Many studies show that people die from inactivity, not just from aging. We know that as people age, they lose muscle, their immunities weaken and because of their weakened immunity, they are more likely to die of cancer and infectious diseases. As you age, you lose your ability to kill germs because of lack of muscle. When germs get into your body, you must make white blood cells and proteins called antibodies to kill them.
 
Antibodies and cells are made from protein and the only place that you can store extra protein is in your muscles. When you have large muscles, you have a ready source of protein to make antibodies and cells. When you have small muscles, you have a very limited source of amino acids to make protein, so your immunity may be inadequate to kill germs.
 
You need antibodies to control cancer cells also. Each day, every healthy body makes millions of cancer cells. Your white blood cells and protein antibodies are necessary to ferret out and kill these cancer cells. You develop cancer when these cancer cells survive and start growing. Having large muscles gives you the source of protein to make antibodies that kill cancer cells as well as germs. Furthermore, when your skeletal muscles are small, so is your heart muscle. A strong heart can withstand arteriosclerosis and infections that can kill a weak heart.
 
Lack of exercise causes muscles to get smaller. With aging, it takes increasingly longer to recover from exercise. When older people get injured or get tired too soon or feel sore too early, they do less and less or they stop exercising altogether. Instead, they should be exercising more intelligently so they can retain their muscles.
A major advantage of competing in sports at any age is that you can learn good training techniques and how to avoid injuries. If you can exercise into your nineties and beyond without quitting or getting injured, you can retain muscle mass, keep up your immunity and live longer and healthier.