Group defends controversial ‘exercise hormone’

As clear as the benefits of exercise are, explaining its effects at the molecular level has been scientifically strenuous. That’s especially true for irisin—a hormone that appears in some animal studies to increase energy expenditure after physical activity and promote healthy metabolism. Experiments to measure irisin in exercising people have set off a bitter scientific dispute, leading some to believe humans don’t produce it at all. Now, the lab that discovered the hormone is coming to its defense, aiming to win over critics by showing its presence in human blood with a more sophisticated, commonly used analytical technique.

Irisin—named for the Greek messenger goddess Iris—first revealed itself in the lab of Bruce Spiegelman, a cellular biologist at Harvard Medical School. His lab was trying to identify key proteins produced by muscles during a workout. “We’re all told to exercise,” he says. “In the end, presumably the [effects] will all come down to a series of molecules.”

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