Knee flexion and extension strength in young Brazilian soccer players: the effect of age and position

Purpose
To compare isokinetic knee flexors and extensors concentric muscle strength in young soccer players of different ages and playing positions.

Methods
Seventy-seven young male soccer players were divided into 3 age categories: U-15, U-17, and U-20, with the consideration of 4 game positions: goalkeepers, defenders, midfielders, and forwards. The concentric tests of the hamstrings (Hcon) and quadriceps (Qcon) were performed at 30°/s, 60°/s, and 180°/s, and the ratio of 180°/30° was calculated.

Results
The values of Qcon for the U-15 turned out significantly lower in comparison with the U-20 in 30°/s and 180°/s and in the 180°/30° ratio. The Hcon values for the U-15 were significantly lower than for the U-20 at 30°/s, 60°/s, 180°/s, as well as in the 180°/30° ratio. Strength levels were shown to be significantly different between the 3 analysed categories. The goalkeepers presented with Qcon and Hcon values significantly higher than the other playing positions, regardless of the angular velocity used.

Conclusions
U-15, U-17, and U-20 athletes do not have the same level of strength. The goalkeepers demonstrated high strength values, suggesting the importance of specific training for each game position.