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GENDER DIFFERENCES IN BODY MASS SCALING OF METABOLIC RATE DURING SUBMAXIMAL STEADY-STATE MOTORIZED TREADMILL CLIMBING

DP Heil, FACSM

Abstract

D.P. Heil, FACSM

Montana State University, Bozeman, MT

Avid rock climbers and the research literature commonly agree that body mass (MB, kg) is the primary determinant of the energy cost of climbing. Given that gravitational resistance is the primary external force being worked against when climbing, it is presumed that the energy cost, as measured by steady-state oxygen uptake (VO2, l/min), should be proportional to both body mass (MB, kg) and the total mass of a climber and their gear (MT, kg) – i.e., VO2 α M b α MTb, where b is the theoretical mass exponent value of +1.0. The research literature, however, has never formally addressed the issue of mass exponents for climbing energy expenditure. PURPOSE: To begin understanding the relationship between mass and steady-state climbing VO2, this study determined MB and MT scaling exponents for energy cost during motorized treadmill climbing. It was hypothesized that both mass exponents would scale to the +1.0 power. METHODS: Data for 16 men and 4 women (Mean±SD: 25±4 yrs age; 22.7±1.5 kg/m2 BMI) from a previously published study (Heil IJPEFS 2019) were used for these analyses. Each climber performed five mins of steady-state climbing at six combinations of “slow” and “fast” climbing speeds (4.6-9.1 m/min) across three treadmill grades: vertical (0°), overhang or negative incline (-5 to -10°), positive inclines (+5 to +10°). Steady-state VO2 data collected with a portable indirect calorimetry system were analyzed using standard log-linear multiple regression analyses using treadmill speed and grade, a dummy-coded gender term, and either MB or MT as independent variables (α=0.05). Derived mass exponents were then compared to the theoretical value of +1.0 using 95% CIs. RESULTS: Without the gender term in the regression model, mass exponents for both MB (b; 95%CI: 1.28; 1.11-1.45) and MT (+1.32; 1.14-1.49) were significantly higher than +1.0 (model P2 = 0.79). With the gender term, however, mass exponents for neither MB (1.05; 0.85-1.25) nor MT (1.09; 0.89-1.29) differed from +1.0 (model P2 = 0.82). CONCLUSION: The mass exponents for both MB and MT did not differ from the theoretical +1.0 value attributed to gravitational resistance when accounting for gender. The reason for the need to include the gender term, however, is not clear and may be an artifact of the imbalance between men (n=16) and women (n=4) in this study.

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