Hodges Nicola J, Hayes Spencer, Horn Robert R, Williams A Mark
Research Institute for Sport and Exercise Science, Liverpool John Moores University, Henry Cotton Campus, 15-21 Webster Street, Liverpool L3 2ET, UK.
Ergonomics. 2005;48(11-14):1672-85. doi: 10.1080/00140130500101312.
It has been proposed that, when learning a motor skill, individuals initially freeze degrees of freedom to simplify control. There is limited empirical evidence to support this proposition. We examined this issue by monitoring the performance of a non-skilled individual learning a soccer chip shot with his non-dominant leg over 9 days of practice (425 trials). Principal component analysis was used to examine dimensional change. The most dramatic change occurred at the hip, with the range of motion decreasing during the first 5 days of practice and then increasing thereafter. A reverse pattern was observed at the knee and ankle. While showing a progression in control from proximal to distal, a further phase was observed where primary control was passed back to the hip. The degree of linear coupling between the joints also increased with practice until day 5, after which independent control was observed. The number of controlled dimensions did not change across practice. Radial error decreased over practice and kinematics relating to the hip were most predictive of error, especially early in practice. Freezing degrees of freedom was a strategy implemented across the first half of practice, after which point-independent control was gradually restored enabling successful consistent performance.
有人提出，在学习运动技能时，个体最初会冻结自由度以简化控制。支持这一观点的实证证据有限。我们通过监测一名非熟练个体在9天的练习（425次试验）中用非优势腿学习足球挑射的表现来研究这个问题。主成分分析用于检验维度变化。最显著的变化发生在髋关节，运动范围在练习的前5天减小，之后增大。在膝盖和脚踝处观察到相反的模式。虽然显示出从近端到远端控制的进展，但还观察到了另一个阶段，即主要控制又回到了髋关节。关节之间的线性耦合程度也随着练习增加，直到第5天，之后观察到独立控制。在整个练习过程中，受控维度的数量没有变化。径向误差随着练习而减小，与髋关节相关的运动学对误差的预测性最强，尤其是在练习早期。冻结自由度是练习前半段实施的一种策略，之后逐渐恢复独立控制，从而实现成功且一致的表现。
