Heavy bags can have an adverse affect if you choose the wrong one. When choosing a heavy bag you should always pick one depending on your weight. Starting off with too big of a bag can be devastating. The normal sizes of these bags range from 50 lbs to 150 lbs. A person weighing 170 lbs may only need to be training on a 70lb boxing bag. Always use boxing wraps on your hands when training with a heavy boxing bag. Be sure to purchase the correct size when your shopping for your bag. Always purchase one that is about 70 or 100 lbs less than your body weight.