Marathon running performance among men and women is generally fastest, as indicated by world record performances, when individuals are 25-35 years old. The time to complete a marathon gradually increases with age, with substantial losses in performance after the age of 70 years. A decline in cardiovascular capacity of 0.5% per decade occurs in highly trained distance runners, while a 1.0% and 1.5% decline per decade occurs in moderately trained and untrained individuals, respectively. In middle-aged veteran runners, skeletal muscle continues to have high aerobic potential, while a decline in muscle cell size and contractile performance are apparent. These changes in the skeletal muscle profile may contribute to distance running performance with age. The changes in physiological function and running performance with age are closely related to the level of distance run training. Current research supports the concept that continued running late into life attenuates a decline in physiological function with age and is beneficial for overall health.