Raiteri Brent J, Cresswell Andrew G, Lichtwark Glen A
Centre for Sensorimotor Performance, School of Human Movement and Nutrition Sciences, The University of Queensland, Brisbane, Queensland, Australia.
Centre for Sensorimotor Performance, School of Human Movement and Nutrition Sciences, The University of Queensland, Brisbane, Queensland, Australia
J Appl Physiol (1985). 2015 May 15;118(10):1193-9. doi: 10.1152/japplphysiol.00825.2014. Epub 2015 Jan 22.
Because of the approximate linear relationship between muscle force and muscle activity, muscle forces are often estimated during maximal voluntary isometric contractions (MVICs) from torque and surface electromyography (sEMG) measurements. However, sEMG recordings from a target muscle may contain cross-talk originating from nearby muscles, which could lead to erroneous force estimates. Here we used ultrasound imaging to measure in vivo muscle fascicle length (Lf) changes and sEMG to measure muscle activity of the tibialis anterior, medial gastrocnemius, lateral gastrocnemius, and soleus muscles during ramp MVICs in plantar and dorsiflexion directions (n = 8). After correcting longitudinal Lf changes for ankle rotation, the antagonist Lf at peak antagonist root-mean-square (RMS) amplitude were significantly longer than the agonist Lf at this sEMG-matched level. On average, Lf shortened from resting length by 1.29 to 2.90 mm when muscles acted as agonists and lengthened from resting length by 0.43 to 1.16 mm when muscles acted as antagonists (depending on the muscle of interest). The lack of fascicle shortening when muscles acted as antagonists indicates that cocontraction was likely to be negligible, despite cocontraction as determined by sEMG of between 7 and 23% MVIC across all muscles. Different interelectrode distances (IEDs) over the plantar flexors revealed significantly higher antagonist RMS amplitudes for the 4-cm IEDs compared with the 2-cm IEDs, which further indicates that cross-talk was present. Consequently, investigators should be wary about performing agonist torque corrections for isometric plantar flexion and dorsiflexion based on the antagonist sEMG trace and predicted antagonist moment.
由于肌肉力量与肌肉活动之间存在近似线性关系，因此在最大自主等长收缩（MVIC）期间，常根据扭矩和表面肌电图（sEMG）测量来估计肌肉力量。然而，目标肌肉的sEMG记录可能包含来自附近肌肉的串扰，这可能导致错误的力量估计。在此，我们利用超声成像测量活体肌肉束长度（Lf）变化，并使用sEMG测量在跖屈和背屈方向进行斜坡MVIC期间胫骨前肌、腓肠肌内侧头、腓肠肌外侧头和比目鱼肌的肌肉活动（n = 8）。在对踝关节旋转引起的纵向Lf变化进行校正后，在该sEMG匹配水平下，拮抗肌在峰值拮抗肌均方根（RMS）振幅时的Lf显著长于主动肌的Lf。平均而言，当肌肉作为主动肌时，Lf从静息长度缩短1.29至2.90毫米，而当肌肉作为拮抗肌时，Lf从静息长度延长0.43至1.16毫米（取决于所关注的肌肉）。当肌肉作为拮抗肌时缺乏肌束缩短表明，尽管通过sEMG测定所有肌肉的共收缩为MVIC的7%至23%，但共收缩可能可忽略不计。在跖屈肌上不同的电极间距（IED）显示，与2厘米的IED相比，4厘米的IED的拮抗肌RMS振幅显著更高，这进一步表明存在串扰。因此，研究人员在基于拮抗肌sEMG轨迹和预测的拮抗力矩对等长跖屈和背屈进行主动肌扭矩校正时应谨慎。
