An optic fiber (Ø 0.5 mm) was utilized for the study of Achilles tendon forces (ATF) in eight volunteers who walked over a 10 m force platform at three speeds (1.1 ± 0.1 m × s⁻¹, 1.5 ± 0.1 m × s⁻¹ and 1.8 ± 0.2 m × s⁻¹). The presented ATF-time curves showed great intersubject variation in magnitudes of the sudden release of force after initial contact and in the peak ATF's (1430 ± 500 N). This intersubject variation in the peak force decreased only by 4% when cross-sectional area of the tendon was considered. Measured ground reaction forces and plantar pressures confirmed that the subjects walked quite normally during recordings. The peak ATF was found to be rather insensitive to speed in contrast to the rate of ATF development which increased 32% ( p < 0.5) from slow to fast walking speed. It is concluded that the optic fiber technique can be applied to study loading of the musculo-tendinous complex during normal locomotion such as walking.