The muscles in your body are naturally toned, and they remain this way as long as you use them on a daily basis. When you build muscle, microscopic tears to the muscle fibers promote the growth of newer, stronger muscle. Thus muscle toning is one thing, and muscle building is another. Muscle toning simply increases the tone or tautness your muscles already have, which can keep them from losing their elasticity.
Relaxation and Tightening
Muscles rely on the brain and spinal cord to tell them what to do. Experts at the University of Pittsburgh's Department of Neurological Surgery explain that normal muscle tone relies on a harmonious balance between inhibitory and excitatory stimulation. During inhibitory stimulation, the brain and spinal cord trigger the release of gamma-aminobutyric acid or GABA, which causes the muscles to relax. During excitatory stimulation, your muscles send signals to your spinal cord, resulting in muscle tightening or contraction.
Isotonic and Isometric
Muscles perform two different types of contractions -- isotonic and isometric. During isotonic movement, your muscles shorten but maintain the same tone throughout the movement. According to the Springfield Technical Community College website, isometric movements do not cause muscles to shorten; they rely heavily on the tendons to support the contraction while the limb is in a fixed position. Isometric muscle movements place contractile force on a targeted muscle group, increasing muscle tone.
Atrophy
When muscles go unused, a condition known as atrophy develops. If you have a sedentary job or limited range of motion due to illness, you may be at risk of developing disuse atrophy. In some cases of disuse atrophy, muscle wasting can occur, resulting in a decrease or complete loss of muscle tone. University of Maryland Medical Center experts explain that certain injuries or nerve diseases produce neurogenic atrophy. Neurogenic atrophy is less common than disuse atrophy, brought on by diseases such as polio, rheumatoid arthritis and Guillain-Barre syndrome.
REM Sleep
Although muscles have tone during the waking hours, muscle tone becomes more relaxed during REM, or rapid eye movement, sleep. The loss of muscle tone during REM sleep is the result of a motor neuron block. Known as atonia, this blockage causes a type of muscle paralysis that prevents you from acting out your dreams as you sleep. In rare cases, sleep paralysis can continue through the early stages of awakening.
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