My son used to lift weights hes 15 he began with lower back pain no he haves leg pain also in both legs he got xrays everything was good but still.

Spondylolysis. Back pain in adolescents is sometimes difficult to find a cause. As a weight lifter, he may have a stress fracture in an area of his spine called the pars interarticularis. This is often missed on routine x-rays and may require a bone scan. This is often seen in football linemen from hyperextension of the lumbar spine. Weight lifting can also increase stress in this area, particularly squatting.