You can gain different benefits from aerobic exercise, ranging from general health improvement and disease prevention to cardiovascular fitness and weight loss.
The bottom line: If you want to achieve weight loss or serious heart health through aerobic exercise alone, it will require more work than the official recommendations tell you.
There are three rungs to healthy activity, each demanding more sustain-ed activity: maintaining your health; losing weight; and achieving true cardiovascular fitness.
For the first rung, maintaining health and preventing illness, follow the government's minimum advice. If you are sedentary, this means 30 minutesa day of moderately intense exercise to change key metabolic factors such as your body-fat distribution and insulin sensitivity (Arch Intern Med, 2004; 164: 31-9; N Engl J Med, 1991; 325: 147-52).
This level of workout is associated with a substantial decrease in your risk of chronic disease-or even death. As a spokesperson from The Cooper Insti-tute succinctly put it: "[This recom-mendation] is all about good old-fashioned health maintenance. It's about having a heart attack or no heart attack, alive or dead."
Moderate activity means that the exercise is non-competitive, builds gradually and can be sustained for a prolonged period of time with no discomfort. A more specific way to measure the intensity of an exercise is to grade each activity in MET units, where 1 MET is the amount of energy burned while sitting quietly at rest (equal to 1.2 kcal/kg/hour).
However, it appears that exercise duration is more important than its intensity. In a study of 133 overweight sedentary men and women, those who walked briskly for 12 miles each week (or for about 125-200 minutes a week) showed significant improvement in aerobic fitness as well as a lowered risk of heart disease. More important, they showed similar signs of fitness as those who jogged 12 miles every week (Chest, 2005; 128: 2788-93).
The key is to get up and get moving, and to make doing so a regular priority, part of your daily routine. Another secret for success is to keep changing your activity so that your body doesn't adapt to the exercise. You don't haveto do structured exercises in the gym-ordinary day-to-day activities such as housework or gardening can be equally effective.
The duration of your chosen moder-ately intense activity can also be broken up into three 10-minute-or two 15-minute-sessions, to the same effect. Trials have shown that shorter, cumulative bouts of walking are as effective as one long bout for increasing aerobic power, improving body composition, reducing cardio-vascular risk and raising your mood (Scand J Med Sci Sports, 2002; 12: 99-105).
However, for some people, the lowest rung of physical activity won't be enough. In a study of 742 out-of-shape people who underwent a 20-week stationary-bicycle endurance-training programme, some people simply did not respond. During the final six weeks, the subjects exercised for 50 minutes three times a week at 75 per cent of the maximum output they could sustain before the study. Although training improved oxygen consumption, some subjects showed no improvement at all.
Similar results were seen for cardiac output, blood pressure, heart rate and insulin sensitivity, suggesting that exercise alone doesn't offer health benefits without dietary changes as well (New Scientist, 2004; 4 December).
Kim Wallace and Tina Tan
It's common knowledge that aerobic exercise is good for your heart, but did you know that it can prevent other chronic diseases as well? Being physically active on a regular basis reduces your chances of falling victim to common, niggling ailments. One study found that employees who took no exercise had more days of illness-related absenteeism compared with those who were physically active (J Occup Environ Med, 2001; 43: 1019-25).
The most basic daily exercise can add a few years to your life expectancy and reduce your risk of a raft of diseases, including:
-Type 2 diabetes: people who exercise cut their risk of developing this form of diabetes by up to half (JAMA, 1992; 268: 63-7)
-Cancer: those averse to regular exercise are more susceptible to certain types of cancer, including of the colon, breast, uterus, prostate and testicles (Crit Rev Oncog, 1997; 8: 219-72)
-Coronary heart disease (CHD): sedentary people almost double their risk of dying from CHD compared with more active people (Am J Epidemiol, 1990; 132: 612-28)
-Stroke: Active or fit people have a 27-per-cent lower risk of stroke or death compared with those who are sedentary or unfit (Stroke, 2003; 34: 2475-81).