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. Weight vests are becoming a very popular form of adding weight around the entire core to, for the most part, simulate the fat storage areas of the human body. It is very useful for adding weight to limb-centric movements, and for handling great weights. Due to the large area available, it can also handle more weight. If well-affixed, it is the safest most natural means of mimicking added body mass without unbalancing the body's muscles. They can be used to add resistance to almost any whole-body movement. A study has shown that using a weighted vest can increase the metabolic costs, relative exercise intensity, and loading of the skeletal system during walking. One problem with some weighted vests is that due to tightness in the shoulder girdle, in movements like pull-ups or high range of motion pushups, the vest can be shearing, either damaging the person or in some cases, the vest itself being slowly torn away. This can also be seen as an advantage, however, in those who wish to limit their range of motion due to lack of strength or flexibility, to avoid injury. The limitations of front and back bending of the core is for example, contrasted by ergonomic construction to encourage good posture in modern weighted vests such as the x-vest, hyper vest or game-breakers pro suit. Another problem with some weighted vests is the constriction of breathing and overheating due to the use of heavy, non-breathing materials such as nylon and neoprene. The latest developments in weighted vest products offer comfortable weight vests with cool wicking fabric that allow full range and direction of movement, chest expansion for breathing, open sides connected with lacing, and low profile design allowing a vest to be worn under clothing or football pads, unlike traditional vests made of nylon or neoprene. Backpacks Using weighted backpacks is a very common form of weight. It is like clothing when properly affixed, although some backpacks require tension in the pectorals or being held on the arms to keep from sliding off if not properly affixed. Simpler to put on and remove than weighted vests, it simulates how humans carry things, like young or injured comrades or camping supplies, rather than the storage