I was extolling the virtues of cycling to a cardiologist. I suspect that he wasn’t one to exercise a lot himself. His first response was to say “That’s all very well unless you rip off a plaque and pop yourself off with an infarct”. There followed a couple of digs about shaving my arms and legs before the coup de grace “It’s a J curve you know”.
J-curves are not uncommon in medicine. Vitamin A for instance is essential, too little is bad for you, the right amount is exactly that while too much is harmful even lethal. Similar curves obtain for other variables such as weight.
Body weight and all cause mortality are high to the right. The risk of death comes down with body weight but rises again to the left as weight reduces below the optimum.
My cardiologist friend was suggesting that a little exercise would be good but too much would put me in an early grave. It is not hard to find evidence to support his point of view.
Lee et al evaluated the records of 23,257,723 Koreans age 20 yr or more who had undergone one biennial medical evaluation by the National Health Insurance Corporation. Their level of physical activity was assessed by questionnaire.
A reverse J-shaped risk curve was observed, with the lowest mortality risk in the participants exercising 4 to 5 days per week
A significantly increased risk of death was found in those that did not exercise and those who exercised 6 or 7 days a week.
There are problems with epidemiological studies based on questionnaires. If you ask people how much they exercise, eat, earn or if they’re unfaithful to their spouse you may not get a truthful answer. In a Norwegian study (Dyrstad et al) 1751 adults (19–84 yr) wore an accelerometer for 7 days and filled out a questionnaire regarding their physical activity. The discrepancy between the self reported and measured activity was revealing. For example men reported 47% more moderate to vigorous physical activity compared with women but there was no difference between sexes in the accelerometer data.
Their conclusion …
The present study shows large variations between self- reported and accelerometer-measured physical activity and sedentary time.
The general agreement between self-reported and accelerometer-measured physical activity was poor
The questionnaire and the accelerometer came in the same envelope. The inaccuracy is unlikely to be due to intentional lying.
So garbage in garbage out.
A review article by Harvey B Simon, in the American Journal of Medicine 2015 entitled Exercise and Health: Dose and Response, Considering Both Ends of the Curve makes good sense of a confusing issue. It is well worth a read in its entirety. To save you the effort I will grab the key quotes but bear in mind that I am not without bias.
The benefits associated with regular exercise include substantial protection against heart attack, stroke, hypertension, peripheral artery disease, diabetes, obesity, erectile dysfunction, sarcopenia, osteoporosis, depression, dementia, and common malignancies such as breast and colon cancers. Regular exercise enhances the quality of life, slows the physiological consequences of aging, and promotes longevity.
Although these benefits have been widely publicized, only a minority of Americans exercise regularly.
It’s good for us but by and large we don’t do it. Could it be because it’s potentially fatal?
Despite the man-bites-dog publicity that announces the death of an athlete during competition, these tragic events are actually quite uncommon. Males are at higher risk than females in all age groups. Among young athletes, about two-thirds of these deaths are due to trauma and other nonmedical causes such as drug abuse and heatstroke; hypertrophic cardiomyopathy and congenital anomalies of the coronary circulation account for most of the cardiac deaths. Among National Collegiate Athletic Association athletes, the incidence of sudden cardiac death is 1:43,770 participants per year. In older athletes, unsuspected atherosclerotic coronary artery disease is the leading cause of cardiac events during exertion. Exercise can trigger events through mechanisms such as plaque rupture and ischemia-induced arrhythmias. The overall risk is low, amounting to 0.3-2.7 events per 10,000 exercise-hours in men.
If a heart attack is in your future it may well occur during exercise …
Sedentary men were 56 times more likely to have a cardiac arrest during exercise than at other times. Habitually active men had a much lower risk during exercise, but they were still 5 times more likely to have a cardiac arrest during exercise than at other times. However, men who exercise regularly had a 60% lower overall risk of cardiac arrest than did sedentary men.
It doesn’t take a lot of exercise to gain most of the health benefits
A 15-year study of 55,137 American adults reported that runners enjoyed a 30%-45% lower risk of all-cause and cardiovascular mortality and a 3-year life expectancy benefit as compared with nonrunners. Even running for 5 to 10 minutes a day at a pace over 10 minutes a mile was beneficial. Protection was maximal at about 150 minutes of running per week
But some of us are prone to obsessive behaviours, A study …
evaluated 204,542 Australians ages 45 to 75 years. Over a follow-up that averaged 6.5 years, there was an inverse relationship between the amount of moderate-to-vigorous activity per week and all-cause mortality. As compared with sedentary individuals, those who performed 10-149 minutes of exercise per week exhibited a 34% reduction in mortality; 150-299 exercise minutes per week was associated with a 47% reduction in mortality, and levels of 300 minutes or higher with a 54% lower mortality rate. In all categories, intense exercise was somewhat more beneficial than similar amounts of moderate exercise. No harm was reported even with the largest amounts of intense exercise.
No sign of a J curve in that study but Marathons are not obligatory.
And now for something lighter …