The Effects Of Load And Sex Differences On Static Postural Stability

Military personnel are required to carry heavy loads (22 kg) for both training and combat. Arguably, these heavy loads have the potential to negatively impact the postural stability of military personnel. PURPOSE: The purpose of the study was to explore the combined influence of load and sex on balance ability. METHODS: 34 recreationally active participants were recruited for this study, 17 males (21.71 ± 2.71 yrs; 179.48 ± 7.96 cm, 87.45 ± 18.55 kg) and 17 females (22.35 ± 3.95 yrs; 168.28 ± 9.28 cm, 68.42 ± 14.00 kg). Participants completed a 30-second normal standing balance task under two conditions: unloaded and loaded. For the unloaded condition, participants wore shorts, t-shirts, and tennis shoes. The loaded condition consisted of a combat helmet, tactical vest, rucksack, and combat boots (≈22 kg). The trial required participants to stand on a 50 cm x 46 cm balance platform with their eyes open and their feet equidistant from the midline of the balance platform at a width equal to their shoe size. The main outcome measure was a stationary stability score (SS). 100% indicates that the participant maintained perfect stillness. 0% indicates that the participant lost their balance completely. A 2-way Mixed ANOVA was used to determine the effects of load condition (unloaded and loaded) and sex (male and females) on SS. RESULTS: There was no statistically significant interaction between load condition and sex, F(1, 32) = .23, p = ..635, partial η2 = .007. The main effect of load condition showed a statistically significant difference in mean SS (unloaded, 95.06 vs. loaded 93.01) at the different conditions, F(1, 32) = 11.17, p < .002, partial η2 = .259. The main effect of the group showed that there was a statistically significant difference in SS between groups F(1, 32) = 17.13, p < .001, partial η2 = .349, with males having significantly higher SS values for both the unloaded (96.00 vs. 94.11, p = .018) and loaded (91.26 vs. 91.78, p = .007) conditions. CONCLUSION: The findings suggest males have better static balance while donning loads ≈22 kg. The donning of military loads resulted in a statistically significant decrease in SS values in both males and females during an NS balance task.