2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
LOAD CARRYING CAPACITY-ENDURANCE TIME RELATIONSHIP
DURING MARCHING WITH LOADS AROUND BODY WEIGHT
C.L. Koerhuis 1 , B.J. Veenstra 2 , M.J van Dijk 2 , N.J. Delleman 1
1 TNO Human Factors, Soesterberg, The Netherlands
2 Training Medicine & Training Physiology, Royal Netherlands Army, Utrecht, The
Netherlands
Contact person: claudy.koerhuis@tno.nl
INTRODUCTION
Most loaded marching studies have focused on metabolic and cardiovascular effects.
However, during marching with high loads, muscle strength may become a limiting factor.
The purpose of this study was to assess the endurance time of combat soldiers marching with
extremely heavy loads, with muscle strength and/or localized discomfort as most likely
limiting factor(s). It was hypothesized that loads relative to individual characteristics
(Maximal Load Carry Capacity (MLCC), body mass, lean body mass) would be better
predictors for endurance time than the load itself. Good prediction is necessary to optimise
team performance. Specifically, lighter subjects carrying heavy loads may have short
endurance times with respect to heavier subjects, thus hampering team performance. As it
requires considerable effort to determine MLCC, a second purpose of the study was to find
out whether it would be beneficial to use muscle strength and/or anthropometric parameters
for predicting MLCC, and eventually endurance time.
METHODS
Twenty-three healthy male combat soldiers participated. MLCC was determined by
increasing the load by 7.5 kg every 4 minutes until exhaustion, starting with body weight. The
marching velocity and gradient were kept constant at 3 km/hour and 5% respectively. For the
determination of the %MLCC-endurance time relationship, endurance time was determined
carrying 70, 80 and 90% of MLCC. Rating scales were used to assess localized postural
discomfort.
RESULTS
The MLCC averaged 102.6 kg (SD: 11.6). A significant difference was found in endurance
time carrying 70% and 80% of MLCC (p=0.0001; 40.9 (SD: 17.2) and 24.5 (SD: 7.4)
minutes) and carrying 70% and 90% of MLCC (p=0.0001; 40.9 (SD: 17.2) and 17.7 (SD: 5.8)
minutes respectively). Postural discomfort was predominantly localized in the shoulder
region, followed by the lower back and hips. %MLCC was the best predictor of endurance
time (R 2 =0.45). Loads expressed as %body weight, as %free fatty mass or carrying the same
loads predict endurance time less well (R 2 = 0.30, R 2 = 0.24 and R 2 =0.23 respectively). The
%MLCC- endurance relationship can be used for redistributing the total load carried by a
group over individual soldiers in order to affect group endurance time. Redistribution of the
total load changed endurance times, which initially ranged from 11.35 to 65 minutes (mean:
30.2 ± 16.1), to endurance times ranging from 13.4 to 45 minutes (mean: 28.3, SD: 8.8).
Although the average endurance time remained about the same, the standard deviation was
twice as low. Redistribution of the total load resulted in a more homogeneous group
performance with an increase in endurance time for the ‘weakest link’.
However, determination of MLCC requires more effort than determination of the body
weight, free fatty mass and the carried load. Since load expressed as %body mass is the
second best predictor of endurance time, it may be a reasonable alternative.
544