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Swing- and support-related muscle actions differentially trigger human walk–run and run–walk transitions

Boris I. Prilutsky^* and Robert J. Gregor

Department of Health and Performance Sciences, Center for Human Movement Studies, Georgia Institute of Technology, Atlanta, GA 30332-0356, USA

View larger version (33K): [in a new window]   Fig. 1. Full-wave-rectified normalised electromyographic (EMG) recordings of major leg muscles during one cycle of walking and running at selected speeds of a typical subject. Speed is given as a percentage of the preferred gait transition speed. One vertical scale division in all plots corresponds to 100% of the corresponding peak of the EMG envelope in maximum isometric contraction; one horizontal scale division in all plots corresponds to 200ms. EMG activity was shifted to the right along the time axis by 40ms to account for the electromechanical delay between muscle activation and joint moments. Vertical lines separate the stance phase (on the left of the line) from the swing phase (on the right of the line). EMG activity of the ankle extensors (SO and GA), knee extensor (VA) and hip extensor (GLM) whose activation was primarily associated with the stance phase has positive values. EMG activity in the ankle flexor (TA), knee flexor (BFL) and hip flexor (RF) whose activation was primarily associated with the swing phase is inverted. SO, soleus; GA, gastrocnemius medialis; VA, vastus medialis; GLM, gluteus maximus; TA, tibialis anterior; BFL; long head of biceps femoris; RF, rectus femoris.

View larger version (41K): [in a new window]   Fig. 2. Averaged normalised electromyographic (EMG) activity (A) and EMG envelope peaks (B) of leg muscles during walking and running at different normalised speeds. A speed of 100% corresponds to the gait transition speed (2.1±0.2ms-1). Swing-related muscles whose EMG activity was averaged over the swing phase (see A) include the tibialis anterior (TA), the long head of the biceps femoris (BFL) and the rectus femoris (RF). Support-related muscles whose EMG activity was averaged over the stance phase (see A) include the soleus (SO), the gastrocnemius medialis (GA), the vastus medialis (VA) and the gluteus maximus (GLM). An asterisk indicates a significant (P<0.05) difference in EMG activity between walking and running at the same speed. Normalised swing-related EMG activities in the TA, BFL and RF were typically lower during running than during walking at preferred running speeds (115, 130 and 145%), whereas support-related EMG activity in the ankle and knee extensors (SO, GA and VA) was typically lower during walking than during running at preferred walking speeds (55, 70 and 85%).

View larger version (18K): [in a new window]   Fig. 3. General electromyographic (EMG) variables during walking and running at different normalised speeds. (A) Normalised EMG activity in the swing- and support-related muscles, averaged over swing and stance, respectively, and then summed across all muscles. (B) Peaks of linear EMG envelopes summed across all muscles. A speed of 100% corresponds to the gait transition speed (2.1±0.2ms-1). An asterisk indicates a significant (P<0.05) difference in EMG activity between walking and running at the same speed.

View larger version (29K): [in a new window]   Fig. 4. Moments at the ankle, knee and hip joints during the swing phase of walking (solid lines) and running (broken lines) at selected speeds. Moments are averaged across three cycles of one subject. Extension moments are positive; flexion moments are negative. A speed of 100% corresponds to the gait transition speed (2.1±0.2ms-1).

View larger version (40K): [in a new window]   Fig. 5. Peaks of joint moments in swing during walking and running at different normalised speeds. A speed of 100% corresponds to the gait transition speed (2.1±0.2ms-1). An asterisk indicates a significant (P<0.05) difference in moment peaks between walking and running at the same speed. Peaks of ankle, knee and hip flexion moments and peaks of hip extension moments were typically smaller during running than during walking at preferred running speeds (115, 130 and 145%).

View larger version (15K): [in a new window]   Fig. 6. Changes in a hypothetical undesirable variable that can trigger gait transitions. As walking speed increases and the magnitude of a variable during walking exceeds that during running by the threshold , the walk–run transition occurs at the speed Vw-r (right vertical line). As running speed decreases and the magnitude of a variable during running exceeds that during walking by the threshold , the run–walk transition occurs at the speed Vr-w (left vertical line). According to this definition of the gait transition trigger, the walk–run transition occurs at a faster speed than the run–walk transition.

View larger version (17K): [in a new window]   Fig. 7. Stick figure of the leg during swing during walking (open circles) and running (filled circles) at three normalised speeds for one subject. The three leg positions shown correspond to toe-off, middle swing and touch-down. Circles denote markers on the calcaneus, the fifth metatarsophalangeal joint, the lateral malleolus, the estimated centre of the knee joint, the greater trochanter and the iliac crest. Walking and running figures at a given speed are aligned such that the hip horizontal coordinates of the stick figures at toe-off coincide. The trajectory of the iliac crest is superimposed on the stick figures. The thigh angular amplitude is larger during walking than during running, whereas the vertical excursion of the iliac crest, the distance travelled during swing and the magnitude of knee flexion during swing are larger during running than during walking. A speed of 100% corresponds to the gait transition speed.