Describe the action of ATPase in skeletal muscle fibres.

Explanation

Types of skeletal muscle fibres:
Fast fibres and slow fibres:
1. Fibres containing myosin with high ATPase activity are classified as fast fibres and with lower ATPase activity are classified as slow fibres.
2. Fibres that contain numerous mitchondria and have a high capacity for oxidative phosphorylation are classified as oxidative fibres. The oxidative fibres are termed as red muscl e fibres. Fibres that contain few mitochondria but possess a high concentration of glycolytic enzymes and large stores of glycogen are called gycolytic fibres. The lack of myoglobin gives pale colour to the fibres, so they are termed as white muscle fibres.
Skeletal muscle fibres are further classified into three types based on the above classification. They are slow- oxidative fibres, fast- oxidative fibres and fast- glycolytic fibres.
1. Slow- oxidative fibres have low rates of myosin ATP hydrolysis but have the ability to make large amounts of ATP. These fibres are used for prolonged, regular activity such as long distance swimming. Long- distance runners have a high proportion of these fibres in their leg muscles.
2. Fast- oxidative fibres have high myosin ATPase activity and can make large amounts of ATP. They are particularly suited for rapid actions.
3. Fast- glycolytic fibres have myosin ATPase activity but cannot make as much ATP as oxidative fibres, beacuse their source of ATP is glycolysis. These fibres are best suited for rapid, intense actions, such as short sprint at maximum speed.