Geriatric Research, Education, and Clinical Center, George E. Whalen VA Medical Center, Salt Lake City, Utah; Department of Exercise and Sport Science, University of Utah, Salt Lake City, Utah;
Geriatric Research, Education, and Clinical Center, George E. Whalen VA Medical Center, Salt Lake City, Utah; Department of Internal Medicine, Division of Geriatrics, University of Utah, Salt Lake City, Utah; and.
Am J Physiol Regul Integr Comp Physiol. 2014 Jun 15;306(12):R934-40. doi: 10.1152/ajpregu.00043.2014. Epub 2014 Apr 16.
Greater peripheral quadriceps fatigue at the voluntary termination of single-leg knee-extensor exercise (KE), compared with whole-body cycling, has been attributed to confining group III and IV skeletal muscle afferent feedback to a small muscle mass, enabling the central nervous system (CNS) to tolerate greater peripheral fatigue. However, as task specificity and vastly differing systemic challenges may have complicated this interpretation, eight males were studied during constant workload trials to exhaustion at 85% of peak workload during single-leg and double-leg KE. It was hypothesized that because of the smaller muscle mass engaged during single-leg KE, a greater magnitude of peripheral quadriceps fatigue would be present at exhaustion. Vastus lateralis integrated electromyogram (iEMG) signal relative to the first minute of exercise, preexercise to postexercise maximal voluntary contractions (MVCs) of the quadriceps, and twitch-force evoked by supramaximal magnetic femoral nerve stimulation (Qtw,pot) quantified peripheral quadriceps fatigue. Trials performed with single-leg KE (8.1 ± 1.2 min; 45 ± 4 W) resulted in significantly greater peripheral quadriceps fatigue than double-leg KE (10 ± 1.3 min; 83 ± 7 W), as documented by changes in the iEMG signal (147 ± 24 vs. 85 ± 13%), MVC (-25 ± 3 vs. -12 ± 3%), and Qtw,pot (-44 ± 6 vs. -33 ± 7%), for single-leg and double-leg KE, respectively. Therefore, avoiding concerns over task specificity and cardiorespiratory limitations, this study reveals that a reduction in muscle mass permits the development of greater peripheral muscle fatigue and supports the concept that the CNS tolerates a greater magnitude of peripheral fatigue when the source of group III/IV afferent feedback is limited to a small muscle mass.
与全身骑自行车相比，单腿伸膝运动（KE）在自愿终止时，四肢的股四头肌疲劳程度更大，这归因于将 III 组和 IV 组骨骼肌传入反馈限制在小的肌肉群中，从而使中枢神经系统（CNS）能够耐受更大的外周疲劳。然而，由于任务特异性和差异很大的系统挑战可能使这种解释复杂化，因此在 85%的峰值工作负荷下，对 8 名男性进行了单腿和双腿 KE 直至疲劳的恒定工作负荷试验。假设由于单腿 KE 期间涉及的肌肉群较小，因此在疲劳时会出现更大程度的四肢股四头肌疲劳。股外侧肌积分肌电图（iEMG）信号相对于运动的前 1 分钟，运动前至运动后股四头肌的最大自主收缩（MVC），以及最大磁股神经刺激（Qtw，pot）诱发的抽搐力量化四肢股四头肌疲劳。单腿 KE （8.1 ± 1.2 分钟；45 ± 4 W）的试验结果导致明显更大的四肢股四头肌疲劳，比双腿 KE（10 ± 1.3 分钟；83 ± 7 W），如 iEMG 信号的变化（147 ± 24 与 85 ± 13%），MVC（-25 ± 3 与-12 ± 3%）和 Qtw，pot（-44 ± 6 与-33 ± 7%）分别为单腿和双腿 KE。因此，本研究避免了对任务特异性和心肺限制的关注，揭示了肌肉质量的减少可导致更大的外周肌肉疲劳，并支持了这样的概念，即当 III/IV 组传入反馈的来源仅限于较小的肌肉群时，CNS 可耐受更大程度的外周疲劳。
