Your body is able to adapt to almost any kind of stimulus or stress. Though exercise is healthy, it stresses the body and challenges it to perform more efficiently and effectively. As soon as you begin exercising, your skeletal muscles begin moving, increasing metabolism and receiving more blood. Over time, your body changes to adapt to exercise in ways that are quite ingenious.
Producing a Contraction
As your muscle is performing exercise, a phenomenon known as the sliding filament theory is occurring. Your muscles are able to contract when the small myofilaments within your muscle fiber pull onto each other, shortening the muscle. Two myofilaments within the muscle fiber are primarily responsible for this movement -- actin and myosin. During exercise myosin cross bridges, a small protrusion off the myosin, become activated. Upon activation, these crossbridges grab hold of the actin filament at the binding site. This allows the actin and myosin to drag and move, thus shortening the muscle causing a contraction and movement.
Short-term Metabolism and Energy Production
The metabolic action inside your muscles changes during exercise and as a result of regular exercise. To produce energy to perform exercise your skeletal muscle cells use either anaerobic or aerobic metabolism. Anaerobic metabolism is the production of energy without oxygen. This usually occurs at the onset of exercise or whenever your blood has not supplied enough oxygen for the intensity of your activity. Most activity relies on aerobic metabolism. This is the production of energy through a complex process that takes place inside the mitochondria of the cell. Your body uses either glucose or fat converted into a usable form to produce a molecule known as ATP. Your muscles use the ATP molecule to facilitate the movement that occurs in the sliding filament theory of contraction.
Long-term Metabolic Changes
Regular endurance activity will produce a change in the mitochondria and metabolic enzymes inside your skeletal muscle cells. This change allows your body to more efficiently produce the energy that physical activity takes. More mitochondria within your muscles means that your body can make more energy with a given amount of oxygen delivered to the muscle via the blood. In addition, enzymes needed for aerobic respiration increase in number to facilitate the increase in mitochondria.
Muscle Structure
The look of your muscle changes depending on the type of exercise you are doing. Endurance training such as jogging is exercise with a small force but a more frequent activation of your skeletal muscle cells. This type of training leads to an increase in the metabolic rate of your muscle and less in the size and shape. Resistance training such as weightlifting is a high-force exercise with less frequent muscle activation. Long-term effects of resistance training lead to hypertrophy of the skeletal muscle, an increase in cross-sectional size, according to "Exercise Physiology" by George A. Brooks.
References
- "Exercise Physiology"; George A. Brooks, Thomas D. Fahey, Kenneth M. Baldwin; 2005
- "Physiology of Sport and Exercise"; Jack H. Wilmore, et al..; 2004
- University of Cincinnati Clermont College: Cellular Respiration and Fermentation; J. Stein Carter; August 2010
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