The effect of walking speed on muscle function and mechanical energetics

Abstract

Modulating speed over a large range is important in walking, yet understanding how the neuromotor patterns adapt to the changing energetic demands of different speeds is not well understood. The purpose of this study was to identify functional and energetic adaptations in individual muscles in response to walking at faster steady-state speeds using muscle-actuated forward dynamics simulations. The simulation data were invariant with speed as to whether muscles contributed to trunk support, forward propulsion or leg swing. Trunk support (vertical acceleration) was provided primarily by the hip and knee extensors in early stance and the plantar flexors in late stance, while trunk propulsion (horizontal acceleration) was provided primarily by the soleus and rectus femoris in late stance, and these muscle contributions all systematically increased with speed. The results also highlighted the importance of initiating and controlling leg swing as there was a dramatic increase at the higher walking speeds in iliopsoas muscle work to accelerate the leg in pre- and early swing, and an increase in the biarticular hamstring muscle work to decelerate the leg in late swing. In addition, walking near self-selected speeds (1.2m/s) improves the utilization of elastic energy storage and recovery in the uniarticular ankle plantar flexors and reduces negative fiber work, when compared to faster or slower speeds. These results provide important insight into the neuromotor mechanisms underlying speed regulation in walking and provide the foundation on which to investigate the influence of walking speed on various neuromotor measures of interest in pathological populations.

Conflict of interest statement

Conflict of interest: There is no conflict of interest regarding the publication of this manuscript.

Figures

Fig. 1

Muscle-driven simulations of walking and corresponding experimental data from right mid-stance to right heel-strike at 0.8 and 1.6 m/s. The musculoskeletal model was driven by 17 Hill-type musculotendon actuators per leg that were combined into the 10 muscle groups shown. The 10 muscle groups were defined as IL (iliacus, psoas), GMAX (gluteus maximus, adductor magnus), GMED (anterior and posterior components of gluteus medius), VAS (3-component vastus), HAM (medial hamstrings, biceps femoris long-head), SOL (soleus), BFsh (biceps femoris short head), GAS (medial and lateral gastrocnemius), RF (rectus femoris) and TA (tibialis anterior). The experimental ground reaction force vectors are shown using the simulation center-of-pressure since the experimental center-of-pressure data was not available from the treadmill measurements.

Fig. 2

Simulation muscle excitation patterns across walking speeds. Also shown are the corresponding EMG patterns for the soleus (EMG-SOL) and gastrocnemius (EMG-GAS) to show how the simulation excitation patterns and changes with walking speed are similar to the experimentally collected EMG data.

Fig. 3

Total muscle fiber and tendon work across walking speeds (net musculotendon work (MTnet), positive tendon work (TenPos, elastic energy recovered from the tendon), negative fiber work (FibNeg) and positive fiber work (FibPos)).

Fig. 4

Individual muscle fiber and tendon work across walking speeds during (A) stance and (B) swing (net musculotendon work (MTnet), positive tendon work (TenPos, elastic energy recovered from the tendon), negative fiber work (FibNeg) and positive fiber work (FibPos)).

Fig. 5

Mechanical power delivered to the trunk in the horizontal direction to provide forward propulsion by SOL and RF across increasing walking speeds. The horizontal bars indicate the regions of double support, which decreased in duration with increasing speed.

Fig. 6

Mechanical power delivered to the ipsilateral leg by IL, GAS and HAM across walking speeds. The horizontal bars indicate the regions of double support, which decreased in duration with increasing speed. Positive (negative) power indicates the muscle acted to accelerate (decelerate) the leg in the direction of its motion.