Studies concerning the cardiovascular responses after endurance training present contradictory results, with either an increase of heart rate variability or an absence of variation in R-R interval. There is a few available studies on physical exercise and the effects of training on heart rate variability (HR) and blood pressure (BP). The use of these parameters remains only limited to some studies and for precise physical activities like running (Pichot 2000 ; Portier 2001). Swimming is a sport that is practised in horizontal position in hypo-gravity environment. To our knowledge there exists no study investigating the vegetative-nervous control of heart rate and blood pressure in high level swimmers. The aim of the present study was to compare the effects of a swimming session on autonomic nervous system response between elite swimmers and non- swimmer subjects trained in endurance. We chose to investigate the autonomic nervous system using time and frequency analysis of heart rate and blood pressure variability. Methods We submitted two groups of elite swimmers (n=19) and other enduring sportmen (n=15) to a swimming test. The session of swimming was adapted according to the group considered. swimming characteristics ( Intensity, duration and recovery) were modified so that each group have the same intensity of practice. To evaluate the cardiovascular responses to postural change, a stand test was performed just before the standardised swimming training and 10 minutes after, with the subjects supporting their own weight during standing. Blood pressure and heart rate were recorded for 10 min in the supine position followed by 10 min in the standing position. Transition between supine and standing position was completed in less than 3 sec. HR and BP were continuously monitored by means of the Finapres system (Ohmeda, USA). There is no different effect on HR and BP after a training session between swimmers and no swimmers. Discussion and conclusion The spectral powers of the various frequency bands for HR and BP were not different between the 2 groups both in decubitus or uprigh positions. It seems that the swimming training does not influence the neurovegetative balance in the long run. The duration of training in water seems relatively too reduced compared to the time spent under normal conditions to generate important modifications of the neurovegetative balance. It is known that the immersion induces an hypogravitary situation leading to a reduction in peripheral vascular resistances, as well as an increased of stroke volume. The reactions to the exercise seem in conformity with those of the various physical activities studied within the literature (cycling and running). It is thus possible to set up a follow-up of the drive aiming to the early detection of the appearance of tiredness from the use of HR and BP variability.
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