Motor Patterns of Gait Transitions
The triggers underlying gait transitions in humans have received much attention, and explanations related to metabolic cost, bone stress, and muscle function have all been proposed. Most of these studies have analyzed steady walking and running at speeds at or near the preferred walk-run transition speed. Yet, humans rarely choose to walk or run at the transition speed, but rather execute gait transitions to switch suddenly between two different speeds. Biomechanical changes during spontaneous transitions between self-selected speeds remain largely unexplored. The objective of this study is to characterize the step-varying activity of lower extremity muscles during the realization of gait transitions between subjects’ self-selected speeds. Specifically, this study sought to answer the following questions: (1) Is there a peak in muscle activity prior to or during the transition step? (2) Are there differences in muscle activity between the transition and contralateral legs?
To address these questions, muscle activations in several leg muscles were recorded using surface electromyography (EMG) electrodes as healthy subjects performed walk-to-run transitions (WRT) and run-to-walk transitions (RWT). Generally, muscle activation increased at the WRT and decreased at the RWT, with consistent activity levels during non-transition steps. Results from previous studies on gait transition speeds suggest there should be a peak in TA or LG activation during the step prior to the WRT. Such peaks in activation near the transition were observed for some subjects, but were generally absent, suggesting that humans appear to avoid large peaks in muscle activity during spontaneous gait transitions between self-selected speeds.
Contrary to expectations, EMG activity levels were similar for both legs. This suggests that despite the asymmetrical nature of gait transitions, these maneuvers do not require substantial differences in activation between the transition and contralateral legs. In conclusion, the human neuromotor system is able to execute gait transitions without an outstanding effort; rather, one leg simply changes gait, followed by the other.