Mar 8, 2019 in Medicine

Definition

Muscle contraction refers to the response that a muscle has to some kind of stimuli which results to shortening in length with consequent development of force that causes some impact on the normal functioning of muscular tissue or fiber. Muscle fiber creates tension due to action of hormone actin and myosin through the cross-bridge cycling. This generation of tension by the muscle fibers is facilitated by motor neurons. Muscle contraction can be involuntary or voluntary. Voluntary muscle contraction is regulated by the central nervous system. The brain sends signals to the motor neuron through the nervous system that innervates many muscle fibers. These signals are in form of action potentials. Involuntary muscle contraction such as heart and smooth muscles which are found in the gut and vascular system contract due to non-conscious brain stimuli which occurs in the body the muscle itself.

Types of Muscle Contractions

Muscle contractions can be divided into three categories. Isotonic muscle contraction, Isometric muscle contraction, isokinetic muscle contraction.

Isotonic Muscle Contractions

Isotonic contractions are those contractions which make the muscle to change length when it contracts to cause movement of a body part. In isotonic contractions, muscular tension does not change as the length of the muscle changes. Isotonic contractions are the general muscle contractions which enable people to move about and perform general activities. Lifting a load to some height at a constant speed is an example of isotonic contraction. There are basically two types of isotonic contractions: concentric contractions and eccentric contractions.

Concentric Contractions

These are contractions which causes the muscle shorten as it contracts and it is typical for most exercise. They are the most common types of muscle contractions that which occur in day-to-day activities and sporting activities. Normally, the force generated by the muscle is greater than the external force on the muscle. Lifting a load to a height by holding it in the right hand and then contracting biceps branchii muscles is an example of concentric contraction.

Eccentric Contractions

These are contractions which occur when the muscle lengthens as the tension in the muscles increases. This happens when the actin and myosin in the muscle fibers contract. The fibers themselves slide alongside each other which lead to overall lengthening of the muscle. Lowering an object from a height by contracting the biceps branchii muscles is an example of eccentric contraction.

Isometric Muscle Contraction

Isometric muscle contraction is a type of contraction where the muscle maintains the same length when the tension in the muscle increases. For example, when holding a load in a static position for a prolonged period of time is an example. This implies during isometric muscle contraction, there is no change in the length of the contracting muscle. The amount of force produced in an isometric contraction largely depends on the length of the muscle at the point of contraction. There is occurrence of force of contraction in the muscle fiber but there is no movement of muscle fibers relative to each other thus the overall length of the muscle does not change.

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Isokinetic Muscle Contraction

Isotonic muscle contractions functions the same way as isotonic contraction. The main distinction is that, in isokinetic contraction, there is maximum contraction of the muscle throughout its full range of movement. The outstanding characteristic of isokinetic muscle contractions is that these contractions effect in movements of a constant speed. The changes in the general length of the entire muscle are largely dependent on the combined effects of the shortening of muscle fibers and the individual movement of muscle fibers alongside each other.

Causes of Muscle Contractions

Muscle contractions are caused by nerve impulses that originate from the central nervous system.  Both muscle tissue and neurons conduct electrical current by movement of ions across cellular membranes. The neuron in the muscle fiber releases acetylcholine and transfers some action potential to the muscle tissue. The signal spread through the tissue and trigger the contraction of sarcomeres which result in the final contraction of the entire muscle. According to William, he reviews that there are several causes of muscle contractions in which are dependent on a number of factors, the environment in which the body is working in and the part of the body that is involved in the activity. Muscle contraction may occur due to muscle overuse or tiredness, especially if it is overstretched or if it is held in a static position for quite a long period of time. As a result, the muscle cell runs out of energy and fluid which consequently becomes hyperexcitable and thus develops a forceful contraction. This contraction may involve the entire muscle, a part of a muscle or even the adjacent muscles. Unfamiliar exercise activities cause muscle contractions to occur. For example, abdominal contractions may occur when an individual begins working their abdominal muscles by doing exercises such as sit-ups. Dehydration and exhaustion of electrolytes lead to muscle contractions. This is because muscle cells require sufficient water, potassium, sodium, calcium, glucose and magnesium to give room to the proteins within them to interact and cultivate an organized contraction. Insufficient supply of these elements makes the muscle to become irritable and go into contraction. Muscle contractions may also occur due to narrowing of arteries because there is inadequate supply of food and nutrients to the muscle.

Signs and Symptoms of Muscle Contractions

Signs of muscle contractions are dependent on the type of involved and the conditions leading up to the contraction. Muscle contractions are characterized by acute onset of pain when the muscle contracts. A bulging muscle is felt or seen beneath the skin where the muscle is situated. The condition resumes after a short period of time.

Treatment

Muscle contraction can be treated by applying warm moist heat or ice packs to the area. Analgesics and muscle relaxants are prescribed by mouth. In addition, applying massage and gradual stretching of the affected muscle may be used to treat contraction. Adequate intake of fluid before and after the exercise may be helpful.

Prevention

In Williams article, he reviews that muscle contraction can be prevented by adequate warm-up and cool down prior and after a physical activity. Sufficient intake of fluid before, during and after an activity is vital also to prevent muscle contraction particularly if the activity duration extends more than an hour. Calcium and magnesium prevents contractions that are associated with pregnancy.

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