Muscle Fiber Types

1. Muscle Fiber Types • Tonic Fibers • Slow Oxidative Fibers I • Fast Oxidative Fibers IIa • Fast Glycolytic Fibers Iib

3. Tonic Muscle • Slow contraction with no twitch and not Aps • Postural Muscles • Few Motor Neurons • Slow attachment and detachment of cross bridges

6. Fast Twitch Fibers provide speed like that needed for escape • Fast twitch fibers are costly in terms of energy • The ratio of V/Vmax determines the power and efficiency of the muscle

7. For a given rate of shortening, the high Vmax muscle produces more force per cross section

8. The high Vmax fiber also produces more power per unit area. For both the generation of power is greatest a an intermediate value of V/Vmax.

9. High Vmax fibers use energy more quickly than low Vmax fibers, but the rate levels off for both.

10. The overall efficiency (ratio of power output to energy utilization) is greater for a low Vmax fiber at slow contraction speeds.

11. In the carp, slow twitch oxidative fibers, (Red Type I) are close to the body surface and run longitudinally. Fast glycolytic fibers (White II b ) are arranged obliquely

13. In steady swimming, red muscle shortens to between 1.89 to 2.25 um at the top of the force curve. But because of their attachment, they would need to shorten to 1.4 um in an escape response.

15. In steady swimming, V/Vmax for red muscle is .17 to .36 – not quite at the top of the power curve. The muscle is contracting 1 to 1.25 lengths per second.

16. In escape the white muscle contracts 5 length/second – at the top of the power range. V/Vmax is .38.