INTRODUCTION: Professional athletes undergo intense and rigorous training regimens during sporting seasons, and whether there are any post-season changes in cardiac function, beneficial or detrimental to performance e.g., cardiac fatigue, is not well known. The aim of this preliminary study was to compare left ventricular (LV) myocardial function before and after a competitive season in a group of adolescent elite football players, using state-of-the-art echocardiographic exercise testing. METHODS: Adolescent male players from an elite football club were recruited. They had a minimum of 12 h per week training, game time and selection, actively participating in international competitions. All players underwent comprehensive cardiac evaluations, including exercise echocardiography, with images being acquired (Artida/Aplio i900 machine, Canon Medical Systems, Japan) at rest, 0, 50, 100, 150 W, 2 minutes, and 6 minutes recovery, pre- and post-season. LV myocardial function was analysed using speckle tracking echocardiography (STE) and expressed as LV longitudinal strain (Sl) and strain rate (SRl), LV circumferential strain (Sc) and strain rate (SRc). A two-way repeated measures ANOVA was used, with pre-/post- season timing and exercise test steps as repeated measures. RESULTS: A total of 25 participants were included, mean age 14.1±0.7 y at pre-season visit (range 12.7-16.1 y). All were cleared for participation, none had cardiac conditions, and all had normal baseline cardiac function. Exercise step test had a significant effect on LV Sl (F(6, 66)=10.7, p=<0.001, n2=0.5), SRl (F(3,36)=100, p<0.001, n2=0.9), basal Sc (F(6,54)=15.2, p<0.001, n2=0.6) and basal SRc (F(6,60)=87.8, p<0.001, n2=0.9), with a gradual increase up to 150 W, and return to baseline in recovery for all parameters. There were no statistically significant effects of pre-/post- season timing on LV Sl (F(1,11)=2.3, p=0.2, n2=0.2), SRl (F(1,11)=0.003, p=0.9, n2=0), basal Sc (F(1,9)=5, p=0.8, n2=0.01) or basal SRc (F(1,10)=0.2, p=0.6, n2=0.02). In addition, there were no statistically significant effects of pre-/post- season and exercise test step on LV Sl (F(6,66)=0.7, p=0.6, n2=0.06), SRl (F(6,66)=1.3, p=0.3, n2=0.1), basal Sc (F(6,54)=0.8, p=0.6, n2=0.1) or basal SRc (F(2,23)=1.5, p=0.2, n2=0.1). Analyses were repeated for baseline to stage 100 W (missing data mostly at 150 W) with similar results, of no significant effect of pre-/post-timing on any of the LV function parameters. CONCLUSION: Resting LV cardiac function, as well as myocardial strain dynamic changes during exercise stages and recovery remain unchanged between pre- and post-season in adolescent footballers. These findings show that intense training periods such as that of professional sports season are not associated with "cardiac fatigue," or other major changes in LV function. More research is needed into the differing effects of teams sports compared to ultra-endurance training, as well as differing impacts on the right ventricle.
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