Department of Health and Sport Science, University of Dayton, Dayton, OH, USA.
Department of Kinesiology and Health, Center for Movement and Rehabilitation Research, Georgia State University, 125 Decatur Street, Atlanta, GA, 30302, USA.
Exp Brain Res. 2019 Jul;237(7):1745-1757. doi: 10.1007/s00221-019-05548-5. Epub 2019 Apr 27.
Adult-like fine control of cyclical motor patterns found in locomotion develops into adolescence. Single-leg hopping in place is one such motor pattern where children have demonstrated a reduced capacity to control horizontal motion and match metronome cues. These developmental differences might arise from immature inter-segment coordination strategies and variability regulation. Therefore, the purpose of this study was to use an uncontrolled manifold (UCM) analysis to evaluate the control of segment angle variance (i.e., local variables) to stabilize leg length and leg orientation (i.e., task variables) in the sagittal plane between young adults and children aged 5-11 years old while hopping at different frequencies. The UCM space and its orthogonal space were constructed and segment angle variance was partitioned into these two spaces. Increased variance in the UCM space represents the stabilization of a task variable, while increased variance in its orthogonal space indicates a greater deviation of a task variable from its mean value. Our results indicated that children have developed an adult-like inter-segment coordination strategy of stabilizing leg length at mid-stance and leg orientation during flight. However, children might have an underdeveloped capacity to modulate leg length at take-off from cycle-to-cycle. Moreover, when increasing hopping frequency, children showed limited capacity to selectively increase leg-length stabilization. When decreasing hopping frequency, children illustrated an increased stabilization of leg orientation over the entire stance phase. Mid-stance leg-length stabilization might emerge with the motor skill; however, other inter-segment coordination strategies might continue to develop beyond 11-years of age.
成人般精细的周期性运动模式控制在运动中发展为青春期。单腿原地跳跃就是这样一种运动模式，儿童在这种运动模式中表现出控制水平运动和匹配节拍器提示的能力降低。这些发育差异可能源于不成熟的节段间协调策略和可变性调节。因此，本研究的目的是使用无控制流形（UCM）分析来评估在不同频率跳跃时，年轻人和 5-11 岁儿童在矢状面中控制节段角度方差（即局部变量）以稳定腿长和腿方向（即任务变量）的能力。构建了 UCM 空间及其正交空间，并将节段角度方差划分为这两个空间。UCM 空间中的方差增加表示任务变量的稳定，而其正交空间中的方差增加表示任务变量偏离其平均值的程度更大。我们的结果表明，儿童已经发展出一种成人般的节段间协调策略，即在中间站立和飞行期间稳定腿长和腿方向。然而，儿童可能在从一个周期到另一个周期的起飞过程中调节腿长的能力不足。此外，当增加跳跃频率时，儿童表现出有限的能力来选择性地增加腿长的稳定。当降低跳跃频率时，儿童在整个站立阶段表现出腿方向的稳定性增加。中间站立时腿长的稳定可能随着运动技能的发展而出现，但其他节段间协调策略可能会在 11 岁以后继续发展。
