The Muscular System

Muscular System and Exercise

The muscular system in an integral component of the human body. Muscular tissue movement within the system is caused by the contraction of muscle fibers within the body. Movement is caused by the conversion of chemical energy into mechanical energy through a variety of processes. Muscle tissue is categorized into three types including skeletal, cardiac, and smooth. Furthermore, these tissues are categorized as voluntary and involuntary muscles. 1(p39) Through proper care and exercise, muscles can strengthen or weaken.

Anatomy and Physiology

Skeletal muscle tissue, also referred to as striated or voluntary muscle tissue, composes 40% to 50% of the body's weight and is called striated muscle due to its striated composition, visible when analyzed under a microscope.1(p126) the contractions of this muscle tissue are voluntary and are controlled by the individual. Organs are compose primarily from muscle cells and connective tissue. Most skeletal muscles in the body extend from one bone to another across joints. The three components of skeletal muscle are the origin at which it is attached through a tendon to the bone that remains stationary when movement is applied to the joint, the insertion that is the point that is attached to the bone that moves when the muscle is contracted, and the main body of the muscle. 1(p126) Muscle contracted will only occur is the stimulus applied to the muscle reaches the threshold. Once the muscle is stimulated by the threshold stimulus, the muscle will contract completely; different muscles are controlled by different motor units with respective unique threshold stimulus levels.1(p127)

Contractions produced within muscles can be divided into three types: twitches and titanic, isotonic, and isometric. While twitch contractions do not play significant roles in muscle contraction, titanic contractions are defined as sustained and steady contractions that are produced through stimuli attacking a muscle in rapid succession.1(p127) Isotonic contractions produce movement at a joint by shortening the muscle and causing the muscular insertion point to move towards the point of origin. Most by movements are caused by isotonic contractions. 1(p127) Unlike isotonic contractions, isometric contractions do not cause movement in the body, though an increase in tension within the muscle can be detected. 1(p127)

In the human body, muscles control movement, posture, and heat production. Movement is produced through the contraction of muscles, usually through the coordinated efforts of a muscle group. Posture within the body is maintained through tonic contraction which restricts the number of muscle fibers that shorten at a time. Good posture reduces strain on the body's muscles, tendons, ligaments and bones. Inadequate posture may lead to fatigue, caused by repeated muscular stimulation without adequate rest, and/or deformities.1(p127)

Cardiac muscle makes up a large portion of the heart. Cardiac muscle is characterized by intercalated disks and the muscle cells branch frequently. The unified nature of cardiac muscle cells allow for the heart to contract efficiently. 1(p126)

Smooth muscle, also known as visceral, non-striated, or involuntary muscle, appears smooth when analyzed under microscopic conditions. These type of muscle tissue can be most commonly found within the digestive tract, blood vessels, and ureters. 1(p 126)

Exercise

Studies have shown that muscle tone and posture may be improved through exercise. The benefits of exercising the body also include more efficient heart and lung functions and the reduction of fatigue within the muscular system. 1(p127)

Muscle function, strength, and condition are effected by the amount of work that is performed. Disuse atrophy of the muscles is caused by prolonged inactivity, which often occurs after sustaining an injury. Hypertrophy of the muscles is achieved through regular diet and exercise. 1(p127) Two types of training, strength and endurance, greatly increase muscle condition. Strength training increases muscle condition through the use of resistance. While conditioning through resistance will increase the number of myofilaments in muscle fiber and increases muscle size, it will not increase the number of muscle fibers.1(p128) Resistance training has been shown to positively affect heart rate, stroke volume, and cardiac output, though not to the same extent as has been found through the extended practice and implementation of endurance training. 2 Long-term resistance training has also been found to reduce the resting heart rate, increase stroke volume at rest and exercise, maintain cardiac output at rest, decrease resting systolic and diastolic blood pressure while at rest, improve resting lipid levels, and show improved glucose sensitivity, insulin response and sensitivity.2(p4)

Endurance training increases the sustainability of moderate exercise over an extended period of time. Endurance training allows for the efficient delivery of oxygen and nutrients to a muscle through increased blood flow. Unlike strength training, endurance training will not result in increased muscle growth. 1(p128)

Precautions must be taken in order to prevent muscle damage through exercise. Damage to muscles is often encountered after eccentric movement or "unaccustomed exercise," especially if the exercise requires an inadequate amount of muscle lengthening contractions.3 Muscle damage incurred during the course of inadequate exercise may be evaluated through muscular biopsy or magnetic resonance imaging (MRI); inherent problems of muscular biopsies are the small amount of muscle tissue analyzed. MRI analysis allows for assessment of the entire muscle.3 (p2)

Damaged muscles must be given enough time to recuperate through time, physical therapy, and rest. While muscles are designed to stretch, upon reaching their threshold, muscles can become torn or strained. Muscle reconstruction commences at the cellular level at the time of injury. When a muscle is slightly damaged, one may experience muscle stiffness, whereas tearing through muscle tissue can result in swelling and bruising.4 on occasion, scar tissue will form instead of regenerated muscle tissue, which may lead to difficulty with normal contraction and elasticity of the skeletal muscle.4