Enhanced joint energy transfer potential by the biarticular gastrocnemii muscles during perturbed walking

Our objective was to explore how the potential for energy transfer between the ankle and knee joint via the biarticular gastrocnemii muscles is modulated during unpredictable and adapted trip-like and drop-like gait perturbations. Using kinematic parameters of the ankle and knee joints, the energy transfer potential between the two joints was determined as the fraction of contact time when the ankle and knee joint angles are in-phase. Additionally, the electromyographic activity of the gastrocnemius medialis and lateralis were captured during the drop-like perturbations. The energy transfer potential increased 1.6-fold in the trip-like and 2.5-fold in the drop-like perturbations compared to unperturbed walking, indicating a relevant involvement of biarticular mechanisms in maintaining body stability. The activation of the gastrocnemii was high (50-60% of a maximum voluntary contraction) in the phases of ankle-to-knee and knee-to-ankle joint energy transfer, which suggests a relevant contribution of biarticular mechanisms to the management of the body's energy during the drop-like perturbations. Considering the similar ankle-to-knee joint energy transfer potential compared to unperturbed walking, the higher activation of the gastrocnemii muscles in the first 20% of the stance indicates a greater contribution of biarticular mechanisms to the absorption of body energy in the unpredictable perturbations.