Body Mass Bias in a Combat Fitness Test

Allometric theory predicts that, pound for pound, lighter individuals will perform better than heavier individuals on strength and endurance tests. This study evaluated body mass bias as a factor in the U.S. Marine Corps Combat Fitness Test (CFT), a test consisting of movement to contact (Movement), an ammunition can lift (Lift), and maneuver under fire (Maneuver). Allometric modeling indicated small to moderate biases, favoring lighter Marines for each CFT element. The biases were smaller than predicted by theory. Age and gender did not modify the bias. Wearing personal protective equipment eliminated the biases for the movement to contact and maneuver under fire. Despite the biases for individual elements, CFT scores were not related to weight. This difference reflects the fact that CFT scores are based on absolute performance. The better performance of heavier individuals on Lift offset their poorer performance on Movement and Maneuver. The CFT elements are biased measures of physical fitness, but the CFT is an unbiased measure of fitness for duty. These apparently contradictory conclusions derive from the difference between fitness defined as relative pound-forpound performance and the absolute performance required by combat tasks. Also, the fact that CFT scores did not correlate with weight means the CFT will not adversely affect personnel decisions.