Force (and power)-velocity characteristics were determined at different stimulation frequencies in in situ rat muscle with nerve stimulation at 36¡C. In isometric contractions (duration, 150 ms), maximal force is generated at ~120 Hz. In contrast, in the high velocity (250 mm s-1) shortening contractions, frequencies of ~400 Hz were needed to obtain maximal dynamic force, while 120 Hz elicited only ~26 % of the maximum. At the highest velocity measured, power production was significantly different (P < 0·05) among frequencies of 80, 120, 200 and 400 Hz, suggesting that maximal shortening velocity should be assessed using very high stimulation frequencies. However, the results further indicate that lower frequencies may be adequate in exercise studies that investigate fatigue and changes in power output during series of repetitive contractions.