Hamstring tears are very common soccer injuries. A study in Scandinavian Journal of Medicine & Science in Sports shows that preseason strength training helps to prevent injuries to these muscles in the back of the upper legs (Volume 13, Issue 4, 2003). Players from two of the best soccer teams in Sweden were divided into two groups. One group received specific hamstring training of 10 weeks of twice a week, using a special device to overload the hamstrings eccentrically. The trained group had less than one third the hamstring injuries of the untrained group, and also had greater improvement in hamstring strength and running speed.
The findings of this study should encourage preseason strength training for other muscle groups stressed in any sports. While stretching can make muscles longer to exert a greater torque on joints, it has not been shown to prevent injuries. Muscles are injured because the force on them is greater than their inherent strength, so they tear. Resistance training makes muscles stronger so that they can withstand greater forces and therefore helps to prevent injuries.