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

Abstract

Exhaustive single-leg exercise has been suggested to reduce time to task failure (Tlim) during subsequent exercise in the contralateral leg by exacerbating central fatigue development. We investigated the influence of acetaminophen (ACT), an analgesic which may blunt central fatigue development, on Tlim- during single-leg exercise completed both with, and without, prior fatiguing exercise of the contralateral leg. Fourteen recreationally-active men performed single-leg, severe-intensity knee extensor exercise to Tlim on the left (Leg1) and right (Leg2) legs without prior contralateral fatigue, and on Leg2 immediately following Leg1 (Leg2-CONTRA). The tests were completed following ingestion of 1 g ACT or maltodextrin (placebo) capsules. Intramuscular phosphorous-containing metabolites and substrates, and muscle activation, were assessed using 31P-MRS and electromyography, respectively. Tlim was not different between the Leg1ACT and Leg1PL conditions (402 ± 101 vs. 390 ± 106 s; P=0.11). There was also no difference in Tlim between Leg2ACT-CONTRA and Leg2PL-CONTRA (324 ± 85 vs. 311 ± 92 s; P=0.10), but Tlim was shorter in these tests compared to Leg2CON (385 ± 104 s; both P<0.05). There were no differences in intramuscular phosphorous-containing metabolites and substrates, or muscle activation, between the Leg1ACT and Leg1PL or the Leg2ACT-CONTRA and Leg2PL-CONTRA conditions (all P>0.05). These findings suggest that levels of metabolic perturbation and muscle activation are not different at task failure during single-leg severe-intensity knee extensor exercise completed with or without prior fatiguing exercise of the contralateral leg. Despite the existence of contralateral fatigue, ACT ingestion did not alter neuromuscular responses or exercise performance.