Pre- and post-season heart rate variability in adolescent cross-country skiers

To investigate the effects on cardiac autonomic control after a competitive cross-country skiing season, 9 females and 8 males, 16-19 years old, perfo rmed tilt-table heart rate variability (HRV) recordings and incremental tre admill tests before (August), and after (April the following year) the most intensive period of training and competition. Spectral analysis of HRV sho wed increased total variability at rest and reduced low frequency variabili ty in the tilted position (LFtilt,) at the second test (P<0.05). The female subgroup showed consistently higher high frequency (HF) and total heart ra te variability than males, Total run time (RunT) increased from 18.5+/-1.9 min to 19.4+/-1.7 min (mean+/-SD) in the entire group (P<0.05), while VO(2) max only showed a non-significant increase (0.05<P<0.10). Submaximal heart rates (HRsubm) were reduced by an average of 4 beats (P<0.01) but maximal H R was unchanged, Performance data suggest a positive training effect. Follo wing training, the increased total HRV, the reduced LFtilt (both at rest), and the lower submaximal heart rates indicate an altered control of heart r ate both at rest and during exercise, The consistently higher HF and total variability in the females indicate an increased parasympathetic activity i n females compared with males.