Muscle Fiber Types
Type IIx, type IIa
2 subtypes of fast twitch fibers
Equal
A muscle's fiber-type composition is typically an ___ mixture of both fast and slow twitch fibers, though some muscle groups are known to be made up of primarily fast or slow twitch fibers
Type IIa muscle fibers
Muscle fiber that is highly adaptable- with endurance training, they can increase their oxidative capacity to levels similar to those observed in slow twitch fibers
Type IIx muscle fibers
Muscle fibers that are the largest and fastest, and are capable of producing the most force of all the skeletal muscle fibers, but are notably less efficient
Fast twitch; slow twitch
Skeletal muscle is divided into 2 general categories based on how quickly it contracts: __ __ muscle fibers and ___ __ muscle fibers
Type IIx muscle fibers
-Muscle fibers that contain a relatively small amount of mitochondria, have a limited capacity for aerobic metabolism, and fatigue easier -Cannot sustain their effort for more than a few seconds -Possess a high number of glycolytic enzmyes, which provide them with a considerable anaerobic capacity -AKA fast-glycolytic fibers
Slow twitch fibers
-Muscle fibers that contain relatively large amounts of mitochondria and are surrounded by more capillaries and have higher concentration of myoglobin -^^ makes them resistant to fatigue and capable of sustaining aerobic metabolism -Create lower force outputs and are more efficient than other fibers -AKA slow-oxidative or type I muscle fibers
Type IIa muscle fibers
-Muscle fibers that possess speed, fatigue resistance, and force production capabilities somewhere between slow twitch and type IIx fibers -Used for strength and power activities, but can sustain an effort for longer than type IIx fibers (up to 3x more in athletes) -AKA intermediate or fast-oxidative glycolytic fibers
Fast twitch; slow twitch
It is believed that successful power athletes possess a relatively large percentage of __ __ fibers, whereas endurance athletes generally possess a large percentage of __ __ fibers