One of the big challenges for recovery research is figuring out what it means to be recovered. Maybe it’s the point at which, after a marathon, you’re able to start walking down the stairs forward instead of backward. Or if you want to be more scientific about it, maybe it’s the point when all the various markers of physiological stress in your bloodstream—low fuel stores, damaged muscles, inflammation, and so on—have returned to normal.
But which markers matter? Scientists have made all sorts of educated guesses over the years. For example, tests at the 1979 Boston Marathon showed that creatine kinase, a marker of muscle damage, jumped on average by 2,000 percent after the race, but was back to normal four weeks later. (The race winner, Bill Rodgers, had still had fairly high levels four weeks later, but that was probably just a result of his normal training.) Subsequent studies have looked at other markers like heart and kidney stress, but the real-world significance of these measures remains hotly debated.
A new study in Frontiers in Physiology takes the physiological markers approach and cranks it up to…
