Exercise Self-Reports Predict Less Benefit for Men Than Women?
What could explain the observation that self-reports of exercise predict less of a benefit for men than women? In the Journal of the American College of Cardiology researchers nimbly leap to a conclusion that women get greater gains in mortality risk reduction from “equivalent doses” of physical activity. But would men exaggerate their self-reports?
When a man reports a 30-minute workout, is it an “equivalent dose” to a woman’s report? Or would men register more physical activity on the reporting tool for this study? To be clear, we believe the latter is true.
An Observational Study of Exercise Self-Reports
The study in question is observational – neither randomized nor controlled. The authors looked for a correlation between self-reported physical activity and mortality in 412,413 U.S. adults between 1997 and 2019. Data came from the National Health Interview Survey.
Investigators found what they were looking for: a correlation between self-reported physical activity and death that differed between males and females. But any caution about the difference between correlation and causality went out the window when they wrote their conclusion:
“Women compared with men derived greater gains in all-cause and cardiovascular mortality risk reduction from equivalent doses of leisure-time physical activity.”
In their press release from Cedars-Sinai, the claims were even bolder:
“Women get the same exercise benefits as men, but with less effort.”
Health reporters took it from there and served up a broad range of bold (and unsubstantiated) headlines.
Crucial Limitations
The authors were clearly aware of the limitations that make these claims unsupportable. They note that self-reports of physical activity are all they have. No objective measurement. Further, they note the potential for “effects of sex differences in self-reported PA level” and “given the observational design of the study, causal relationships cannot be presumed.”
In fact, studies have shown that discrepancies in self-reports of physical activity from men versus women can be striking. One study found that men reported 47% more moderate to vigorous physical activity than women when there were no differences between them in accelerometer-measured MVPA.
Looking for a Claim
At the end of the day, it seems that these investigators were looking for a claim they could use for urging women to exercise – more than they were looking for rigorous scientific findings. Author Martha Gulati says:
“The beauty of this study is learning that women can get more out of each minute of moderate to vigorous activity than men do. It’s an incentivizing notion that we hope women will take to heart.”
But puffery pretending to be science is not helpful. It undermines trust.
Click here for the study in JACC, here for more on the importance of trust in science, and here for perspective on scientific integrity, and here for more on puffery about diet and exercise.
The Creation of Adam and Eve, woodcut by Paul Nash / WikiArt
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February 29, 2024
