Weight training has the biggest effect on the skeletal muscles (D). The skeletal muscles are the muscles which keep the various bones in our skeleton together allowing us to stand, sit down, lie down and move. People do weight training to strengthen these muscles allowing them to be more active and pick up heavier items etc. If we don't strengthen out skeletal muscles we will battle to keep ourselves upright. We don't have to weight train but we do have to exercise and work at strengthening our skeletal muscles
