Effect of armor and carrying load on body balance and leg muscle function

•Uneven weight distribution created a greater sway of center of plantar pressure while standing.•Added weight on non-dominant side of the body creates greater impairment of static balance.•Garment weight less than 10% of the body mass decreases sway of center of plantar pressure.•Increased garment weight elevates EMG amplitude in rectus femoris and medial gastrocneminus in gait.

This study investigated the impact of weight and weight distribution of body armor and load carriage on static body balance and leg muscle function. A series of human performance tests were conducted with seven male, healthy, right-handed military students in seven garment conditions with varying weight and weight distributions. Static body balance was assessed by analyzing the trajectory of center of plantar pressure and symmetry of weight bearing in the feet. Leg muscle functions were assessed by analyzing the peak electromyography amplitude of four selected leg muscles during walking. Results of this study showed that uneven weight distribution of garment and load beyond an additional 9 kg impaired static body balance as evidenced by increased sway of center of plantar pressure and asymmetry of weight bearing in the feet. Added weight on non-dominant side of the body created greater impediment to static balance. Increased garment weight also elevated peak EMG amplitude in the rectus femoris to maintain body balance and in the medial gastrocnemius to increase propulsive force. Negative impacts on balance and leg muscle function with increased carrying loads, particularly with an uneven weight distribution, should be stressed to soldiers, designers, and sports enthusiasts.