In the
realm of
sports and exercise, great emphasis is often placed on physique as an
indicator of muscle mass and fat content. When we exercise, play sports, or
lift weights, our
muscle mass naturally increases to meet the higher demand of
the action.
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Usually,
however, not much thought is put into the type of muscle being built. By
building the right type of muscles for your needs, you can maximize the benefit
of your exercises and how they serve you in your area of training.
Types
of muscle fibers
Generally,
there are three types of muscle fibers: type I and type IIx being the main
type. The third is known as type IIb. Colloquially, type I is referred to as
slow-twitch muscle fibers, type IIx as fast-twitch, and type IIb as
intermediate.
Slow-twitch
and fast-twitch are the most dissimilar and serve near opposite functions,
whereas intermediate tends to have characteristics from both main types.
Fast-twitch
vs slow-twitch
1- Function
Slow-twitch
muscle fibers are predominately used in activities that require prolonged,
steady contraction. We unconsciously use our muscles to stay upright in a chair
or while standing, and even while resting.
The
muscles in our legs, back, and neck contract to varying degrees. Slow-twitch
muscle fibers sustain contraction for long periods but at the cost of speed.
Although seemingly insignificant to
human perception, slow-twitch muscle fibers
in the leg can take as long as 100 milliseconds to reach maximum tension.
Fast-twitch muscle fibers, on the other hand, only take 7.3 milliseconds to
reach maximum tension, making them useful in situations where a rapid response
is needed.
While
their tensions are stronger than those held by slow-twitch muscle fibers, these
contractions are not sustainable and fatigue quickly.
2- Energy use
The
human body’s main energy source comes from a molecule known as adenosine
triphosphate (ATP). Slow-twitch fibers use this energy source at a slower and
steadier pace than fast-twitch fibers, which use more energy over a shorter
period.
This
allows fast-twitch fibers to produce higher tension than slow-twitch fibers.
3- Need for
oxygen
ATP is
produced in the body by two different processes: aerobic and anaerobic
metabolism. Aerobic metabolism requires oxygen to convert sugars into energy
(ATP). Although slow, it is sustainable and produces more ATP per sugar. This
process is used in slow-twitch and determines function, energy use, and
contraction speed.
Fast-twitch
fibers use anaerobic metabolism, which does not require oxygen, to produce ATP
at a much faster rate but far less efficiently. It also produces lactic acid as
a by-product which contributes to muscle fatigue.
4- Blood
supply
There
is a vast network of blood supply in place to deliver constant and adequate
amounts of oxygen to slow-twitch muscle fibers. Slow-twitch muscle fibers have
a high concentration of the protein myoglobin, which improves oxygen delivery
to them.
Due to
myoglobin’s color, slow-twitch muscle fibers are also called red fibers. Since
fast-twitch fibers do not have a high oxygen demand, the blood supply to them
is considerably less, worsening the effects of lactic acid since accumulations
cannot be removed quickly.
Intermediate
muscle fibers
Intermediate
muscle fibers are the happy medium between slow-twitch and fast-twitch fibers.
By classification, they are a type of fast-twitch fiber that uses aerobic
metabolism. The rate at which intermediate fibers produce ATP is much higher
than slow-twitch fibers. This allows them to have high tension, speed, and
resist fatigue. This type of muscle fiber is mostly used in general movements
like walking.
How
to grow certain fibers
When we
exercise, the high demand placed on our muscles causes tiny tears in the fiber.
These tears typically go unnoticed or may present themselves as soreness. After
a workout, the body repairs or replaces damaged muscle fibers. In doing so, the
number of fibers increases and thickens, growing and developing the muscles.
People
are usually born with a relatively even amount of slow-twitch and fast-twitch
fibers, but it can vary slightly based on genetics. By engaging in certain
exercises, you can significantly improve the specific types of muscle fibers
you lack.
1- Slow-twitch
muscle exercises
Jogging
or running — especially for long distances — is ideal for building slow-twitch
fibers. As you build these fibers, you will be able to go further and build
your stamina without feeling fatigued. Other exercises include yoga, Pilates,
biking, and swimming at a steady pace.
2- Fast-twitch
muscle exercises
Exercises
that require bursts of energy utilize fast-twitch muscles. A common example is
weightlifting, requiring short, quick contractions between each repetition.
Similarly, engaging in sprinting and boxing can build these muscles.
Which
type is better?
The
answer to which muscle type is better is purely subjective. From a practical
standpoint, slow-twitch fibers tend to have more applicable uses since daily
activities, such as walking and posture, are heavily reliant on them.
For
athletes, the choice of fiber is dependent on their chosen sport. Long-distance
runners, yoga practitioners, and avid walkers should opt to improve their
slow-twitch muscles. On the other hand, sprinters, weightlifters, and boxers
need fast-twitch muscles more.
There
are certain sports like soccer that require a combination of both: players must
run long distances, which uses slow-twitch fibers, and also sprint, which
requires fast-twitch. It would be reasonable for the average person to engage
in activities that improve both types. Building slow-twitch fibers in the legs
and back while simultaneously building fast-twitch in the legs and arms will
create the most practical outcomes.
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