Fast-twitch and Slow-twitch Fibers
⚡Most of our skeletal muscles have fast-twitch and slow-twitch fibers.
⚡Slow-twitch fibers work best during low- to moderate-intensity activities because they require a good supply of oxygen. They get called on first for most endurance and stability activities and can keep acting for long periods.
⚡Fast-twitch fibers step into the breach to create bursts of power during high-intensity anaerobic activities such as jumping and sprinting. They supply more force, but are more quickly exhausted.
⚡When you exercise or do your daily routine activity, both the muscle fibers are pressed into service. More force requires more fibers working in unison. But only a small percentage of muscle fibers are available for a task at one time. Once they are drained of glycogen (the stored sugar that’s their main energy supply), depleted slow-twitch and fast-twitch fibers pass the baton to fresh reinforcements, so that activity can continue. This relay goes on until you’ve exhausted the muscle fibers held in reserve.