicate that acute ACT ingestion might increase performance and CP during maximal cycling exercise by enhancing muscle activation.