Author(s): THEODORAKIS, C., BOHM, S., EPRO, G., MERSMANN, F., WERTH, J., KARAMANIDIS, K., ARAMPATZIS, A., Institution: HUMBOLDT-UNIVERSITÄT ZU BERLIN, Country: GERMANY, Abstract-ID: 548

INTRODUCTION:
Due to their biarticularity, the gastrocnemii muscles are able to transfer and redistribute energy between the ankle and knee joints ¹ ². Opposite signs in the mechanical power of the gastrocnemii at the ankle and knee joint (in-phase) lead to an energy transfer between the two joints ², while same signs in the mechanical power (anti-phase) indicate a simultaneous energy absorption or production at the two joints ². The contribution of such biarticular mechanisms of the gastrocnemii to counteract locomotor perturbations is currently unknown. Therefore, the current study aimed to gain a better understanding of how the potential for energy transfer between the ankle and knee joint via the gastrocnemii muscles is modulated during unpredictable and adapted walking perturbations.
METHODS:
In two separate experiments we investigated horizontal (trip-like, n=20) and vertical (15 cm drop of the support surface, n=26) unpredictable and adapted walking perturbations. Whole body kinematics were measured by a motion analysis system. The coupling angle (CA) of the ankle and knee joint angles was calculated during the perturbed stance phase based on a vector coding technique. The potential (λ) of the energy transfer and simultaneous energy absorption or production by the gastrocnemii was derived from the relative CA frequency of in-phase and anti-phase during the stance phase. In addition, the electromyographic (EMG) activities of the gastrocnemii, soleus and tibialis anterior muscles were captured during the vertical perturbations.
RESULTS:
There was a significant increase (p<0.05) of the knee-to-ankle joint energy transfer potential during both horizontal (λ=0.26) and vertical (λ=0.40) perturbations compared to normal unperturbed walking (λ=0.02). The results evidenced an important ankle-to-knee joint energy transfer in the first 20% of the stance (λ=0.29) during the vertical perturbations. The energy transfer potentials between unpredictable and adapted perturbations did not show significant differences. The EMG-activity of the gastrocnemii muscles was significantly greater (p<0.05) in the perturbed trials compared to unperturbed walking and highest (p<0.05) during the unpredictable perturbations.
CONCLUSION:
The increased knee-to-ankle joint energy transfer potential via the gastrocnemii muscles during perturbed walking demonstrates a crucial modulation of biarticular mechanisms to counteract locomotor perturbations. Further, the ankle-to-knee joint energy transfer at the beginning of the stance during the vertical perturbations suggests an important contribution of biarticular mechanisms to the absorption of the center of mass energy. Finally, the increased activation of the gastrocnemii during the ankle-to-knee and knee-to-angle joint energy transfer phases provide evidence for an enhanced energy transfer between the two joints during perturbed walking.
REFERENCES:
1) van Ingen Schenau 1989, Hum Mov Sci 8, 301-337
2) Kharazi et al. 2023, Biology 12, 872