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

Abstract

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 (Pmax) in the fatigued ipsilateral leg (FATleg) as well as the rested contralateral leg (RESTleg). On separate days, 12 trained cyclists performed right leg Pmax trials before and again 30s, 3, 5, and 10min after a cycling time trial (TT, 10min) performed either with their right or left leg. Fatigue was estimated by comparing exercise-induced changes in Pmax and maximum handgrip isometric force (Fmax). Mean power produced during the right and left leg TT’s did not differ (203±8 vs. 199±8W). Compared to pre-TT, FATleg Pmax was reduced by 22±3% at 30s post-TT and remained reduced by 9±2% at 5min post-TT (both P<0.05). Despite considerable power loss in the FATleg, post-TT RESTleg Pmax (596–603W) did not differ from pre-TT values (596±35W). There were no alterations in handgrip Fmax (529–547N). Our data suggest that any potential cross-over of fatigue, if present at all, was not sufficient to measurably compromise RESTleg Pmax in trained cyclists. These results along with the lack of changes in handgrip Fmax indicate that impairments in maximal voluntary neuromuscular function were specific to working muscles.

Effect of unilateral knee extensor fatigue on force and balance of the contralateral limb

“…In the literature, crossover fatigue effects have been observed as a decrease in voluntary muscle activation (Rattey et al 2006), force (Martin and Rattey 2007) and an increase in postural sway (Paillard et al 2010) of the contralateral non-fatigued limb. The findings of the present study are similar to published studies that have found no evidence of crossover force deficits associated with unilateral fatigue (Zijdewind et al 1998;Grabiner and Owings 1999;Todd et al 2003;Regueme et al 2007;Strang et al 2009;Place et al 2004;Ross et al 2007Ross et al , 2010Elmer et al 2013). The study by Zijdewind et al (1998) used a similar protocol with 30 % MVICs regularly interrupted with MVICs and brief rest periods in the right first dorsal interosseus muscle until failure and found no evidence of crossover force deficits.…”

“…This crossover or non-local fatigue effect has been identified for upper (Humphry et al 2004;Halperin et al 2014a, b) and lower limbs (Rattey et al 2006;Martin and Rattey 2007;McLean and Samorezov 2009;Paillard et al 2010;Halperin et al 2014a, b). Despite this evidence of crossover fatigue, controversy about its existence remains with many studies being unable to confirm its occurrence (Zijdewind et al 1998;Grabiner and Owings 1999;Todd et al 2003;Regueme et al 2007;Strang et al 2009;Place et al 2004;Ross et al 2007Ross et al , 2010Elmer et al 2013;Halperin et al 2014a, b). Hence there is a conflict in the literature that needs further exploration.…”

Neuromuscular Adaptations to Different Modes of Combined Strength and Endurance Training

“…E + S also showed unchanged and S + E increased maximum EMG after 24 weeks during maximal isometric muscle actions. A high correlation (p < 0.001, r = 0.83) between the individual changes in voluntary activation and maximal knee extension force was found for E + S during weeks [13][14][15][16][17][18][19][20][21][22][23][24]. Neural adaptations showed indications of being compromised and highly individual relating to changes in isometric strength when E + S-training was performed, while gains in one-repetition maximum, endurance performance and hypertrophy did not differ between the training modes.…”

“…Possible residual fatigue from a cycling endurance loading could be expected to compromise the quality of a subsequent lower-body strength loading session, as it is known that the quadriceps femoris muscle group contributes to continuous cycling with a significant percentage of its maximum activity even at relatively low workloads [19]. Additionally, impairments in maximal voluntary neuromuscular function following fatiguing cycling appear to be specific to the working muscles [18], and prolonged cycling exercise appears to limit the force-generating capacity to the muscles via both central and peripheral mechanisms, thus leading to a reduction in muscular capacity in the working muscles during subsequent activities [2,18,33]. Further clarification is needed as to whether fatigue-induced neural responses from the endurance component alone through inhibitory mechanisms can be regarded as responsible for disadvantageous neural adaptations following the present E + S training program, or whether the immediate addition of a strength-loading is the factor overloading the nervous system.…”

Unilateral isometric muscle fatigue decreases force production and activation of contralateral knee extensors but not elbow flexors

“…Todd et al (2003) showed that a sustained elbow flexor MVC was not affected by a previous sustained MVC with the contralateral elbow flexors. Finally, it was repeatedly found that extended aerobic activity such as cycling and marathon runs did not affect grip force, despite significant decrements in force and power production, as well as central activation with the lower limbs (Elmer et al 2013;Millet et al 2003;Place et al 2004;Ross et al 2010). Hence these conflicting results emphasize the need for further investigations.…”