Individual muscle force-energy rate is altered during crouch gait: A neuro-musculoskeletal evaluation

Abstract

Children with pathological movement patterns like crouch gait present with excessive knee and hip flexion during stance phase due to multiple factors. A good treatment requires that the primary factor is reduced or eliminated to optimise the relationship between muscle energy expenditure and muscle force production during walking. In this way, neuro-musculoskeletal simulations are reliable tools to evaluate how individual muscles contribute to gait. However, previous studies have reported that changes in energy consumed per unit time have not correlated with crouch gait severity. In this study, EMG-informed musculoskeletal simulations combined with analytical approaches (which include altered muscle composition and morphology presented in children with CP) were used to evaluate individual muscle force, energy expenditure and their relationship in five typically developing children and eleven children with different degrees of crouch gait severity. In agreement with the literature, our results show an increase in Watts required per Newton of muscle force during walking in children with crouch gait when compared to unimpaired gait. This is true for all levels of crouch but does not correlate with severity. Hamstrings required more than three times the muscle energy per Newton of muscle force during crouch gait compared with unimpaired gait. Also, a different strategy in muscle force-energy rate of quadriceps and plantarflexors muscle groups was present in crouch gait. Finally, our results showed weakness in hamstrings and gastrocnemius with an increment in their muscle energy expenditures during moderate and severe crouch gait. This could suggest that well controlled strength training (i.e. personalised and designed to improve both the muscle strength and functional mobility) focused in these muscle groups could improve knee extension of these children by providing a more efficient plantarflexor-knee extension couple during stance phase (action of the ankle plantarflexor muscles to control the progress of the tibia over the foot and the knee kinetics) and more control of the distal limb at initial contact. However, strength training of hamstrings only could be better for children with mild crouch gait.

Keywords: Cerebral palsy; Crouch gait severity; Muscle energy expenditure; Muscle force; Neuro-musculoskeletal simulation.