Ohio Musculoskeletal & Neurological Institute (OMNI), Athens, OH, USA.
Exp Gerontol. 2013 Sep;48(9):920-5. doi: 10.1016/j.exger.2013.06.008. Epub 2013 Jul 4.
The interrelationship between muscle strength, motor unit (MU) number, and age is poorly understood, and in this study we sought to determine whether age-related differences in muscle strength are moderated by estimates of functioning MU number and size. Eighteen older adults (OA; 67 ± 1.20 years) and 24 young adults (YA; 22 ± 0.74 years) participated in this study. Maximum voluntary pinch-grip strength of the nondominant hand was determined and estimates of MU number were obtained from the abductor pollicis brevis muscle using the noninvasive motor unit number index (MUNIX) technique. The MUNIX technique was also utilized to derive a motor unit size index (MUSIX). An analysis of covariance (Age Group × MUNIX or MUSIX) was used to test heterogeneity of regression slopes, with body mass and gender serving as covariates. We observed that the slope of pinch-grip strength on the estimated number of MUs between YA and OA differed, indicated by an Age Group × MUNIX interaction (p = 0.04). Specifically, after controlling for the effect of body mass and gender, the slope in OA was significantly positive (0.14 ± 0.06 N/MUs, p = 0.03), whereas no such relationship was found in YA (-0.08 ± 0.09 N/MUs, p = 0.35). A significant Age Group × MUSIX interaction was also observed for strength (p < 0.01). In contrast to MUNIX, the slope in younger adults was significantly positive (0.48 ± 0.11 N/μV, p < 0.01), whereas no such relationship was found in older adults (-0.30 ± 0.22 N/μV, p = 0.18). These findings indicate that there is an interrelationship between muscle strength, MU numbers, and aging, which suggests that a portion of muscle weakness in seniors may be attributable to the loss of functioning motor units.
肌肉力量、运动单位（MU）数量和年龄之间的相互关系尚未得到充分理解，本研究旨在确定肌肉力量的年龄相关性差异是否受功能 MU 数量和大小的估计值调节。18 名老年人（OA；67±1.20 岁）和 24 名年轻人（YA；22±0.74 岁）参与了这项研究。使用非侵入性运动单位数量指数（MUNIX）技术，测定非优势手的最大自愿捏力，并从拇短展肌获得 MU 数量的估计值。MUNIX 技术还用于得出运动单位大小指数（MUSIX）。协方差分析（年龄组×MUNIX 或 MUSIX）用于检验回归斜率的异质性，以体重和性别为协变量。我们观察到，YA 和 OA 之间的捏力与估计的 MU 数量之间的斜率存在差异，这表明年龄组与 MUNIX 的相互作用（p=0.04）。具体来说，在控制体重和性别的影响后，OA 中的斜率明显为正（0.14±0.06 N/MUs，p=0.03），而在 YA 中则没有发现这种关系（-0.08±0.09 N/MUs，p=0.35）。还观察到强度的显著年龄组与 MUSIX 相互作用（p<0.01）。与 MUNIX 相反，年轻成年人的斜率明显为正（0.48±0.11 N/μV，p<0.01），而在老年人中则没有发现这种关系（-0.30±0.22 N/μV，p=0.18）。这些发现表明肌肉力量、MU 数量和衰老之间存在相互关系，这表明老年人的部分肌肉无力可能归因于功能运动单位的丧失。
