Neuroscience Research Australia, Randwick, NSW, Australia.
J Physiol. 2013 Jul 15;591(14):3591-604. doi: 10.1113/jphysiol.2012.248559. Epub 2013 May 7.
During muscle fatigue, firing of small-diameter muscle afferents can decrease voluntary activation of the fatigued muscle. However, these afferents may have a more widespread effect on other muscles in the exercising limb. We examined if the firing of fatigue-sensitive afferents from elbow extensor muscles in the same arm reduces torque production and voluntary activation of elbow flexors. In nine subjects we examined voluntary activation of elbow flexors by measuring changes in superimposed twitches evoked by transcranial magnetic stimulation of the motor cortex during brief (2-3 s) maximal voluntary contractions (MVC). Inflation of a blood pressure cuff following a 2-min sustained MVC blocked blood flow to the fatigued muscle and maintained firing of small-diameter afferents. After a fatiguing elbow flexion contraction, maximal flexion torque was lower (26.0 ± 4.4% versus 67.9 ± 5.2% of initial maximal torque; means ± s.d.; P < 0.001) and superimposed twitches were larger (4.1 ± 1.1% versus 1.8 ± 0.2% ongoing MVC, P = 0.01) with than without ischaemia. After a fatiguing elbow extensor contraction, maximal flexion torque was also reduced (82.2 ± 4.9% versus 91.4 ± 2.3% of initial maximal torque; P = 0.007), superimposed twitches were larger (2.7 ± 0.7% versus 1.3 ± 0.2% ongoing MVC; P = 0.02) and voluntary activation lower (81.6 ± 8.2% versus 95.5 ± 6.9%; P = 0.04) with than without ischaemia. After a fatiguing contraction, voluntary drive to the fatigued muscles is reduced with continued input from small-diameter muscle afferents. Furthermore, fatigue of the elbow extensor muscles decreases voluntary drive to unfatigued elbow flexors of the same arm. Therefore, firing of small-diameter muscle afferents from one muscle can affect voluntary activation and hence torque generation of another muscle in the same limb.
在肌肉疲劳期间，小直径肌传入纤维的放电可能会降低疲劳肌肉的主动激活。然而，这些传入纤维可能对运动肢体的其他肌肉产生更广泛的影响。我们研究了同一手臂肘伸肌疲劳敏感传入纤维的放电是否会降低屈肘肌的扭矩产生和主动激活。在 9 名受试者中，我们通过测量经颅磁刺激运动皮层诱发的叠加 twitch 在短暂（2-3 s）最大自主收缩（MVC）期间的变化来检查肘屈肌的主动激活。在 2 分钟持续 MVC 后充气血压袖带会阻断疲劳肌肉的血流并维持小直径传入纤维的放电。在疲劳的肘屈肌收缩后，最大屈肘扭矩降低（26.0 ± 4.4%与初始最大扭矩的 67.9 ± 5.2%；平均值 ± s.d.；P < 0.001），叠加 twitch 更大（4.1 ± 1.1%与 1.8 ± 0.2%持续 MVC，P = 0.01）有缺血时。在疲劳的肘伸肌收缩后，最大屈肘扭矩也降低（82.2 ± 4.9%与初始最大扭矩的 91.4 ± 2.3%；P = 0.007），叠加 twitch 更大（2.7 ± 0.7%与 1.3 ± 0.2%持续 MVC；P = 0.02）和主动激活更低（81.6 ± 8.2%与 95.5 ± 6.9%；P = 0.04）有缺血时。在疲劳收缩后，来自小直径肌传入纤维的持续传入会降低疲劳肌肉的主动驱动。此外，肘伸肌的疲劳会降低同一手臂未疲劳肘屈肌的主动驱动。因此，来自一块肌肉的小直径肌传入纤维的放电会影响同一肢体的另一个肌肉的主动激活和扭矩产生。
