Slowing of contractile properties in quail skeletal muscle with aging.

The effect of aging on muscle contractile function was examined in the anterior latissimus dorsi (ALD) muscle of Japanese quails aged 8 weeks (young adults), 26 weeks, 60 weeks, or 90 weeks (old birds). In vitro contractile measures of the ALD were made at 25 degrees C (stimulus pulse = 0.1 ms). Twitch contraction time in 90-week-old muscles was significantly greater than 8 to 26-week-old muscles (150 +/- 8 ms vs 168 +/- 18 ms). Similarly, one-half relaxation time of the twitch was increased in the ALD from old birds (221 +/- 17 ms) relative to adult birds 8-26 weeks (173 +/- 11). Aging produced a greater fusing of twitches at stimulation frequencies of 5 and 10 Hz, and this resulted in a leftward shift of the force-frequency curve at these frequencies. Shortening velocity measured by the force-velocity method (Vmax) decreased from 2.6 +/- 0.2 muscle length/s (mL/s) to 1.19 +/- 0.02 mL/s in 8 and 90-week-old muscles, respectively. Maximal velocity of unloaded shortening as measured by the slack test decreased from 3.6 +/- 0.7 mL/s to 2.4 mL/s in 8-week-old and 90-week-old muscles, respectively. Maximal tetanic force (60.6 +/- 3.1 mN) and specific force (11.3 +/- 0.3 N/cm2) were similar in young adult and old muscles. These data indicate that aging induces a slowing of both twitch contractile characteristics and shortening velocity in the ALD, without affecting maximal force capabilities.