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.
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机译:在肌肉疲劳期间,小直径肌肉传入神经的击发会减少疲劳肌肉的自发激活。但是,这些传入球可能会对运动肢体中的其他肌肉产生更广泛的影响。我们检查了同一手臂中肘关节伸肌对疲劳敏感传入神经的发射是否减少了扭矩产生和自愿屈肘屈肌。在九名受试者中,我们通过测量短暂(2–3 s)最大自主收缩(MVC)期间经颅磁刺激运动皮层引起的叠加抽搐的变化,检查了肘部屈肌的主动激活。持续2分钟的MVC后血压袖带的膨胀会阻止血液流向疲劳的肌肉,并保持小直径传入神经的发射。在使肘部屈曲疲劳后,最大屈曲扭矩降低(26.0±4.4%对初始最大扭矩的67.9±5.2%;平均值±sd; P <0.001),并且叠加的抽搐较大(4.1±1.1%对1.8±0.2%进行性MVC,P = 0.01)伴缺血性缺血。在疲劳的肘部伸肌收缩后,最大屈曲扭矩也降低了(82.2±4.9%比初始最大扭矩的91.4±2.3%; P = 0.007),叠加的抽搐也更大(2.7±0.7%比1.3±0.2%的持续MVC; P = 0.02)和有意识缺血时的自愿激活率较低(81.6±8.2%对95.5±6.9%; P = 0.04)。在疲劳收缩之后,通过小直径肌肉传入者的持续输入,减少了对疲劳肌肉的自愿驱动。此外,肘部伸肌的疲劳会减少对同一手臂的未屈肘屈肌的自发驱动力。因此,从一根肌肉发射小直径的肌肉传入会影响自愿激活,从而影响同一肢体中另一根肌肉的扭矩生成。
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