A value for the percent of total muscle area that each fiber type composed was measured using computer imaging techniques in four randomly chosen sample areas for different tissue samples per muscle. Fast twitch fibers stain darker for myosin-ATPase activity than slow twitch fibers due to a greater density of the faster ATPase enzyme. Note that in the frog gastrocnemius, fast glycolytic fibers compose the majority of total muscle area. In the toad gastrocnemius, fast glycolytic and slow oxidative fibers compose approximately equal amounts of area. Solid bars represents the frog gastrocnemius.
Striped bars represent the toad gastrocnemius.
Discussion We have shown that the differences in locomotory behavior that are observed in the frog and toad are clearly reflected in the physiological properties of the gastrocnemius, a principle muscle of movement. The toad gastrocnemius has a significantly larger area composed of slow twitch oxidative fibers, which allows it to maintain lower levels of tension more efficiently than the frog. However, its lack of glycolytic fibers render it incapable of maintaining higher levels of tension for more than a few seconds. The frog gastrocnemius has a significantly larger area composed of fast twitch glycolytic fibers, and can maintain higher tension longer, but fatigues fairly rapidly at lower tension levels. Fast twitch glycolytic fibers are more capable of quick, powerful contractions than slow oxidative fibers due to their larger area, more developed sarcoplasmic reticulum, and larger amounts of glycolytic enzymes for rapid release of energy through anaerobic glycolysis.