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This is an excerpt from Practical Guide to Exercise Physiology-2nd Edition by Robert Murray & W. Larry Kenney.
Older women and men respond to training similarly to younger people, increasing performance capacity along with physiological and metabolic function. For that reason, it is not unusual for 60-year-old athletes to have performance capacities that are greater than the capacities in people half their age. The ability to maintain impressive performance capacities occurs despite the fact that maximum cardiac output declines with age because both maximum heart rate and maximum stroke volume fall with age, as does blood flow to the arms and legs.
One of the challenges in establishing the effects of aging on physical fitness and performance is that it is difficult for scientists to separate the effects of aging from the effects of decades of relative inactivity in sedentary individuals. The same complication is true with older adults who have remained active but have reduced training intensity and duration over the years. Regardless, the good news is that proper training clearly improves all facets of physical capacity, including muscle mass, strength, endurance, aerobic capacity, agility, balance, coordination, flexibility, and anaerobic capacity.
After age 60, the failure rate for opening the lid on a jar rises substantially. Loss of strength and muscle mass are due to decreased anabolic signaling, increased muscle catabolism, reduced physical activity, and inadequate protein intake.
The Strong Live Long
After age 40, sedentary individuals lose an average of 1% of their muscle mass each year (a range of 0.5-1.2% per year) along with a loss in strength that averages 3% per year. This loss of muscle mass is not unusual; all mammals experience something similar as they age. But when the loss of muscle mass and strength become so severe that muscular weakness interferes with the activities of daily living, there is a substantial negative impact on health care, living conditions, illnesses, and injuries. The severe loss of muscle mass and functional strength associated with aging and a sedentary lifestyle is called sarcopenia, a word coined in 1988 that means “poverty of flesh” in Greek. Sarcopenia occurs as a result of the loss of motoneurons and their associated motor units, combined with an increase in muscle protein breakdown and a decrease in muscle protein synthesis, leading to gradual decline in muscle mass and strength.
Performance Nutrition Spotlight
In addition to helping support muscle strength and mass in older adults, diets higher in protein (e.g., 1 g of protein per lb of body weight per day [0.5 g per kg BW per day] ) are associated with greater weight loss, more fat loss, and better protection of lean body mass.
Protein synthesis in the muscle cells in older adults is less sensitive to dietary protein intake and to the normal stimulation of exercise. This anabolic resistance is one characteristic of aging muscle that predisposes many older adults to sarcopenia. Dynapenia is the term that refers to inordinate muscular weakness. Fortunately, regular training and physical activity in general can substantially reduce the rate at which muscle mass, strength, and neuromuscular function are lost, even in very old adults (e.g., >90 years of age).
Figure 12.2 shows a striking example of the effect of strength training on muscle mass in later middle age. Strength training can also slow the loss of type II muscle fibers, and physical activity that incorporates weight-bearing exercises such as running and jumping (impact exercise) helps slow bone loss. Reducing the loss of muscular strength, muscle mass, and bone mass during aging is critical in maintaining the ability to live independently, decreasing the incidence of accidental falls, promoting more rapid recovery from injury and illness, and improving the overall quality of life.