Abstract
Background: Training preparation in soccer is thought to improve body composition and performance level, especially the maximal aerobic capacity (VO 2 max). However, an enhancement in performance may be attenuated by the increase of fatigue. Heart rate variability (HRV) as a non-invasive index of autonomic nervous system (ANS) activity has been considered to be a sensitive tool in fatigue assessment. Objective: This study was focused to evaluate the response of ANS activity and morpho-physiological parameters to eight week training preparation. Methods: Study included 12 trained soccer players aged 17.2 ± 1.2 years. Athletes underwent pre- and post-preparation testing that included the ANS activity assessment by spectral analysis of HRV in supine and upright position. Further, body composition was analyzed via electrical bio-impedance method and physiological parameters were assessed during maximal stress tests. ANS activity and subjective feeling of fatigue was assessed continuously within subsequent weeks of preparation. Results: No significant differences in all HRV variables within weeks were found. Pre vs. post analyses revealed a significant (p < .05) increase in body weight, fat free mass, body mass index, and peak power. A significant decline in mean maximal heart rate (HR) and resting HR at standing was identified at the end of preparation. Since no significant changes between pre- post-preparation in the mean VO 2 max occurred, the positive correlation between the individual change in VO 2 max and the vagally related HRV [supine LnHF (r = .78), Ln rMSSD (r = .63), and the standing LnHF (r = .73, p < .05)] was found. Conclusions: This study showed that an 8 week training program modified particularly fat free mass and short-term endurance, whereas both the autonomic cardiac regulation and the feeling of fatigue remained almost unaffected. Standing position seems to be more sensitive in terms of the HR response in relation to fatigue perception than supine.
Highlights
Success during a soccer match is dependent, amongst other factors, on technical ability, tactics and a high level of physical conditioning, especially repeated sprint ability and aerobic endurance (Stølen, Chamari, Castagna, & Wisløff, 2005)
Note. 95% CI = 95% confidence interval, p = significance of paired t-test, d = Cohen’s d effect size, BMI = body mass index, FFM = fat free mass, HRmax = maximum heart rate, VO2max = maximum oxygen uptake per kg, Pmax = maximum mechanical power, Standing = standing phase of orthoclinostatic maneuver, Supine = supine phase of orthoclinostatic maneuver, HR = heart rate, LnLF = natural logarithm of low-frequency power, LnHF = natural logarithm of high-frequency power, logarithm transformation (Ln) LF/high frequency (HF) = natural logarithm of low-frequency/high-frequency ratio, Ln root of mean square successive differences (rMSSD) = natural logarithm of root mean square successive difference of RR intervals. +moderate or large effect size
Non-significant decrease (p = .089) in supine Ln LF/HF was detected in post-testing period, effect size for Ln LF/HF (d = 0.54) suggested a moderate practical significance
Summary
Success during a soccer match is dependent, amongst other factors, on technical ability, tactics and a high level of physical conditioning, especially repeated sprint ability and aerobic endurance (Stølen, Chamari, Castagna, & Wisløff, 2005). Some authors have suggested that the inter-individual variation in adaptive responses to training is related to the individual training status (“trainability”) They have argued that “trainability” is associated with the resting level of autonomic nervous system (ANS) activity, vagal activity (Botek, McKune, Krejčí, Stejskal, & Gába, 2014; Boutcher et al, 2013; Hautala, Kiviniemi, & Tulppo, 2009; Hautala et al, 2003; Kiviniemi, Hautala, Kinnunen, & Tulppo, 2007; Vesterinen et al, 2013). Conclusions: This study showed that an 8 week training program modified fat free mass and short-term endurance, whereas both the autonomic cardiac regulation and the feeling of fatigue remained almost unaffected. Standing position seems to be more sensitive in terms of the HR response in relation to fatigue perception than supine
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