K.E. Kamrud, R.J. Skoric, B.A. Ruple, J.T. Strang, C.J. Alfiero, M.W. Bundle

University of Montana, Missoula, MT

PURPOSE: Field trials evaluating the metabolic rates of individuals performing sustained bouts of overground load carriage are rare and difficult to compare to laboratory values. We evaluated whether the metabolic cost of load carriage was similar between 5min steady-speed treadmill trials administered at the average speed used during a 4.83 km outdoor field trial. METHODS: Subjects (n=10 [4 female], Mb = 74.4±12.4kg) performed a 4.83 km loaded (20.45kg) walking trial around a local athletic track (Missoula MT elev 975m). Subject speed was recorded every 400m throughout the trial, and expired gases were collected for 90 sec and stored in a Douglas bag for subsequent gas faction and volume analysis beginning at the 5, 20 and 35 min points. During a separate visit, we measured VO2from the subjects as they completed loaded, 5min, treadmill trials at speeds selected to match those used throughout the field trial. RESULTS: Average speed (1.88±0.09 m s-1) during the field trial fluctuated by an average maximum of 10.5±3.3% per subject throughout the trials. Accordingly, we compared the measured speed during the three periods of gas collection to similar speeds administered on the treadmill (i.e. within 0.1 m s-1). Measured rates of VO2throughout the overground trial were similar across time; t5= 29.0±4.5, t20= 30.1±4.5, t35= 31.1±4.3ml kg-1 min-1. During treadmill walks at speeds corresponding to those used overground, laboratory measures of VO2were t5= 27.8±5.7, t20= 39.4±5.4, t35= 30.4±4.8ml kg-1 min-1. As a result the greatest difference between laboratory and field measures was 2.0±6.2ml kg-1 min-1, obtained at the 20 min point of the trial. CONCLUSION: The strong numerical agreement and statistically indistinguishable values obtained during the overground vs treadmill loaded trials suggest that, speed dependent rather than environmental factors influence metabolic cost. We further conclude that laboratory based treadmill results can provide valid insight to the energy use patterns of overground, self-selected, locomotion patterns.

This work was supported by a multi-investigator award, US Forest Service Agreement # 16-CR-11138200-005, to MB and colleagues.

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