Strength training is the use of resistance to muscular contraction to build the strength, endurance, and size of  muscles. There are many different methods of strength training, the most common being the use of gravity or elastic/hydraulic forces to oppose muscle contraction. When properly performed, strength training can provide significant functional benefits and improvement in overall health and well-being, including increased bone, muscle, tendon and ligament strength and toughness, improved joint function, reduction in injury, increased bone density, an increase in metabolism, improved cardiac function, and elevated HDL (good) cholesterol. Training commonly uses the technique of progressively increasing the force output of the muscle through incremental increases of weight, elastic tension or other resistance, and uses a variety of exercises and types of equipment to target specific muscle groups. Strength training is primarily an anaerobic activity, although some have adapted it to provide the benefits of aerobic exercise through circuit training.

You do not need to be a bodybuilder to benefit from strength training. A well-designed strength-training program can provide the following benefits:

• Increased strength of bones, muscles and connective tissues (the tendons and ligaments)—This increased strength decreases the risk of injury.
• Increased muscle mass—Most adults lose about one-half pound of muscle per year after the age of 25, largely due to decreased activity. Muscle tissue is partly responsible for the number of calories burned at rest (the basal metabolic rate, or BMR). As muscle mass increases, BMR increases, making it easier to maintain a healthy body weight.
• Enhanced quality of life—As general strength increases, the performance of daily routines (carrying groceries, working in the garden) will be less taxing.

The Core Curriculum

Many exercises can be combined into a program that works all the major muscle groups. Neglecting certain groups can lead to strength imbalances and postural difficulties. A certified fitness professional can help you develop a safe, effective program.

You may also wish to consult with a certified fitness professional to learn safe technique before beginning a strength-training program. One set of eight to 12 repetitions, working the muscles to the point of fatigue, is usually sufficient. Breathe normally throughout the exercise. Lower the resistance with a slow, controlled cadence throughout the full range of motion. Lifting the weight to a count of 2 and lowering it to a count of 3 or 4 is effective.

When you are able to perform 12 repetitions of an exercise correctly (without cheating), increase the amount of resistance by 5 to 10% to continue making safe progress.

Staying Motivated

An encouraging aspect of strength training is the fact that you’ll likely experience rapid improvements in strength and muscle tone right from the start of your program.  To help keep your motivation up, find a partner to train with you.

Aim to exercise each muscle group at least two times per week, with a minimum of two days of rest between workouts.

Vary Your Program

Machines and free weights are effective tools for strength training, and a combination of the two is generally recommended. Utilizing both machines and free weights provides exercise variety, which is important for both psychological and physiological reasons. Variety not only reduces boredom, but also provides subtle exercise differences that will enhance progress.
The benefits of strength training are no longer in question. Research continues to demonstrate that strength training increases both muscle and bone strength and reduces the risk of osteoporosis. A safe strength-training program combined with cardiovascular and flexibility training will give you the benefits of a total fitness program.

Bibliography

http://www.acefitness.org/fitfacts/fitfacts_display.aspx?itemid=2661