Quantifying Training Load During Physically Demanding Tasks in U.S. Army Soldiers: A Comparison of Physiological and Psychological Measurements.

INTRODUCTION: There are many ways to quantify the training loads required to perform soldiering tasks. Although indirect calorimetry may provide the most accurate measures, the equipment can be burdensome and expensive. Simpler measures may provide sufficient data, while being more practical for measuring soldiers in the field. The purpose of this study was to examine the relationship between total relative oxygen uptake (TotalRelVO2) measured by indirect calorimetry during three soldiering tasks, with two field-expedient measures of training load: summated heart rate zone (sumHR) and session rate of perceived exertion (sRPE). MATERIALS AND METHODS: 33 male and 28 female soldiers performed three soldiering tasks while wearing a 32.3-kg fighting load: sandbag fill, sandbag carry, and ammunition can carry. Metabolic measurements were monitored and completion times were recorded (min). TotalRelVO2 (average relative VO2*time) and age-predicted maximal heart rate (220-age) were calculated. SumHR was calculated by multiplying time spent in each of the five heart rate zones by a multiplier factor for each zone (50-59% = 1, 60-69% = 2, 70-79% = 3, 80-89% = 4, and ≥90% = 5). RPE (Borg 6-20 scale) was collected at the end of each task, then sRPE was calculated (RPE*time). Pearson and Spearman correlations were performed to examine the relationship between TotalRelVO2, sumHR and sRPE. Wilcoxon signed rank tests were conducted to determine if there was a difference in median rankings between the three variables for each task. Linear regressions were performed to determine predictability of TotalRelVO2 from sumHR and sRPE. The study was approved by the U.S. Army Research Institute of Environmental Medicine Institutional Review Board. RESULTS: Significant, positive correlations were revealed for all three tasks between TotalRelVO2, sumHR and sRPE (r ≥ 0.67, p ≤ 0.01; rho≥0.74, p ≤ 0.01). Wilcoxon signed rank tests revealed no significant differences in rankings between TotalRelVO2, sumHR and sRPE for all three tasks (p ≥ 0.43). Both sumHR and sRPE are significant predictors of TotalRelVO2 (p ≤ 0.01). CONCLUSIONS: SumHR and sRPE are acceptable alternatives to TotalRelVO2 when attempting to quantify and/or monitor training load during soldiering tasks.

The Relationship Between Soldier Performance on the Two-Mile Run and the 20-m Shuttle Run Test.

Background: The 20-m shuttle run test (MSRT) is a common field test used to measure aerobic fitness in controlled environments. The U.S. Army currently assesses aerobic fitness with the two-mile run (TMR), but external factors may impact test performance. The aim of this study is to examine the relationship between the Army Physical Fitness Test TMR performance and the MSRT in military personnel. Methods: A group of 531 (403 males and 128 females) active duty soldiers (age: 24.0 ± 4.1 years) performed the MSRT in an indoor facility. Heart rate was monitored for the duration of the test. Post-heart rate and age-predicted maximal heart rate were utilized to determine near-maximal performance on the MSRT. The soldiers provided their most recent Army Physical Fitness Test TMR time (min). A Pearson correlation and multiple linear regression analyses were performed to examine the relationship between TMR time (min) and MSRT score (total number of shuttles completed). The study was approved by the Human Use Review Committee at the U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts. Findings: A significant, negative correlation exists between TMR time and MSRT score (r = -0.75, p < 0.001). Sex and MSRT score significantly predicted TMR time (adjusted R2 = 0.65, standard error of estimate = 0.97, p < 0.001) with a 95% ratio limits of agreement of ±12.6%. The resulting equation is: TMR = 17.736-2.464 × (sex) - 0.050 × (MSRT) - 0.026 × (MSRT × sex) for predicted TMR time. Males equal zero, females equal one, and MSRT score is the total number of shuttles completed. Discussion: The MSRT is a strong predictor of the TMR and should be considered as a diagnostic tool when assessing aerobic fitness in active duty soldiers.