**4.1 Two-parameter model**

164 Bioenergetics

Each of the five intensity domains (Dekerle & Pelayo, 2011) is characterized by acute specific physiological responses. Dekerle & Pelayo (2011) establish the lactate threshold (LT) as the boundary between moderate and heavy domain. The LT is defined as the first increase in

The exercise is performed in intensity very close to the LT, but a little higher, which causes a small increase in [La] (no more than 1 mmol·l-1) in the first minutes, with subsequent stabilization close to resting levels (≈ 2.1 mmol·l-1). The maximum exercise intensity at which [La] stabilization occurs is defined as maximal lactate steady state (MLSS, ≈ 3-5 mmol·l-1) (Beneke, 1995). The MLSS is the heavy intensity domain upper limit (Barstow 1994). The intensity corresponding to LT can be maintained for a very long period (e.g. aquatic marathons) and occurs at a slower speed when compared to MLSS (*tlim* ≈ 60 min). MLSS is located in the smaller SS than CV2par (*tlim* ≈ 14.3 to 39.4 min). Importantly, for being difficult to detect the MLSS through the curve obtained in [La] and SS, and also to avoid any misinterpretation, the term "anaerobic threshold" should not be associated to the MLSS. Swimming in a very low SS is a difficult task (<0.4 to 0.5 ms-1 or 50-60% of V400 -average speed of 400 m front *crawl* in maximal effort). Thus, the lowest speed that can be adopted by

swimmers using a good technique, it is almost equal to LT (Dekerle & Pelayo 2011).

In SS above the MLSS (heavy intensity domain upper limit) there is an increase in [La], HR and VO2 (occurrence of the slow component). Initially, it was suggested that the increase in VO2 in these intensities reach the maximum (VO2max) before exhaustion, which characterizes the severe intensity domain). This statement is controversial and difficult to investigate because of the low reliability of time to exhaustion obtained in constant intensity tests (variability of *tlim*) (Hinckson & Hopkins, 2005). The SS equivalent to the Severe intensity domain includes performances of approximately 2 to 60 minutes (VO2max reaching the end of the exercise) with the performance of 400 m in front *crawl*, the maximum aerobic speed (MAS) and CV2par lying within that domain (Lavoie & Montpetit et al 1981; Lavoie et al. 1983; Lavoie & Leone 1988; Rodrigues 2000; Pelayo et al. 2007; Billat et al. 2000; Dekerle et al.

This domain includes performances of very short duration (< 2 min). Due to the limited response of VO2, VO2max is not reached during exercise, although the task is performed to

Dekerle & Pelayo (2011) suggest the subdivision of Heavy intensity domain. According to these authors, the range of effort associated to this area is wide (performances of ≈ 2 to 60 min) and associated with many chronic responses to training, i.e., the physiological adaptations of a training period in SS near the MLSS are different from the training

lactate response to an incremental test (Wasserman et al. 1990).

**3.4.1 Heavy intensity domain** 

**3.4.2 Severe intensity domain** 

**3.4.3 Extreme intensity domain** 

**3.4.4 Very heavy intensity domain** 

adaptations induced by a training period in MAS or above.

2010).

exhaustion.
