Deschenes Michael R, Holdren Ashley N, McCoy Raymond W
Department of Kinesiology, College of William & Mary, Williamsburg, VA 23187-8795, USA.
Med Sci Sports Exerc. 2008 May;40(5):856-63. doi: 10.1249/MSS.0b013e318164f4b6.
The purpose of this investigation was to determine whether young (21.7 yr) and aged (68.5 yr) men experienced similar responses to 7 d of muscle unloading (N = 10 per group).
Unilateral lower limb suspension (ULLS) was used to impose muscle unloading of the knee extensors. To compare the effects of unloading on aged and young men, a repeated-measures factorial ANOVA was used to assess those effects on isometric strength, as well as strength, total work, and average power during isokinetic contractions conducted at 0.53, 1.05, and 2.09 rad.s(-1).
Data showed that at slower speeds of movement, only a main effect of unloading was identified with young and aged men displaying similar and significant (P < 0.05) ULLS-induced decrements in strength, work, and power. The decrease in isometric strength correlated well with loss of electromyographic activity of contracting muscles (r = 0.79, P = 0.0002). At higher speeds of isokinetic contractions, not only was a main effect of age detected (young > aged), but it was also revealed that aged men, but not young men, experienced significant unloading-induced declines in muscle performance. Moreover, unloading resulted in a significant increase in plasma cortisol, a potent catabolic hormone, only among aged men. In contrast to other variables assessed, muscle endurance, quantified during 30 repetitions completed at 3.14 rad.s(-1), did not differ between age groups, nor was it altered by unloading.
These findings suggest that young and aged men respond differently to muscle unloading, but in assessing muscle performance, these differences are manifested only during faster contractile velocities.
本研究的目的是确定年轻男性（21.7岁）和老年男性（68.5岁）对7天肌肉卸载的反应是否相似（每组n = 10）。
采用单侧下肢悬吊（ULLS）来造成膝伸肌的肌肉卸载。为了比较卸载对老年男性和年轻男性的影响，使用重复测量析因方差分析来评估其对等长力量以及在0.53、1.05和2.09弧度·秒-1进行等速收缩时的力量、总功和平均功率的影响。
数据显示，在较慢的运动速度下，仅发现卸载的主效应，年轻男性和老年男性在力量、功和功率方面表现出相似且显著（P < 0.05）的ULLS诱导的下降。等长力量的下降与收缩肌肉肌电活动的丧失密切相关（r = 0.79，P = 0.0002）。在较高的等速收缩速度下，不仅检测到年龄的主效应（年轻>老年），而且还发现老年男性而非年轻男性经历了卸载诱导的肌肉性能显著下降。此外，卸载仅在老年男性中导致血浆皮质醇（一种强效分解代谢激素）显著增加。与评估的其他变量不同，在3.14弧度·秒-1完成30次重复期间量化的肌肉耐力在年龄组之间没有差异，也未因卸载而改变。
这些发现表明，年轻男性和老年男性对肌肉卸载的反应不同，但在评估肌肉性能时，这些差异仅在较快的收缩速度下才会表现出来。
