The purpose of using a weight vest is to add extra weight for body-weight exercises and to create an overload effect for walking, distance running or speed, agility and quickness (SAQ) drills. Research demonstrates that using an overload during sprinting or speed drills requires lower-body muscles to generate more force against the ground which could lead to gains in strength and power and ultimately faster acceleration during running. Weight vests are used by athletes to increase strength and efficiency during speed, power and agility drills; producing a unique training effect that is unavailable with traditional free weight training equipment. They can also be used by casual walkers or runners.