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 1.25m/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.

Keywords: Biomechanics; Decline; Gait; Incline; Modeling and simulation.

Copyright © 2016 Elsevier Ltd. All rights reserved.

Figures

Figure 1

Average joint angles (left column) and joint moments (right column) during stance. Net joint moments were calculated from the residual reduction algorithm (RRA) and are normalized by body mass. Positive angles and moments represent hip flexion, hip adduction, hip internal rotation, knee flexion, and ankle plantarflexion.

Figure 2

Comparison of mean (±SD) processed electromyographic (EMG) signals (gray shaded area) with the similarly processed mean of computed muscle control excitations (±SD shown in solid blue). The relative timing and magnitude of excitations in the simulations compared well with EMG as slope varied.

Figure 3

Mean body COM acceleration (±SD) induced by left leg muscle groups and gravity during left leg stance. Significant differences relative to level-ground are indicated by ‘*’.

Figure 4

Net power delivered to the trunk (pelvis and torso; top row) and legs (toes, calcaneus, talus, tibia, and femur; middle and bottom rows) during stance by the ipsilateral (left) leg muscles, normalized by segment mass and averaged across participants.

Figure 5

Mean (±SD) segment power delivered to the trunk and legs during left leg stance, normalized by segment mass. Significant differences relative to level ground are indicated by ‘*’.

Figure 6

Average joint accelerations induced in the ipsilateral (Ipsi) leg joints by SOL during stance. Acceleration into extension is defined positively for all three joints.

Figure 7

Accelerations induced in the ipsilateral (Ipsi) hip and all contralateral (Contra) leg joints by HAM and GMAX during stance. Acceleration into extension is defined positively for all joints.