Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, California 90089, and Department of Biomedical Engineering, University of Southern California, Los Angeles, California 90089.
J Neurosci. 2013 Sep 18;33(38):15050-5. doi: 10.1523/JNEUROSCI.1968-13.2013.
Developmental improvements in dynamic manipulation abilities are typically attributed to neural maturation, such as myelination of corticospinal pathways, neuronal pruning, and synaptogenesis. However the contributions from changes in the peripheral motor system are less well understood. Here we investigated whether there are developmental changes in muscle activation-contraction dynamics and whether these changes contribute to improvements in dynamic manipulation in humans. We compared pinch strength, dynamic manipulation ability, and contraction time of the first dorsal interosseous muscle in typically developing preadolescent, adolescent, and young adults. Both strength and dynamic manipulation ability increased with age (p < 0.0001 and p < 0.00001, respectively). Surprisingly, adults had a 33% lower muscle contraction time compared with preadolescents (p < 0.01), and contraction time showed a significant (p < 0.005) association with dynamic manipulation abilities. Whereas decreases in muscle contraction time during development have been reported in the animal literature, our finding, to our knowledge, is the first report of this phenomenon in humans and the first finding of its association with manipulation. Consequently, the changes in the muscle contractile properties could be an important complement to neural maturation in the development of dynamic manipulation. These findings have important implications for understanding central and peripheral contributors to deficits in manipulation in atypical development, such as in children with cerebral palsy.
动态操作能力的发展改善通常归因于神经成熟，例如皮质脊髓通路的髓鞘形成、神经元修剪和突触发生。然而，外周运动系统变化的贡献还不太清楚。在这里，我们研究了肌肉激活-收缩动力学是否存在发育变化，以及这些变化是否有助于提高人类的动态操作能力。我们比较了典型发育的青少年前、青少年和年轻成年人的第一背侧骨间肌的捏力、动态操作能力和收缩时间。力量和动态操作能力都随着年龄的增长而增加（p<0.0001 和 p<0.00001，分别）。令人惊讶的是，成年人的肌肉收缩时间比青少年低 33%（p<0.01），并且收缩时间与动态操作能力有显著的（p<0.005）关联。虽然动物文献中已经报道了肌肉收缩时间在发育过程中的减少，但据我们所知，我们的发现是这种现象在人类中的首次报告，也是其与操作能力关联的首次发现。因此，肌肉收缩特性的变化可能是动态操作发展中神经成熟的重要补充。这些发现对于理解中枢和外周因素对非典型发育中操作缺陷的贡献具有重要意义，例如脑瘫儿童。
