A lot of the most popular fitness studies only looked at how people improved on their own after a workout or supplement, not how they did compared to people who didn’t do anything — which might make those treatments seem way more effective than they really are.

A big review found that in most top-rated studies about strength and fitness training, about 85% made at least one common math mistake—like using the wrong numbers to show results or including results that seem way too extreme.

In nearly half of the most popular science reviews on strength and fitness, researchers made a math mistake—they used the wrong number to calculate how strong an exercise or supplement’s effect was. This made the effects look way bigger than they really were, and most of the super huge effects (over 3.0) were just due to this error.

When scientists combine results from lots of fitness studies, sometimes they get really big numbers—bigger than 3.0—and this claim says almost 6 out of 10 of those huge numbers are probably mistakes because they used the wrong math formula.

In fitness research, nearly half of the big summary studies ignored how reliable each individual study was and treated them all the same — even tiny, shaky studies got the same weight as big, solid ones, which can mess up the final conclusion.