Despite the stereotype of a weight lifter – muscle-bound, hefting and grunting, big but weak – weight training can be used by everyone, not just those interested in becoming body builders. Paired with regular aerobic exercise, weight training increases your strength and muscle endurance as well as your overall feeling of fitness in ways that no other single exercise can. Bicycling develops one set of muscles, basketball another, but weight training works out a whole range of muscles in a very short amount of time.
Specific weight-training routines can be used to help you develop particular muscle groups that will improve your performance in your chosen sport. True enough, nothing improves your tennis games as much as playing tennis: specificity is the iron rule of modern sports training. Nonetheless, upper-body training will give you an extra edge in tennis, and developing your leg muscles will improve your swimming kick.