The general purpose of a weighted vest is to add extra weight for body-weight exercises, walking, distance running or speed, agility and quickness drills. ... It can also increase intensity of an activity or exercise that would normally be easy and even help with bone density by loading the skeletal system.
While there are no studies on how much weight a vest should have, most therapists recommend anywhere from five to ten percent of a person's body weight. This recommendation is based on studies on maximum weight allowances for backpacks. Too much weight can result in over-stimulation and/or injury.
Wearing a weight vest that is 10 percent of your body weight can help you burn up to 8 percent more calories than doing the same activity without a weight vest. You must burn 3,500 calories to lose one pound of fat, so the more calories you burn per activity, the faster you will lose weight.
Running with a weight vest can improve your running posture. It might also help you increase your speed. One small study of 11 long-distance runners showed a peak speak increase of 2.9 percent after weight vest training. Weight vests work by training your body to exert more force to run during training sessions