1. Discussion Figure 3 shows data from the same subject’s lead leg during planned gait termination. The lead leg arrived first at the quiet stance position. It had the greatest changes from normal walking of the two legs. Its termination process began with a brief dorsiflexor moment that controlled foot slap, followed by two bursts of negative work by the plantiflexors and no positive work as is the usual case during walking. The knee extensors performed a burst of negative work immediately after heel- strike. This burst was briefer than the ankle plantiflexors and therefore dissipated less energy. The hip flexors provided additional energy dissipation. As expected the ankle plantiflexors acted isometrically during quiet stance while the knee moments of both legs were essentially inactive. In contrast, the hip flexors acted isometrically to hold the hip in a slightly extended position, which differs to what occurs during initiation of gait when the extensors are active in preparation for forward motion. Discussion Figure 3 shows data from the same subject’s lead leg during planned gait termination. The lead leg arrived first at the quiet stance position. It had the greatest changes from normal walking of the two legs. Its termination process began with a brief dorsiflexor moment that controlled foot slap, followed by two bursts of negative work by the plantiflexors and no positive work as is the usual case during walking. The knee extensors performed a burst of negative work immediately after heel- strike. This burst was briefer than the ankle plantiflexors and therefore dissipated less energy. The hip flexors provided additional energy dissipation. As expected the ankle plantiflexors acted isometrically during quiet stance while the knee moments of both legs were essentially inactive. In contrast, the hip flexors acted isometrically to hold the hip in a slightly extended position, which differs to what occurs during initiation of gait when the extensors are active in preparation for forward motion. Introduction Ambulation is a basic necessity for human independence. People must be able to start, maintain and then finally terminate their gait safely. Problems arise when people who are elderly, disabled or have neurological disorders cannot safely terminate their gait (O’Kane et al., 2003). Some studies have focused on EMG and kinematics to describe gait termination but the purpose of this study was to quantify the joint kinetics during planned gait termination. Introduction Ambulation is a basic necessity for human independence. People must be able to start, maintain and then finally terminate their gait safely. Problems arise when people who are elderly, disabled or have neurological disorders cannot safely terminate their gait (O’Kane et al., 2003). Some studies have focused on EMG and kinematics to describe gait termination but the purpose of this study was to quantify the joint kinetics during planned gait termination. Methods Eighteen subjects (9 female, 9 male) participated in the study. Subjects were asked to walk five times with a natural cadence and come to a stop on two side-by-side force platforms (Kistler). A third force platform quantified the penultimate step. The forces and motion data were collected using a Vicon MX system with 6 MX13 cameras. Figure 1 shows the walkway layout. The kinematic data were combined with force platform data by inverse dynamics to determine the net moments and powers at the ankle, knee and hip in both trail and lead legs using Visual3D (Robertson et al., 2004). Moment powers were calculated by multiplying the net moments of force times the joint angular velocities. Data were ensemble averaged and normalized to body mass for intersubject comparisons. Data were analyzed for one second before and for two seconds after lead leg heel-strike (HS). Methods Eighteen subjects (9 female, 9 male) participated in the study. Subjects were asked to walk five times with a natural cadence and come to a stop on two side-by-side force platforms (Kistler). A third force platform quantified the penultimate step. The forces and motion data were collected using a Vicon MX system with 6 MX13 cameras. Figure 1 shows the walkway layout. The kinematic data were combined with force platform data by inverse dynamics to determine the net moments and powers at the ankle, knee and hip in both trail and lead legs using Visual3D (Robertson et al., 2004). Moment powers were calculated by multiplying the net moments of force times the joint angular velocities. Data were ensemble averaged and normalized to body mass for intersubject comparisons. Data were analyzed for one second before and for two seconds after lead leg heel-strike (HS). BIOMECHANICS OF PLANNED GAIT TERMINATION Joe Lynch, MSc and D. Gordon E. Robertson, PhD, FCSB School of Human Kinetics, University of Ottawa, Ontario, Canada BIOMECHANICS OF PLANNED GAIT TERMINATION Joe Lynch, MSc and D. Gordon E. Robertson, PhD, FCSB School of Human Kinetics, University of Ottawa, Ontario, Canada Results and Discussion The trail leg’s (Figure 2) main goal in gait termination was to bring the trail leg parallel with the lead leg while dissipating any remaining forward momentum. To accomplish this, the trail leg’s moments of force acted similar during the penultimate step to what they do during normal gait. The dorsiflexors acted briefly to control foot-slap after terminal heel-strike, followed by negative and then positive work from the plantiflexors. The knee flexors acted eccentrically but briefly after heel-strike followed by a positive period during midstance. The knee extensors then worked eccentrically to reduce the rate of knee flexion. At the hip, the extensors initially performed positive work to extend the leg then the flexors dissipated energy during midstance and switched to positive work to cause swing through. During the swing phase and terminal step, little work was done by the ankle plantiflexors during the placement of the trail leg in the final quiet stance position. During swing, the knee flexors controlled extension prior to the final HS before quiet stance while the hip extensors acted isometrically to stiffen the hip. During the final step the knee extensors produced a small amount of work to straighten the leg while the hip flexors worked isometrically to hold the hip from collapsing while the ankle plantiflexors did a similar job at the ankle. Results and Discussion The trail leg’s (Figure 2) main goal in gait termination was to bring the trail leg parallel with the lead leg while dissipating any remaining forward momentum. To accomplish this, the trail leg’s moments of force acted similar during the penultimate step to what they do during normal gait. The dorsiflexors acted briefly to control foot-slap after terminal heel-strike, followed by negative and then positive work from the plantiflexors. The knee flexors acted eccentrically but briefly after heel-strike followed by a positive period during midstance. The knee extensors then worked eccentrically to reduce the rate of knee flexion. At the hip, the extensors initially performed positive work to extend the leg then the flexors dissipated energy during midstance and switched to positive work to cause swing through. During the swing phase and terminal step, little work was done by the ankle plantiflexors during the placement of the trail leg in the final quiet stance position. During swing, the knee flexors controlled extension prior to the final HS before quiet stance while the hip extensors acted isometrically to stiffen the hip. During the final step the knee extensors produced a small amount of work to straighten the leg while the hip flexors worked isometrically to hold the hip from collapsing while the ankle plantiflexors did a similar job at the ankle. Biomechanics Laboratory References O’Kane FW, McGibbon CA, Krebs DE. Kinetic analysis of planned gait termination in healthy subjects and patients with balance disorders. Gait & Posture, 2003;2:170-9. Robertson, DGE et al. Research Methods in Biomechanics, Champaign: Human Kinetics, 2004. Winter DA. Human balance and posture control during standing and walking. Gait & Posture, 1995;3:193-214. References O’Kane FW, McGibbon CA, Krebs DE. Kinetic analysis of planned gait termination in healthy subjects and patients with balance disorders. Gait & Posture, 2003;2:170-9. Robertson, DGE et al. Research Methods in Biomechanics, Champaign: Human Kinetics, 2004. Winter DA. Human balance and posture control during standing and walking. Gait & Posture, 1995;3:193-214. Figure 3. Mean angular velocities (top), moments (middle) and powers (bottom) of the lead leg ankle (left), knee (middle) and hip (right) of an exemplar subject. The vertical blue line indicates trail leg penultimate HS; black line indicates lead leg heel-strike; and red line indicates trail leg final HS. Figure 1. Laboratory setup and stopping position for subjects Figure 2. Mean angular velocities (top), moments (middle) and powers (bottom) of the trail leg ankle (left), knee (middle) and hip (right) of an exemplar subject. The vertical blue line indicates trail leg penultimate HS; black line indicates lead leg heel-strike; and red line indicates trail leg final HS.