Maximum and sustained power of extensor digitorum longus muscles from young, adult, and old mice.

We tested the hypothesis that extensor digitorum longus (EDL) muscles in old mice would generate lower maximum powers and sustain lower powers than EDL muscles in young or adult mice. Power was measured in situ at 35 degrees C during single and repeated isovelocity shortening contractions through 10% of fiber length at optimum velocity for power. Sustained power was measured during repeated contractions at a stimulation frequency of 150 Hz. The train rate, and consequently the duty cycle, of repeated contractions was incremented every 5 to 10 min until force could not be maintained throughout the shortening contraction. During single contractions, the maximum absolute powers of muscles in young and old mice were 30% lower than that of adult mice, and power normalized by muscle mass (watts/kg) was 20% lower for muscles in old than for those in adult mice (p less than .05). During repeated contractions, EDL muscles in old and adult mice tolerated lower train rates and duty cycles and sustained lower absolute and normalized powers than EDL muscles in young mice.