By: Dr. Daniel B. Judd
As many residents in the Wood River Valley illustrate, a significant deterioration of physical function is not an inevitable consequence of aging. While aging is associated with a predicable decline in the function of the musculo-skeletal system, the majority of age-related changes can be significantly slowed by regular physical activity. A recent U.S. surgeon general's report from the CDC cites numerous studies showing that regular physical activity, in addition to its positive effects on bone, muscle and joint tissue, reduces the mortality from cardiovascular disease, stroke, hypertension, diabetes and some forms of cancer.
Changes to the musculo-skeletal system
The exact mechanism of age-related muscle loss is quite complex and not totally understood, but a reduction in the nerve fibers from the spinal cord to the muscle tissue likely plays a role in the decrease of muscle mass that occurs in older people. This loss is different from the muscle atrophy that occurs with disuse, but both can occur simultaneously, and result in substantial muscle loss per year in older, sedentary people.
Additionally, changes in the biologic matrix of collagen results in progressive stiffening of tendon, muscle and joint tissue. This diminished flexibility increases one's susceptibility to injury.
However, people can decrease the rate of decline of the above changes. Specifically, muscle adapts to physical training by increases in size, blood flow and efficiency of oxygen use. In one study, men and women over 60 who did aerobic endurance exercises for 45 minutes four times a week for an average of 10 months experienced a 55 percent increase in muscle-energy-producing enzymes and a 23 percent increase in muscles' capacity to consume oxygen. Regular endurance exercise can reduce the rate of decline in cardiovascular function by 50 percent.
Resistance training is also an important and effective means to preserve muscle function. A number of investigations have revealed a 100 to 150 percent increase in strength after only three months of resistance training. The ability of master athletes to maintain high levels of performance demonstrates how successfully physical activity can retard the age-related changes. For example, the world record time for the 400 meter run is 43.18 seconds, held by Michael Johnson; world record times are about 50 seconds for 40-year-olds and are under 60 seconds until the early 70s.
What exercise program?
Your exercise program depends on your goals—obtaining better cardiovascular fitness and reduced disease risk or becoming a better athlete. To receive the health benefits of exercise, decreased risk of stroke, cardiovascular disease, diabetes, etc., the activity requirements can actually be quite minimal—three to five times a week for 20-60 minutes with an intensity of 60 to 90 percent of your maximum heart rate.
To help get the desired results, three components of a fitness program should be considered: endurance, resistance and flexibility. Of course, the response to physical activity is proportional to the quantity, quality and intensity put into it. Whole-body exercises that activate large muscle groups, such as walking, hiking and cross-country skiing, can all accomplish the goal of cardiovascular fitness and disease risk reduction.
Resistance training implies the concept of muscle overload, i.e. subjecting the body to a greater load than it usually encounters. This controlled overload initiates the desired muscle physiologic response. Resistance training is generally safe and very effective in people of all ages. Increase in muscle size and strength can be obtained by exercising major muscle groups two to three times a week. Flexibility should be incorporated into any fitness program. Regular stretching restores flexibility to muscles and joints, reducing the risk of injury.
It's worthwhile to check with your doctor if you have any medical conditions that may make exercise dangerous for you, especially a history of heart disease.
Lastly, time spent with a physical therapist or personal trainer can be valuable in optimizing your time, and help design an exercise regimen tailored to safely reach your fitness goals.
Dr. Daniel B. Judd works at St. Luke's Sun Valley Sports Medicine.