老年人对渐进性抗阻训练的强度反应的异质性：肌肉收缩性的贡献。
Heterogeneity of the strength response to progressive resistance exercise training in older adults: Contributions of muscle contractility.
机构信息
Ohio Musculoskeletal and Neurological Institute, Ohio University, Athens, OH, USA; Department of Biomedical Sciences, Ohio University, Athens, OH, USA.
School of Physical Therapy & Rehabilitation Sciences, University of South Florida, Tampa, FL, USA.
出版信息
Exp Gerontol. 2021 Sep;152:111437. doi: 10.1016/j.exger.2021.111437. Epub 2021 Jun 4.
BACKGROUND
Older adults display wide individual variability (heterogeneity) in the effects of resistance exercise training on muscle strength. The mechanisms driving this heterogeneity are poorly understood. Understanding of these mechanisms could permit development of more targeted interventions and/or improved identification of individuals likely to respond to resistance training interventions. Thus, this study assessed potential physiological factors that may contribute to strength response heterogeneity in older adults: neural activation, muscle hypertrophy, and muscle contractility.
METHODS
In 24 older adults (72.3 ± 6.8 years), we measured the following parameters before and after 12 weeks of progressive resistance exercise training: i) isometric leg extensor strength; ii) isokinetic (60°/sec) leg extensor strength; iii) voluntary (neural) activation by comparing voluntary and electrically-stimulated muscle forces (i.e., superimposed doublet technique); iv) muscle hypertrophy via dual-energy x-ray absorptiometry (DXA) estimates of regional lean tissue mass; and v) intrinsic contractility by electrically-elicited twitch and doublet torques. We examined associations between physiological factors (baseline values and relative change) and the relative change in isometric and isokinetic muscle strength.
RESULTS
Notably, changes in quadriceps contractility were positively associated with the relative improvement in isokinetic (r = 0.37-0.46, p ≤ 0.05), but not isometric strength (r = 0.09-0.21). Change in voluntary activation did not exhibit a significant association with the relative improvements in either isometric or isokinetic strength (r = 0.35 and 0.33, respectively; p > 0.05). Additionally, change in thigh lean mass was not significantly associated with relative improvement in isometric or isokinetic strength (r = 0.09 and -0.02, respectively; p > 0.05). Somewhat surprising was the lack of association between exercise-induced changes in isometric and isokinetic strength (r = 0.07).
CONCLUSIONS
The strength response to resistance exercise in older adults appears to be contraction-type dependent. Therefore, future investigations should consider obtaining multiple measures of muscle strength to ensure that strength adaptations are comprehensively assessed. Changes in lean mass did not explain the heterogeneity in strength response for either contraction type, and the data regarding the influence of voluntary activation was inconclusive. For isokinetic contraction, the strength response was moderately explained by between-subject variance in the resistance-exercise induced changes in muscle contractility.
背景
老年人在抗阻训练对肌肉力量的影响方面表现出广泛的个体差异（异质性）。导致这种异质性的机制尚不清楚。了解这些机制可以允许开发更有针对性的干预措施和/或更好地识别可能对抗阻训练干预有反应的个体。因此，本研究评估了可能导致老年人力量反应异质性的潜在生理因素：神经激活、肌肉肥大和肌肉收缩性。
方法
在 24 名老年人（72.3±6.8 岁）中，我们在进行 12 周渐进式抗阻训练前后测量了以下参数：i）等长腿部伸肌力量；ii）等速（60°/秒）腿部伸肌力量；iii）通过比较自愿和电刺激肌肉力量来测量自愿（神经）激活（即叠加双脉冲技术）；iv）通过双能 X 射线吸收法（DXA）估计区域瘦组织量来测量肌肉肥大；v）通过电诱发的单次收缩和双脉冲扭矩测量内在收缩性。我们检查了生理因素（基线值和相对变化）与等长和等速肌肉力量的相对变化之间的关联。
结果
值得注意的是，股四头肌收缩性的变化与等速（r=0.37-0.46，p≤0.05）但不是等长力量的相对改善呈正相关（r=0.09-0.21）。自愿激活的变化与等长或等速力量的相对改善均无显著相关性（r=0.35 和 0.33，分别；p>0.05）。此外，大腿瘦体重的变化与等长或等速力量的相对改善均无显著相关性（r=0.09 和 -0.02，分别；p>0.05）。令人惊讶的是，等长和等速力量的运动诱导变化之间缺乏关联（r=0.07）。
结论
老年人对抗阻训练的力量反应似乎取决于收缩类型。因此，未来的研究应该考虑获得多种肌肉力量测量值，以确保全面评估力量适应。对于两种收缩类型，瘦体重的变化都不能解释力量反应的异质性，而关于自愿激活影响的数据则不确定。对于等速收缩，力量反应在一定程度上可以通过肌肉收缩性在阻力训练诱导变化方面的个体间差异来解释。
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