Contralateral fatigue during severe-intensity single-leg exercise: influence of acute acetaminophen ingestion

Exhaustive single-leg exercise has been suggested to reduce time to task failure (T-lim) during subsequent exercise in the contralateral leg by exacerbating central fatigue development. We investigated the influence of acetaminophen (ACT), an analgesic that may blunt central fatigue development, on T-lim during single-leg exercise completed with and without prior fatiguing exercise of the contralateral leg. Fourteen recreationally active men performed single-leg severe-intensity knee-extensor exercise to T-lim on the left (Leg(1)) and right (Leg(2)) legs without prior contralateral fatigue and on Leg(2) immediately following Leg(1) (Leg(2)-(CONTRA)). The tests were completed following ingestion of 1-g ACT or maltodextrin [placebo (PL)] capsules. Intramuscular phosphorus-containing metabolites and substrates and muscle activation were assessed using P-31-MRS and electromyography, respectively. T-lim was not different between Leg(1ACT) and Leg(1PL) conditions (402 +/- 101 vs. 390 +/- 106 s. P = 0.11). There was also no difference in T-lim between Leg(2ACT-CONTRA) and Leg(2PL-CONTRA) (324 +/- 85 vs. 311 +/- 92 s, P = 0.10), but T-lim was shorter in Leg(2ACT-CONTRA) and Leg(2PL-CONTRA) than in Leg(2CON) (385 +/- 104 s, both P < 0.05). There were no differences in intramuscular phosphorus-containing metabolites and substrates or muscle activation between Leg(1ACT) and Leg(1PL) and between Leg(2ACT-CONTRA) and Leg(2PL-CONTRA) (all P > 0.05). These findings suggest that levels of metabolic perturbation and muscle activation at Thin are not different during single-leg severe-intensity knee-extensor exercise completed with or without prior fatiguing exercise of the contralateral leg. Despite contralateral fatigue. ACT ingestion did not alter neuromuscular responses, muscle metabolites, or exercise performance.