Researchers say that you should be able to maintain your muscles as you age, including the muscle enzymes needed for good athletic performance, and you should be able to maintain your ability to exercise for long periods near your so-called lactic threshold, meaning you are near maximum effort. But you have to know how to train, doing the right sort of exercise, and you must keep it up. "Train hard and train often," said Hirofumi Tanaka, a 41-year-old soccer player and exercise physiologist at the University of Texas. Dr. Tanaka said he means doing things like regular interval training, repeatedly going all out, easing up, then going all out again. These workouts train your body to increase its oxygen consumption by allowing you to maintain an intense effort. "One of the major determinants of endurance performance is oxygen consumption," Dr. Tanaka said. "You have to make training as intense as you can."
The New York Times
Staying a Step Ahead of Aging