Exercise: Why, how, and what

EXERCISE buffs may be delighted to know that there is substantial evidence that higher levels of physical activity and fitness are associated with a lower incidence of death, a lower rate of cardiovascular disease, and a lower prevalence of several known malignancies. In real terms, these benefits from exercise may translate into a 20-30 per cent reduction in cardiovascular and all-cause death, compared to potato couches.

For healthy individuals, the latest 2020 European Society of Cardiology Guidelines recommend a minimum of 150 minutes of moderate intensity endurance exercise training over five days, or 75 minutes of vigorous exercise per week over three days.

For the sports aficionado, doubling the exercise duration - to 300 minutes of moderate intensity or 150 minutes of vigorous intensity aerobic physical activity per week - can result in incremental benefits.

Exercise and obesity

Current World Health Organization (WHO) and international guidelines recommend Body Mass Index (BMI) cut-offs of 25 and 30 kg/m2 to define overweight and obesity respectively. Based on studies conducted among Asian populations in China, Singapore, Pakistan and Taiwan, and taking into account body fat equivalence and the risk of co-existing medical disease, the adjusted BMIs of 23 and 27.5 kg/m2, for overweight and obesity respectively, have been recommended in Asians.

Studies have shown strong associations between obesity and the so called "obesity-related cancers" such as large intestine, gullet, kidney, and pancreatic cancer. In addition, for males, there is also an increased risk of thyroid cancer; and for females there is an increased risk of gall bladder, endometrial and post-menopausal breast cancer. Obesity is also related to an entire plethora of medical maladies including heart disease, diabetes, obstructive sleep apnoea and joint problems.

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Exercise recommendations for the obese: The guidelines recommend for obese individuals a 150 minutes per week of moderate intensity endurance exercise training combined with three weekly sessions of resistance exercise. In addition to reduction of intra-abdominal fat and increments in muscle and bone mass, the exercise programme can lead to a reduction in blood pressure, improve sugar tolerance, improve insulin sensitivity (reduce diabetic risk), and improve the lipid profile.

While exercise can reduce fat mass, without a dietary reduction of calorie intake, the impact of exercise alone on fat mass is modest. For obese individuals to achieve meaningful fat loss, an exercise regime of more than 225 minutes per week of high endurance-type exercise volume is required.

What to watch out for: Caution should be exercised in planning the programme as abrupt increases in training volume can result in musculoskeletal injuries. Hence, high-volume weight-bearing exercises on a hard surface should be gradually increased and should not exceed two hours per training session until significant weight loss has been achieved.

Exercise and blood pressure

European and Asian guidelines use a persistent systolic blood pressure (SBP) equal or more than 140 mmHg and/or diastolic blood pressure (DBP) equal or more than 90 mmHg as the cut-off points for high blood pressure.

The immediate consequence of exercise is a reduction in SBP which can persist for 24 hours. A regular sustained exercise programme over a long period results in more sustained reductions in blood pressure (BP).

Exercise recommendations for the hypertensive: Hypertension can increase the risk of stroke and heart disease. Hypertensives who walk, jog, cycle or swim at least for 30 minutes for five to seven days a week can look forward to a mean reduction in SBP of 7 mmHg and DBP of 5 mmHg. Resistance training is highly effective in reducing BP, and when included as part of the exercise programme two to three times a week, the BP can be further reduced.

What to watch out for: Do ensure that your resting SBP is less than 140 mm Hg before commencing on a regular exercise programme. For normotensives who have an exaggerated elevated SBP response of more than 200 mm Hg on a treadmill test, the risk of developing sustained hypertension is increased and a discussion with your doctor on the intensity of exercise in relation to BP response will be beneficial. Exercises that involve the Valsalva manoeuvre (breath holding during muscular contraction) is associated with BP elevation and should generally be avoided, and this includes intensive heavy weightlifting.

Exercise and lipids

Lipids comprise cholesterol and triglycerides. Highly elevated cholesterol levels are associated with clogging of the heart and brain arteries leading to increased risk of stroke and heart attacks.

Exercise has been shown to be able to lower triglycerides by up to 50 per cent and reduce the low-density lipoprotein (LDL) cholesterol or "bad" cholesterol by up to 5 per cent. In addition, it can cause the body to shift the more atherogenic small, dense LDL fraction (which are more likely to deposit in arterial vessel wall) towards larger LDL particles (which are less likely to clog arteries) in a dose-dependent correlation.

Exercise recommendations in hyperlipidaemia: To achieve the beneficial changes in the lipid profile described, a moderately vigorous exercise programme of 30-60 minutes on most days of the week is required. For those with high triglycerides or high cholesterol levels, increasing the intensity of the exercise will bring about further reductions in lipid levels and lower the cardiovascular risk.

What to watch out for: For severely hyperlipidaemic patients embarking on high intensity exercise, medical assessment and testing before commencement is advocated. Don't be disappointed to know that exercise alone is not going to reduce your cholesterol to optimal levels. This will invariably require dietary modifications and, often, the use of cholesterol-lowering therapy.

Exercise and diabetes mellitus

Diabetes is associated with many complications including stroke, heart attacks, amputations, nerve disorders, kidney failure and eye problems.

The risk of developing type 2 diabetes mellitus is 50-80 per cent higher in a physically inactive cohort as compared to a physically active one. Hence, exercise in pre-diabetics may prevent the development of full-blown diabetes. Studies seem to show that the intensity of exercise seems to be of greater importance than the amount of exercise. Hence, for a similar amount of energy expenditure, individuals who exercise at moderate or high intensity have a lower risk of developing diabetes compared with those who exercise at a lower intensity. Exercise improves sugar control, reduces visceral fat and increases insulin sensitivity .

Exercise recommendations for diabetics: Following exercise, the sugar uptake by the muscles may be increased for two hours post-exercise. With increasing intensity and amount of exercise, this post-exercise sugar drop can last for up to 48 hours and precautions should be taken to avoid hypoglycaemia. The current guidelines recommend a daily exercise of at least moderate intensity (such as brisk walking) for at least 30 minutes, resistance training for 15 minutes on most days, and lighter intensity activities (standing, walking) every 30 minutes.

What to watch out for: All diabetics should undergo a cardiovascular examination prior to the commencement of high intensity exercise programmes. Asymptomatic diabetics who have passed their cardiovascular examination and their maximal exercise test may engage in all forms of exercise but should always keep in mind the risk of excessively low sugar levels if they do not consume sufficient calories prior to commencement of exercise. As diabetics are generally at higher risk of coronary artery disease, they should seek medical advice if they develop exertional chest discomfort or increased exertional shortness of breath during exercise.

In summary, unless there is a medical contraindication, exercise is beneficial and the sedentary individuals who start on a moderated exercise programme stand to reap the greatest amount of health benefits.

• This article is produced in collaboration with Royal Healthcare Heart, Stroke & Cancer Centre