The functional roles of muscles during sloped walking

Abstract

Sloped walking is biomechanically different from level-ground walking, as evidenced by changes in joint kinematics and kinetics. However, the changes in muscle functional roles underlying these altered movement patterns have not been established. In this study, we developed a total of 273 muscle-actuated simulations to assess muscle functional roles, quantified by induced body center-of-mass accelerations and trunk and leg power, during walking on slopes of 0°, ±3°, ±6°, and ±9° at 1.25 m/s. The soleus and gastrocnemius both provided greater forward acceleration of the body parallel to the slope at +9° compared to level ground (+126% and +66%, respectively). However, while the power delivered to the trunk by the soleus varied with slope, the magnitude of net power delivered to the trunk and ipsilateral leg by the biarticular gastrocnemius was similar across all slopes. At +9°, the hip extensors absorbed more power from the trunk (230% hamstrings, 140% gluteus maximus) and generated more power to both legs (200% hamstrings, 160% gluteus maximus) compared to level ground. At −9°, the knee extensors (rectus femoris and vasti) accelerated the body upward perpendicular to the slope at least 50% more and backward parallel to the slope twice as much as on level ground. In addition, the knee extensors absorbed greater amounts of power from the ipsilateral leg on greater declines to control descent. Future studies can use these results to develop targeted rehabilitation programs and assistive devices aimed at restoring sloped walking ability in impaired populations.

Segmental contributions to sagittal-plane whole-body angular momentum when using powered compared to passive ankle-foot prostheses on ramps

“…Although the gastrocnemius also contributes to positive H in late stance, it does so by absorbing energy from the trunk and generating energy to the leg [12], [15]. Our findings suggest that restoring ankle push-off power with a powered prosthesis increases the amount of energy and momentum in the trunk, consistent with the functional role of the soleus.…”

“…Thus, the increased momentum in the prosthetic leg must be generated by the person, not the device. People with transtibial amputation may compensate for the lack of gastrocnemius function using the hip extensors, which contribute to positive H [21] and generate energy to the contralateral leg to help initiate swing [15]. Future simulation studies of powered prosthesis function on slopes would help further investigate this possibility.…”

“…The contributions of powered and passive prostheses to segment momenta may also be affected by ramp walking. The function of the gastrocnemius is largely unchanged across slopes, but the soleus transitions from generating energy to the trunk on inclines to absorbing energy from the trunk on declines [15]. Replicating these different functional roles with a prosthetic device is challenging, and understanding the relationship between the structure of an assistive device and its resulting biomechanical function could aid in design of future devices.…”

“…We also hypothesized that there would be an interaction effect between prosthesis and slope in the trunk contributions to H . Our hypotheses were based on the powered prosthesis anatomically emulating the uniarticular soleus muscle, and prior work demonstrating that the soleus absorbs energy from the trunk when walking downhill but generates energy to the trunk when walking uphill [15]. …”

Triceps surae torque-length relationships relevant for walking activity levels with and without an ankle exoskeleton

“…Human walking is the most utilized energy-consuming activity for healthy humans and is closely associated with a person’s quality of life and the prevalence of secondary disease states (Tudor-Locke et al, 2011). Walking is remarkably adaptable to changes in terrain, such as slopes (Alexander et al, 2017; Lay et al, 2006; Pickle et al, 2016), stairs (Lewis et al, 2015), surface compliances (MacLellan and Patla, 2006), and unexpected perturbations (Vlutters et al, 2018) because of robust neural control strategies and intrinsic muscle properties (Clark, 2015).…”