Parasympathetic contribution to bradycardia induced by endurance training in man.
Seven normal subjects of sedentary habits were submitted to a 10 week period of endurance physical training on a cycloergometer. The training programme produced a mean 15.6 +/- 1.4% (+/- SE) increase in VO2max (from 39.7 +/- 2.0 ml . kg-1 . min-1 to 45.9 +/- 2.4 ml . kg-1 . min-1) and a reduction in resting heart rate (HR) from 69 +/- 1.9 to 58 +/- 1.7 beats . min-1 in the supine position. After pharmacological blockade of the parasympathetic system with atropine sulphate, HR rose on average by 53 +/- 3.9 beats . min-1 before training and 47 +/- 3.6 beats . min-1 after training, the difference being statistically nonsignificant. The magnitude of respiratory sinus arrhythmia (RSA) was similar before and after the period of physical conditioning. The respiratory variation in HR ( Delta HR) at the 1 litre tidal volume was 20 +/- 2.4 beats . min-1 and 20 +/- 2.6 beats . min-1 before and after training, respectively. At the 2 litre tidal volume, these values were 25 +/- 3.2 and 27 +/- 4.5 beats . min-1. Similar results were obtained with the RSA test when a group of 13 sedentary individuals (VO2max = 39.4 +/- 1.3 ml . kg-1 . min-1) was compared with a group of 7 athletes who are medium distance runners (VO2max = 53.8 +/- 1.3 ml . kg-1 . min-1).(ABSTRACT TRUNCATED AT 250 WORDS)
D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D001146:Arrhythmia, Sinus / Q000503:physiopathology; D001285:Atropine / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D010101:Oxygen Consumption; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D010807:Physical Endurance; D012119:Respiration; D013177:Sports
D001285:Atropine