An in vitro experiment was designed to identify whether tensile force on different triceps surae components would result in nonhomogenous force distribution across the human Achilles tendon. Medial tendon forces were significantly higher than lateral (23.2 +/- 6.6%; P < or = 0.05) when only the gastrocnemius medialis was subjected to force. Lateral forces were significantly higher when both gastrocnemii (30.6 +/- 16.5%) or all three muscles (20.7 +/- 10.9%) were loaded. Experimental identification of force concentrations in the human Achilles tendon contributes to the understanding of the origin of its injury.