The electrically evoked contractile properties of the triceps surae and short-term ( < 2 s) maximal power output during vertical jumping have been examined before and after heating (by water immersion) in 5 elderly men aged 70 ± 5 years. Leg immersion in water at 44°C for 30 min produced a 3.4°C rise in muscle temperature (Tm) and was associated with a significant (p < 0.001) reduction in maximal time to peak tension and half relaxation time of the twitch, but was without affect on maximal twitch, tetanic (20 and 50 Hz) and voluntary tensions. However, at 10 Hz maximal tetanic tension was reduced (p < 0.05) from 604 ± 104 to 422 ± 142 N. During vertical jumping from a force platform, peak power output (W) was significantly (p < 0.05) increased from 1,155 ± 212 to 1,381 ± 307 W after heating. The rise in W was due to a small increase in both take-off velocity and the exerted force, and was reflected in a 3-cm increase in the height jumped from the force platform. It is concluded that the contractile characteristics of elderly triceps surae can be modified by heating and a rise in Tm does effect a change in the capacity of the muscle to generate