Mino Soushi, Tanaka Shigeharu, Teshima Takanori, Kubo Keitaro
Department of Life Science, The University of Tokyo, Meguro, Japan.
Department of Physical Education, Kokushikan University, Tokyo, Japan.
J Sports Med Phys Fitness. 2025 Mar;65(3):299-305. doi: 10.23736/S0022-4707.24.16434-1. Epub 2024 Dec 9.
Joint stiffness endurance is considered essential in many sports events. We previously reported that reduced joint stiffness due to repetitive hopping was associated with reduced active muscle stiffness. However, the determinants of active muscle stiffness endurance were unknown. This study aimed to compare the effects of repeated isometric contractions (ISO), which induced metabolic muscle fatigue, and repeated eccentric contractions (ECC), which induced muscle damage, on active muscle stiffness endurance.
Fourteen males performed two kinds of fatigue tasks (ISO and ECC) using only ankle joint. Before and after the fatigue tasks, changes in estimated muscle force and fascicle length during fast stretching were used to calculate the active muscle stiffness of the medial gastrocnemius muscle. In addition, the thickness of the plantar flexor muscles was measured before and after fatigue tasks.
After fatigue tasks, no difference in the relative increase of muscle thickness was found between ISO and ECC. The increase in torque during fast stretching did not change after both ISO and ECC. The increase in fascicle length during fast stretching significantly increased after ECC but not ISO. Active muscle stiffness significantly decreased after ECC but not ISO.
Active muscle stiffness decreased after repeated eccentric contractions damaging fascicles and did not change with repeated isometric contractions causing metabolic fatigue. These results implied that the joint stiffness reduction due to repetitive stretch-shortening cycle exercises shown in previous studies involved a reduction in active muscle stiffness due to repeated eccentric contractions.
关节僵硬耐力在许多体育赛事中被认为至关重要。我们之前报道过，由于反复单脚跳导致的关节僵硬降低与主动肌僵硬降低有关。然而，主动肌僵硬耐力的决定因素尚不清楚。本研究旨在比较诱导代谢性肌肉疲劳的重复等长收缩（ISO）和诱导肌肉损伤的重复离心收缩（ECC）对主动肌僵硬耐力的影响。
14名男性仅使用踝关节进行两种疲劳任务（ISO和ECC）。在疲劳任务前后，利用快速拉伸过程中估计的肌肉力量和肌束长度的变化来计算腓肠肌内侧的主动肌僵硬。此外，在疲劳任务前后测量跖屈肌的厚度。
疲劳任务后，ISO和ECC之间在肌肉厚度的相对增加方面未发现差异。快速拉伸过程中的扭矩增加在ISO和ECC后均未改变。快速拉伸过程中肌束长度的增加在ECC后显著增加，但在ISO后未增加。主动肌僵硬在ECC后显著降低，但在ISO后未降低。
反复进行离心收缩损伤肌束后，主动肌僵硬降低，而反复进行等长收缩导致代谢性疲劳时，主动肌僵硬没有变化。这些结果表明，先前研究中所示的由于反复进行拉长-缩短循环运动导致的关节僵硬降低涉及由于反复进行离心收缩导致的主动肌僵硬降低。
