Munoz-Martel Victor, Santuz Alessandro, Bohm Sebastian, Arampatzis Adamantios
Department of Training and Movement Sciences, Humboldt-Universität zu Berlin, Berlin, Germany.
Berlin School of Movement Science, Humboldt-Universität zu Berlin, Berlin, Germany.
Front Bioeng Biotechnol. 2021 Dec 16;9:761766. doi: 10.3389/fbioe.2021.761766. eCollection 2021.
Stability training in the presence of perturbations is an effective means of increasing muscle strength, improving reactive balance performance, and reducing fall risk. We investigated the effects of perturbations induced by an unstable surface during single-leg landings on the mechanical loading and modular organization of the leg muscles. We hypothesized a modulation of neuromotor control when landing on the unstable surface, resulting in an increase of leg muscle loading. Fourteen healthy adults performed 50 single-leg landings from a 30 cm height onto two ground configurations: stable solid ground (SG) and unstable foam pads (UG). Ground reaction force, joint kinematics, and electromyographic activity of 13 muscles of the landing leg were measured. Resultant joint moments were calculated using inverse dynamics and muscle synergies with their time-dependent (motor primitives) and time-independent (motor modules) components were extracted via non-negative matrix factorization. Three synergies related to the touchdown, weight acceptance, and stabilization phase of landing were found for both SG and UG. When compared with SG, the motor primitive of the touchdown synergy was wider in UG ( < 0.001). Furthermore, in UG the contribution of gluteus medius increased ( = 0.015) and of gastrocnemius lateralis decreased ( < 0.001) in the touchdown synergy. Weight acceptance and stabilization did not show any statistically significant differences between the two landing conditions. The maximum ankle and hip joint moment as well as the rate of ankle, knee, and hip joint moment development were significantly lower ( < 0.05) in the UG condition. The spatiotemporal modifications of the touchdown synergy in the UG condition highlight proactive adjustments in the neuromotor control of landings, which preserve reactive adjustments during the weight acceptance and stabilization synergies. Furthermore, the performed proactive control in combination with the viscoelastic properties of the soft surface resulted in a reduction of the mechanical loading in the lower leg muscles. We conclude that the use of unstable surfaces does not necessarily challenge reactive motor control nor increase muscle loading per se. Thus, the characteristics of the unstable surface and the dynamics of the target task must be considered when designing perturbation-based interventions.
在存在干扰的情况下进行稳定性训练是增强肌肉力量、改善反应性平衡能力和降低跌倒风险的有效方法。我们研究了单腿落地时不稳定表面引起的干扰对腿部肌肉机械负荷和模块化组织的影响。我们假设在不稳定表面上着陆时神经运动控制会发生调节，从而导致腿部肌肉负荷增加。14名健康成年人从30厘米高度进行50次单腿落地，分别落在两种地面条件上：稳定的坚实地面（SG）和不稳定的泡沫垫（UG）。测量了落地腿13块肌肉的地面反作用力、关节运动学和肌电图活动。使用逆动力学计算合成关节力矩，并通过非负矩阵分解提取肌肉协同作用及其随时间变化的（运动基元）和不随时间变化的（运动模块）成分。在SG和UG条件下均发现了与落地的触地、承重和稳定阶段相关的三种协同作用。与SG相比，UG中触地协同作用的运动基元更宽（<0.001）。此外，在UG中，触地协同作用中臀中肌的贡献增加（=0.015），而外侧腓肠肌的贡献减少（<0.001）。两种落地条件下的承重和稳定阶段在统计学上没有显著差异。UG条件下的最大踝关节和髋关节力矩以及踝关节、膝关节和髋关节力矩发展速率显著更低（<0.05）。UG条件下触地协同作用的时空变化突出了着陆神经运动控制中的主动调整，这种调整在承重和稳定协同作用期间保留了反应性调整。此外，所执行的主动控制与软表面的粘弹性特性相结合，导致小腿肌肉的机械负荷降低。我们得出结论，使用不稳定表面不一定会挑战反应性运动控制，也不一定会增加肌肉负荷本身。因此，在设计基于干扰的干预措施时，必须考虑不稳定表面的特性和目标任务的动力学。
