Name: skeletal muscle fiber speed and energy
Uploaded: 2019-03-11T09:21:30.000Z
Duration: 1 min 48 s
Channel: JoVE

Skeletal muscles consist of three main fiber types, one slow- and two fast-twitch, each distinct and adapted to a particular function based on their speed and duration of contraction, as well as the source of ATP used to power the muscle.
The first type, slow-twitch oxidative fibers, contract slowly and can sustain repeated muscle contraction over long periods of time for endurance activities, such as marathon running.
They are typically referred to as red fibers, since they are enriched by many capillaries and abundant myoglobin, a pigment that stores and diffuses oxygen reserves from the blood into cells as a form of aerobic energy.
The second type, fast-twitch oxidative fibers, have a rapid speed of contraction and use mostly aerobic energy sources, necessary for sprinting, which requires power and speed. Structurally, they are very similar to their slow counterpart.
The third group, fast-twitch glycolytic fibers, contract rapidly and with greater force, but fatigue quickly due to their short-lived glycogen reserves for fuel, making them suitable for intense bursts, like power-lifting.
These large white fibers have less blood supply and myoglobin content, and are not dependent o

classification of skeletal muscle fibers

Classification of Skeletal Muscle Fibers

Skeletal muscles continuously produce ATP to provide the energy that enables muscle contractions. Skeletal muscle fibers can be categorized into three types based on differences in their contraction speed and how they produce ATP, as well as physical differences related to these factors. Most human muscles contain all three muscle fiber types, albeit in varying proportions.
<h4>Slow-Twitch Muscle Fibers</h4>
Slow oxidative, muscle fibers appear red due to large numbers of capillaries and high levels of myoglobin, an oxygen-storing protein. These fibers contain more mitochondria, which produce ATP through oxidative phosphorylation, than fast-twitch muscle fibers. 
Slow oxidative muscle fibers use aerobic respiration, involving oxygen and glucose, to produce ATP. In addition to contracting more slowly than fast-twitch fibers, the slow oxidative fibers receive nerve signals more slowly, contract for longer periods, and are more resistant to fatigue. These fibers primarily store energy as fatty substances called triglycerides.
<h4>Fast-Twitch Muscle Fibers</h4>
Relative to the slow oxidative fibers, the fast-twitch muscle fibers receive nerve signals and contract more quickly, but contract for shorter periods and fatigue more quickly. Fast-twitch muscle fibers primarily store energy as ATP and creatine phosphate.
Fast oxidative, muscle fibers primarily use aerobic respiration to produce ATP. However, they also use anaerobic respiration. Fast glycolytic, muscle fibers primarily use anaerobic respiration, which produces less ATP per cycle than aerobic respiration. Thus, Fast glycolytic fibers tire faster than the other fiber types.
More recently, scientists identified additional muscle fibers with characteristics intermediate between the above three types.

Skeletal muscles continuously produce ATP to provide the energy that enables muscle contractions. Skeletal muscle fibers can be categorized into three ...

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skeletal muscle fiber speed and energy

Skeletal muscle fibers can be grouped by how fast they contract and how they make ATP, the energy cells use for movement. These differences also shape their physical features. Most human muscles contain all three fiber types, but in different amounts.

Slow oxidative fibers, also called slow-twitch fibers, appear red because they have many capillaries and high levels of myoglobin, an oxygen-storing protein. They also contain more mitochondria, which make ATP through oxidative phosphorylation, than fast-twitch fibers. These fibers use aerobic respiration, which depends on oxygen and glucose. They contract more slowly, receive nerve signals more slowly, and can work for longer periods without tiring as quickly. They mainly store energy as triglycerides, a type of fat.

Fast-twitch fibers receive nerve signals and contract more quickly than slow oxidative fibers. They also contract for shorter periods and fatigue more quickly. These fibers mainly store energy as ATP and creatine phosphate.

Fast oxidative fibers mostly use aerobic respiration to make ATP, but they can also use anaerobic respiration. Fast glycolytic fibers rely mainly on anaerobic respiration, which makes less ATP per cycle than aerobic respiration. As a result, fast glycolytic fibers tire faster than the other fiber types. Scientists have also identified additional muscle fibers with traits that fall between these three main types.

Skeletal Muscle Fiber Speed and Energy

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Skeletal muscle fibers can be grouped by how fast they contract and how they make ATP, the energy cells use for movement. These differences also shape their physical features. Most human muscles contain all three fiber types, but in different amounts. Slow oxidative fibers, also called slow-twitch fibers, appear red because they have many capillaries and high levels of myoglobin, an oxygen-storing protein. They also contain more mitochondria, which make ATP through oxidative phosphorylation,...

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key terms and concepts

Explore how skeletal muscle fibers differ in speed, ATP production, and fatigue resistance, including slow oxidative, fast oxidative, and fast glycolytic fibers.

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Skeletal Muscle Fiber Speed and Energy

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