Instability analysis of perturbed gait in dyads: holding a stick together provides effective assistance and is accompanied by information exchanges

Physical interaction between two walking individuals, such as holding hands, is thought to influence gait stability, especially in response to unexpected perturbations. This study investigated how simple mechanical coupling (via a rigid stick or elastic) between partners walking side by side affects balance recovery after slips and trips. Twelve dyads walked on a dual treadmill while one or both partners received brief, unanticipated anteroposterior perturbations. Whole-body motion capture and ground reaction forces were used to analyse the distance centre of mass–minimal moment axis as a measure of instability. Granger–Geweke causality was used to assess directional interactions in the frequency domain. Physical interaction significantly improved stability after slip perturbations, particularly with rigid coupling, which enhanced assistance and accelerated recovery. Solo perturbations (affecting one partner) led to better stabilization than simultaneous ones, underlining the role of the undisturbed partner. Causality analysis showed increased directional influence from the assisting to the perturbed partner.