Effects of aerobic training on heart rate

The regular practice of physical exercises is an important factor to reduce morbidity and mortality rates of cardiovascular and all other conditions1,2; there also seems to have further and independent benefits from the practice of physical exercises and improvement of the aerobic condition3-6, which speaks for their being practiced more and more frequently. The American Heart Association recommends individuals to practice physical exercises in most days of the week, every day if possible, with intensity ranging from moderate to strenuous, according to their physical capability, for a period of 30 minutes or more7. Even though moderate exercises enhance health conditions, there are recent and consistent evidences that high intensity or strenuous exercises have even more significant positive effects on lipid profile8, reducing up to two times mortality rates over a decade9-12. Acute and chronic effects of physical exercises on the human body have been targeted by many researches over the last few decades13-18, and are identified as responses to exercise, such as higher HR at the initial transient of the exercise, and adjustments to training, with a lower HR for the same intensity of submaximal exercise, respectively. Because it is easy to measure, heart rate (HR) behavior has been extensively studied under different exercise-related types and conditions. HR is primarily controlled by direct activity of the autonomic nervous system (ANS), through actions on its sympathetic and parasympathetic branches on the sinus node autorhytmicity, especially resting vagal activity (parasympathetic), which is progressively inhibited since the exercise was started19, and sympathetic when exercise intensity is further incremented (figure 1). Different mechanisms act to adjust HR at different moments of a physical exercise. For instance, the mechanism through which HR raises on the first four seconds of a physical exercise has been extensively studied, including under Effects of aerobic training on heart rate