The relationship between plantar sensation and muscle onset during automatic postural responses in people with multiple sclerosis and healthy controls

Background: Plantar sensation is critical for balance control in people with multiple sclerosis (PwMS). While previous research has described its impact on standing balance, the influence of plantar sensation during automatic postural responses (APRs) is not well understood in PwMS. The purpose of this study was to characterize the relationship between plantar sensation and APRs in PwMS and controls. A secondary aim was to determine whether the relationship between plantar sensation and APRs is different across PwMS and control groups. Methods: 122 PwMS and 48 age-matched controls underwent forward and backward support-surface perturbations from stance. The onset of the tibialis anterior (TA) and medial gastrocnemius (MG) were the primary reactive balance outcome measures for backward and forward losses of balance, respectively. Plantar sensation was measured as the vibration sensation threshold (VT). Results: As expected, PwMS had significantly higher (i.e., worse) VT (p<0.001) and an increased MG and TA onset latency (TA: p<0.001, MG: p = 0.01) compared to the control group. A higher VT was related to increased MG (p<0.001) and TA latency (p<0.001) across all participants. However, no moderating effect of group (control or PwMS) was observed for the relationship between VT and muscle onset (MG: p = 0.14; TA: p = 0.34). Conclusion: PwMS demonstrated poorer plantar sensation and delayed muscle onset during APRs compared to controls. Plantar sensation was also related to muscle onset after perturbations in all participants. Although this relationship was not moderated by group, this may be related to the lack of dynamic range of VT scores in controls. These results indicate that plantar sensation may be related to reactive balance and provides insight into a potential contributing factor of delayed automatic postural responses in people with MS.