Exercise Science Program, Department of Physical Therapy, Marquette University, Milwaukee, Wisconsin 53201, USA.
J Appl Physiol (1985). 2012 Mar;112(5):849-58. doi: 10.1152/japplphysiol.00799.2011. Epub 2011 Dec 15.
This study determined the contribution of supraspinal fatigue and contractile properties to the age difference in neuromuscular fatigue during and recovery from a low-intensity sustained contraction. Cortical stimulation was used to evoke measures of voluntary activation and muscle relaxation during and after a contraction sustained at 20% of maximal voluntary contraction (MVC) until task failure with elbow flexor muscles in 14 young adults (20.9 ± 3.6 yr, 7 men) and 14 old adults (71.6 ± 5.4 yr, 7 men). Old adults exhibited a longer time to task failure than the young adults (23.8 ± 9.0 vs. 11.5 ± 3.9 min, respectively, P < 0.001). The time to failure was associated with initial peak rates of relaxation of muscle fibers and pressor response (P < 0.05). Increments in torque (superimposed twitch; SIT) generated by transcranial magnetic stimulation (TMS) during brief MVCs, increased during the fatiguing contraction (P < 0.001) and then decreased during recovery (P = 0.02). The increase in the SIT was greater for the old adults than the young adults during the fatiguing contraction and recovery (P < 0.05). Recovery of MVC torque was less for old than young adults at 10 min post-fatiguing contraction (75.1 ± 8.7 vs. 83.6 ± 7.8% of control MVC, respectively, P = 0.01) and was associated with the recovery of the SIT (r = -0.59, r(2) = 0.35, P < 0.001). Motor evoked potential (MEP) amplitude and the silent period elicited during the fatiguing contraction increased less for old adults than young adults (P < 0.05). The greater fatigue resistance with age during a low-intensity sustained contraction was attributable to mechanisms located within the muscle. Recovery of maximal strength after the low-intensity fatiguing contraction however, was impeded more for old adults than young because of greater supraspinal fatigue. Recovery of strength could be an important variable to consider in exercise prescription of old populations.
本研究旨在确定在低强度持续收缩过程中和恢复期间，中枢神经系统疲劳和收缩性能对神经肌肉疲劳的年龄差异的贡献。使用皮质刺激在 14 名年轻成年人（20.9 ± 3.6 岁，7 名男性）和 14 名老年成年人（71.6 ± 5.4 岁，7 名男性）的肘屈肌中进行收缩时和收缩后测量自愿激活和肌肉放松的指标，收缩强度为最大自愿收缩（MVC）的 20%，直到任务失败。老年成年人比年轻成年人花费更长的时间来完成任务（分别为 23.8 ± 9.0 分钟和 11.5 ± 3.9 分钟，P < 0.001）。失败时间与肌肉纤维初始峰值松弛率和加压反应有关（P < 0.05）。经颅磁刺激（TMS）在短暂 MVC 期间产生的扭矩增量（叠加 Twitch；SIT）在疲劳收缩期间增加（P < 0.001），然后在恢复期间减少（P = 0.02）。在疲劳收缩和恢复期间，老年成年人的 SIT 增加幅度大于年轻成年人（P < 0.05）。与年轻成年人相比，老年成年人在疲劳收缩后 10 分钟的 MVC 扭矩恢复更差（分别为对照 MVC 的 75.1 ± 8.7%和 83.6 ± 7.8%，P = 0.01），并且与 SIT 的恢复相关（r = -0.59，r(2) = 0.35，P < 0.001）。在疲劳收缩期间诱发的运动诱发电位（MEP）幅度和静息期在老年成年人中增加幅度小于年轻成年人（P < 0.05）。在低强度持续收缩期间，年龄导致的抗疲劳性增加归因于肌肉内的机制。然而，由于中枢神经系统疲劳程度更大，在低强度疲劳收缩后，老年成年人的最大力量恢复受到更大的阻碍。在老年人的运动处方中，力量恢复可能是一个重要的考虑因素。
