Background

When landing from a jump or a drop, muscles contract before touchdown to anticipate imminent collision with the ground, soften ground contact and allow to return to a stable standing position without stepping or rebounding.

Research question

This study assesses the effect of the unsteadiness of the environment on the motor control of landing. The ‘unsteady environment’ was induced by asking participants to perform drop landings inside an aircraft that underwent trajectories parallel to Earth’s surface. The participants also performed the same task in a ‘steady environment’ in our laboratory.

Methods

Ground reaction forces, lower limb joints’ movements and the activity of lower limb muscles were recorded. The stability of the landing was assessed by the vertical and anterior-posterior stability indexes, center of pressure measures and by the coefficient of variation of kinetic and kinematic parameters.

Results

On one hand, participants slowdown their joint movements and reduce the knee joint excursion during landing, probably to avoid excessive movements that may induce imbalance. On the other hand, the stability of the landing is reduced while the variability of the movement is increased, illustrating a less stable and less consistent landing. In addition, whatever the environment, landing parameters associated with increased stiffness (i.e., increased impact forces and decreased joint range of motion) are correlated with decreased landing stability.

Significance

Overall, landings in the‘unsteady environment’ appear to be more cautious but less stable and less finely tuned. Since the stability of the landing is not directly influenced by the steadiness of the environment, this more cautious behavior could be, at least in part, related to the fear/apprehension induced by sudden acceleration variations of the frame of the aircraft.

中文翻译：

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不稳定环境中着陆的机动控制

背景

当从跳跃或跌落着陆时，肌肉在触地前收缩以预测即将与地面发生碰撞，软化地面接触并允许返回稳定的站立位置而不会踩踏或反弹。

研究问题

本研究评估了环境不稳定对着陆运动控制的影响。“不稳定环境”是通过要求参与者在飞机内进行降落着陆而引起的，该飞机的轨迹与地球表面平行。参与者还在我们实验室的“稳定环境”中执行了相同的任务。

方法

记录地面反作用力、下肢关节运动和下肢肌肉活动。通过垂直和前后稳定性指数、压力中心测量值以及动力学和运动学参数的变异系数来评估着陆的稳定性。

结果

一方面，参与者在着陆时减慢他们的关节运动并减少膝关节偏移，可能是为了避免可能导致不平衡的过度运动。另一方面，着陆的稳定性降低了，而运动的可变性增加了，说明着陆的稳定性和稳定性较差。此外，无论环境如何，与刚度增加相关的着陆参数（即，冲击力增加和关节活动范围减小）都与着陆稳定性降低相关。

意义

总体而言， “不稳定环境”中的着陆似乎更加谨慎，但稳定性较差，调整也较差。由于着陆的稳定性不受环境稳定性的直接影响，因此这种更谨慎的行为可能至少部分与飞机框架的突然加速变化引起的恐惧/忧虑有关。