Contractile properties of aged avian muscle after stretch-overload.

The effects of ageing on muscle contractile adaptations to stretch-overload was examined in the anterior latissimus dorsi (ALD) muscle of 12 old (90 weeks of age) and 12 young adult (10 weeks of age) Japanese quails. A weight corresponding to 12% of the birds' body weight was attached to one wing for 30 days, while the contralateral wing served as the intra-animal control. In vitro contractile measurements were made at 25 degrees C by indirect stimulation of the ALD by its nerve (pulse 0.2 ms). Compared with young adult twitch characteristics, aged muscles had significantly greater contraction time (149 +/- 9 ms vs. 174 +/- 16 ms). Stretch-overload increased contraction time to 162 +/- 7 ms in young muscles and 215 +/- 14 ms in old muscles. Ageing and overload resulted in a greater fusing of twitches at stimulation frequencies of 5 and 10 Hz which resulted in a leftward shift of the force-frequency curve at these frequencies, relative to young adult control muscles. Maximal shortening velocity (Vmax) decreased from 2.6 +/- 0.3 to 1.2 +/- 0.1 muscle lengths/s in young muscles after overload. Vmax in old control muscles was similar to young muscles after stretch, but stretch further decreased Vmax in old muscles to 0.8 muscle lengths/s. Maximal tetanic force and specific force were similar in young and old muscles, both before and after stretch. These data indicate that ageing induces a slowing of both twitch contractile characteristics and shortening velocity in the ALD, without affecting maximal force capabilities.