Seasonal variation in fitness levels of professional youth footballers over a competitive season

The use of applied sports science in soccer is growing rapidly. Fitness testing and monitoring of training intensities are now becoming common place in the modern game. Anecdotally it appears that fitness may decrease over the season after initially being high following pre-season. While field tests also suggest this, more precise measures made in controlled lab settings are scarce. Therefore, the current study considered the seasonal variation in fitness parameters of footballers over the course of a professional season. Nineteen professional youth players from Celtic Football Club (age = 18.2 + 0.3 years; height = 175.4 + 6.2 cm; weight = 66.8 + 2.56 kg) completed lab-based tests of aerobic capacity, muscle strength and power at three times throughout the season. Aerobic measures of VO2max were among the highest values for soccer players reported in published literature (at the end of pre- season). Body weight changes occurred in the younger players over the season, and appear to be largely dependant on maturation status. Maximal strength parameters increased across the season and this was reflected in maximal jump heights. However, in the older players increased strength did not improve sprint performance over 5m and 10m. In younger players increasing maximal strength did correlate with improvement in sprint performances. The results suggest that fitness levels can be maintained across the season in older age groups or more mature players. Changes seen in younger players are primarily a result of maturation and resultant changes in body morphology. Furthermore, lab-based tests appear to provide a more detailed profile of a players’ physical status than field-based tests