Weight training, other wise known as resistance training is a form of exercise used to develop strength and size of skeletal muscles. Any type of external load or form of resistance in which a muscle must develop force against can produce hypertrophy, or growth in that muscle. Presently, this style of fitness training is used in every sport and at every level of competition. Properly performed, weight training can provide significant functional benefits and improvement in overall health and well-being. Weight training has been known to be paramount for patients needing to increase lean body mass as well as for patients that suffer from Osteoperosis and Osteoarthritis. One common training method involves lifting progressively increasing amounts of weight, and uses a variety of exercises machines to target specific muscle groups. Other styles of training involve equipment that can focus on multiple muscle groups simultaneously. Resistance can be provided by iron plates, rubber, air, or water. Weight training is primarily an anaerobic activity, although some proponents (circuit training) have adapted its methods to provide the benefits of aerobic exercise. Many different strategies exist in the weight training arena regarding Sets & Reps and these choices should be goal oriented and supported by sound research. Weight training differs from bodybuilding, weightlifting, or power-lifting, which are sports rather then forms of exercise.