**3. Intensity domains (training zones)**

Some authors (Gaesser et al. 1996; Greco et al. 2008) suggest a range of intensities of three domains (sometimes referred as training zones) and others (Dekerle & Pelayo 2011) a scale of five domains and their physiological effects. According to Table 1, exercise can be conducted in three different intensity domains, resulting in very distinctive physiological effects in each of these domains (Gaesser et al. 1996; Greco et al. 2008).


Table 1. Intensity domains and their physiological effects (Gaesser et al. 1996; Greco et al. 2008)

#### **3.1 Moderate intensity domain**

[La] stabilizes quickly and can be maintained almost similar to resting levels. Similarly, VO2 shows a quick set (1-3 min) before stabilization, and the individual can maintain the intensity for hours without exhaustion. The main explanation for the "end" of the exercise refers to substrate depletion (muscle and liver glycogen), changes related to hydration and electrolytes or problems related to the process of thermoregulation (Greco et al. 2008).

#### **3.2 Heavy intensity domain**

Production and removal rates of lactate levels are high due to a high metabolic demand. Consequently, [La] tends to stabilize at higher concentrations when compared to exercise at moderate intensity. Moreover, the efficiency of the specific motor gesture seems to be smaller, generating higher VO2 values than the linear relationship between VO2 and exercise intensity that characterizes the Moderate intensity domain (development of a slow component of VO2). Although the metabolic stress is high, it is possible to maintain a state of physiological balance and to perform the exercise for a long period (Greco et al. 2008). However, Baron et al. (2008) found exercise performed at maximum intensity possible to maintain the stabilization of the [La], i.e., in the maximal lactate steady state (MLSS), depletion occurred while physiological reserve capacity still existed, but in association with an increase in PE assessments, as predicted by the central regulator model (Noakes & St Clair Gibson 2004; Noakes et al. 2005). The end of the exercise could then be induced by an integrative homeostatic control of peripheral physiological system to ensure specifically the maintenance of homeostasis.
