Almost all people should do some form of strength training as they age. Aging causes loss of muscles which increases your risk for metabolic syndrome, diabetes, obesity, heart attacks and premature death (Sports Medicine, May 2010). Contracting muscles remove sugar from the bloodstream to prevent high blood sugar levels which damage every cell in your body.
The authors reviewed the world's literature and found 13 placebo-controlled studies of the effect of lifting weights on health in later life. Weight lifting reduced HbA1c (a measure of cell damage caused by sugar stuck on cells), body fat, and systolic blood pressure. It did not affect diastolic blood pressure, triglycerides, HDL, LDL or total cholesterol.
The only way you can enlarge muscles is to exercise them against progressive resistance. However, a recent report explains why middle-aged people are at such high risk for injury when they start a weightlifting program (American Journal of Lifestyle Medicine, May 2010). To enlarge muscles, you have to lift weights heavy enough to cause pain while you lift. This damages muscle fibers. Your immunity responds to this cell damage as it responds to an infection: with pain, swelling, and increases in white blood cells, cytokines and blood flow. You usually recover within hours or days. However, if you repeat a heavy workout before you recover from the previous one, it takes longer to recover and the tissue weakens, rather than being given time to heal and become stronger. You develop a condition called inflammation in which your immunity stays active all the time and attacks your own body (in the same way that it attacks invading germs) to prevent healing. Older people have exaggerated changes of inflammation in their muscles (American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, April 2010). If you continue to take stress and recover workouts over many months and years, your muscles become stronger and heal faster so you can lift heavier weights to grow larger muscles.
If you are a middle-aged person who wants to start a weight lifting program to gain the incredible health benefits of being stronger and having larger muscles, and at the same time, avoid the extremely high rate of injury in older weight lifters, you should avoid lifting heavy weights when your muscles feel sore and are still damaged from your previous intense workout. Check with your doctor to see if you have any condition that could be aggravated by lifting weights.
The first rule is that beginners should lift light for several months before they try to lift heavy. Join a gym and use 10 to 20 machines every day. Pick the heaviest weight that you can lift 10 times in a row comfortably without hurting, and do this every day. If you feel sore, take a day or more off. As it becomes easier to lift a weight, increase the repetitions until you can lift that weight 25 times in a row without discomfort.
After you have followed this program for several months, you are probably ready to lift heavier weights that cause pain while you lift them. Unfortunately, the correct way to grow muscles also puts you at increased risk for injuring yourself. Pain is necessary for the muscle damage to grow larger and stronger muscles. I recommend getting special instruction on how to perform multiple sets that hurt, using proper form to minimize the risk of injury. Many lifters pick the heaviest weight that they can lift 10 times in a row, do three sets of 10 and feel very sore in their last set. After an intense workout, you should not lift heavy again until the soreness goes away. More