© 2016 Wiley Periodicals, Inc. Introduction: The extent to which gastrocnemius muscle and Achilles tendon properties contribute to the impaired walking endurance of claudicants is not known. Methods: Ultrasound images quantified muscle architecture of the lateral and medial gastrocnemius (GL and GM) and were combined with dynamometry during plantarflexor contractions to calculate tendon stress, strain, stiffness, the Young modulus, and hysteresis. Key parameters were entered into multiple regression models to explain walking endurance. Results: Worse disease severity was significantly associated with longer fascicle: tendon length ratios (GL R=-0.789 and GM R=-0.828) and increased tendon hysteresis (R=-0.740). Walking endurance could be explained by GL and GM pennation angle, maximum tendon force, tendon hysteresis, and disease severity (R 2 =∼0.6). Conclusions: Peripheral arterial disease was associated with functionally important changes in muscle and tendon properties, including the usage of stored elastic energy. Interventions known to target these characteristics should be adopted as a means to improve walking endurance.