Squats improve all of the major muscle groups of the body, but they are most geared toward increasing quadriceps mass and strength. Squats are important for improving all speed-related sports that involve ground contact, including sprinting, football, soccer, baseball, and basketball.
What to do when your lower back hurts after your squat? Try practicing more time stretching your hamstrings.
Do your knees hurt after you squat? Try practicing stretching your calves.