Fatigue is specific to working muscles: no cross-over with single-leg cycling in trained cyclists

Fatigue induced via a maximal isometric contraction of a single limb muscle group can evoke a “cross-over” of fatigue that reduces voluntary muscle activation and maximum isometric force in the rested contralateral homologous muscle group. We asked whether a cross-over of fatigue also occurs when fatigue is induced via high-intensity endurance exercise involving a substantial muscle mass. Specifically, we used high-intensity single-leg cycling to induce fatigue and evaluated associated effects on maximum cycling power (P _max) in the fatigued ipsilateral leg (FAT_leg) as well as the rested contralateral leg (REST_leg). On separate days, 12 trained cyclists performed right leg P _max trials before and again 30 s, 3, 5, and 10 min after a cycling time trial (TT, 10 min) performed either with their right or left leg. Fatigue was estimated by comparing exercise-induced changes in P _max and maximum handgrip isometric force (F _max). Mean power produced during the right and left leg TTs did not differ (203 ± 8 vs. 199 ± 8 W). Compared to pre-TT, FAT_leg P _max was reduced by 22 ± 3 % at 30 s post-TT and remained reduced by 9 ± 2 % at 5 min post-TT (both P < 0.05). Despite considerable power loss in the FAT_leg, post-TT REST_leg P _max (596–603 W) did not differ from pre-TT values (596 ± 35 W). There were no alterations in handgrip F _max (529–547 N). Our data suggest that any potential cross-over of fatigue, if present at all, was not sufficient to measurably compromise REST_leg P _max in trained cyclists. These results along with the lack of changes in handgrip F _max indicate that impairments in maximal voluntary neuromuscular function were specific to working muscles.