For best results, aim for 30 minutes of aerobic exercise, three to four times a week. Aerobic activity improves the efficiency of your heart and lungs, helps control weight, and increases muscle and joint flexibility. Over time, your heart and breathing rates will decrease, during the same amount of effort. Circulation often improves, too. Anaerobic exercises are short-term, and emphasize building muscle, rather than burning oxygen.
Anaerobic exercise can also increase bone mass.
An ideal exercise program will feature both aerobic and anaerobic activities. If you're over 35, or have had any medical problems, consult your doctor before starting an exercise routine. He or she can advise on the activities and frequency that might work best for you.