Dominic Stone
The human body has over 600 muscles, and they are constantly working whether we are aware of them or not. Muscles are responsible for two types of movements: voluntary and involuntary. Voluntary movements are actions we consciously control, such as sprinting or scrolling on a phone, while involuntary movements occur automatically and are essential for keeping our body functioning, like breathing or our heartbeat. While exercise is necessary to maintain muscle health, it is important to understand that it can have both positive and negative effects on muscles, joints, ligaments, and bones. Poorly executed or excessive exercise can cause negative adaptations, such as reduced flexibility, agility, and freedom of movement, a phenomenon sometimes referred to as muscle-bound. This term describes a person who has gained muscle mass and strength in a way that hinders their overall movement.
| Characteristics | Values |
|---|---|
| Muscle function loss | Partial or total |
| Types of muscle function loss | Voluntary or involuntary |
| Voluntary muscle function loss causes | Diseases affecting muscles or nervous system |
| Involuntary muscle function loss causes | Failure in nerves that send signals from the brain to the muscles |
| Types of involuntary muscles | Cardiac and smooth muscles |
| Types of cardiac muscle cells | Autorhythmic and contractile |
| Types of smooth muscle cells | Single-unit and multi-unit |
| Types of muscle contractions | Eccentric and concentric |
| Types of muscle insufficiency | Active and passive |
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What You'll Learn
Muscle contraction
There are three types of muscles: skeletal, cardiac, and smooth. Skeletal muscles are attached to bones and are responsible for body movement, posture, and structural support. They are under voluntary control. Cardiac muscles, on the other hand, are striated muscle fibers under involuntary control by the body's autonomic nervous system (ANS). They comprise the walls of the heart, allowing blood to be pumped through the vasculature. Smooth muscles are found throughout the body, lining the inside of organs and blood vessels. They are also involuntary and help with essential functions like moving waste through the intestines and expanding the lungs during breathing.
The process of muscle contraction, known as excitation-contraction coupling, begins with an action potential causing depolarization in the myocyte membrane. This depolarization spreads via the transverse (T) tubules, which are invaginations of the muscle cell membrane. The T tubules then undergo a conformational change, opening the nearby ryanodine receptors on the sarcoplasmic reticulum (SR)—the storage site for calcium within muscle cells. When calcium is released from the SR, it binds to troponin C, leading to a shift in tropomyosin and allowing the myosin heads to attach to the actin filaments. This creates a cross-bridge, and cross-bridge cycling begins when ATP binds to an ATP-binding domain on the myosin head. The contraction produced can be described as a twitch, summation, or tetanus, depending on the frequency of action potentials.
In skeletal muscles, muscle tension is greatest when the muscle is stretched to an intermediate length, as per the length-tension relationship. Muscle contractions can be isometric, with muscle tension changing but length remaining the same, or isotonic, where muscle tension remains the same but the length changes. If the muscle shortens, the contraction is concentric, and if it lengthens, the contraction is eccentric. An example of an eccentric contraction is when a muscle works to decelerate a joint at the end of a movement, acting as a braking force to protect the joints.
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Types of muscle
Muscles are tissues that move the body and its organs. They are grouped by their location, such as chest, leg, or back muscles, or by the kind of movement they perform, such as abductors, flexors, or extensors. There are more than 600 muscles in the human body, and they can be classified into three types: skeletal, smooth, and cardiac.
Skeletal Muscles
Skeletal muscles are part of the musculoskeletal system and work with bones, tendons, and ligaments to support the body's weight and enable movement. These muscles are attached to the skeleton and are under voluntary control. They are responsible for movements such as flicking your thumb or sprinting. Skeletal muscles also provide structural support, maintain posture, store amino acids, and help regulate core body temperature through shivering. Some skeletal muscles contract quickly and use short bursts of energy (fast-twitch muscles), while others, like back muscles, move slowly.
Smooth Muscles
Smooth muscles are involuntary muscles that line the inside of some organs, including the liver, pancreas, and intestines, but not the heart. They have a spindle shape and are essential for various body systems, including the female and male reproductive systems, urinary system, respiratory system, and digestive system. Smooth muscles help with tasks such as moving waste through the intestines and facilitating lung expansion during breathing. There are two types of smooth muscle cells: single-unit and multiunit. Single-unit smooth muscle cells are found in the gut and blood vessels, allowing for contraction as a functional syncytium. Multiunit smooth muscle cells are found in the muscles of the eye and at the base of the hair follicles.
Cardiac Muscles
Cardiac muscles, also known as myocardium, make up the middle layers of the heart and are not found anywhere else in the body. These muscles are under involuntary control and contract rhythmically to pump blood through the cardiovascular system. Cardiac muscle cells have a rectangular shape and are striated, resembling skeletal muscles. There are two types of cardiac muscle cells: autorhythmic and contractile. Autorhythmic cardiac cells do not contract but set the pace of contraction for other cardiac muscle cells. Contractile cardiac cells, or cardiomyocytes, constitute the majority of the heart muscle and are responsible for its contraction.
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Muscle function loss
When muscle function loss occurs, it is important to seek medical help right away. After receiving medical treatment, healthcare providers may recommend a range of measures to support recovery. These can include prescribed therapies, dietary adjustments, eye protection, range-of-motion exercises, splints, physical therapy, occupational therapy, or speech therapy.
To assess muscle strength and performance, healthcare professionals use tools such as the Medical Research Council (MRC) scale or the Manual Muscle Testing (MMT) scale. The MMT scale grades muscle strength from 0 to 5 and is used in rehabilitation and recovery practices to identify impairments and deficits in muscle performance, including strength, power, and endurance. Identifying specific muscle impairments is crucial in determining the appropriate course of rehabilitation, which may include therapy exercises, bracing, or functional movement training.
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Muscle relaxation
PMR has been found to be effective in managing stress, anxiety, insomnia, and certain types of chronic pain. It is often used in conjunction with standard treatments to provide symptom relief for conditions such as headaches, cancer pain, high blood pressure, and digestive issues. The technique is simple and accessible, requiring only 10 to 20 minutes per day of practice. It can be performed seated or lying down, in a quiet and comfortable space, free from distractions.
To begin PMR, one starts by relaxing the entire body and taking a few deep breaths. Then, working through one muscle group at a time, each muscle group is tensed for 5 to 10 seconds by inhaling and contracting, and then relaxed by exhaling and releasing the tension. It is important to focus on the physical sensations and the changes felt when the muscles are tensed and then relaxed. This process is repeated for various muscle groups, gradually moving up the body, from the lower extremities to the face, abdomen, and chest.
In addition to PMR, there are other ways to support muscle relaxation and overall muscle health. Orthopaedic specialists can provide guidance on exercises, movements, and physical activities that promote muscle strength and flexibility. Maintaining muscle health is crucial, as muscles are responsible for voluntary and involuntary movements that enable the body to function properly. They also provide structural support, maintain posture, store amino acids, and regulate core body temperature.
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Muscle stabilisation
The human body has over 600 muscles, which are constantly in use, whether consciously or unconsciously. These muscles can be grouped by their location, such as chest, leg, or back muscles, or by the type of movement they enable, such as abductors, flexors, or extensors.
Every superficial muscle in the body can act as a stabilizer muscle, depending on the exercise or movement being performed. Stabilizer muscles are crucial for optimal movement, injury prevention, and long-term physical health. They are generally deeper within the body and closer to the joints they stabilize, providing support and stability to joints during movement. Their primary function is to keep certain body parts stable and steady so that primary mover muscles can perform the exercise efficiently, effectively, and safely. For example, during a bench press, the rear deltoids are the main stabilizer muscles, helping to control and decelerate the weight.
Stabilizer muscles are essential for maintaining proper posture and performing everyday tasks such as walking, lifting, and reaching. By strengthening these muscles, individuals can improve their balance and coordination, making it easier to carry out daily activities. This is particularly important for older adults who may be more prone to falls and injuries due to age-related changes in balance and coordination.
Some of the most essential stabilizer muscles in the body include those that wrap around the abdomen, providing stability to the spine and pelvis, and those that run along the spine and help stabilize the vertebrae, supporting proper posture and movement. Additionally, muscles such as the tensor fasciae latae and adductor longus help stabilize the hip joint during walking and standing, while the serratus anterior, rhomboids, and trapezius muscles help stabilize the shoulder blades, reducing the risk of shoulder injuries.
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Frequently asked questions
Muscle-bound is a term used to describe a person who has gained a lot of muscle through exercise but has lost flexibility, agility, and freedom of movement. This is often seen in powerlifters who lift extremely heavy loads.
Voluntary movements are actions you choose to perform, like sprinting or scrolling on your phone. Involuntary movements happen automatically, like your heart beating or breathing.
Active insufficiency occurs when a multi-joint muscle shortens across all joints simultaneously, reducing its ability to generate optimal tension and force. This can limit the range of motion at each joint.
Passive insufficiency occurs when a multi-joint muscle lengthens at all the joints it crosses, limiting the range of motion as the muscle is not long enough to allow a full range of motion at each joint.
