Arm swing in human walking: What is their drive?

• We aimed to determine the contribution of passive dynamics in arm swing.
• We ran simulations with and without arm muscle excitations.
• Significant decrease in arm swing amplitude when muscle excitations were excluded.
• Significant decrease in relative phase when muscle excitations were excluded.

Although previous research has studied arm swing during walking, to date, it remains unclear what the contribution of passive dynamics versus active muscle control to arm swing is.In this study, we measured arm swing kinematics with 3D-motion analysis. We used a musculoskeletal model in OpenSim and generated dynamic simulations of walking with and without upper limb muscle excitations. We then compared arm swing amplitude and relative phase during both simulations to verify the extent to which passive dynamics contribute to arm swing.The results confirm that passive dynamics are partly responsible for arm swing during walking. However, without muscle activity, passive swing amplitude and relative phase decrease significantly (both p < 0.05), the latter inducing a more in-phase swing pattern of the arms. Therefore, we conclude that muscle activity is needed to increase arm swing amplitude and modify relative phase during human walking to obtain an out-phase movement relative to the legs.