Menopause is associated with an accelerated loss of muscle mass, strength, and power. Changes in muscle-tendon properties may contribute to these effects and whole-body locomotion. However, reliable protocols evaluating muscle-tendon properties and function in active postmenopausal females require development. Muscle-tendon properties also influence stretch-shortening cycle (SSC) function, but their contribution has yet to be quantified in active pre and postmenopausal women. PURPOSE: 1) Assess the test-retest reliability of a muscle-tendon function protocol in active pre and postmenopausal females. 2) Quantify between-group differences in Achilles tendon (AT) stiffness, cross-sectional area (CSA), stress, strain, plantar flexor strength, and SSC function by measuring the energy cost of running (Erun) and external mechanical power using countermovement jump (CMJ) testing. 3) Examine the CSA along the AT in active women not using exogenous hormone therapy. METHODS: Active pre and postmenopausal women participated in two testing sessions to assess the test-retest reliability of the muscle-tendon protocol using interclass correlation coefficients, coefficient of variation, and Bland-Altman analysis. Each session included maximal plantar flexor strength, AT stiffness, and AT CSA measurements via ultrasound and dynamometry. Erun was calculated from expired V̇O2 and V̇CO2 during a 10-minute run. CMJ testing was performed on a force plate and mechanical power was obtained through force-time analysis. RESULTS: Good to excellent reliability was reported for all selected variables. AT stiffness was significantly lower post menopause and significantly related to CMJ jump height and relative peak power. No differences were seen between groups in maximal plantar flexion strength, AT CSA, stress, or strain. Group differences in Erun and AT CSA and stress, varied significantly across the length of the AT. CONCLUSIONS: The testing protocol resulted in good to excellent reliability, supporting its use in future longitudinal research among active women. Postmenopausal women show reduced AT stiffness without a concurrent reduction in plantar flexor muscle strength, which may predispose them to tendon strain injuries. The reduction in AT stiffness post menopause may contribute to elevations in whole-body Erun. AT stiffness was associated with mechanical power, and lower AT stiffness may be a result of altered serum estrogen levels associated with menopause.