Physical Activity

Physical Activity and Metabolism

Daniela S. Khidir/ Fitness Trainer
08 April, 2018

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Any corporal movement created by skeletal muscles that result in energy expenditure further than resting expenditure is defined as physical activity. Exercise is a subdivision of physical activity that is planned, structured, repetitive, and focused on the improvement or maintenance of physical fitness. Physical fitness includes cardiorespiratory fitness, muscle strength, body composition, and flexibility.

The amount of physical activity or exercise is defined by the interrelationship between the total dose of activity and the intensity at which the activity is performed. Dose refers to the total amount of energy expended in physical activity, while intensity reflects the rate of energy expenditure while working out.

Metabolism refers to the body's systems for using or converting energy.  This includes breathing, digestion, the building of muscle, and the storage of fat, circulation of blood - anything that's part of the body's systems for converting energy into an activity needed to live.

Metabolism involves two distinct types of processes:

  • "anabolic" reactions, which involve building cellular structures and the storing of energy
  •  "catabolic" reactions, which involve breaking down molecules for energy

"Metabolic rate" is the speed of the metabolism, or the rate at which calories are burned, while the body is at rest.

The metabolism and metabolic rate are determined by a number of factors.  Genes play an extremely important role; they're one reason why some people can remain thin no matter how much they eat, while others have a tougher time losing weight.

Lifestyle - particularly diet and exercise - can also play an important role. No matter what sort of metabolism everyone has, or how well was maintained, it's likely to slow down with age. Most of the calories that the body uses are burned during physical action. More calories are burned while the body is maintaining the vital processes than physical activity. In fact, 65% to 75% of the calories burned in a day are burned by the metabolism in the process of maintaining the body's basic vital processes.

Physical activity contributes up to 30% of the total daily calorie burn and is still one of the best ways to boost the metabolic rate.

With age, the metabolic rate slows down, tending to lose muscle. This results in a metabolic rate that begins declining as early as twenties.

Diets that are too severe can prove self-defeating, in part because of their effect on metabolic rate, and dangerous. Studies have shown that people who eat less than 1,200 calories per day are likely to wind up with a slower metabolic rate - which, ironically, can make it more difficult to burn calories and lose weight. Even going too long between meals can slow metabolic rate. That’s why experts recommend eating a small healthy meal or snack every 2 to 3 hours. Plus, eating helps boost calorie burn as the body works to digest foods.

In general, the more muscle and less fat on the bodies, the higher the metabolic rate. The metabolic rate is strongly influenced by the body composition. People with more muscle and less fat generally have a faster metabolic rate, while people with more fat and less muscle generally have a slower metabolic rate. The thyroid gland regulates the metabolism, producing hormones that influence almost every aspect of how the body performs: how fast or slow the calories are burned, when or whether you build proteins or store energy as fat, and how your body responds to other hormones.

Not surprisingly, disorders of the thyroid can cause problems for the metabolism. An underactive thyroid (hypothyroidism) produces fewer-than-normal thyroid hormones, causing a slower metabolism, and, consequently often causes weight gain. An overactive thyroid (hyperthyroidism) can cause the metabolism to speed up, often resulting in weight loss.




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