Generating Energy in Different Muscle Types

Muscle fibers can generally be divided into two types: fast-twitch and slow-twitch. Fast-twitch muscles are specialized for short, intense bursts of strength; slow-twitch fibers are specialized for endurance. Both muscle types generate energy and utilize oxygen differently due to their respective specializations.

Energy in Slow-Twitch Muscles

When you exercise for a long period of time, such as walking, dancing, or running and marathon, you use slow-twitch fibers. In these activities, muscle contractions are often repeated over a long period of time, which does not involve a large amount of strength. Slow-twitch muscles must provide enough oxygen to maintain oxidative phosphorylation in order to generate enough energy to contract for such a long period of time.
The term aerobic exercise refers to any endurance exercise which requires a high level of oxygen. In slow-twitch muscles, blood vessels thread throughout the fibers, ensuring enough oxygen is delivered to the muscles to produce ATP.
The citric acid cycle creates carbon dioxide from oxygen in the lungs and returns it to the body in these blood vessels. Water is also absorbed by blood vessels during the electron transport chain’s last step.
A slow-twitch muscle contains several blood vessels that carry oxygen into the muscles, as well as a protein called myoglobin that removes oxygen from the blood. To distinguish fast-twitch fibers from slow-twitch fibers, physiologists originally used myoglobin to give the fibers a red color.
Fast-twitch muscles do not contain as many mitochondria as slow-twitch muscles in order to utilize all the oxygen coming in from the blood vessels efficiently. A muscle fiber’s mitochondria account for 20 percent of its volume in some cases.
Generating Energy in Different Muscle Types
Generating Energy in Different Muscle Types – When you exercise for a long period of time, such as walking, dancing, or running and marathon, you use slow-twitch fibers. Photo Credit – Pexels

Energy in Fast-Twitch Muscles

Muscles with fast-twitch fibers are used for bursts of speed, which cause the heart to beat faster before it can provide more oxygen to the muscles. Fast-twitch muscle fibers are adapted to be extremely efficient at glycolysis in order to be able to generate enough ATP for contractions without depending on the electron transport chain. In order to replenish the ATP supply, they store more creatine phosphate, which has fewer blood vessels than slow-twitch muscles.
To ensure a continuous supply of sugar to feed glycolysis, fast-twitch muscles contain more glycolysis molecules and store a greater amount of glycogen than slow-twitch muscles. The fast-twitch muscles can be classified into two types: type IIa and type IIb. The fibers of type IIb are those that are specialized for doing fast, sprint-type tasks.
Muscle fibers with the least mitochondria, myoglobin and glycolysis enzymes are found in these tissues. Slow-twitch fibers are found on the opposite side of the spectrum from type IIa fibers. Like IIb fibers, their myosin heads pull and release actin filaments quickly, so they are used for sprinting instead of endurance training.
As a result of containing some myoglobin, they have more mitochondria than IIb fibers. When slow-twitch muscles fatigue, these fibers often step in to help.

Energy Use in Cardiac Muscle

Energy is generated and used by skeletal muscles in the previous material. The cardiac muscle and the smooth muscle each generate ATP in a unique manner. In the same way as slow-twitch skeletal muscles, cardiac muscles must continually contract at low intensity.
Between cardiac muscle fibers, mitochondria provide steady energy supplies to the cells. There are also fat droplets near the mitochondria that are almost exclusively used for energy by the heart cells.

Light and Dark Meat Represent Fast-and Slow-Twitch Muscles

It is easy to distinguish between fast- and slow-twitch muscles by looking at chicken or turkey meat. All the fatty membranes surrounding the blood vessels and mitochondria make the dark meat on the thighs juicier. An oxygen-transporting protein called myoglobin is responsible for the color difference between muscles and blood.
Due to the constant use of walking and standing, the muscles of poultry’s thighs are dark and contain many slow-twitch fibers. A short burst of flying exercise involving the lighter muscles in the breast meat requires tremendous strength but lasts only a short time. Muscles with less myoglobin and less fatty cell membranes are dryer and lighter in color.
A steady blood supply is absolutely necessary to provide oxygen to the heart. The blood vessels that supply blood to the heart muscles are blocked during a heart attack.
If the heart is deprived of oxygen even temporarily, it will not be able to produce enough ATP and contract normally, preventing the brain from receiving blood. Creatine phosphate stores and glycolysis cannot compensate for the lack of oxygen in the heart.
Generating Energy in Different Muscle Types
Generating Energy in Different Muscle Types – The cardiac muscle and the smooth muscle each generate ATP in a unique manner. Photo Credit – Pexels

Energy Use in Smooth Muscle

Muscles that contract smoothly are different from those that contract skeletally or within the heart. A myosin head in these cells cycles through ATP about ten times more slowly than a myosin head in the heart or skeletal muscle.
Since the smooth muscle burns through ATP very slowly once it is contracted, the contraction can last for a very long time. Smooth muscles are particularly adept at squeezing, which can be seen in squeezing food through the digestive system or maintaining a blood vessel’s diameter.
Because smooth muscle generates ATP in a relatively small amount, it doesn’t require any special adaptations for ATP production. ATP is generated by mitochondria, which are found in every cell of the body, from the sugar or fat that circulates in the blood. There are no mitochondria or energy stores in smooth muscle cells.
It is common for mitochondria to congregate near actin and myosin fibers in smooth muscle cells, as in most cells of the body.

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