Estrogen and gender do not affect fatigue resistance of extensor digitorum longus muscle in rats

The effects of estrogen on skeletal muscle fatigue are controversial. To determine the effects of estrogen and gender on rat extensor digitorum longus (EDL) muscle, we either injected 40 mu g beta-estradiol 3/benzoate.kg BW-1 to female rats or sham injected male or female rats for 14 days. Subsequently a 90 min fatigue protocol consisting of electrical stimulation at 10 Hz delivered in 500 ms trains was administered. Force was recorded for a 5 s period at the start of the protocol (0 min) and at 5 min intervals until completion following 90 min of stimulation. After 90 min, EDL force generation at 10 Hz stimulation declined in all groups to between 50-60 % of initial values. However, no significant difference in fatigue rate or final 10 Hz stimulated force was seen between females administered estrogen, sham injected females or males. Hence, estrogen administration and gender did not significantly affect EDL muscle fatigue in this model.