Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance

by Alex Hutchinson

Overall, according to Roger Enoka, who directs the University of Colorado Boulder’s Neurophysiology of Movement Lab, the modern consensus from these studies echoes Merton’s finding: most healthy people can achieve “voluntary activation scores” of close to 100 percent. In Mark Burnley’s lab, at the University of Kent, typical scores for all-out quadriceps contractions are 92 to 97 percent, and anything less than 90 percent suggests something has gone wrong with the test. Under normal conditions, in other words, we’re utilizing pretty much all the strength our muscles have to offer. There are, however, two possible loopholes, Enoka notes. One is that you can’t sustain 100 percent activation indefinitely, so the idea of a hidden muscle reserve makes more sense for cyclists and rowers and runners than for piano movers. The other is the difference between twitching your thumb and, say, deadlifting a car—a movement that requires a deceptively intricate synchronized pattern of activation involving at least thirteen different muscle groups. It’s possible that these complex real-world actions make it harder to reach full voluntary activation in all the relevant muscle groups, meaning there might be some reserve accessible in stressful situations. This prospect hasn’t been tested, Enoka says, and it’s not clear that such a test is even possible with current technology (which is why Zatsiorsky’s claims are so intriguing).