Can handling a weapon make soldiers more unstable?

Gait stability in soldiers can be affected by task constraints that may lead to injuries. This study determined the effects of weapon handling and speed on gait stability in seventeen soldiers walking on a treadmill with and without a replica weapon at self-selected (SS), 3.5 km·h^-1, 5.5 km·h^-1, and 6.5 km·h^-1 while carrying a 23-kg load. Local dynamic stability was measured using accelerometry at the sacrum (LDE_SAC) and sternum (LDE_STR). No significant weapon and speed interaction were found. A significant effect of speed for the LDE_SAC, and a significant effect of speed and weapon for the LDE_STR were found. Per plane analyses showed that the weapon effect was consistent across all directions for the LDE_STR but not for LDE_SAC. Weapon handling increased trunk but did not affect pelvis stability. Speed decreased stability when walking slower than SS and increased when faster. These findings can inform injury prevention strategies in the military. Practitioner summary: We determined the effects of two constraints in soldier's walking stability, weapon handling and speed, measured at the trunk and sacrum. No constraints interactions were found, however, lower stability when walking slow and greater stability with the weapon at the trunk can inform preventive strategies in military training.