Strength, But Not Power, is Reduced in Females But Not Males Following a Simulated Ruck March

Strength and power are critical to the successful completion of military duties and missions. Although males are generally stronger and more powerful than females, females better resist fatigue during endurance-based activities. Maintenance of strength and power is also critical to prevent and recover from slip, trip, fall events, which are the top cause of acute non-combat injury in the military. It is not known if military activities, such as ruck marching, differentially affect strength and power between the sexes. The purpose of this study was to compare the effect of unloaded and loaded treadmill walking on strength and power between sexes.

Ten males (23 ± 3 years; 74.3 ± 12.8 kg; 173 ± 6 cm; 49.8 ± 4.8 mL·kg-1·min-1) and 10 females (25 ± 4 years; 66.1 ± 10.1 kg; 162 ± 6 cm; 40.4 ± 2.4 mL·kg-1·min-1) completed two 4.8 km time trial walks, once while unloaded and once loaded with 30% of their body mass in a military rucksack. Before and after the walks, subjects completed a 3-repetition maximum deadlift and vertical jump to assess strength and power, respectively.

At baseline, males deadlifted more than females before both the unloaded (UNL, 112.3 ± 23.4 kg, 67.7 ± 19.5 kg, P < .01) and loaded trials (LD, 110.9 ± 29.2 kg, 69.1 ± 19.9 kg, P < .01). Males had a higher vertical jump before both trials compared to females (UNL: 47.8 ± 6.2 cm, 37.2 ± 5.9 cm, P < .01; LD: 48.6 ± 6.0 cm, 37.4 ± 6.0 cm, P < .01). There were no differences within sex between the unloaded and loaded trials at baseline for strength (M: P = .64, F: P = .30) or vertical jump height (M: P = .51, F: P = .68). Greater decreases in strength occurred in the loaded trial compared to the unloaded trial (P = .02). This was driven by greater decrease in the loaded trial in females compared to the unloaded trial (P < .01), whereas no differences between the loaded and unloaded trials occurred in males (P = .81). The change in strength did not differ between sexes (P = .12). To assess power, the change in vertical jump height did not differ between the loaded and unloaded trials (P = .17), nor between sexes (P = .86).

A loaded time trial walk resulted in greater decrements in strength than an unloaded time trial walk, which was driven by greater decreases in females. However, loaded and unloaded time trial walks resulted in similar changes in power between sexes. Future work is needed to determine whether other multi-joint dynamic strength assessments result in similar decreases after loaded walking and the implications on military populations.

This project is registered at clinicaltrials.gov; identifier: NCT05309603.