title: Human hopping on damped surfaces: strategies for adjusting leg mechanics.
abstract: Fast-moving legged animals bounce along the ground with spring-like legs and agilely traverse variable terrain. Previous research has shown that hopping and running humans maintain the same bouncing movement of the body's centre of mass on a range of elastic surfaces by adjusting their spring-like legs to exactly offset changes in surface stiffness. This study investigated human hopping on damped surfaces that dissipated up to 72% of the hopper's mechanical energy. On these surfaces, the legs did not act like pure springs. Leg muscles performed up to 24-fold more net work to replace the energy lost by the damped surface. However, considering the leg and surface together, the combination appeared to behave like a constant stiffness spring on all damped surfaces. By conserving the mechanics of the leg-surface combination regardless of surface damping, hoppers also conserved centre-of-mass motions. Thus, the normal bouncing movements of the centre of mass in hopping are not always a direct result of spring-like leg behaviour. Conserving the trajectory of the centre of mass by maintaining spring-like mechanics of the leg-surface combination may be an important control strategy for fast-legged locomotion on variable terrain.
authors.affiliation: Department of Integrative Physiology, University of Colorado, Boulder, CO 80309-0354, USA. ctmoritz@socrates.berkeley.edu
authors.forename: Chet T
authors.initials: CT
authors.lastname: Moritz
authors.forename: Claire T
authors.initials: CT
authors.lastname: Farley
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D035002:Lower Extremity / Q000502:physiology*; D009043:Motor Activity / Q000502:physiology*