Exercise: How much is enough?
The benefits of regular exercise to reduce the future risk of heart problems are well documented and apply to both those with documented heart disease and those without documented disease but at risk for future heart problems:
- For patients with heart disease who engage in regular, aerobic exercise there is approximately a 25% reduction in mortality over a 1鈥? year time period.
- For individuals who are regularly active and who do not have documented heart disease there is a 50% reduction in risk of death from a heart attack.
Most authorities agree that aerobic exercise (rhythmical activity employing large muscle groups鈥?i.e. walking, cycling, swimming, dancing) performed at least 3 times per week (and preferably on most days of the week) at a moderate intensity is necessary to gain a cardioprotective benefit. The amount of exercise at each session necessary to protect the heart has been less well understood.
Recommendations have been for at least 30 minutes of exercise per session but guidelines for up to 60 minutes of exercise per day have also been recommended. It has been unclear whether the exercise has to be completed all in one session or if it can be split over multiple sessions during the day.
A recent study from Harvard University, looking at self-reported activity patterns of a large group of university alumni revealed that a significant cardiovascular risk reduction was realized if over 1000 kcal were spent doing vigorous activity per week. Vigorous activity was defined as walking at speeds faster than 3.5 mph or participation in vigorous sport or recreational activities.
In a similar study, the intensity of the activity was not as critical as the total number of calories spent in activity/week. The researchers showed a dose response benefit associated with activities of walking, stair climbing and participation in sports and recreational activities. The more calories spent in exercise per week the greater the benefit with those spending >4200 kcal/week at the lowest risk for developing heart disease. This study also revealed that there was no added benefit from performing all the exercise in one session. Multiple sessions/day of at least 15 minutes/session imparted the same benefit as one longer session.
The key issue was the total number of calories expended in exercise/week and the benefit of exercise continued even if other risk factors were present.
These studies again support the benefit of regular exercise in reducing the risk of developing coronary artery disease. The total number of calories spent on activity per week appears to be a key factor, providing flexibility in the intensity and individual exercise session duration. The trade off is one of time efficiency. For vigorous aerobic activity an expenditure of approximately 1000 Kcal/week (equivalent to at least 2 miles of brisk walking 5 days per week or 3.5 miles of brisk walking 3 days per week) is required. However, the exercise can be broken up into several smaller sessions of at least 15 minutes each throughout the day, without losing the cardioprotective benefit.
The total number of calories per week spent on exercise is the key
For those with greater time to devote to exercise, less vigorous activity also imparts a cardioprotective effect with the greatest benefit being realized if over 4200 Kcal/week are spent doing even moderate intensity aerobic activity.
