Changes in performance and heart rate during a soccer specific repeated sprint protocol, with and without instep-kick.
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Purpose of this study: The main purpose of this study was to investigate the magnitude of changes in heart rate, and external parameters such as velocity and power, in young elite soccer players, following a protocol consisting of repeated sprints with directional change. Method: 20 players, male (mean age 17.6 years ± 1.1, mean heigth 181 cm ± 5.8, mean weight 73 ± 6.7), selected from the junior department of an elite soccer club. Test protocol consisted of 2 test days including 6 sprints with instep-kick, and 6 sprints without instep-kick, seperated by 3 minutes recovery. Sprint distance 16+16 meters, start every 30th second. Mesurements of heart rate using Polar Pulse Team2 systems, and ZXY Sport Tracking motion analysis for registration of velocity parameters. Protocol design AB-BA. Results: There is no significant effect on heart rate average and rate of increase (p>0.05) when comparing sprint blocks with and without ball. A significant difference was found for heart rate average with a p-value of 0.006, comparing day 1 with day 2. A significant reduction in peak velocity and peak power acceleration/deceleration (with p-values lower than 0.050) was found occuring mainly between sprint 2 and 3. Conclusion: Main findings indicated significant reductions in sprint performance for peak velocity and power around sprint 3. A significant increase was found for heart rate average from block 1 to block 2, thus indicating that heart rate changes was dependent on order. Instep-kick or no instep-kick had no significant impact on performance or heart rate average. Key words: Soccer, repeated sprint, intermittent activity, instep-kick, heart rate, accelerometer, velocity, power.