Bazzy A R, Korten J B, Haddad G G
J Appl Physiol (1985). 1986 Sep;61(3):1012-7. doi: 10.1152/jappl.1986.61.3.1012.
We studied the relationship between changing elbow joint angle and the power spectral density of the biceps brachii muscle electromyogram (EMG) during submaximal isometric contractions. For this purpose, we recorded the EMG of the biceps brachii muscle with surface electrodes in 13 subjects. Each subject held a 2.8-kg weight and contracted the biceps isometrically for 30 s at one of two lengths. The length of the muscle was changed by flexing the forearm toward the upper arm to form an angle of 135 degrees (L1) or 45 degrees (L2). We found that the mean centroid frequency (fc) of the EMG power spectral density was 26% lower at L1 than at L2 (P less than 0.01). For each subject there was no significant change in fc during the isometric contraction at either angle. In addition, in nine subjects who sustained fatiguing contractions of the biceps with a 6-kg load, fc decreased by 15% (P less than 0.025). These data suggest that a change in the length at which a muscle contracts isometrically can alter or induce indirectly an alteration in the frequency content of its EMG. This finding may have important implications for the assessment of respiratory muscle EMG especially during loaded breathing.
我们研究了次最大等长收缩期间肘关节角度变化与肱二头肌肌电图（EMG）功率谱密度之间的关系。为此，我们用表面电极记录了13名受试者肱二头肌的EMG。每位受试者手持2.8千克重物，在两个长度之一上等长收缩肱二头肌30秒。通过将前臂向上臂弯曲形成135度（L1）或45度（L2）的角度来改变肌肉长度。我们发现，L1时EMG功率谱密度的平均质心频率（fc）比L2时低26%（P<0.01）。对于每位受试者，在任一角度进行等长收缩期间，fc均无显著变化。此外，在9名用6千克负荷持续进行肱二头肌疲劳性收缩的受试者中，fc下降了15%（P<0.025）。这些数据表明，肌肉等长收缩时长度的变化可直接改变或间接诱导其EMG频率成分的改变。这一发现可能对呼吸肌EMG的评估具有重要意义，尤其是在负荷呼吸期间。
