Alec Titan
Supercompensation is a sports science theory that refers to the post-training period during which the trained parameter has a higher performance capacity than it did prior to the training period. The theory, first put forth by Russian scientist Nikolai N. Yakovlev in 1949–1959, breaks down the fitness level of a human body in training into four periods: initial fitness, training, recovery, and supercompensation. During the training period, an athlete trains harder and subjects their body to more training stress than they’ve experienced before. This is followed by a recovery period, during which the athlete focuses on recovery, typically by doing a deload week, having active recovery sessions, or simply taking time off training. Finally, the body enters the supercompensation phase, during which the body adapts and prepares itself for the next challenge, resulting in a higher level of fitness than before the training period.
| Characteristics | Values |
|---|---|
| Basis of theory | Observing changes in the sarcomeres as muscle tissue shortened |
| Year of proposal | 1954 |
| Proposers | A. F. Huxley and R. Niedergerke, H. E. Huxley and J. Hanson |
| Muscle contraction | A cycle of molecular events in which thick myosin filaments repeatedly attach to and pull on thin actin filaments, so they slide over one another |
| Role of calcium ions | Release of calcium ions initiates muscle contractions |
| Role of ATP | Muscle contraction requires ATP |
| Role of motor neurons | Motor neurons stimulate muscle fibers to contract |
| Muscle relaxation | Occurs when muscle fibers return to a low-tension state |
| Muscle tension | Refers to the amount of force built up within a muscle |
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What You'll Learn
Muscle contraction and locomotion
The physiological concept of muscle contraction is based on two variables: length and tension. Muscle shortening and contraction are not synonymous. Tension can be produced without a change in length, for example, when holding a dumbbell or a sleeping child. Upon termination of muscle contraction, muscle relaxation occurs, returning the muscle fibres to a low-tension state.
The complex process of muscle contraction, known as excitation-contraction coupling, begins with an action potential causing depolarization in the myocyte membrane. This action potential originates in the brain, which sends electrochemical signals through the nervous system to the motor neuron that innervates several muscle fibres. The depolarization causes a conformational change in the dihydropyridine receptors, which then opens nearby ryanodine receptors on the sarcoplasmic reticulum (SR), releasing calcium. Calcium then binds to troponin C, causing another conformational change that shifts tropomyosin and allows the myosin heads to attach to the actin filaments, creating a cross-bridge.
The sliding filament theory explains the mechanism of muscle contraction, where the binding of myosin to actin generates cross-bridges that result in filament movement. This theory was developed to explain the differences observed in the named bands on the sarcomere during muscle contraction and relaxation.
There are three types of muscle contractions: isometric, isotonic, and concentric. Isometric contractions occur when muscle tension changes but length remains the same, such as when gripping an object. Isotonic contractions keep muscle tension constant despite changes in length, and they occur when the force of contraction matches the total load on the muscle. Concentric contractions happen when muscle tension is sufficient to overcome the load, resulting in muscle shortening.
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Neurotransmitters
Billions of nerve cells make up the human body. Each nerve cell is composed of a cell body, an axon, and an axon terminal. The cell body is responsible for producing neurotransmitters and maintaining nerve cell function. The axon carries electrical signals to the axon terminal, where the electrical message is converted into a chemical message using neurotransmitters. Neurotransmitters are then released into the synaptic junction, a fluid-filled space between the nerve cell and the target cell, where they bind to specific receptors on the target cell. This binding triggers a change or action in the target cell, such as an electrical signal, a muscle contraction, or the release of hormones.
Acetylcholine (ACh) is an important excitatory neurotransmitter that stimulates muscle contraction. It is secreted by motor neurons and acts on muscle cells, basal ganglia, and various neurons of the autonomic nervous system. ACh binds to receptors on the motor end plate, opening ion channels and allowing ions to cross the membrane, leading to muscle contraction. However, excessive ACh can cause unwanted extended muscle contraction, and its breakdown is essential to prevent this.
Other neurotransmitters, such as norepinephrine (also known as noradrenaline), are involved in muscle function. Norepinephrine increases alertness, arousal, attention, and focus. It is implicated in mood disorders like depression and anxiety, where its concentration may be abnormally low. Additionally, abnormally high levels of norepinephrine can lead to an impaired sleep cycle.
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Calcium ions
The mechanism of calcium-induced contraction involves regulatory proteins. In the absence of calcium, these proteins prevent the interaction of actin and myosin filaments. There are two regulatory systems: actin-linked and myosin-linked. In actin-linked regulation, troponin and tropomyosin block sites on actin required for complex formation with myosin. Calcium ions bind to cardiac troponin C, moving the troponin complex away from the actin-binding site. This removal of the troponin complex frees actin to bind with myosin, initiating contraction.
In myosin-linked regulation, sites on myosin are blocked in the absence of calcium ions. The presence of calcium ions causes a conformational change, shifting tropomyosin and allowing the myosin heads to attach to the actin filaments, forming cross-bridges that generate filament movement. The cross-bridge cycling is further facilitated by the binding of ATP to an ATP-binding domain on the myosin head.
The contraction of cardiac muscle, specifically, involves a process called excitation-contraction coupling (ECC), which utilizes calcium-induced calcium release (CICR). An electrical stimulus (action potential) is converted into a mechanical response (muscle contraction). CICR involves the conduction of calcium ions into the cardiomyocyte, leading to the release of more ions into the cytoplasm. This process prolongs the period of cardiac muscle cell depolarization, with contraction occurring due to the binding of the myosin head to ATP, pulling on the actin filaments.
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Muscle relaxation
Progressive muscle relaxation (PMR) is a technique that helps with muscle relaxation. It involves tightening and relaxing muscle groups, one at a time, in a specific pattern. The goal is to release tension from the muscles while helping you recognize what that tension feels like. This technique was developed by American physician Edmund Jacobson in the 1920s and 1930s. It is based on the theory that physical relaxation can promote mental relaxation.
PMR is a deep relaxation technique that has been effectively used to control stress and anxiety, relieve insomnia, and reduce symptoms of certain types of chronic pain. Doctors have used PMR in combination with standard treatments for symptom relief in conditions, including headaches, cancer pain, high blood pressure, and digestive disturbances. Research has also found that it has therapeutic benefits for conditions like generalized anxiety disorder or anxiety due to a stressful situation.
PMR involves tensing each muscle group and holding for 5 seconds. Then, you exhale as you let your muscles relax for 10 to 20 seconds before moving on to the next muscle group. It is recommended to set aside 15 to 20 minutes for PMR in a quiet, comfortable area. It is also important to avoid holding your breath, which can cause more tension. Instead, inhale deeply when you tense your muscles and exhale fully when you relax.
- Start by lying or sitting down. Relax your entire body.
- Take five deep, slow breaths.
- Lift your toes upward. Hold, then let go.
- Pull your toes downward. Hold, then let go.
- Tense your calf muscles. Hold, then let go.
- Move your knees toward each other. Hold, then let go.
- Squeeze your thigh muscles. Hold, then let go.
- Clench your hands. Pause, then let go.
- Tense your arms. Hold, then let go.
- Squeeze your buttocks. Pause, then let go.
- Contract your abdominal muscles. Pause, then let go.
- Inhale and tighten your chest. Hold, then exhale and let go.
- Raise your shoulders to your ears. Pause, then let go.
- Purse your lips together. Hold, then release.
- Open your mouth wide.
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Muscle types
The human body has more than 600 muscles that help us move, breathe, and perform other vital functions. Muscles are tissue, and healthcare providers organise them by tissue type. There are three types of muscle tissue in the body: skeletal, smooth, and cardiac.
Skeletal muscles are part of the musculoskeletal system, working with bones, tendons, and ligaments to support the body's weight and enable movement. Tendons attach skeletal muscles to bones all over the body. These muscles are voluntary, moving when we think about moving a part of our body. Some skeletal muscle fibres contract quickly and use short bursts of energy (fast-twitch muscles), while others move slowly, like back muscles that help with posture. There are approximately 650 skeletal muscles in the human body, each composed of muscle fibres.
Cardiac muscle, or myocardium, makes up the middle layers of the heart. It is not found anywhere else in the body. Cardiac muscle contracts involuntarily, rhythmically, and strongly to pump blood through the cardiovascular system. Cardiac muscle cells are rectangular and striated in appearance.
Smooth muscle is involuntary muscle tissue that lines the inside of some organs, including the liver, pancreas, and intestines. Smooth muscle cells are spindle-shaped and contract slowly and rhythmically.
While muscles are often grouped by location or movement type, healthcare providers classify them based on the type of tissue they are made of.
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Frequently asked questions
Acetylcholine is a neurotransmitter that acts as a chemical messenger, allowing neurons to communicate with each other and with specialised cells like myocytes. It is released by motor neurons and binds to receptors in the motor end plate, causing an influx of sodium ions that leads to muscle contraction.
Muscle relaxation occurs when the motor neuron stops releasing acetylcholine, which is broken down by the enzyme acetylcholinesterase. This prevents unwanted extended muscle contraction.
The sliding filament theory is the most widely accepted explanation for muscle contraction. It suggests that muscle contraction is a cycle of molecular events where thick myosin filaments attach to and pull on thin actin filaments, causing them to slide over each other and resulting in the shortening of the sarcomere.
Calcium ions (Ca2+) are released from the sarcoplasmic reticulum and produce attractive forces between actin and myosin filaments. This causes them to slide alongside each other, leading to muscle contraction.
