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First published online January 31, 2007
Journal of Experimental Biology 210, 578-585 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02693
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Dynamics of the body centre of mass during actual acceleration across transition speed

Veerle Segers*, Peter Aerts, Matthieu Lenoir and Dirk De Clerq

Ghent University, Department of Movement and Sport Sciences, Watersportlaan 2, Ghent B-9000, Belgium


Figure 1
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  		Fig. 1. Comparison of the vertical displacement of the COM by ground reaction forces (GRF) and kinematically. One representative walking and one running step in the present protocol are shown. This comparison is made for available steps (at least one for each subject).

 

Figure 2
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  		Fig. 2. Energy fluctuations of the COM. (A) Out-of-phase (walking; red arrows) and in-phase oscillations (running; blue arrows) of kinetic energy and gravitational potential energy of the COM on a normalized time-basis with an indication of the efficiency of energy exchange (%=percentage of recovery pendulum). (B) Total kinetic energy (black line) is presented as a fraction of the total kinetic energy at transition (blue line). The red lines are the regressions for walking and running steps. (C) Kinetic energy due to vertical velocity of the COM, with horizontal regressions for walking and running steps. The black line indicates the mean of the average of all trials (N=3–5) with each subject (N=9). Grey lines indicate standard deviation (s.d.) between subjects. Grey and black bars on the x-axis represent contact with the ground by alternate feet.

 

Figure 3
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  		Fig. 3. Kinematics of the transition. (A) Average kinematics of the last walking step, the transition step and the first running step. The red line represents the last walking step, the grey line the transition step and the blue line the first running step. Stick figures were created at specific key events of each step, being heel contact (HC), opposite toe-off (OT), midstance (MS), opposite heel contact (OH) and toe-off (TO). (B) Hip, knee and ankle angles during swing in the last walking steps. Light grey line, step –3; dark grey line, step –2; black line, step –1. Negative sign stands for flexion (ankle, dorsiflexion), a positive sign for extension (ankle, plantar flexion). The vertical blue line indicates the beginning of the final 15% of the swing phase.

 

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  		Fig. 4. Average power fluctuations of the COM; (A) horizontal, (B) vertical. The black line indicates the mean of the average of all trials (N=3–5) of each subject (N=9). Grey lines indicate s.d. between subjects. Grey and black bars on the x-axis represent contact with the ground by alternate feet.

 




© The Company of Biologists Ltd 2007