Correlations Between Systemic Work and Summed Measures of Lower Extremity Mechanical Demand

Abstract

0720 Integrated measures, such as net joint moment impulse and mechanical energy expenditure, may be more appropriate than peak measures when quantifying lower extremity demand. Currently, it is not known which of these measures may be more appropriate when analyzing dynamic exercise. PURPORSE: To determine the relations between the work performed at the center of mass (WCOM) and the summed measures of mechanical output at the hip, knee, and ankle. METHODS: Older adult participants (N = 20) performed a forward step-up under three loading conditions (no external resistance, and external resistances equal to 5% and 10% of the participants' body weight) for a total of 60 data sets. Support moment impulse (SMI) was calculated as the algebraic sum of the integrals of the moment-time curves at the hip, knee, and ankle. Total mechanical energy expenditure (MEE) was calculated as the algebraic sum of the integrals of the absolute power-time curves at the hip, knee, and ankle. Associations were determined for both concentric and eccentric phases of the movement using Pearson's Product moment correlation coefficient (á = 0.05). RESULTS: Results are presented in Table 1. Both measures were correlated with WCOM during both phases at the 0.01 level. A stronger association was seen between WCOM and MEE than with WCOM and SMI: 79%–80% of the variability in WCOM was accounted for by MEE, while 51%–64% of the variability in WCOM was accounted for by SMI. Additionally, MEE appeared to be less affected by movement phase and had a lower coefficient of variation.Table 1: Correlation coefficients (r), common variance (R2), and coefficients of variation (CV).CONCLUSION: Results suggest total mechanical energy expenditure may be a more appropriate measure of mechanical demand during this dynamic activity. Similar analyses should be conducted for different types of exercises (i.e., exercises with a large isometric component). Supported by NIA AG19320-01.