1. Real-world walking economy: can laboratory equations predict field energy expenditure?
- Author
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Weyand, Peter G., Ludlow, Lindsay W., Nollkamper, Jennifer J., and Buller, Mark J.
- Abstract
We addressed a practical question that remains largely unanswered after more than a century of active investigation: can equations developed in the laboratory accurately predict the energy expended under free-walking conditions in the field? Seven subjects walked a field course of 6,415 m that varied in gradient (-3.0 to + 5.0%) and terrain (asphalt, grass) under unloaded (body weight only, Wb) and balanced, torso-loaded (1.30 X W
b ) conditions at self-selected speeds while wearing portable calorimeter and GPS units. Portable calorimeter measures were corrected for a consistent measurement-range offset ( + 13.8 ± 1.8%, means ± SD) versus a well-validated laboratory system (Parvomedics TrueOne). Predicted energy expenditure totals (mL O2 /kg) from four literature equations: ACSM, Looney, Minimum Mechanics, and Pandolf, were generated using the speeds and gradients measured throughout each trial in conjunction with empirically determined terrain/treadmill factors (asphalt = 1.0, grass = 1.08). The mean energy expenditure total measured for the unloaded field trials (981 ± 91 mL O2 /kg) was overpredicted by + 4%, + 13%, + 17%, and + 20% by the Minimum Mechanics, ACSM, Pandolf, and Looney equations, respectively (corresponding predicted totals: 1,018 ± 19, 1,108 ± 26, 1,145 ± 37, and 1,176 ± 24 mL O2 /kg). The measured loaded-trial total (1,310 ± 153 mL O2 /kg) was slightly underpredicted by the Minimum Mechanics equation (-2%, 1,289 ± 22 mL O2 /kg) and overpredicted by the Pandolf equation ( + 13%, 1,463 ± 32 mL O2 /kg). Computational comparisons for hypothetical trials at different constant speeds (range: 0.6–1.8 m/s) on variable-gradient loop courses revealed between-equation prediction differences from 0% to 37%. We conclude that tread mill-based predictions of free-walking field energy expenditure are equation-dependent but can be highly accurate with rigorous implementation. NEW & NOTEWORTHY Here, we investigated the accuracy with which four laboratory-based equations can predict field-walking energy expenditure at freely selected speeds across varying gradients and terrain. Empirical tests involving 6,415-m trials under two load conditions indicated that predictions are significantly equation dependent but can be highly accurate (i.e., ±4%). Computations inputting identical weight, speed, and gradient values for different theoretical constant-speed trials (0.6–1.8 m/s) identified between-equation prediction differences as large as 37%. [ABSTRACT FROM AUTHOR]- Published
- 2021
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