In conclusion, to avoid injury of the back, perform exercises with a straight back. Injuries of the knee can be prevented by ensuring that your knees go straight over your toes when performing exercises that require a 90 degree or more bend of the knee. With regard to the elbow or shoulder don't perform exercises that could cause a sudden force to move the shoulder farther than its normal range of motion. Performing exercises in the mirror or watching the movements of your muscles while you are working out will help this.