Written with Dr. Gordon Blackburn Preventive Cardiology and Rehabilitation Program
We now have more proof that exercise is good for you and your heart.
In the Sept. 18, 2001, issue of Circulation 1, the respected medical journal, researchers reported results of a study on the effects of exercise on heart health. They examined five, now middle-aged men – the same men who were subjects of a similar study in 1966. In the 1966 study, known as the Dallas Bed Rest and Training Study, the then 20-year-olds spent 20 days on total bed rest. Their cardiovascular fitness was then compared to their levels before going to bed. As expected, their heart health declined significantly. Then the men underwent an eight-week cardiovascular fitness program, and all regained and surpassed their original level of fitness.
One of the important conclusions the researchers drew 30 years ago was that prolonged periods of inactivity and bed rest, as seen with illness or following surgery, cause dramatic decreases in cardiovascular fitness (about 1% loss of capacity/day of bed rest). However, these losses can be regained if appropriate exercise is initiated soon after recovery for the illness or surgery.
In the present study, the same investigators located the five men and again assessed their cardiovascular fitness. Each had declined in their "aerobic power," or cardiovascular capacity (the ability of the heart to pump blood to meet the body's needs), as is expected to some degree with age. The authors concluded that 3 weeks of bedrest in these same men at 20 years of age (1966) had a more profound impact on physical work capacity than did 3 decades of aging 2.
The men then were prescribed a six-month, structured, endurance training program. They walked, jogged or rode a stationary bicycle, gradually increasing the intensity of their workout. By the end of the six months, they were exercising four or five times a week for a total of about 4-1/2 hours. The men wore wristwatch-type heart-rate monitors to help them adjust their exercise intensity to reach prescribed target heart rates. Researchers used information from these monitors to evaluate their progress.
After measuring and analyzing a number of parameters that indicate aerobic power, the researchers concluded:
"One hundred percent of the age-related decline in aerobic power among these five middle-aged men occurring over 30 years was reversed by a six-month endurance training program." 1
The men did not achieve the same level of aerobic power they had attained at age 20, however, the researchers noted. But they lost an average of about nine pounds and lowered their blood pressure from an average of 140/88 mmHg to 132/84 mmHg. Their average maximal heart rate (measured after treadmill exercise testing) dropped from 181 to 171 beats per minute.
The authors acknowledge that this is a small study of only five middle-aged men. The trial did not include women or use a "control group" so that the effects of lifestyle, nutrition, illnesses and genetic differences on cardiovascular response could be understood. As a result, the study has limitations and its conclusions cannot be generalized definitively to larger or different populations.
Despite its limitations, this study provides added evidence that physical activity improves functional capacity at all ages of life and is beneficial in managing a variety of cardiovascular risk factors, says Dr. Blackburn. The study also underscores the importance of appropriate levels of regular exercise, such as offered in cardiac rehabilitation programs, for patients who have had heart procedures. It is never too late to get up and at 'em!
- McGuire DK, Levine BD, Williamson JW, et al. A 30-Year Follow-Up of the Dallas Bed Rest and Training Study II. Effect of Age on Cardiovascular Adaptation to Exercise Training, Circulation 2001 Sep 18:104(12):1358.
- McGuire DK, Levine BD, Williamson JW, et al. A 30-Year Follow-Up of the Dallas Bed Rest and Training Study I. Effect of Age on the Cardiovascular Response to Exercise, Circulation 2001 Sep 18:104(12):1350.