Irisin sounds like a Tolkien construction, the name of a mysterious character straight out of Lord of the Rings. But while irisin certainly is mysterious, it’s a scientific term for a hormone that has been linked to exercise. The strange thing about irisin, however, is that no one is completely sure if it exists; this has been vehemently debated in the medical community.

But a recent study published in Cell Metabolism argues that irisin is real, and it’s not a myth at all, as past scientific literature has claimed. The study — led by Bruce Spiegelman of the Dana-Farber Cancer Institute and Harvard Medical School (along with a team of Harvard researchers who had originally discovered the hormone) — found human irisin in the blood at nanogram levels.

The researchers analyzed irisin in blood samples from sedentary individuals as well as people who had 12 weeks of aerobic training; they found that irisin levels were at 3.6 nanograms per milliliter in sedentary people, and 4.3 nanograms per milliliter in active people. The results show that irisin does in fact exist, and is altered during exercise, the authors state.

Why has the topic been so contentious? Spiegelman argues that past research that portrayed irisin as a myth misunderstood its signal, known as ATA, to start its production. As a result, past researchers — such as those who completed this study earlier this year — thought the ATA meant that the gene was a pseudogene, serving no function. Spiegelman and his team, however, used mass spectrometry techniques to examine irisin in humans, paying attention to its ATA signaling.

“The data are compelling and clearly demonstrate the existence of irisin in circulation,” Francesco Celi of the Virginia Commonwealth University Medical Center, said in the press release. Celi was not involved in the study. “Importantly, the authors provide a precise and reproducible protocol to measure irisin.”

Initially, the discovery of irisin in 2012 created excitement in the media due to its claimed potential to aid in weight loss and keep us healthy. It also helped explain why exercise is so good for us — and why it fights chronic diseases and aids us in living longer. This earned it the nickname as the “magic hormone,” or the “mythical hormone.”

Will the study settle the debate? One chemical physiologist of the Scripps Research Institute, who also was not involved in the study, believes so. “Spiegelman and colleagues have unequivocally shown that the ‘mythical’ irisin peptide is produced as a result of exercise,” John Yates said in the press release. “This data should settle the controversy surrounding the existence of irisin and its increase in blood as a function of exercise.”

However, the scientists still aren’t sure exactly how the hormone works in the system after exercise — or what its consequences of our health might mean. More research will be needed on that front.

“There’s so much that we don’t know about the molecular mechanisms of exercise,” Alisa Blazek, a graduate student at the Ohio State University’s Department of Molecular, Cellular and Developmental Biology, told LiveScience. “And if we could learn more about them, it can help us to design therapeutics, and learn how effective our exercise or physical therapy programs are.”

Source: Jedrychowski M, Wrann C, Paulo J, Gerber K, Szpyt J, Robinson M. Detection and Quantitation of Circulating Human Irisin by Tandem Mass Spectrometry. Cell Metabolism. 2015.