By Justin Worland
April 8, 2015

A health researcher is walking back his claim that strenuous exercise places runners at equal risk of death as people who don’t exercise at all, after the study received widespread media attention.

The researchers should have presented the result as a possibility rather than a concrete finding, study lead author Peter Schnohr told the BBC. “We should have said we suspect that it is so, but we can’t say for sure. Everybody makes some mistakes in papers,” he said.

The study concluded that “strenuous joggers have a mortality rate not statistically different from that of the sedentary group.”

Schnohr’s research, which received attention across many media outlets, including TIME, looked at data on the health of thousands of runners and non-runners over a 12-year period. But its conclusions on strenuous exercise were drawn from a sample of only 36 people. The study reported the small sample size, something that Schnohr said sophisticated readers should have noticed.

“It shouldn’t have been misunderstood,” he told the BBC. “If you normally read papers you could say ‘Ah!'”

Strenuous exercise was defined as running at a speed of more than 7 mph for at least four hours per week.

Write to Justin Worland at justin.worland@time.com.

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