title: Optimal walking speed following changes in limb geometry.
abstract: The principle of dynamic similarity states that the optimal walking speeds of geometrically similar animals are independent of size when speed is normalized to the dimensionless Froude number (Fr). Furthermore, various studies have shown similar dimensionless optimal speed (Fr ∼0.25) for animals with quite different limb geometries. Here, we wondered whether the optimal walking speed of humans depends solely on total limb length or whether limb segment proportions play an essential role. If optimal walking speed solely depends on the limb length then, when subjects walk on stilts, they should consume less metabolic energy at a faster optimal speed than when they walk without stilts. To test this prediction, we compared kinematics, electromyographic activity and oxygen consumption in adults walking on a treadmill at different speeds with and without articulated stilts that artificially elongated the shank segment by 40 cm. Walking on stilts involved a non-linear reorganization of kinematic and electromyography patterns. In particular, we found a significant increase in the alternating activity of proximal flexors-extensors during the swing phase, despite significantly shorter normalized stride lengths. The minimal metabolic cost per unit distance walked with stilts occurred at roughly the same absolute speed, corresponding to a lower Fr number (Fr ∼0.17) than in normal walking (Fr ∼0.25). These findings are consistent with an important role of limb geometry optimization and kinematic coordination strategies in minimizing the energy expenditure of human walking.
authors.affiliation: Laboratory of Neurophysiology and Movement Biomechanics CP601, Université Libre de Bruxelles, 1070 Brussels, Belgium.
authors.forename: Françoise
authors.initials: F
authors.lastname: Leurs
authors.forename: Yuri P
authors.initials: YP
authors.lastname: Ivanenko
authors.forename: Ana
authors.initials: A
authors.lastname: Bengoetxea
authors.forename: Ana-Maria
authors.initials: AM
authors.lastname: Cebolla
authors.forename: Bernard
authors.initials: B
authors.lastname: Dan
authors.forename: Francesco
authors.initials: F
authors.lastname: Lacquaniti
authors.forename: Guy A
authors.initials: GA
authors.lastname: Cheron
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004576:Electromyography / Q000379:methods*; D004734:Energy Metabolism; D005080:Exercise Test; D005121:Extremities / Q000033:anatomy & histology* / Q000502:physiology*; D005260:Female; D005684:Gait; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D009043:Motor Activity; D010101:Oxygen Consumption; D016138:Walking