Examining External Load Variability in a Cadet Population: Impact on Vertical Jump Performance

Carrying external loads is a fundamental aspect of military training and operational readiness. Added weight and its distribution on the body significantly alters biomechanics and may increase the risk of physical injury. The vertical jump test, a widely accepted measure of lower-body strength and explosiveness, offers a reliable, low-fatigue method for assessing physical readiness in military populations. Despite its utility, researchers have not examined how varying percentages of body weight carried in the MOLLE 4000, a standard military load carriage system, affects biomechanics and movement patterns. Therefore, the primary aim of this study is to determine the effects of various relative external loads on vertical jump height in a cadet sample.

This study was conducted utilizing a cross-sectional design at a senior military college in the southeastern United States. Cadets were recruited with convenience sampling (N = 41; female [F]=20). Each participant completed three unloaded jumps (control) and three jumps although holding a rubber rifle. Loaded conditions included weights equivalent to 0.00%, 22.0%, 44.0%, and 66.0% of body weight added to the MOLLE 4000 rucksack. Dependent variables analyzed included jump height, flight time, reactive strength index modified (RSI-mod), concentric duration, and eccentric duration.

Male (M) cadets demonstrated significantly greater jump height and flight time compared to F cadets. The most notable decline in performance was observed between the control condition (with and without rifle) and the 22% body weight load condition (control mean: females = 21.60 ± 6.46 cm; males = 34.79 ± 6.80 cm).

Findings highlight that increasing external load from 0% to 22% of body weight significantly reduces vertical jump height in both sexes.