The purpose of the present study was to examine the relationships among the passive properties of the muscle-tendon unit and muscle cross-sectional area (CSA). Our findings indicated significant relationships between muscle CSA and passive stiffness (P < 0.05; r = 0.830) and muscle CSA and passive energy absorption (P < 0.05; r = 0.765). Since passive stiffness and the ability to absorb passive energy decreases with many diseases, these findings may support the need to maintain or increase muscle CSA.