The Proportional Work of Lifting the Center of Mass During Walking1

Abstract

The present study determined the proportion of energy consumption used to lift the center of mass vertically during walking. By assuming that the vertical oscillations of the trunk were identical to those of the center of mass, the complexity of studying the human gait was simplified. The work performed on the center of mass, defined as lift work, was calculated using the subject's mass and the vertical displacement of the trunk. Compensating for the fact that human muscles are approximately 25% efficient in performing external work, the mechanical work was compared with the total energy expenditure, determined using an expired air analysis. At 1.34 and 1.79 m/s, 53.2 +/- 9.3% and 62.8 +/- 8.6%, respectively, of the total energy can be explained by lift work. At 0.45 and 0.90 m/s, the proportions are considerably less, 21.6 +/- 6.6% and 37.6 +/- 8.2%, respectively. These findings provide a rationale for why the metabolic energy cost per unit distance is greater at slower speeds than comfortable or fast speeds of walking. The total energy consumption can be accounted for by changes in the potential and kinetic energies and internal muscular work, defined as the less readily observable work probably needed for balance. The present study demonstrated that the metabolic energy cost of changing the potential energy of the center of mass during walking is significantly less relative to the total energy consumption at slower speeds than at higher speeds. Because kinetic energy is proportional to the square of the velocity, the metabolic energy cost of changing this energy is relatively small at slower speeds. Internal muscular work must therefore play a large role in total energy consumption at slow speeds of walking.

Muscle mechanical work requirements during normal walking: the energetic cost of raising the body's center-of-mass is significant

“…4, region 2: external power >0), and their summed net work output in region 2 represented nearly 80% of the net musculotendon work produced over the entire gait cycle. Thus, our analysis suggests that a major determinant of the net muscle work output required for walking is raising the COM of the body, which is consistent with others' suggestions that a major determinant of the metabolic cost of walking is raising the COM (e.g., Duff-Raffaele et al, 1996;Saunders et al, 1953).…”

Hip, Knee, and Ankle Osteoarthritis Negatively Affects Mechanical Energy Exchange

“…However, the effect of OA in all three major lower extremity joints on the mechanical work of the center of mass is poorly understood. Although calculation of energy recovery is a long-standing technique that has been applied to studies of nonhuman animals and asymptomatic humans [4][5][6][7]15], only a few studies have examined gait in subjects older than 45 years and gait as affected by disorders [10,13,18], and those who have examined OA have examined the effect of knee OA on recovery [11,27]. There is little information regarding the effect of hip and ankle OA on recovery, although it can be predicted from models of energy recovery [4][5][6][7]27].…”

Age-related mechanical work expenditure during normal walking: The Baltimore Longitudinal Study of Aging

“…Walking slower may also be thought of as a compensatory strategy aimed at increasing stability, avoiding falls or reducing the energetic cost of mobility (Pavol et al, 1999; Duff-Raffaele et al, 1996). However, whether the presence of sub-clinical impairments that typically affect older persons stimulates the emergence of less energetically costly walking patterns has not been fully investigated.…”