Muscles are made up of long cells known as muscle fibers, innervated by a nerve cell (neuron) which stimulates the muscle to contract. Stimulating the right type of muscle fiber can impact your physique!
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One nerve cell can stimulate many muscle fibers to contract at once, known as a motor unit. A small motor unit is a neuron which innervates just a few muscle fibers, while a large motor unit innervates many muscle fibers.
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Muscle fibers themselves differ as well in that some are more durable but less powerful (slow twitch) while others are more powerful but less durable (fast twitch).
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1. Slow twitch fibers (type 1)
2. Fast twitch OXIDATIVE fibers (type 2A).
3. Fast twitch GLYCOLYTIC fibers (type 2X aka 2B aka 2D).