筋肉の疲労対策に関する生物学的バックアップ機構を解明(Built-In Backup System Helps Muscles Counteract Fatigue)

2025-10-21

2025-10-20 レンセラー工科大学(RPI)

レンセラー工科大学(RPI)のダグ・スワンク教授らの研究チームは、筋肉が疲労に抗うための「内蔵バックアップ機構」を発見した。研究では、マウスの筋線維を用いて疲労時の挙動を解析し、速筋線維(瞬発力を担う筋肉)で「ストレッチ活性化」と呼ばれる現象が疲労時に強く働くことを確認。これは筋肉が収縮前にわずかに伸びると、追加の力を発生させる仕組みであり、疲労が進むほど寄与率が高まり、最大で全力の約30%を補うことが分かった。従来、骨格筋では無視されてきた現象だが、実際には疲労軽減の鍵を握る可能性があるという。研究成果は『Journal of General Physiology』誌に掲載され、アスリートや筋疾患患者のリハビリ支援、筋持久力向上策への応用が期待されている。

The effect is specific to fast-twitch fibers, which are used to generate rapid, powerful movements like sprinting and jumping. (Getty Images)

<関連情報>

伸張活性化は、マウスの骨格筋線維の高速収縮における疲労による力の低下を抑制する
Stretch activation combats force loss from fatigue in fast-contracting mouse skeletal muscle fibers

Philip C. Woods,Douglas M. Swank,Mark S. Miller
Journal of General Physiology Published:August 11 2025
DOI:https://doi.org/10.1085/jgp.202413679

Stretch activation (SA) is the delayed increase in force following a rapid stretch and improves muscle performance during repetitive cyclical contractions in insect flight and cardiac muscles. Although historically considered too low to be physiologically relevant in skeletal muscle, our recent work showed that higher phosphate concentrations ([P_i]) increased SA in mouse soleus fibers. These results suggest SA has a role combating fatigue, which increases [P_i], lowers pH, and reduces active calcium concentration ([Ca²⁺]). To test this, we measured SA during Active, High [Ca²⁺] Fatigue and Low [Ca²⁺] Fatigue conditions in myosin heavy chain (MHC) I, IIA, IIX, and IIB fibers from mouse soleus and extensor digitorum longus muscles. In the fast-contracting MHC II fibers, calcium-activated isometric tension (F₀) decreased from Active to High [Ca²⁺] Fatigue to Low [Ca²⁺] Fatigue, as expected. Remarkably, SA tension (F_SA) was not decreased but remained unchanged or increased under High and Low [Ca²⁺] Fatigue, except for a small decrease in MHC IIB fibers in Low [Ca²⁺] Fatigue compared with Active. This results in SA’s percent contribution to total tension production (F_SA/[F₀ + F_SA]) being much greater (58–114%) under fatiguing conditions in fast-contracting MHC II fibers. The SA tension peak for MHC I fibers was not visibly apparent under either fatigue condition, and the peak was about 20% of MHC II fibers’ peaks under active conditions. Our results show SA improves force production under fatiguing conditions in MHC II fibers, which could play an important role in increasing endurance for muscles that are lengthened prior to shortening.