Physiology of the Cardiac Autonomic System

Heart rate variability is related to training load variables in interval running exercises

“…In addition, parts of the cerebral cortex and limbic systems affect autonomic control by transmitting impulses. Autonomic signals are transmitted to the organs through two subdivisions, the sympathetic and parasympathetic (vagal) systems (Hainsworth, 1998). In general, the vagal system promotes functions associated with growth and restoration, while the sympathetic system, in contrast, promotes increased metabolic output to deal with challenges from outside the body (Porges, 1995).…”

“…Most of the postganglionic sympathetic neurons are adrenergic. The sympathetic and vagal systems are continually active, and the basal rates of activity are known as sympathetic tone and vagal tone, respectively (Hainsworth, 1998). …”

“…The heart is supplied with both sympathetic and vagal nerves, which affect cardiac pumping by changing the heart rate and the strength of contractions of the heart. Cardiac impulses are controlled by the membrane processes of sinoatrial (S-A) node, which is the pacemaker of the heart (Berntson et al 1997;Hainsworth, 1998). The intrinsic heart rate of a human, modulated by the S-A node, varies between 110-120 bpm at rest (Hainsworth, 1998).…”

“…Cardiac impulses are controlled by the membrane processes of sinoatrial (S-A) node, which is the pacemaker of the heart (Berntson et al 1997;Hainsworth, 1998). The intrinsic heart rate of a human, modulated by the S-A node, varies between 110-120 bpm at rest (Hainsworth, 1998). In general, increased sympathetic activity increases the overall activity of the heart, and vagal activity causes mainly opposite effects.…”

“…Vagal stimulation has a very short latency, the maximum response occurring in only 400 ms. Therefore, changes in vagal activity can influence heart rate on a beat-to-beat basis, whereas the maximum sympathetic effect may not occur for as long as 20-30 s (Hainsworth, 1998).…”