Impact of frequency and intensity of exercise on health

SOME of the commonest questions posed to physicians pertain to the potential benefits, frequency and intensity of physical exercises. The release of the 2018 Physical Activity Guidelines (PAG) for Americans issued by the US Department of Health and Human Services provides useful advice and is based on an extensive review of the latest evidence from available published research.

Benefits of exercise

The benefits of physical exercise are derived mainly from the impact of exercise on risk factors for heart disease and stroke and this includes the impact on blood pressure, blood sugar, blood lipids, and body weight. Exercise has a positive effect on these risk factors including reducing blood pressure, reducing the incidence of high blood pressure and Type 2 diabetes mellitus, and improving the lipid profile. The net effect translates into decreased incidence of heart disease, heart failure, stroke and reduction in death from heart disease and strokes. In addition, not only does exercise result in weight loss but it can also prevent or reduce weight regain after weight loss.

Quantity of exercise

It is obvious that total inactivity is worse than some activity and as a rule of thumb, the more active you are, the better it is. The question on many people's minds is how much should one exercise to start reaping tangible health benefits. The PAG recommends that adults should do at least 150 to 300 minutes of moderate-intensity exercise a week, or 75 to 150 minutes of vigorous-intensity aerobic physical activity a week, or an equivalent combination of aerobic activity.

Instead of calculating your heart rate to determine your exercise intensity, you can use a simple talk test which is both simple and practical. If your exercise is of moderate intensity, you should be able to talk but not sing. If your exercise intensity is vigorous, you will need to pause for a breath for every few words you speak.

If you are a regular couch potato with sheer inertia, you may be motivated in knowing that you can start improving your health and get better outcomes even if your exercise is below the recommended threshold of 150 minutes a week for most outcomes. You will also be encouraged to know that the largest health benefit is seen in those inactive couch potatoes who have transitioned into being more physically active. Beyond considering the duration of exercise a week, it is preferable that the exercise activity be divided into a few sessions within the week rather than achieving the desired quantity of exercise within one session.

So, if you are really into exercise and want to know whether there are additional benefits if you exceed the PAG recommendation, you will be pleased to know that exceeding the recommendation does confer additional benefits without apparent health risk, even if you ramp up the exercise to five times the recommended 150 minutes a week.

Just in case you think that exercise means pounding the roads with your running shoes or attempting a marathon, you will be delighted to know that any amount of physical activity counts towards that weekly total.

It could mean walking in the mall, taking a walk in the park or climbing up the stairs, and all these minutes of activity can count towards your weekly total. In addition to aerobic activities, performing exercises to strengthen all major muscle groups at least twice a week can provide additional health benefits.

Heart and brain

When compared to sedentary couch potatoes, meeting the PAG recommendations is associated with a 14 per cent reduction in the risk of developing heart artery disease and a 40 per cent reduction in death resulting from stroke and heart attacks.

Those who meet or exceed the PAG recommendations will also have a reduction from all-cause mortality. Currently, research has not identified an upper limit of activity, beyond which there are no more health benefits.

Exercise has a beneficial impact on blood pressure. It results in lowering of blood pressure in those with normal blood pressure and even more so for those who are considered prehypertension. Prehypertension refers to blood pressure readings with a systolic pressure from 120 to 139 mm Hg or a diastolic pressure from 80 to 89 mm Hg.

For those with normal blood pressure or prehypertension, the blood pressure reductions associated with regular exercise can reduce the risk of heart artery disease by 4 to 5 per cent and stroke by 6 to 8 per cent.

Another important health benefit of exercise is the reduction in the risk of developing Type 2 diabetes mellitus and this benefit is observed irrespective of body weight. Meeting the PAG thresholds can reduce the risk of developing Type 2 diabetes mellitus by 25 to 35 per cent.

This may be important for Asians where the pancreas is less able to produce insulin as a result of dysfunction of the insulin-producing beta cells in the pancreas. In addition, Asians have more visceral fat than their Western counterparts. As exercise can burn sugar and decrease body fat, the benefits of exercise in reducing Type 2 diabetes mellitus risk may be even greater in Asians.

Beyond the heart, the Advisory Committee also examined the potential benefits of exercise on brain health. The current evidence showed that the immediate benefit of exercise was a reduction in anxiety and an improvement in cognition.

In addition, physical activity over the long term was associated with a reduction in the risk of dementia, reduction in the risk of depression, and an improvement in the quality of life.

Look before you leap

There are a few important points to remember when you embark on exercise. You must be well hydrated before, during and after exercise wherever possible. Those who exercise and are dehydrated can develop blood clots in the heart arteries resulting in heart attacks, including those doing less strenuous exercises such as golf. Those who exercise in hot weather should be cognisant of the dangers of heat stroke which can be potentially fatal. Adequate hydration is essential in preventing these complications.

Any form of physical activity is better than inactivity and hence you should embark on exercise that is appropriate for your age and physical condition. Walking, swimming and cycling are common types of physical activity that do not generally cause injuries to the body when performed in a non-competitive environment.

For the elderly, they should avoid any form of physical exercise that will increase their risk of falls. Before deciding on your choice of exercise, it will be useful to understand the impact of the activity on your body. Certain sports are associated with certain types of injuries, for example, degeneration of the spine is often seen in avid golfers; knee and ankle injuries are common in footballers.

Finally, for all the couch potatoes out there, do not feel daunted about changing your sedentary lifestyle into a physically active one. Your heath benefits start when you walk out of your house to the garden, to the mall, to the market or to the food centre. Get started and improve the duration of your physical activity gradually. Last but not least, for the super-zealous exercise fanatic, hydrate yourself and take precautions to avoid injuries.

This series is produced on alternate Saturdays in collaboration with Singapore Heart, Stroke & Cancer Centre.