It is simply a natural function of the human form to be physically active. Physical activity is, in fact, a consistent product that many of our core physiological processes anticipate by their very nature. Two consequences arise from this relationship. Firstly, a lack of activity has profound consequences on basic normal metabolic functioning. Secondly, the consequent flip-side of the fact that human physiology anticipates consistent physical activity is the observation that the human movement system is highly efficient. What does this basic two-sided relationship mean? It means that the common notion that exercise is merely a weight-loss tactic is entirely and radically WRONG-headed. A lack of physical activity has basic implications far "outweighing" simply a tendency for weight-gain.
Activated muscle is required to retain insulin and blood-sugar health, independent of the goal we often hear for exercise; i.e., "burning calories". Skeletal muscle serves as a vast reservoir for utilizing insulin-mediated blood sugar. This is not a trivial role for 'normal' activated muscle, as the alarming rate of pre-diabetes and diabetes disclose in the unnatural state that is the modern sedentary lifestyle. In addition to basic cardiometabolic functioning— stress management, emotional health, and increased protection against neurodegenerative disorders remain equally "basic" to the function of consistent physical activity. Unfortunately, many commercial weight-loss plans, and even some clinical diet programs, de-emphasize the importance of exercise due to the observation that exercise engaged as an exclusive and primary strategy for weight-loss is inefficient. The larger point is that it is inefficient precisely because the body's natural state is to anticipate consistent movement. From the point of view of our basic physiology: a rudimentary level of physical activity is not an option.
The energy available to you from your diet undergoes dramatic changes when you engage in consistent exercise. But all exercise is not the same, and fuel availability is not simply on or off. The details are important, both for the performance athlete and for the person interested in exercise only as part of a health-management program. Many fitness advocates do not appreciate the fundamental relationship between the body's fuel use dynamics, and the dietary and sleep patterns that impact performance. It is not simply about marshalling available energy for exercise, it's about which energy stores are tapped into for everyday living. For example, when sleep is altered, lean muscle tissue is preferentially torn down, as opposed to the fat we want to burn. This has been demonstrated even for young, healthy athletes who exercise consistently. Poor sleep impacts fuel-use dynamics. Moreover, even a modest shift in our basic circadian rhythm— which underlies the orchestration of our basic sleep-wake cycle and all of the associated hormones that dictate our energy and performance— can impact our mental and metabolic performance significantly.