First you put good strain on your joints as well as your bones when you lift weights. This strengthens your bones. Strong bones protect our bodies against breakage and osteoporosis.
Another important point about weight lifting is that as your muscles increase in size your body becomes more shapely and firm - more attractive.
Weight lifting also helps you more vigorously perform your aerobic exercise, which in turn will increase your cardiovascular endurance and help your heart. The reason you are able to perform at a higher level is the weight lifting has increased your muscular strength, and therefore your ability to tolerate more intense exercise.
Weight lifting also gives you nice after effects to your metabolism. By adding muscle to your body through weight lifting, you likely will increase your metabolic rate. If you increase your metabolism you increase the amount of fat burning enzymes in your body. This means you'll burn more body fat even at rest! What a great bonus!
When you lift weights you should find the right weight that allows you to do 8-12 repetitions of the same movement with the same weight. If you are able to repeat it more than 12 times the weight is too light for you. If you can't do at least 8 reps the weight is too heavy.
This 8-12 repetition practice is called a set. A beginning weight lifter should only be doing one or two sets of any weight lifting movement at one time.
Beginners often forget to breathe when they lift weights, which is dangerous because it can elevate your blood pressure. You should concentrate on inhaling on the eccentric or lowering phase of the lift and exhale on the concentric or lifting phase of the lift.
When weight lifting, you should always work your largest muscles first. Smaller muscles get tired faster. If they tire too quickly they can't help you work your large muscles. The first things you are going to work are your chest, back, shoulders and thighs. Then you do weight lifting exercises for your arms, abdominals and calves last. If you're new to weight lifting, I would suggest picking 6-8 exercises that covers all the major body parts above. Perform these exercises 2-3 times per week making sure you allow at least 48 hours between workout sessions, so your body has time to recover.
