Purpose The present study aimed to test if a long-term passive stretching training causes adaptations of the medial gastrocnemius architecture and the Achilles tendon (AT) tangent modulus. Methods A total of 20 males took part in the study. The stretching group (n = 12), performed stretching exercises for the plantar flexors for 10 weeks, 4-5 times a week, which comprised two static positions sustained twice each during 30 s. Results For the stretching group, maximum dorsiflexion angle, peak passive torque, and muscle-tendon unit maximum length significantly increased after training. No other differences were found related to muscle architecture and AT tangent modulus. Conclusion Joint amplitude gain after a long-term stretching of the triceps surae was not accompanied by structural or mechanical changes of the medial gastrocnemius and AT tendon, and seems to reflect an increasing stretch tolerance level.