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.

Basic Principles of Weight Training
The basic principle of any sort of muscle development is that of overload: contracting a muscle group against added resistance. The way a muscle grows is by splitting, longitudinally, under the strain placed on it, and "healing" after the workout by adding protein. Over a period of time, the overload placed on the muscles is increased a step at a time, and so the muscles continue to develop.

The three modes of exercise for developing muscles are isometric, isotonic, and isokinetic. In isometric exercises, you contract a muscle group without moving the joint to which the muscles are attached - for instance, pushing steadily against an immovable wall. These exercises build muscle, but the gain occurs mainly at the angle at which the muscle is exercises. Isotonic exercises, by contrast, contract a muscle through a range of motion - as you can do with movable weights. The virtue of isotonic exercises is that they build muscle through this full range of isometric exercises. Isokinetic exercises also consist of contracting a muscle through a range of movement. But isokinetic exercises, which are performed on machines, use equipment designed to apply maximum stress to the muscles through the whole range of movement.

Isotonic exercises use both free weights and machines. Free weights are barbells and dumbbells - ordinarily used in pairs, one in each hand. The advantage of free weights is that they allow movement in any direction and so lend themselves to an enormous variety of exercise routines; and they are relatively inexpensive. Their disadvantage is that they do not isolate muscles as clearly as machines do; and the stress that they provide is not nearly as uniform over the full range of motion as that provided by some machines.

Machines can isolate muscle groups very efficiently by maintaining your body in a particular position and by making you move a weight along a predetermined path. And isokinetic machines are also designed to provide variable resistance through the full range of motion, so that as you move a limb, the resistance stays at or close to maximum.

Weight training tips
A typical workout with weights includes a warm-up of five to ten minutes followed by an exercise routine that leaves the muscles thoroughly exhausted. Your exact exercise routine should be formulate with an exercise specialist in a gym, who will tell you just how to position yourself, how to lift so as to prevent strain or injury, which weights or machines to use, and how many repetitions and sets to do. If you continue to work out with a trainer or a friend, he or she will keep your routines interesting, give you emotional support, and help see to it, through proper "spotting" techniques, that you do not injure yourself.

A good exercise routine for overall fitness will work out different parts of the body. It will consist of about a dozen exercises - six for the upper body, six for the lower body. Above all, it will be scheduled so that you give each muscle a full day's rest before you exercise it again. If you exercise the same muscle two days in a row, it won't recuperate; it will become weaker, not stronger. Therefore, you should either exercise different muscles on successive days (upper body on day, lower body the next, for example) or space workouts at least two days apart.

Also, remember to exercise the "large" muscles before the smaller ones. For example, if you are weight training both the upper and lower muscles on the same day, start with the leg muscles.