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Purpose <p>To compare post-exercise twitch contractile properties and M-wave characteristics after 60-km self-paced cycling in the heat following placebo (PLA) or 6% carbohydrate (CHO) ingestion as beverages or capsules.</p> Methods <p>Ten well-trained male cyclists completed five randomised Latin-square trials: water (H₂O), CHO beverage (CHO<sub>b</sub>), PLA beverage (PLA<sub>b</sub>), CHO capsules (CHO<sub>c</sub>), and PLA capsules (PLA<sub>c</sub>). Neuromuscular function was assessed before and after the time trial, and after a sustained knee-extensor contraction at 20% MVC to task failure. Measures included MVC, voluntary activation (VA), M-wave amplitude, evoked twitch properties, and integrated electromyography (iEMG).</p> Results <p>Performance time (<i>p</i> = 0.336) and time to task failure (<i>p</i> = 0.394) did not differ between conditions. iEMG increased during the 20% MVC in all trials (all <i>p</i> &lt; 0.0001). There were no condition × time interactions for MVC, VA, M-wave amplitude (all <i>p</i> ≥ 0.335), or twitch contractile variables (all <i>p</i> ≥ 0.115). Time effects were observed for rate of relaxation, which decreased in all trials (<i>p</i> = 0.0302 to <i>p</i> = 0.000239), contraction duration, which increased in all trials (<i>p</i> = 0.0412 to <i>p</i> = 0.000091), and half-relaxation time, which increased in H₂O, PLA<sub>c</sub> and CHO<sub>c</sub> (<i>p</i> ≤ 0.00322).</p> Conclusions <p>Prolonged self-paced cycling in the heat produced a reproducible neuromuscular response dominated by slowed twitch relaxation. However, 6% CHO ingestion did not clearly attenuate these changes compared with PLA, suggesting that the principal impairment reflected exercise and heat load rather than CHO availability or delivery mode.</p>

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Skeletal muscle twitch relaxation kinetics following heat stress endurance: carbohydrate versus placebo

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月21日

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  • Camila Nassif,
  • Jack Cannon,
  • Frank E. Marino

摘要

Purpose

To compare post-exercise twitch contractile properties and M-wave characteristics after 60-km self-paced cycling in the heat following placebo (PLA) or 6% carbohydrate (CHO) ingestion as beverages or capsules.

Methods

Ten well-trained male cyclists completed five randomised Latin-square trials: water (H₂O), CHO beverage (CHOb), PLA beverage (PLAb), CHO capsules (CHOc), and PLA capsules (PLAc). Neuromuscular function was assessed before and after the time trial, and after a sustained knee-extensor contraction at 20% MVC to task failure. Measures included MVC, voluntary activation (VA), M-wave amplitude, evoked twitch properties, and integrated electromyography (iEMG).

Results

Performance time (p = 0.336) and time to task failure (p = 0.394) did not differ between conditions. iEMG increased during the 20% MVC in all trials (all p < 0.0001). There were no condition × time interactions for MVC, VA, M-wave amplitude (all p ≥ 0.335), or twitch contractile variables (all p ≥ 0.115). Time effects were observed for rate of relaxation, which decreased in all trials (p = 0.0302 to p = 0.000239), contraction duration, which increased in all trials (p = 0.0412 to p = 0.000091), and half-relaxation time, which increased in H₂O, PLAc and CHOc (p ≤ 0.00322).

Conclusions

Prolonged self-paced cycling in the heat produced a reproducible neuromuscular response dominated by slowed twitch relaxation. However, 6% CHO ingestion did not clearly attenuate these changes compared with PLA, suggesting that the principal impairment reflected exercise and heat load rather than CHO availability or delivery mode.