Objectives: This study aimed to report (1) the correlation between net metabolic cost (NMC) of running and Achilles tendon (AT) and ankle plantar flexor passive stiffness and (2) explore the relationship between passive stiffness and key running biomechanics.
Methods: Twenty-two male recreational runners participated in this study. The runners performed a 5-minute run at 50% of their maximal aerobic speed as a warm-up on an instrumented treadmill, followed by a 6-minute run at 65% of their maximal aerobic speed wherein NMC was recorded.