Comparison of Pandolf Equation and Measured Metabolic Cost of Load Carriage in UK Military Personnel

Abstract

PURPOSE: The metabolic cost of load carriage (LC) is frequently predicted using the Pandolf et al. (1977) equation. Recent laboratory investigations have identified that the Pandolf equation under-predicts the metabolic cost of LC in untrained personnel during treadmill walking (Drain et al., 2017). However, the relationship between the actual and Pandolf predicted metabolic cost of outdoor LC in UK Armed Forces personnel has not been established. METHODS: Twenty-two UK Armed Forces personnel (Royal Marine Commandos and Parachute Regiment, mean ± SD: age 23 ± 3 years; stature 180.9 ± 4.9 cm; body mass 83.1 ± 6.6 kg; predicted V[Combining Dot Above]O2max 54.0 ± 3.1 ml·kg-1·min-1) completed 15, 20 minute stages of outdoor LC, with external load masses ranging from 25 to 70 kg. The stages were completed at a patrol, forced, and insertion marching speed (2.5, 4.8, and 5.5 km·h-1, respectively). During the final 2-4 minutes of each LC stage, oxygen uptake (V[Combining Dot Above]O ) was measured using the Douglas bag technique. Predicted V[Combining Dot Above]O2 for each speed-load mass combination was calculated using the Pandolf equation and compared to the measured V[Combining Dot Above]O2 using paired t-tests and 95 % Limits of Agreement (LoA). RESULTS: The Pandolf equation systematically under-predicted the metabolic cost of LC for all speeds and load masses combined [mean difference 3.2 ± 2.9 ml·kg-1·min-1 2 p<0.001), 95% LoA -2.5-8.9 ml·kg-1·min-1] resulting in a V predictive error of 17.5 %. Mean difference and 95% LoA at the different speeds were: (a) 2.5 km·h-1 [4.8 ± 1.9 ml·kg-1·min-1, (p<0.001), 95% LoA 1.0-8.6 ml·kg-1·min-1], (b) 4.8 km·h-1 [1.5 ± 2.7 ml·kg-1·min-1 (p<0.001), 95% LoA -3.9-6.9 ml·kg-1·min-1], and (c) 5.5 km·h-1 [4.2 ± 3.3 ml·kg-1·min-1 (p<0.001), 95% LoA -2.1-10.7 ml·kg-1·min-1], with prediction errors of 30 %, 6 % and 14 %, respectively. CONCLUSIONS: The current study demonstrates a systematic under-prediction of V[Combining Dot Above]O2 for British Army personnel during outdoor LC when applying the Pandolf equation, supporting the findings of previous laboratory studies. Furthermore, the error appears to be of greater magnitude when LC speeds are lower, i.e. at a representative patrolling pace. This in part could be attributed to the load mass distribution of the modern solider, which differs from the back mounted load carried data used to develop and refine the Pandolf equation.