To evaluate the strain on a sutured Achilles tendon during walking in a short leg cast the EMG activity of the triceps surae muscles was studied. The regression line of the EMG/torque relationship of the triceps surae in the noninjured leg was investigated during isometric contractions with the foot in the same plantarflexed position as the injured foot immobilized in plaster cast. A linear relationship was found between EMG activity (EMG signals converted to rectified mean square values) and torque, measured with Cybex II. The torque provided by the triceps surae of the injured leg was calculated from the registered EMG activity during walking and the regression line. The strain acting on the sutured Achilles tendon was calculated after measurement of the lever arm. There was no significant difference in calculated strain on the sutured Achilles tendon during nonweight bearing in a short leg cast and full weight bearing without external rotation movement of the leg. External rotation movement of the leg during full weight bearing gave increased strain on the sutured Achilles tendon. The actual strain is considered somewhat lower than the calculated one since other muscles than the triceps surae contribute to plantar flexion of the ankle joint. The results indicate that the strain during weight bearing in a short leg cast is unlikely to exceed the strength of a sutured Achilles tendon.