The functional strength, flexibility, and ranges of motion of the lower extremities, as well as hormonal balance, estimated by urinary excretion of adrenaline and noradrenaline and serum determinations of testosterone and cortisol, were studied with six physically active army officers participating in a 4-day march totaling 185 km. Catecholamine excretion rates showed cumulatively increased sympathoadrenal stress, and the effects on serum testosterone and cortisol concentrations were minor. Also, leg measurements showed no signs of edema, decreases in flexibility, or decreases in functional strength. Most pain (75%) experienced by the subjects was located in the feet and caused by abrasions and blisters. Only a small portion of perceived pains (25%) was associated with muscle soreness. Serum creatine kinase activity was slightly (ca. 400-650%) increased during the marching days. Thus, soldiers who are in good physical condition and are accustomed to marching are able to walk four marathons on successive days, while carrying 10-kg backpacks, without any major adverse effects on the musculature of their lower extremities.