運動単位活動の変化からみた筋疲労の研究

Changes of the Motor Unit Activities in Muscle Fatigue

Yamasaki Masahiro

Yamasaki Kazuhiko

Hisanaga Hajime

人類学雑誌

右手首に10kgの重さの負荷を課し, 上腕二頭筋の等張等尺性収縮を疲態に至るまで行なわせた。その後30秒の間隔を置き, 同様な作業を12回繰り返させた。これらの作業前及び第9回作業以降の作業終了後に, 針及び表面電極を用いて上腕二頭筋から筋電図を導出した。疲憊後には多相性活動電位の増加と活動電位の持続時間短縮が認められた。その結果を筋炎患者に見られる多相性活動電位発現機序及び筋疲労時の筋電図における従来の知見と比較考察した。表面筋電図では疲憊後, 周波数の徐波成分が増大した。この徐波化は疲憊後の多相性活動電位の増加と関連していることを指摘し, 多相性活動電位の増加は運動単位発射の不完全な同期化によるものと推論した。

Changes of the surface and needle electromyogram (EMG) of the biceps brachii in fatigue were investigated.

The subjects kept a 10kg weight applied to the wrist with the elbow flexed about 90°, until they were not able to maintain the elbow this position. This exhausting contraction was repeated twelve times with a pause of 30 sec between each contraction until eight times. The pause durations from 9th contraction to 12th were longer than 30 sec in order to record the EMG.

The surface EMG were recorded durings slight contraction in the biceps brachii after the 9th sustained contraction, and the needle EMG after 10th, 11th and 12th contractions.

In fatigue which followed exhausting contractions, the percentage of polyphasic action potentials recorded with a concentric needle electrode increased, and the duration of all action potentials decreased (Table 1 & 2). These results were discussed comparing with the characteristic EMG of myopathy and with the previous electromyographic studies on muscle fatigue. The power spectra of the bipolar surface EMG showed the frequency lowering in fatigue (Fig. 2 & Table 3).

It was ascertained that the correlation between the percentage of polyphasic action potentials and that of lower frequency components (below 40 Hz) was significant (Fig. 3). It was inferred that increased polyphasic action potentials and the frequency lowering in fatigue was due to synchronization between discharges from different motor units.

Biology [ 460 ]

jpn

日本人類学会

[ISSN] 0003-5505

[NCID] AN0012418X

[URI] http://www.journalarchive.jst.go.jp/japanese/jnlabstract_ja.php?cdjournal=ase1911&cdvol=85&noissue=3&startpage=229