Minimizing center of mass vertical movement increases metabolic cost in walking

• Published in: Journal of applied physiology (1985) Vol. 99; no. 6; pp. 2099 - 2107
• Main Authors: Ortega, Justus D, Farley, Claire T
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.12.2005; American Physiological Society
• Subjects: Acceleration; Adult; Biological and medical sciences; Computer Simulation; Energy Metabolism - physiology; Energy Transfer - physiology; Female; Fundamental and applied biological sciences. Psychology; Gait - physiology; Humans; Male; Metabolism; Models, Biological; Muscle, Skeletal - physiology; Physical Exertion - physiology; Walking; Walking - physiology; Biomechanics; mechanical work; Locomotion; Walking; Vertebrata; Mammalia; Gait; determinants of gait; Center of mass; inverted pendulum
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00103.2005

Locomotion Laboratory, Department of Integrative Physiology, University of Colorado, Boulder, Colorado Submitted 28 January 2005 ; accepted in final form 22 July 2005 A human walker vaults up and over each stance limb like an inverted pendulum. This similarity suggests that the vertical motion of a walker's center of mass reduces metabolic cost by providing a mechanism for pendulum-like mechanical energy exchange. Alternatively, some researchers have hypothesized that minimizing vertical movements of the center of mass during walking minimizes the metabolic cost, and this view remains prevalent in clinical gait analysis. We examined the relationship between vertical movement and metabolic cost by having human subjects walk normally and with minimal center of mass vertical movement ("flat-trajectory walking"). In flat-trajectory walking, subjects reduced center of mass vertical displacement by an average of 69% ( P = 0.0001) but consumed approximately twice as much metabolic energy over a range of speeds (0.7–1.8 m/s) ( P = 0.0001). In flat-trajectory walking, passive pendulum-like mechanical energy exchange provided only a small portion of the energy required to accelerate the center of mass because gravitational potential energy fluctuated minimally. Thus, despite the smaller vertical movements in flat-trajectory walking, the net external mechanical work needed to move the center of mass was similar in both types of walking ( P = 0.73). Subjects walked with more flexed stance limbs in flat-trajectory walking ( P < 0.001), and the resultant increase in stance limb force generation likely helped cause the doubling in metabolic cost compared with normal walking. Regardless of the cause, these findings clearly demonstrate that human walkers consume substantially more metabolic energy when they minimize vertical motion. biomechanics; determinants of gait; inverted pendulum; locomotion; mechanical work Address for reprint requests and other correspondence: J. D. Ortega, Locomotion Laboratory, Dept. of Integrative Physiology, 354 UCB, Boulder, CO 80309-0354 (e-mail: ortegajd{at}colorado.edu )