In fast-twitch oxidative-glycolytic fibers, their rapid increases in force rely on the activity where rapid relaxation requires activity.

1. myosin ATPase

2. Ca2+-ATPase

Explanation:

ATPase activity of myosin head hydrolysis ATP and energize the myosin head. The energized myosin head forms cross bridges to facilitate the power stroke of muscle contraction. The fast-twitch oxidative-glycolytic fibers have the ability to produce ATP by aerobic respiration.  

These fibers have the  ATPase in their myosin heads that hydrolyze ATP three to five times faster than the myosin ATPase in slow fibers. This ensures the faster speed of contraction of these fast-twitch muscle fibers.

During their relaxation, Ca2+ ATPase pumps the calcium ions back to the sarcoplasmic reticulum. As the level of Ca2+ ions in the sarcoplasm decreases, calcium ions are released from troponin. Tropomyosin is allowed to cover the myosin-binding sites on actin and the muscle fiber relaxes faster.

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