Meeting Abstract
115.5 Monday, Jan. 7 Collision-based analysis of human walking versus running with and without additional vertical loading LEE, D/V*; COMANESCU, T/N; BERTRAM, J/EA; University of Nevada Las Vegas; University of Nevada Las Vegas; University of Calgary david.lee@unlv.edu
Collision-based analysis quantifies geometrically and energetically the interaction between the center of mass (CoM) and the environment. This approach is applied here for the first time to bipedal locomotion. The force-velocity angle is the deviation from perpendicular of the angle between the instantaneous velocity and force vectors. If these vectors were to remain perpendicular throughout a cycle of locomotion, the force-velocity angle would be zero and the mechanical cost of transport would also be zero. Furthermore the ‘actual collision’ given by the instantaneous force-velocity angle can be expressed as a fraction of the ‘potential collision’ given by the sum of instantaneous force and instantaneous velocity angles. This collision fraction would be zero in the previous idealized example, whereas a compliant spring-like inverted pendulum (SLIP) would produce a collision fraction of unity. During walking, the force-velocity angle was 0.08 radians on average throughout the stride. Collision fraction was 0.50 during walking, hence the dynamics of walking afforded on average a 50% reduction of the potential mechanical cost. During running, the force-velocity angle was 0.29 radians – 260% greater than that of walking. Consequently, collision fraction was 0.83 during running compared with 0.50 during walking and the dynamics of running reduced the potential mechanical cost by only 17%. We also simulated hyper-gravity by applying a constant downward vertical force equal to 35% body weight through a climbing harness. Despite a significant reduction in force angle due to this manipulation, the force-velocity angle and mechanical cost of transport remained statistically similar Collision fractions show striking similarities between bipedal and quadrupedal walking as well as bipedal running and quadrupedal trotting.
