In vivo passive and active mechanical characteristics of muscles: an intra-operative approach

To better understand human locomotion, it is necessary to assess the mechanical behaviour of individual muscles in vivo and relate it to joint function. For this purpose, we developed a novel intra-operative method that measures hamstring muscle forces with respect to knee angles in vivo. We applied this approach during remedial surgery and found that (i) if the hamstring muscles of patients with cerebral palsy (CP) are activated alone, they do not show mechanical characteristics causing knee joint restriction, however, (ii) if the hamstring is activated together with antagonistic or synergistic muscles, an increase in exerted forces measured at the tendons is observed. These findings demonstrated the importance of inter- and extra-muscular myofascial connections in force exertion. In part, these experiments explain joint restrictions in CP.