Differences in the mean (± standard error, SE) (a) and individual concentration of catecholamines (b), vasoconstrictor peptides (c) and cortisol (d) between after and before test for the volunteers normalized with the basal concentration level of each corresponding neuroendocrine hormone and vasoconstrictor peptide.

<p>Significant differences (<i>p</i> < 0.05 and <i>p</i> < 0.01) are indicated with one or two asterisk(s), respectively; See text for exact <i>p</i> values. Arabic numbers in Fig 1b–1d represent the volunteer identification code in the given group for which the difference in at least three hormone concentration levels after and before test was higher than the mean of the hormonal concentration difference.</p

After—before concentration ratios of the investigated catecholamines, vasoconstrictor peptides and cortisol normalized with the maximal oxygen uptake.

<p>Significant differences (<i>p</i> < 0.05 and <i>p</i> < 0.01) are indicated with one or two asterisk(s), respectively; See text for exact <i>p</i> values.</p

Echocardiographic parameters in professional soccer players and age matched controls.

<p>IVSd: interventricular septum thickness during diastole; LVPWd: left ventricular posterior wall thickness; LVIDd, LVIDs: left ventricular internal diameter during diastole and systole; n = 23 in each group,</p><p>*<i>p</i><0.05,</p><p>**<i>p</i><0.01 vs. control.</p

Frequency corrected QT interval of age-matched controls and professional soccer players before and following a competitive game.

<p>QTc interval calculated with the Bazett formula was not different in soccer players before the game and was significantly prolonged after the game (<b>A</b>). QTc values calculated with the Fridericia and Hodges formulae but not the Framingham formula showed significant difference between groups before the game, and none of the three calculations yielded any difference between before and after game values in soccer players (<b>B</b>, <b>C</b> and <b>D</b>; n = 76 persons/group; Means ± S.E.M.; *p<0.05; **p<0.01; ***p<0.001 vs. age-matched control; ^###p<0.001 vs. before game values).</p

Histograms showing the distribution of the QT interval.

<p>(<b>A</b>) Controls (empty bars) and soccer players before game (full bars) and (<b>B</b>) controls (empty bars) and soccer players after the game (hashed bars). Bin size is 10 ms. (n = 76 persons/group).</p

Short-term beat-to-beat temporal variability of the RR (STV_RR) and QT (STV_QT) intervals in age-matched controls and professional soccer players before and following a competitive game.

<p>Soccer players had a significantly higher STV_RR compared to controls before the game. STV_RR was similar to controls in soccer players immediately after the game (<b>A</b>). Poincaré plots illustrating short-term temporal variability of the QT interval at rest in a control individual and in a professional soccer player before the game. Note the shift of QT values to the right and upwards in the soccer player indicating QT prolongation and the increased scattering of QT interval values in the soccer player demonstrating increased beat-to-beat variability of the QT interval (<b>B</b>). Short-term QT variability was significantly higher in soccer players both before and after the game compared to controls but also decreased in players compared to pre-game values (<b>C</b>). (n = 76 persons/group; Means ± S.E.M.; ***p<0.001 vs. age-matched control; ^##p<0.01; ^###p<0.001 vs. before game values).</p

The QT intervals of age-matched controls and professional soccer players before and following a competitive game.

<p>The QT interval was significantly longer in soccer players before the game (n = 76 persons/group; ***p<0.001 vs. age-matched control; Means ± S.E.M.; ^###p<0.001 vs. before game values).</p

Histograms showing the distribution of short-term beat-to-beat variability of the QT interval (STV_QT).

<p>(<b>A</b>) Controls (empty bars) and soccer players before game (full bars) and (<b>B</b>) controls (empty bars) and soccer players after the game (hashed bars). Bin size is 0.5 ms. (n = 76 persons/group).</p