Aim: The impact of aging on muscle performance is not fully understood. The purpose was to measure muscle strength and stiffness of the calf muscle in healthy subjects of different ages. Methods: Thirty-six men between 21 and 88 years participated. Maximal voluntary contraction (MVC) and active/passive stiffness were measured with an isokinetic dynamometer. During the stiffness test the calf muscle was stimulated tetanically and when a plateau of isometric tension was obtained, a short fast stretch (200˚/s) was given.Results: MVC, active and passive stiffness declined significantly with increasing age. Age correlated well with MVC (0.78), and passive stiffness (0.63). MVC correlated with active stiffness (0.61). Active stiffness was significantly influenced by MVC and age (r2 0.36). For passive stiffness (r2 0.36) age makes the strongest contribution.Conclusion: This investigation showed that age itself contributed to passive stiffness while muscle strength was more closely related to active stiffness and the contractile components of the muscle.