- Foot orthoses are widely prescribed both to treat existing pathological conditions and to prevent overuse injuries, but little is known about the effect of their material composition and fabrication technique on patient comfort and the incidence of overuse injuries. The acceptance rates and comfort scores of soft custom, soft prefabricated, semirigid biomechanical, and semirigid prefabricated orthoses and their effect on the incidence of stress fractures, ankle sprains, and foot problems were studied in a prospective, randomized, single-blinded clinical trial among 874 infantry recruits during basic training. A statistically significantly lower number of recruits given soft prefabricated orthoses (53%) finished basic training in their assigned devices than in the soft custom group (72%), in the semirigid biomechanical group (75%), and in the semirigid prefabricated group (82%) (p = .003). For recruits who finished training in their assigned orthoses, the soft custom (3.54) and soft prefabricated (3.43) orthoses had significantly higher comfort scores than the semirigid biomechanical (3.23) and prefabricated (3.17) orthoses, (p = .0001). There was no statistically significant difference in the incidence of stress fractures, ankle sprains, or foot problems between recruits using the different types of orthoses. These findings suggest that if a foot orthosis is being dispensed as prophylaxis for overuse injuries in an active, healthy population, there is little justification for prescribing semirigid biomechanical orthoses. Their cost is high compared to other types of orthoses, without an advantage in comfort or a reduction in stress fractures, ankle sprains, and foot problems.