Is exercise beneficial or hazardous to your heart?

In the U.S. an estimated 1.5 million heart attacks occur every year. Of these, 75,000 (about five percent), occur after heavy exertion (shoveling snow, recreational jogging, sexual activity), leading to 25,000 deaths. Similar statistics are reported from Canada and Europe. Some studies report up to 17 per cent deaths after heavy exertion.

There are mainly four risk factors which are associated with complications during exercise: age, presence of heart disease and intensity of exercise.

Normally, if the muscles are deprived of oxygen and energy then they easily fatigue. Delivery of oxygen and energy and removal of carbon dioxide and lactic acid (break down product of metabolism) are essential for sustained exercise. This depends on the health of our lungs and heart.

Glycogen is the principal carbohydrate stored in liver and muscles and it is the immediate source of energy. Safe prolonged exercise depends on the amount of glycogen in the muscles. Although fat stores are a huge reservoir of potential energy, the rate at which fat can be utilized for immediate energy is approximately one quarter of the rate at which glycogen can be utilized.

Increased oxygen and energy demand by the muscles, rapidly increases the heart rate to ensure adequate supply. That means hard work for the heart, at the expense of other organs. The risk of sudden death increases.

Can we reduce the risk of sudden death during or after vigorous exercise?

Yes, we can. A prospective data from a study of U.S. male physicians confirms this. Physical activity clearly benefits cardiovascular health (NEJM November 9, 2000). It has been shown that excess risk of heart attack during strenuous exertion was limited, for the most part, to persons who did not exercise regularly. Among those who exercised at least four or five time per week, there was little or no excess risk (NEJM December 2, 1993).

Although the exact reasons why physical exertion triggers heart attacks are not known, the possible factors are the disruption of atherosclerotic plaques (the deposits which narrows the coronary arteries), and the shearing stress on the heart caused by increased heart rate and blood pressure.

In sedentary people or couch potatoes, the risk of heart attack was seven times higher in a German study and more than 100 times greater in a U.S. study during vigorous exertion than during lighter activity or no activity. If you compare this to among people who exercised regularly, there was almost no increased risk. Another beneficial effect of regular exercise is that it increases the blood level of HDL (good cholesterol). HDL is another line of defense against heart attack.

What are the other hazards of vigorous exercise?

Dehydration. Drink plenty of fluids before, during and after a workout. You should adjust your activity according to the weather and reduce it when fatigued or ill.

Hyperthermia can result in light headedness, nausea, headache, hyperventilation, fatigue and loss of concentration. Heatstroke is the most dangerous complication of hyperthermia.

Avoid injuries to bones and muscles. High-impact exercise can also damage the inner ear, causing dizziness, ringing in the ear, motion sickness or loss of high-frequency hearing.

How can you exercise safely?

Most important thing is to listen to your body’s warning signs during exercise: chest pain, irregular heartbeat, undue fatigue, nausea, unexpected breathlessness or light-headedness. It is estimated that at least 40 percent of young men who die suddenly during a workout have previously experienced and ignored, warning signs. Remember to warm up, cool down and stretch.

For the general public the message is clear – regular exercise has important health benefits over the long term. Sudden vigorous exertion by people who are unaccustomed to it can sometimes end in tragedy (NEJM December 2, 1993). Consult your doctor and fitness expert.

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