Final answer:
Exercise increases the basal metabolic rate by building lean muscle, leading to more calories burnt even at rest, and helps prevent muscle and bone atrophy. Immobility causes muscle weakening and atrophy, lowering the metabolic rate and contributing to a cycle of reduced physical activity and further muscle loss.
Step-by-step explanation:
Metabolic System Effects of Exercise and Immobility
The effects of exercise and immobility on the metabolic system are quite significant. Physical activity not only aids in weight management by burning calories but it also helps raise the basal metabolic rate (BMR) by building extra lean tissue, which is more metabolically demanding than fat tissue. As a result, more calories are burnt even during rest periods, aiding in weight loss. Moreover, exercise stimulates muscle strengthening and prevents atrophy, contributing to increased energy transfer from the body in the form of both heat and work.
Immobility, such as prolonged bed rest or zero-gravity conditions experienced by astronauts, leads to muscle weakening and atrophy. In the absence of regular movement, there is a decrease in muscle cell size and number, as well as a reduction in muscle protein content. Consequently, there is a decrease in metabolic rate, especially as the body composition changes with increased fat tissue relative to lean muscle mass. Aging further compounds this issue, as the body's metabolic rate naturally decreases approximately 2 percent per decade after age 30.
All organ systems in the body, including the skeletal and muscular systems, are interdependent. Exercise impacts not only muscle mass but also bone density, with the digestive and endocrine systems playing a crucial role in bone health. Conversely, immobility can lead to a positive-feedback system where muscle loss results in reduced metabolism and even less physical activity, contributing to further muscle and bone deterioration.