DataSheet1_Acquisition of bipedal locomotion in a neuromusculoskeletal model with unilateral transtibial amputation.DOCX

Adaptive locomotion is an essential behavior for animals to survive. The central pattern generator in the spinal cord is responsible for the basic rhythm of locomotion through sensory feedback coordination, resulting in energy-efficient locomotor patterns. Individuals with symmetrical body proportions exhibit an energy-efficient symmetrical gait on flat ground. In contrast, individuals with lower limb amputation, who have morphologically asymmetrical body proportions, exhibit asymmetrical gait patterns. However, it remains unclear how the nervous system adjusts the control of the lower limbs. Thus, in this study, we investigated how individuals with unilateral transtibial amputation control their left and right lower limbs during locomotion using a two-dimensional neuromusculoskeletal model. The model included a musculoskeletal model with 7 segments and 18 muscles, as well as a neural model with a central pattern generator and sensory feedback systems. Specifically, we examined whether individuals with unilateral transtibial amputation acquire prosthetic gait through a symmetric or asymmetric feedback control for the left and right lower limbs. After acquiring locomotion, the metabolic costs of transport and the symmetry of the spatiotemporal gait factors were evaluated. Regarding the metabolic costs of transportation, the symmetric control model showed values approximately twice those of the asymmetric control model, whereas both scenarios showed asymmetry of spatiotemporal gait patterns. Our results suggest that individuals with unilateral transtibial amputation can reacquire locomotion by modifying sensory feedback parameters. In particular, the model reacquired reasonable locomotion for activities of daily living by re-searching asymmetric feedback parameters for each lower limb. These results could provide insight into effective gait assessment and rehabilitation methods to reacquire locomotion in individuals with unilateral transtibial amputation.

适应性运动是动物生存不可或缺的核心行为。脊髓内的中枢模式发生器（central pattern generator）通过协调感觉反馈调控运动的基本节律，从而生成能量高效的运动模式。身体比例对称的个体在平坦地面可呈现出能量高效的对称步态；与之相对，存在下肢截肢、身体比例形态不对称的个体，则会表现出不对称的步态模式。然而目前学界仍未明确神经系统如何调控下肢运动。因此，本研究借助二维神经肌肉骨骼模型（two-dimensional neuromusculoskeletal model），探究了单侧胫骨截肢（unilateral transtibial amputation）患者在运动过程中如何控制左右下肢。该模型包含由7个节段、18块肌肉构成的肌肉骨骼模型，以及搭载中枢模式发生器与感觉反馈系统的神经模型。具体而言，本研究探讨了单侧胫骨截肢患者是否通过对左右下肢采用对称或不对称的反馈控制，来习得假肢步态。在运动模式习得完成后，我们对运动代谢成本（metabolic costs of transport）与时空步态参数（spatiotemporal gait factors）的对称性进行了评估。就运动代谢成本而言，对称控制模型的数值约为不对称控制模型的两倍；而两种实验场景下的时空步态模式均呈现出不对称性。本研究结果表明，单侧胫骨截肢患者可通过调整感觉反馈参数重新获得运动能力。尤其值得注意的是，本模型通过为每侧下肢重新搜寻不对称的反馈参数，成功习得适配日常生活活动的合理运动模式。上述研究结果可为单侧胫骨截肢患者重新获得运动能力的有效步态评估与康复方案提供理论参考。