One major way that running style varies between individuals is how their foot strikes the ground (forefoot strike or rearfoot strike). Running generates a torque about the ankle that depends on the individual’s foot strike pattern, length of their plantar flexor moment arm, and force generated from the plantar flexor muscles. The foot strike pattern during running, gastrocnemii muscle thickness, and heel length (used as an approximation for plantar flexor moment arm) were determined in 41 runners. Forefoot and rearfoot strike runners had the same thickness of the gastrocnemii muscles. However, in comparison with sedentary walkers, the runners had thicker calf muscles. These results imply a “peak” muscle thickness seems to be attained by running. Runners with longer heels were more likely to use a forefoot strike running style, possibly due to a mechanical advantage in the generation of torque.