Is High Intensity Running Bad for You?
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As an observational study and not a randomized one, associations, not causes, are all that can be pointed out. The study authors do not actually imply that hard running increases mortality risk. And they acknowledge that the number of hard runners in the study was quite small: just 80 men and women. Any statistical information about death rates in this group must be viewed very cautiously.

Even more importantly, the researchers did not determine how and why the runners and non-runners had died. This makes it impossible to draw conclusions about what negative effects hard exercise might have on people. Combined with the decidedly vague definition of slow, medium and fast self-reported running, the study is a bit of a non-starter for uncovering useful relationships between running intensity and various health benefits.

Differing Conclusions
As cardiologist and Running & FitNews editorial board member Charles Schulman points out, another study—looking at some 55,000 adults over 15 years—reported that runners (vs. non-runners) had 30% and 45% lower risks of all-cause and cardiovascular mortality, respectively, with a mean improvement in life expectancy of three years. Maximal benefit from running was not at the highest speeds or training volume, but the difference between the moderate and highest levels was close, and far less than the difference between sedentary and active.

Far from concluding that vigorous exercise is no better than no exercise at all, we should conclude that any exercise is better than no exercise at all, and that any exercise, however light in intensity, when held up to vigorous exercise, still holds tremendous value.

Steven Blair, and later Walter Bortz II, using Big Data, found immense correlation in moving one's body and longevity. Lower mortality rates in higher fitness categories were seen specifically for cardiovascular disease and cancer. Also, low fitness level was an important risk factor.

Intense vs. High Volume
Ultimately, it's important to avoid confusing intensity with high levels of activity. The two can overlap, but are far from identical. High training volume at moderate or even low intensity (i.e., for long durations) is extremely beneficial, and anyone who draws the unfortunate conclusion that high levels of activity are no more beneficial than no activity is missing this important distinction.

The three most well accepted modifiable risk factors for heart disease are hypertension, high blood cholesterol and smoking. Relative risk of myocardial infarction is 2.1 times baseline for hypertension, 2.4 for high cholesterol, and 2.5 for smoking. The relative risk for physical inactivity is as high or higher than these. Dozens of studies have shown that people who are fit/physically active are less likely to die over a defined period than inactive/unfit people (due in large part to lower occurrence of cardiovascular disease). Depending on exactly who you define as least fit, the numbers range from double the relative risk (the bottom 20% of subjects measured as least fit), or as high as 5 times the risk of the most fit subjects.

One of the earliest and largest of these investigations was the 1989 Blair et al. Aerobics Center Longitudinal Study, in which time to exhaustion on a treadmill test was measured with thousands of person-years of follow up and number of deaths to determine relative risk. In men with the lowest levels of fitness, risk was 3.44 times as great as men with the highest fitness scores. In the least fit women, risk was 4.65 times as great as the highest fitness levels.

The study concluded, “Higher levels of physical fitness appear to delay all-cause mortality primarily due to lowered rates of cardiovascular disease and cancer.” Blair followed this up in 1996 with an even larger data set, finding that low fitness soundly beat out hypertension, high cholesterol and overweight and was only edged out by a tenth of one percent in men who smoked.

If You Choose, Choose Duration
As noted in “Burn After Running” in this issue, for up to half a day following exercise, oxygen consumption remains elevated, burning more fuel and promoting weight loss. This phenomenon is positively correlated with intensity and duration of exercise.

Evidence from multiple intervention studies shows that the positive effects of exercise on lifestyle concerns (like insulin sensitivity) are probably more induced overall by the volume of training than by its intensity.

Still, any suggestion that inactivity and vigorous exercising somehow deliver the same non-benefits to longevity is ultimately preposterous, implying a causation that is simply not there.

In another recent large analysis published in the Annals of Internal Medicine, researchers examined data from 47 studies that assessed the health effects of sedentary behavior adjusted for physical activity. Increased exercise blunted — but did not completely eliminate — the excess risks associated with sedentary behavior.

Given that this study found the ill effects of sedentarism will not be completely offset by even vigorous exercise, it seems doubly irresponsible for the media to suggest that vigorous exercise is no better than no jogging at all. Compare that with the Copenhagen study authors' original conclusion:

“The findings suggest a U-shaped association between all-cause mortality and dose of jogging as calibrated by pace, quantity, and frequency of jogging. Light and moderate joggers have lower mortality than sedentary nonjoggers, whereas strenuous joggers have a mortality rate not statistically different from that of the sedentary group.” Nowhere is causation implied.

Annals of Int. Med., 2015, Vol. 162, No. 2

JACC, 2015, Vol. 65, No. 5,

JAMA, 1989, Vol. 262, No. 17, pp. 2395-2401

Physical Activity and Health: The Evidence Explained by A. Hardman and D. Stensel, 2003, Routledge, London, U.K., 289 pp.

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