Graded Walking Energetics under Cold Strain.

Introduction: Although research supports selecting steeper routes to minimize metabolic rate (M˙) in mountain racers, the "steeper is cheaper" strategy has yet to be confirmed for slower, more typical graded walking speeds under cold stress.

Purpose: This study aimed to confirm whether "steeper is cheaper" is true for typical graded walking speeds in individuals exposed to incremental cold stress.

Methods: Fourteen healthy, military-aged adults (age, 24 ± 6 yr; height, 1.72 ± 0.08 m; body mass, 72 ± 16 kg) completed four 20-min treadmill walks in three ambient temperatures (20°C, 10°C, and 0°C) in light clothing (i.e., shorts, t-shirt, light gloves). Each walk involved five stages at incremental vertical speeds (0.00, 1.93, 3.86, 5.79, 7.79 m·min -1 ) but variable treadmill speeds (0.54, 0.72, 1.07 m·s -1 ). To verify the "steeper is cheaper" strategy, we compared M˙ between treadmill speeds at matched vertical speeds in each temperature. We also tested if the 90% confidence interval around the mean percent paired difference between Load Carriage Decision Aid (LCDA) metabolic model predictions and measured M˙ was within ±10%.

Results: M˙ was significantly higher for the faster treadmill speed at matched vertical speeds in all but two comparisons at 20°C, all but two comparisons at 10°C, and all comparisons at 0°C ( P < 0.05). LCDA metabolic model predictions were statistically equivalent to measured M˙ during graded walking at 20°C (90% confidence interval, -3.1% to 0.6%) and 10°C (-7.8% to -2.6%) but not 0°C (-16.2% to -9.5%).

Conclusions: Route planners should recommend steeper but shorter routes to minimize M˙ in individuals that walk in temperate-to-cold environments. The LCDA metabolic model provides accurate M˙ predictions in lightly dressed individuals in temperatures down to 10°C, but users should expect underestimated M˙ in 0°C or colder.