Phisical activity, regularly performed, give us a lot of health benefit, especially in preventing cardiovascular disease, diabetes mellitus (DM) and obesity. Physical exercise, defined as a controlled, progressive, supervised, requires muscular activity, involving energy consumption through metabolic and thermoregulatory processes. It can be classified as aerobic and anaerobic, according to the metabolic processes that take place. The metabolic equivalent (MET) represents the body’s energy consumption during rest and it is used for quantifying fhisical activity (for example, a MET value of 3 would require 3 times the energy that is consumed at rest). Muscle contraction has two different phases: the isometric one (usually during the first part of the contraction) and the isotonic one. This article presents the interrelation of phisical activity with with the complexity of metabolic patwais, bringing the arguments for the necessity of performing regular and controlled phisical activity.