Perceived exertion, not muscle failure, determines “exhaustion”
There’s an interesting preprint available online from the European Journal of Applied Physiology, by Samuele Marcora and a colleague from Bangor University in Wales. Its title is “The limit to exercise tolerance in humans: mind over muscle?,” so you might think it’s another paper supporting Tim Noakes’s “central governor” theory. It is, and it isn’t — but either way, it’s interesting.
Marcora took 10 elite rugby players and (after various preliminary testing and so on) had them do a five-second “maximum voluntary cycling power” (MVCP) test. Then they did a very intense cycling trial to exhaustion which took about 10 minutes (they offered cash prizes to the top performers and circulated the results publicly to stimulate competition and make sure the subjects went all-out), followed immediately (within one second) by another MVCP test.
Now, if you subscribe to traditional exercise physiology, you’d say that the subjects stopped the test-to-exhaustion when they were no longer physically able to generate enough power to continue. Possible reasons for their failure would include “limited oxygen delivery, metabolic and ionic changes within the active muscles, supraspinal reflex inhibition from muscle afferents sensitive to these changes, and altered cerebral blood flow and metabolism.” But that’s not what Marcora saw. The subjects had to maintain an output of (on average) 242 watts in the test to exhaustion. But as soon as they stopped, one second later, they were able to output (on average) 731 watts in a five-second burst — nearly triple the required power! Clearly the subjects didn’t stop the test because their couldn’t physically produce the needed power:
These results challenge the long-standing assumption that muscle fatigue causes exhaustion during high-intensity aerobic exercise, and suggest that exercise tolerance in highly motivated subjects is ultimately limited by perception of effort.
The interpretation of these results gets a little tangled. Marcora is an advocate of something he calls the “psychobiological model of exercise tolerance,” which seems to basically mean that we stop exercising when it gets hard. He says this is different from — and much simpler than — Noakes’s central governor theory. I’m not sure I really a see a difference that extends beyond semantics, but perhaps that’s because I haven’t given it enough thought. I downloaded a couple of Marcora’s other papers where he explains the theory in more detail, so I’ll be interested to see what he has to say. Either way, these results are certainly interesting in that they once again support the notion that, when we collapse from exhaustion, we’re generally running up against barriers imposed by our brain rather than absolute physical limits imposed by our body.