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RESEARCH PRODUCT

Effects of eight weeks of physical training on physical performance and heart rate variability in children

subject

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Kraama, Liisa. 2013. Effects of eight weeks physical training on physical performance and heart rate variability in children. University of Jyvaskyla, Department of Biology of Physical Activity. Master’s Thesis in Exercise Physiology. 52 pp. Physical activity and aerobic capacity have decreased among children and adolescents during the last decades. Physically active adults have been shown to have higher heart rate variability (HRV) than less active adults. In adults training-induced changes in physical performance have been shown to be related to increase in HRV, especially in high frequency component (HF), which is a marker of parasympathetic activity. The purpose of this study was to examine, if the physical activity level of secondary school pupils is associated with the functions of the autonomic nervous system and if 8 weeks of instructed physical training could improve both the physical performance and cardiac autonomic function in children. The functions of the autonomic nervous system were measured by heart rate variability. The test group had 12 girls and 12 boys and the control group 7 girls and 7 boys. All the subjects were 13-15 years old pupils. Physical training included warm up (10min), circuit training (20min), endurance training (running and playing 20-30 min), stretching and relaxing (10 min) 3 times a week for eight weeks. Intensity during endurance training was 70-75% of maximal heart rate. The following measurements were done both before and after the physical training period: endurance test (running tests starting from 7km/h and increasing by 0.2 km every 30 s), flexibility test (sit and reach), speed (30m sprinting) and power (3kg medicine ball throwing, standing long jump) tests. The low frequency (LF) and high frequency (HF) components of HRV were also measured in supine rest and in standing conditions before and after the eight weeks period as well as body mass, body mass index, fat percentage and skeletal muscle mass. Time to exhaustion in the endurance test increased in the test group (p<0.001) and did not change in the control group. Flexibility and ball throwing improved in the test group (p<0.05) while no changes were observed in the control group. Although LF/HF in standing condition decreased (p=0.114) and HF increased (p=0.187) slightly in the test group, no significant changes were observed in HRV variables in either group. Neither were there any significant correlations found between HRV and endurance parameters. Increased instructed physical training was clearly beneficial as shown by many improved performance parameters in the test group. Even though endurance capacity increased and slight changes were seen in LF/HF and HF in the test group, the association between was not as clear as earlier seen among adults. In conclusion, eight weeks physical training improves adolescents’ physical performance, but it does not affect autonomic cardiac function.