Skeptics of exercise say that jogging has caused deaths, even among quite celebrated runners. Jim Fixx, the author of The Complete Book of Running, for example, dropped dead while jogging at the age of 52 last year. Just last weekend a runner collapsed and died a few hundred yards from the finish of the Glasgow Marathon.
It would be foolish, indeed dangerous, to suggest that jogging or any other form of vigorous physical activity does not in some individuals increase the risk of a heart attack. If someone suddenly began running without training after years of sedentary habits, for instance, they would be in danger. And, as the Jim Fixx case showed, if there is a family predisposition to heart attacks (his father had his first heart attack at 35 and died eight years later) then even carefully graduated exercise cannot guarantee a long life.
The risk can be minimized by following a well-planned training program. Anyone who suffers from fainting spells, unusual shortness of breath, heart problems or pain in the chest should also consult their doctor before beginning intensive exercise.
But as Sir Roger Bannister pointed out in 1978: “There is more risk for people in not exercising than in exercising.” The evidence overwhelmingly supports his argument.
One important reason why exercise diminishes the risk of heart disease and stroke is that it reduces blood pressure: a carefully graduated exercise schedule can replace medication for some people, or at least allow it to be reduced. Exercise also alters basic biochemical processes that are at the root of atherogenesis – the silting-up of arteries. Cholesterol and fats in the blood are changed in such a way that the risk of heart attack is reduced.
But research now shows that the benefits are even more abundant than first suspected. Backache, commonly associated with sedentary occupations, can be prevented with exercise; bones can be strengthened; the common cold and other infections possibly even be prevented because the number of white blood cells is increased by exercise, and it is these that are the front-line fighters against infection.
Exercise also increases the amount of another substance, pyrogen, in the body. Pyrogen produces a transient fever after exercise, which stimulates the immune system to resist infection.
The rewards of exercise were in fact first demonstrated dramatically more than 30 years ago by Professor Jeremey Morris of the London School of Hygiene and Tropical Medicine. In a pioneering study he found that bus conductors who walked up and down stairs all day suffered fewer heart attacks and died less often from them than bus drivers. He also showed that postmen, walking several miles daily, had less heart disease than supervisors, clerks and telephonists who spent most of their working time sitting down.
But probably the largest and most comprehensive study has been one carried out with the alumni of America’s Harvard University, where Dr Ralph Paffenbarger and colleagues at the School of Public Health have studied the exercise habits and incidence of heart disease and death among some 17,000 former students who attended Harvard between 1916 and 1950.
Paffenbarger found that the alumni who developed sedentary habits after they left college had the same high risk of heart disease and strokes as those who never took much exercise. Playing for the first team, in other words, offers no long-term protection unless a moderate level of exercise is maintained.
Conversely the study provides encouraging news for men and women who are late starters: those alumni who took no exercise at college but started afterwards were found to have a reduced risk of heart disease and stroke. “Men who are physically active in their youth do not have a lower risk of heart disease unless they maintain their vigorous activity throughout their life,” says Paffenbarger. “Moreover, those physically inactive in adolescence or early adulthood are at decreased risk of coronary heart disease if their adult life acquires an adequate, sustained, physically active lifestyle.”