Abstract Different stressors, like athletic training, can change the autonomic modulation of the heart. This can be evaluated with heart rate variability (HRV) analysis. Acute hypoxia is also known to attenuate parasympathetic activity and accentuate the sympathetic activity. Whether these changes in autonomic modulation will disappear with altitude acclimatization remains unclear. PURPOSE: This study was made to investigate the effects of 3-week moderate altitude training on HRV in elite swimmers. METHODS: 9 elite swimmers (Hi) of international level (5 women and 4 men, age 19.4 ± 1.6 years) lived and trained 3 weeks at Sierra Nevada, Spain (2,320 m). Control group (Lo) consisted of 11 swimmers of similar level (7 women and 4 men, age 17.9 ± 1.9 years), who lived and trained at sea level. RR-intervals were recorded every morning in supine (8-min) and orthostatic (6-min) positions with beat-by-beat heart monitors. Breathing was paced to 12 breaths/min. Recordings were done during the 3-week intervention period and one week before and after. HRV was analyzed from the last 5-min period of both positions with FFT spectral power analysis. TRIMPs of every training session were calculated to estimate training load. HRV results are averaged over every week and presented as relative percentage changes. RESULTS: The training load was similar in both groups during the 3-week intervention but was lower during the week after in Hi-group when compared to Lo-group (P=0.003). An interaction of group, time and TRIMPs was found in change in spectral power of supine LF (-40% vs. +36%, P=0.02) and HF (-46% vs. +55%, P=0.01) during the intervention period showing increased HRV in Lo group and decreased HRV in Hi-group. Also LF (+93% vs. +12%, P=0.01) and LF/HF ratio (+79% vs. -2%, P=0.01) during standing increased more in Hi-group than in Lo-group in the end of the intervention. CONCLUSION: The present findings of lower HRV in Hi-group than in Lo-group suggest that the physiological stress of training at moderate altitude leads to parasympathetic withdrawal and possibly increased sympathetic activity even after night rest. These changes in autonomic modulation seem to last longer than for the first week after altitude training camp.

Introduction Different stressors, like athletic training, can change the autonomic modulation of the heart. This can be evaluated with heart rate variability (HRV) analysis. Acute hypoxia is also known to attenuate parasympathetic activity and to accentuate the sympathetic activity. Whether these changes in autonomic modulation will disappear or be accentuated with altitude acclimatization remains unclear. This study was made to investigate the effects of 3-week altitude training (AT) on HRV in elite swimmers.

Methods

Effects of Altitude Training on Heart Rate Variability in Orthostatic Test in Elite Swimmers

F.A. Rodríguez, FACSM1, X. Iglesias1, B. Feriche2, C. Calderón3, X. Ábalos1, J. Vázquez1, A. Barrero1, L. Rodríguez1, E. Hynynen4, B.D. Levine, FACSM5

1 INEFC, University of Barcelona, Spain, 2 FCAFyD, University of Granada, Spain, 3 Sierra Nevada High Altitude Training Center, Granada, Spain, 4 KIHU – Research Institute for Olympic Sports, Jyväskylä, Finland, 5 IEEM / UT Southwestern, Dallas, TX, USA

Results The training load was not different in both groups during the 3-week intervention but was lower during the week after in Hi-group when compared to Lo-group (P=0.003). An interaction of group, time and TRIMPs was found in change in spectral power of supine LF and HF during the intervention period showing increased HRV in Lo group and decreased HRV in Hi-group (Fig. 1). Also LF and LF/HF ratio during standing increased more in Hi-group than in Lo-group during the intervention at low TRIMPs only at the <TRIMPs=median=169 au (Fig. 2).

Institute for Exercise and Environmental Medicine

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Figure 2. Changes in orthostatic LF power and LF/HF ratio (% Pre)

Discussion This study showed that: 1) supine HRV decreased during AT whereas it increased during sea level training, and returned to baseline levels one week later, 2) in contrast, standing HRV gradually increased at the end of the AT period and tended to remain high level after one week, and 3) the band power spectra suggest that AT, in contrast to training at sea level, induced parasympathetic withdrawal and likely increased sympathetic activity. Classically, acute exposure to high altitude is believed to induce a decrease in HRV and an increase in LF/HF in supine position, perhaps as a defense against hypoxic stress; after acclimatization HF increases whereas LF activity decreases (cit. Schmitt et al. 2006). Similarly, strenuous training has been shown to induce a conversion from vagal to sympathetic predominance in elite athletes (Iellamo et al. 2002). In contrast with previous reports (Atlaoui et al. 2007), HRV showed significant changes in the follow-up of these elite swimmers and using the orthostatic test may reveal additional information on the autonomic modulation of the heart. We could speculate that the upright position revealed information about carotid chemosensitivity, perhaps increasing baroreceptor–chemoreceptor interaction.

Conclusions §  Elite swimmers living and training for 3 weeks at 2,320 m experienced

a decline in supine HRV and a gradual increase in standing HRV. Sea level training at similar load induced a mirror like pattern during the supine position and no change during standing

§  HRV was lower during altitude training as compared to sea level, suggesting that the physiological stress of training at moderate altitude leads to parasympathetic withdrawal and possibly increased sympathetic activity even after night rest; these changes seem to last longer than the first week after the altitude training camp

References 1. Atlaoui D. et al. 2007. Int J Sports Med, 28: 394-400 2. Cornolo J. et al. (2006) Eur J Appl Physiol 96:389-96 3.  Iellamo F. et al. (2002) Circulation 105:2719–2724 4. Schmitt L. et al. (2006) Int J Sports Med 27:226-31

Supported by CSD (35/UPB10/10, 05/UPB32/10) and MICINN (DEP2009-09181) grants

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