Hello there . I have read through your question and understand your concern. Since you said you had injured your back and after that you are experiencing heaviness in the legs and cramping there is a chance that you have a nerve compression at the spinal level. An MRI spine will help in the diagnosis. Meanwhile you should avoid sudden bending and lifting heavy weights. Try doing some stretching exercises under the guidance of a chiropracter. I hope that answers your question. If you have any further questions please feel free to write. Thank you for choosing healthcare magic.