Relationship Between Mechanical And Physiological Energy Costs And Efficiency Of Treadmill Walking In Active And Inactive Females

Abstract

Energy costs of walking are traditionally examined from two perspectives biomechanical and physiological. Biomechanists use mechanical energy costs to calculate mechanical work (MW) performed by the body. Physiologists use energy expenditure to calculate metabolic cost (MC) of the activity. These two values are then used to calculate efficiency values for walking. However, few researchers have examined the rela tionship between these two forms of energy cost (MW and MC) and the calculated efficiency value (EFF). The purpose of this study was to examine the relationship between MW and MC, MW and EFF, and MC and EFF during treadmill walking in active (ACT) and inactive (INCT) females. It was hypothesized that a high correlation would exist between MW and MC because the amount of work done by the segments would be dependent on the amount of energy expended by the muscles for muscle contraction to move the segments. Two groups (ACT and INCT) of 12 females participated in a 10-min submax walking test. Submax V02 and 3D film records (100 fps) were obtained during the final minute of the test. MW, MC, and EFF were calculated using the method recommended by Cavanagh and Williams (1983). Correlations for each group were calculated between MW and MC (ACT: r= .340; INCT: r= .429), MC and EFF (ACT: r= -.271; INCT: r = -.149), and MW and EFF (ACT: r= .854; INCT: r= .817). Significant correlations were found between MW and EFF for both groups (p f. .01). No relationship was found between MW and MC for either group. Biomechanists have attempted to adjust MW by developing methods for approximating the amount of mechanical energy conserved by energy transfer within and between segments, by the storage of elastic energy, and by the performance of negative work as opposed to positive work. This leads to a more accurate representation of mechanical energy cost related t<? the specific activity. However, no attempt has been made to adjust MC for energy that is lost in the form of heat. This leads to an overestimation of MC related to the specific activity. Physiologists report the efficiency of metabolic conversion at the muscular level to be between .2 and .3. If this adjustment were made, a higher correlation between MW and MC might be found, as would be expected. Future research on the energy cost of physical activity should attempt to correct these values so that a more accurate analysis of the relationship between these variables can be performed.