As you age, you lose muscle size and strength much faster than you lose endurance or coordination. Researchers at the University of Nottingham in England show that a major cause of loss of muscle is that aging prevents muscles from responding to insulin and that exercising helps to slow this loss of muscle size and strength ( The American Journal of Clinical Nutrition, September 2009).
Insulin drives amino acids into muscles to help them recover from exercise and maintain their size. Researchers traced radioactive amino acids and showed that insulin drives the amino acids into muscles much more effectively in 25-year-olds than in 60-year-olds. They also showed that the blood flow in younger people's legs is much greater and supplies far more nutrients and hormones. However, three exercise sessions per week over 20 weeks markedly increased blood flow in the legs of the older subjects, enough to reverse muscle wasting.
People of all ages can use this information to help themselves become stronger. Athletes in all sports train by stressing and recovering. They take a hard workout, damage their muscles, feel sore the next morning, and then take easy workouts until the muscles heal and the soreness goes away. The athlete who can recover the fastest can do the most intense workouts and gain the most strength.
Eating a high carbohydrate-high protein meal within half an hour after finishing a workout raises insulin levels, increases amino acid absorption into muscle and hastens recovery ( Journal of Applied Physiology, May 2009). The carbohydrates cause a high rise in blood sugar that causes the pancreas to release insulin. Insulin drives the protein building blocks (amino acids) in the meal into muscle cells to hasten healing from intense workouts. Muscles are extraordinarily sensitive to insulin during exercise and for up to a half hour after finishing exercise, so the fastest way to recover is to eat protein- and carbohydrate-rich foods during the last part of your workout or within half an hour after you finish.
Here's how Diana and I (ages 67 and 74) use this information on insulin sensitivity. We ride hard and fast for about 20 miles on Tuesdays, Thursdays and Saturdays. On our recovery days, we ride slowly for one to three hours. Mid-day we go to a buffet restaurant and eat a large meal with fish, shrimp, vegetables and other sources of protein and carbohydrates. After eating, we ride slowly for one or two more hours. Riding before we eat makes our muscles very sensitive to insulin. This causes insulin to drive amino acids rapidly into our muscles and help them recover faster. Riding after we eat helps us to avoid a high rise in blood sugar that damages cells. You can use either plant or animal sources of protein; both contain all of the essential amino acids necessary for cell growth. More on principles of training