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Is high intensity running bad for you?

Exercise does not have to be vigorous to be beneficial. Trading intensity for duration is a well-known strategy for still ensuring positive outcomes like reduced fat content in the blood after eating. However, the debate about the efficacy of intense exercise has become distorted recently with the publication of a study in the Journal of the American College of Cardiology that found running intensely will not improve your lifespan over remaining sedentary.

What the study found unsettled many people but it is really its misrepresentation in the media that is causing most of the confusion. For starters, it's worth reviewing what the study is actually saying.

The researchers, mostly from the University of Copenhagen, used the database of 1,100 men and women from the Copenhagen City Heart Study to draw their conclusions. They found that slow joggers tended to live longer than those who ran faster. They also found that people who ran the most often and at the fastest pace had lifespans similar to those who did not exercise at all. So to be clear, the researchers report first and foremost what many other studies have found: some running is better for you than being sedentary. What should we make of the other part?

An effect Without a Cause

Today we have vastly more tools than at any other epoch in human history to look at sweeping patterns over long periods and unearth statistically significant causal relationships. It's important to remember that the problem with Big Data isn't the data. There is much to learn by careful analysis of huge data sets, looking for patterns--always keeping in mind that correlation does not imply causation.

The problem usually lies in the reportage of the day's hot finding. The media's natural inclination to distort the results when delivering the news is as deeply unfortunate as it is understandable. The widely reported conclusion that a high level of running has the same effect as no running at all is problematic for several reasons.

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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Publication:Running & FitNews
Geographic Code:1USA
Date:Jan 1, 2015
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