Metabolic Effects of Soldier Performance on a Simulated Graded Road March while Wearing Two Functionally Equivalent Military Ensembles

Military Medicine, Jun 2007 by Crowder, Todd A, Beekley, Matthew D, Sturdivant, Rodney X, Johnson, Christopher A, Lumpkin, Angela

Objectives: The purpose of this study was to examine metabolic effects of soldier performance on a simulated road march, comparing two functionally equivalent military ensembles (FEMEs) with changing gradation of marching, and to create prediction equations addressing workload with different loads and treadmill grades. Methods: Fourteen male military subjects were tested while wearing two different FEMEs on a graded (0%, 5%, or 10%), 3.5 miles/h, road march for 30 minutes. Data collected included oxygen uptake (VO^sub 2^), carbon dioxide output, ventilation, respiratory exchange ratio, and heart rate (HR). Results: No significant differences were found between the two FEMEs in each graded condition. Combining ensemble data, significant differences occurred in all conditions, comparing all grades. A 10% graded road march (3.5 miles/h, ~27-kg load) represented 61% to 90% of maximal values. For treadmill grades of

Introduction

Technological advances have led to improvements In soldiers' personal body armor (lethality and protection), resulting in potential weight overload. As equipment weight increases, so does the subsequent soldier physiological demand.1 Soldiers' increasing load, the emergence of advanced equipment, and the interest in soldier physical performance provided a foundation for seeking to better understand how soldiers can optimize their abilities to carry out their missions, protect themselves, and perform physically.

Historically, several estimations of the acceptable soldier load have been documented. In the book The Soldier's Load and the Mobility of a Nation, General S.L.A. Marshall2 stated, "We are still troubled by commanders who do not fear overloading the infantry soldier with arms" (p 8). German research referenced therein stated, "The carrying of sixty pounds (27.3 kg) into a prolonged engagement would result ultimately in physical breakdown and further 48 lbs (21.8 kg) per man were the absolute limit under the stress and fatigue of the combat field" (p 49). Marshall concluded that the optimal approach load should be no more than one-third of the soldier's body mass (BM) and that the maximal combat load should be no more than four-fifths of the optimal approach load. Marshall calculated that the average soldier weighed 153 pounds (69.5 kg) and thus the optimal approach load would be 51 pounds (23.2 kg) and the maximal combat load would be 40.8 pounds (18.5 kg).2 Knapik et al.3 reported that each 1 kg added to the foot (foot wear) increased energy expenditure 7% to 10% and that each 1 kg added to the thigh increased energy expenditure 4%. Quesada et al.4 reported that, for each 15% body weight load increment, a proportional increase in metabolic cost of approximately 5% to 6% was incurred.

In the past 30 years in the United States, BM has increased.5 Therefore, the historic one-third rule would allow for an increase in load carriage weight. Related to the military population, Sharp et al.6 reported that in 1978 male and female recruits entering the U.S. Army had BMs of 155.5 pounds (70.7 kg) and 130 pounds (59.1 kg), respectively. In 1998, however, a similar cohort of recruits demonstrated that the BMs of male and female recruits had increased to 173.6 pounds (78.9 kg) and 137.7 pounds (62.6 kg), respectively, in 20 years (1978-1998). Although the 1998 recruits tended to have more BM and greater percentage of body fat, they also had greater aerobic capacity, muscular strength, and fat-free mass, compared with the 1978 group. It is not known whether the latter three physiological factors offset the detrimental impact of the former (both greater BM and percentage of body fat).

Data from a U.S. service academy (2000-2005 fitness testing data) indicated that the average service academy male and female cadet weighed 180 pounds (81.8 kg) and 140 pounds (63.6 kg), respectively. Allowing for calculations based on the historical data of Marshall,2 theoretically the average male and female cadets would have optimal approach loads of 60 pounds (27.3 kg) and 46.7 pounds (21.2 kg) and maximal combat loads of 48 pounds (21.8 kg) and 37.3 pounds (17.0 kg), respectively. With these increased "theoretical soldier loads," what would be the attending physiological demands necessitated by the load, particularly in a forced graded road march scenario with modern, but heavier, equipment?

Modern body armor with the attending supporting gear (onboard computer, global positioning system, and hydration system) weighs 40 to 45 pounds (18.2-20.5 kg), to which would be added a weapon, pack, and/or additional equipment. With this up-to-date protection and lethality, is today's approach load in excess of 60 pounds (27.3 kg) becoming the "acceptable weight?" A recently deployed brigade commander reported that total loads of 90 to 110 pounds (40.9-50 kg) per soldier were normal and loads as great as 130 pounds (59.1 kg) were not uncommon in some situations (K. Stramara, personal communication). These loads were absolute weights not standardized to BM. However, the relationship between soldier load and subsequent metabolic physiological performance is critical. Quesada et al.4 investigated soldier load (percentage of BM) and physiological demand (percentage of maximal oxygen uptake [VO^sub 2^]). After 40 minutes of road marching at 0%, 15%, and 30% of BM, subjects reached 30%, 36%, and 41% of maximal VO^sub 2^, respectively. Knapik et al.7 examined heavy loads during a 20-km foot march and determined that, as load increased, pace decreased. Heart rate (HR) was used to determine physiological demand.