Hydration is very important in tolerance to long-term exercise, therefore, it has operations in thermoregulation and thus controls body temperature (SHARPE et al, 2008;. MONTAIN, 2008) and also ensures the maintenance of physiological functions (MONTAIN, 2008) .
The heart has its activity modulated by the autonomic nervous system (ANS), it promotes adaptations according to the demand of the peripheral regions (Hartikainen; Tahvarnainen; Kuusela, 1998; Rosenwinkel, Bloomfield et al., 2001). The heart rate (HR) is changed through the sympathetic and parasympathetic nervous activity, influenced the activity and physiological situation, as in the rest (Rosenwinkel and Bloomfield, 2001) and transitional situations such as physical assessments, transition home exercise and exercise home.
Some forms of hydration to exercise have been studied, such as water (Vianna et al., 2008), isotonic solution (Moreno et al., 2013), and coconut water (Kalman et al., 2012). The main comparisons occur between the use of water or isotonic (Sawka et al, 2007;. Montain, 2008; Shirreffs et al., 2004).
In the current study on the subject, Vanderlei et al. (2015), recruited a group of healthy young adults to consider a comparison of hydration in three evaluations: The first was an assessment control without hydration during activity, the second used hydration with water and the third used an isotonic solution ( Gatorade®). The authors evaluated the change in temperature, recovery of autonomic modulation, and body weight of the subjects involved.
In its findings, the research team found changes in body weight only in the evaluation without hydration, promoting a reduction on average of 1.4kg, while in other assessments did not change. With regard to body temperature in all evaluations was increased, however, using hydration with water and isotonic, the increase was smaller. There was a significant difference only when comparing the non-use of hydration and the use of isotonic, the last proving interesting for the control of body temperature in prolonged physical exercise.
When comparing the recovery of autonomic modulation and heart rate, the authors found faster recovery when they used some form of hydration, with water or isotonic. The faster heart rate recovery happens, according to some authors, because hydration provides increased baroreflex, a marked decrease in sympathetic activity and hence increase in parasympathetic cardiac modulation (Charkoudian et al. 2003;. Yun et al, 2005 ).
Dehydration increases body temperature, therefore, maintains high sympathetic modulation reduces the vagal modulation and can produce a delay in the recovery of cardiac autonomic modulation (Charkoudian et al., 2005).
The literature highlights the importance of hydration during long-term training therefore enables recovery of basal temperature faster and cardiac autonomic modulation. Hot topic is the need of replacing electrolytes during rehydration. According to some studies (Cheuvront et al. 2003; Convertino et al., 1996; Sawka, 1992), dehydration up 2% of body weight may impair physiologic function and influence the physical performance due to loss of water and electrolytes . The study Vanderlei et al. (2015) was within these values, which may explain why there was no difference between the hydration media, possibly because these amounts do not require electrolyte replacement.
Thus, it indicates the importance of hydration during and after exercise. Due to its importance would be interesting new studies treated with different means of hydration and in different populations and age groups.