Department of Physiology, Monash University , Clayton, Victoria , Australia.
J Appl Physiol (1985). 2018 Feb 1;124(2):388-399. doi: 10.1152/japplphysiol.00535.2017. Epub 2017 Oct 26.
Isometric exercise is often prescribed during rehabilitation from injury to maintain muscle condition and prevent disuse atrophy. However, such exercise can lead to muscle soreness and damage. Here we investigate which parameters of isometric contractions are responsible for the damage. Bouts of 30 repetitions of maximum voluntary contractions of elbow flexors in 38 subjects were carried out and peak force, soreness, and tenderness were measured before the exercise, immediately afterwards, at 2 h, and at 24 h postexercise. When one arm was held near the optimum angle for force generation (90°), the force it produced was greater by 28% than by the other arm held at a longer length (155°). However, despite the smaller contraction forces of the muscle held at the longer length, after the exercise it exhibited a greater fall in force that persisted out to 24 h (20% fall) and more delayed soreness than the muscle exercised at 90° (7% fall at 24 h). The result indicates a length dependence of the damage process for isometric contractions at maximum effort. In four additional experiments, evidence was provided that the damage occurred during the plateau of the contraction and not the rising or relaxation phases. The damage had a prompt onset and was cumulative, continuing for the duration of the contraction. We interpret our findings in terms of the nonuniform lengthening of sarcomeres during the plateau of the contractions and conclude that muscle damage from isometric exercise is minimized if carried out at lengths below the optimum, using half-maximum or smaller contractions. NEW & NOTEWORTHY Isometric exercise, where muscle contracts while the limb is held fixed, is often possible for individuals rehabilitating from injury and can help maintain muscle condition. Such exercise has been reported to cause some muscle damage and soreness. We confirm this and show that to minimize damage, exercising muscles should be held at shorter than the optimum length for force and carried out at half-maximum effort or less.
等长运动常用于受伤康复期间，以保持肌肉状态并防止废用性萎缩。然而，这种运动可能会导致肌肉酸痛和损伤。在这里，我们研究了导致损伤的等长收缩的哪些参数。在 38 名受试者中进行了 30 次最大自主收缩的 30 次重复的肘部屈肌等长运动，在运动前、运动后即刻、2 小时和 24 小时后测量峰值力、酸痛和压痛。当一只手臂保持在产生力的最佳角度（90°）附近时，它产生的力比另一只手臂保持在较长长度（155°）时大 28%。然而，尽管保持在较长长度的肌肉的收缩力较小，但运动后，它的力下降更大，持续到 24 小时（下降 20%），并且比在 90°下运动的肌肉更延迟酸痛（24 小时下降 7%）。结果表明，在最大努力下，等长收缩的损伤过程与长度有关。在另外四项实验中，有证据表明损伤发生在收缩的平台期，而不是上升或松弛期。损伤的发生非常迅速，并且是累积性的，持续到收缩的整个过程。我们根据收缩平台期肌节的非均匀伸长来解释我们的发现，并得出结论，如果在最佳长度以下进行等长运动，使用半最大或更小的收缩，则可以最大程度地减少肌肉损伤。新的和值得注意的是，等长运动是指当肢体固定时肌肉收缩，这种运动对于受伤康复的个体来说通常是可行的，可以帮助保持肌肉状态。这种运动已被报道会引起一些肌肉损伤和酸痛。我们证实了这一点，并表明为了最大程度地减少损伤，应将运动的肌肉保持在短于产生力的最佳长度，并以半最大努力或更小的力量进行运动。
