Speed related changes in muscle activity from normal to very slow walking speeds.

The study of neuromuscular activity at very slow walking speeds may lead to a better understanding of the mechanisms underlying speed regulation during walking, and may aid the interpretation of gait data in patients who walk slowly. Extreme reductions in walking speed will cause changes in locomotor task demands that may eventually result in modifications of the patterning of muscle activity that underlies walking. The aim of the present study was to investigate patterns of lower limb muscle activity during very slow walking (< 0.28 m s(-1)), and to study the neuromuscular gain functions that reflect the phase dependent effects of walking speed on electromyographic (EMG) amplitude. Nine healthy young adults walked at seven different walking speeds (1.39, 0.83, 0.28, 0.22, 0.17, 0.11, and 0.06 m s(-1)) while EMG was recorded from eight lower extremity muscles. Results showed that the phasing of muscle activity remained relatively stable over walking speeds despite substantial changes in its amplitude. However, between 1.39 and 0.28 m s(-1), epochs of Rectus femoris, Biceps femoris and Tibialis anterior activities were found that were typical for specific speed ranges. When walking speed decreased further to almost standing still (0.06 m s(-1)), negative gain values were found in Peroneus longus during midstance and Rectus femoris in late swing, indicating the emergence of new bursts of activity with decreasing walking speed. It is proposed that these extra activities may be attributed to increased demands on postural stability, and the altered dynamics of the swinging limb at very slow speeds.