Supraspinal fatigue impedes recovery from a low-intensity sustained contraction in old adults.
Supraspinal fatigue impedes recovery from a low-intensity sustained contraction in old adults.
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脊柱上疲劳会阻碍老年人从低强度持续收缩中恢复。
DOI：
10.1152/japplphysiol.00799.2011
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
Hunter,SandraK
中科院分区：
文献类型：
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作者：
Yoon,Tejin;Schlinder-Delap,Bonnie;Keller,MandaL;Hunter,SandraK
这项研究确定了脊柱上疲劳和收缩特性对低强度持续收缩期间和恢复期间神经肌肉疲劳的年龄差异的贡献。14名年轻人(20.9±3.6岁，7名男性)和14名老年人(71.6±5.4岁，7名男性)在持续20%的最大自主收缩(MVC)直至肘屈肌任务失败的收缩过程中和之后，使用皮质刺激诱发自主激活和肌肉松弛。老年人的任务失败时间比年轻人长(分别为23.8±9.0min和11.5±3.9min，P<；0.001)。失败时间与肌纤维松弛的初始峰值速率和升压反应有关(P<；0.05)。经颅磁刺激产生的扭矩增量(叠加抽动；SIT)在短暂的MVC中增加，在疲劳收缩时增加(P<；0.001)，在恢复时减少(P=0.02)。在疲劳收缩和恢复期间，老年人的SIT增加幅度大于年轻人(P<；0.05)。在疲劳收缩后10min，老年人平均静脉扭矩恢复率低于青年组(分别为对照组的83.6±7.8%和75.1±8.7%，P=0.0 1)，且与SIT恢复有关(r=−0.5 9，R2=0.35，P<；0.001)。运动诱发电位(MEP)波幅和疲劳性收缩时的静止期老年人较年轻人增加较少(P<；0.05)。在低强度持续收缩中，随着年龄的增长，疲劳抵抗力更强，这归因于肌肉内部的机制。然而，在低强度疲劳性收缩后，最大强度的恢复对老年人比年轻人更不利，因为更严重的脊柱上疲劳。力量恢复可能是老年人群运动处方中需要考虑的一个重要变量。
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,r2= 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.