We investigated the role of rate limiting factors in development using walking as a model system. The achievement of bipedal posture and locomotion are among the most significant achievements in an infant's first year, with poor balance and weak muscles long proposed as the rate limiting factors. Compensating for either may reveal upright motor skill that has not yet emerged in the infant's natural repertoire. To probe this question, we unweighted prewalking infants and measured their performance in various standing and walking behaviors while unweighted compared to baseline. Our secondary objective was to determine if the influence of unweighting was related to infants’ locomotor experience. Infants stood unsupported for longer durations with 20% or 40% unweighting. Infants took more independent steps and more steps with one hand held with 40% unweighting. No differences in transition to/from standing were observed. Locomotor experience was related to the influence of unweighting during cruising and walking with a push toy. This is the first report of more advanced motor skills—longer periods of unsupported standing and the emergence of independent walking—revealed by unweighting infants. We interpret our observations to suggest that the refinement of motor control needed to support bipedal posture and locomotion precedes the functional emergence of these skills in infants. In other words, the musculoskeletal components required for walking are slower to develop than the neurological factors – and consequently may be the rate limiters. We further suggest that training regimens including unweighting should be explored in infants with motor delays.

中文翻译：

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减轻婴儿体重揭示隐藏的运动技能

我们使用步行作为模型系统研究了速率限制因素在发育中的作用。双足姿势和运动的成就是婴儿第一年最重要的成就之一，长期以来，平衡能力差和肌肉无力被认为是速度限制因素。对任何一个进行补偿都可能揭示婴儿的自然技能中尚未出现的直立运动技能。为了探究这个问题，我们对行走前的婴儿进行了加权，并测量了他们在未加权时与基线相比在各种站立和行走行为中的表现。我们的次要目标是确定减重的影响是否与婴儿的运动体验有关。婴儿在 20% 或 40% 的减重情况下长时间无支撑站立。婴儿在 40% 失重的情况下采取更多的独立步骤和更多的单手扶持步骤。没有观察到从站立过渡到/从站立过渡的差异。运动体验与使用推动玩具巡航和行走时减重的影响有关。这是关于更高级的运动技能的第一份报告——更长的无支撑站立时间和独立行走的出现——通过减轻婴儿体重来揭示。我们解释我们的观察结果表明，支持双足姿势和运动所需的运动控制的改进先于婴儿这些技能的功能性出现。换句话说，步行所需的肌肉骨骼成分比神经因素发育得更慢——因此可能是速度限制器。