Victor Forge
The human body has over 600 muscles that help us perform a variety of functions, from involuntary actions like breathing and keeping our hearts pumping to voluntary actions like walking, running, and jumping. Our muscles move our bodies by contracting and relaxing, which generates movement. However, not all muscle contractions produce movement. Isometric contractions, for example, increase muscle tension without causing a body part to move. On the other hand, isotonic contractions are required for muscle-building exercises like weightlifting. The brain, nerves, and skeletal muscles work together to cause movement, and this is known as the neuromuscular system.
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What You'll Learn
Skeletal muscles
The primary function of skeletal muscle is to convert chemical energy into mechanical energy, generating force and power. This mechanical energy enables the body to perform various movements, from holding still to running a marathon. Skeletal muscles are composed of muscle fibers, which stretch and press together to move the body and its organs. These fibers are made up of myofibrils, the basic units of the muscle fiber, which are surrounded by the muscle cell membrane (sarcolemma).
In summary, skeletal muscles are essential for producing movement and maintaining posture, and they work in groups to achieve precise, voluntary movements in conjunction with the skeleton and other muscle groups.
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Smooth muscles
Single-unit smooth muscle, also known as visceral smooth muscle, is found in the walls of most internal organs, blood vessels (excluding capillaries and large elastic arteries), the urinary tract, and the digestive tract. It is not found in the heart, which has cardiac muscle. In single-unit smooth muscle, a single cell in a bundle is innervated by an autonomic nerve fiber (myogenic). This means it can contract regularly without input from a motor neuron, even when it is not receiving any neural stimulation.
Multi-unit smooth muscle, on the other hand, is found in the trachea, in the iris of the eye, and lining the large elastic arteries. It is neurogenic, meaning its contraction must be initiated by an autonomic nervous system neuron.
- Transporting substances: Smooth muscles can flex together to push substances through tubelike passages, such as in the digestive tract.
- Gatekeeping: Smooth muscles in sphincters, like the bladder or anus, stay flexed and only relax when needed.
- Skin: Smooth muscle causes hairs to stand on end, like with goosebumps.
- Eyes: Smooth muscles in the ciliary body of the eye control how the eyes focus, while smooth muscles in the iris control how the pupils dilate or constrict.
- Uterus: Smooth muscles are responsible for contractions during labor.
- Blood pressure and circulation: Smooth muscles play a vital role in regulating blood pressure and tissue oxygenation.
- Regulation of body temperature: The high metabolic rate of contracting muscles produces a significant amount of the body's natural heat.
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Isometric contractions
Not all muscle contractions produce movement. Isometric contractions are those that increase tension in the muscle without exerting enough force to move a body part. In other words, they are contractions where the length of the muscle and the angle of the joint do not change, although the contraction strength may vary. Isometric contractions are light contractions, and they occur when people tense their bodies due to stress, or when holding an object still or maintaining posture.
Isometric exercises involve the static contraction of a muscle without any visible movement in the angle of the joint. The term "isometric" combines the Greek words "isos" (equal) and "metria" (measuring). The three main types of isometric exercise are isometric presses, pulls, and holds. They may be included in a strength training regime to improve the body's ability to apply power from a static position, or to improve the body's ability to maintain a position for a period of time.
Isometric exercises are also known as isometric preloads. In a yielding isometric exercise, the goal is to maintain a particular body position, also known as an isometric hold. In an overcoming isometric exercise, the goal is to push or pull against either another part of the body, which pushes or pulls back with equal force, or to move an immovable object. This may also be referred to as an isometric press or an isometric pull. In unweighted isometrics, the exerciser uses only themselves for resistance, for example, by pressing the palms of the hands against each other or holding a crouched position.
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Isotonic contractions
While not all muscle contractions produce movement, isotonic contractions do. Isotonic contractions are performed with joint motion, and the length of the muscle changes, producing limb motion. Isotonic contractions can be either concentric or eccentric. In concentric contractions, the muscle shortens, generating force and overcoming resistance. For example, when lifting a heavy weight, a concentric contraction of the biceps would cause the arm to bend at the elbow, lifting the weight towards the shoulder.
Eccentric contractions occur when the muscle lengthens. They are also a form of isotonic contraction and occur when the muscle controls movement against resistance (including gravity) by lengthening or slowing the movement. For example, the heart's ventricles contract to expel blood into the pulmonary artery and aorta. As the blood flows out, the previous built-up load is decreased, and less force is required to expel the rest of the blood. Greater forces can be produced during eccentric contraction than during concentric (shortening) actions, which leads to positive changes in tissue structure and mechanical properties.
Isotonic exercises are commonly used to strengthen muscles so they can protect joints or inert structures from being painfully overstretched. They are also used to strengthen weakened muscles, such as in arthritis or after local or generalized immobilization. If passive movements are limited, the isotonic exercises should be performed within a painless range to avoid increasing synovial inflammation.
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Muscle tone
The human body has over 600 muscles, which are used constantly, whether consciously or not. Some muscles are visible and can be felt, while others, like the heart and the muscles that line some organs, work silently to keep us alive.
In the context of movement, muscle tone may reflect a state of preparedness to move. According to Bernstein's hierarchical model of movement construction, muscle tone is an adaptive function of the neuromotor apparatus that responds to commands from upper levels of movement construction by adjusting the excitability of sensory and motor cells for active postural or movement control.
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Frequently asked questions
No, not all muscles produce movement. While some muscles help move your body, others are internal organs that keep you alive. For example, the cardiac muscle makes up the walls of the heart, powering its contraction and relaxation to enable circulation.
There are over 600 muscles in the human body, and they can be grouped by location, movement, or tissue type. The three main types of muscle tissue are skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and allow movement, smooth muscles are found in the digestive and urinary systems, and cardiac muscles are in the heart.
Muscles produce movement through contraction and relaxation, which is fuelled by glucose from carbohydrates in our diet. The brain sends a message to the motor neurons, triggering the release of acetylcholine, which causes the muscle to contract.
