Effects of endurance training on neuromuscular fatigue in healthy active men. Part I: Strength loss and muscle fatigue

Abstract

Purpose

The adaptations induced by endurance training on the neuromuscular function remain under investigation and, for methodological reasons, unclear. This study investigates the effects of cycling training on neuromuscular fatigue and its peripheral contribution measured during and immediately after cycling exercise.

Methods

Fourteen healthy men performed a fatigue test before a 9-week cycling program (PRE) and two tests after training: at the same absolute power output as PRE (POST_ABS) and based on the post-training maximal aerobic power (POST_REL). Throughout the tests and at exhaustion (EXH), maximal voluntary contraction (MVC) and peripheral fatigue were assessed in the quadriceps muscle by electrical nerve stimulation [single twitch (Pt); high-frequency doublet (Db₁₀₀) and low-to-high-frequency ratio (Db_10:100)].

Results

Time to EXH was longer in POST_ABS than PRE (34 ± 5 vs. 27 ± 4 min, P < 0.001), and POST_REL tended to be longer than PRE (30 ± 6 min, P = 0.053). MVC and peripheral fatigue were overall less depressed in POST_ABS than PRE at isotime. At EXH, MVC and Db_10:100 were similarly reduced in all sessions (–37 to − 42% and − 30 to − 37%, respectively). Db₁₀₀ tended to be less depressed in POST_ABS than PRE (–40 ± 9 vs. − 48 ± 16%, P = 0.050) and in POST_REL than PRE (–39 ± 9%, P = 0.071). Pt decreased similarly in POST_ABS and PRE (–52 ± 16 vs. − 54 ± 16%), but POST_REL tended to be less depressed than PRE (–48 ± 14%, P = 0.075).

Conclusions

This study confirms fatigue attenuation at isotime after training. Yet lower or similar fatigue at EXH indicates that, unlike previously suggested, fatigue tolerance may not be upregulated after 9 weeks of cycling training.

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