A new study by the peerless Samuele Marcora suggests perception of exercise effort is all in the brain.
The 1999 film The Matrix depicts a dystopian future where human beings are strapped to machines that stimulate their brains in such a way that they experience a convincing alternate reality that is completely indistinguishable from the normal waking state. It’s a far-out premise (ripped off 1972 novella The Futurological Congress by Polish science fiction writer Stanislaw Lem) but hardly unrealistic. Our brains are the source of everything we experience, so in principle we don’t need our eyes to see or our muscles to experience a sensation of movement.
It’s been 13 years since The Matrix was released and in those years science has inched us closer to the possibilities rendered in that hopelessly overrated movie. Earlier this year a quadriplegic woman was able to drink coffee by using her thoughts to manipulate a robotic arm. Such things are possible because a complete map of the muscular system exists inside our brains. Scientists implanted a microchip in the “right arm” part of Cathy Hutchinon’s brain and snaked wires through her skull, connecting the ends to the mechanical arm. By willing her own paralyzed right arm to move exactly as she used to do before her stroke she was able to move the substitute arm instead.
What does all of this have to do with running? I’ll tell you. In recent years there has been a debate among exercise scientists about how the perception of effort during exercise originates. Some believe that perception of effort is the feeling of activity in the muscles, hence similar to other tactile perceptions such as the sensation of cold air against the skin. But Samuele Marcora, a brilliant exercise physiologist working at the University of Kent, England, believes that our bodies have very little to do with perception of effort. Rather, he contends, the perception of effort is nothing more than “conscious awareness of the central motor command sent to the active muscles.” In other words, the parts of your brain that “light up” when you run (or whatever) not only cause your muscles to act but also generate the feeling of how hard your muscles are working. Sensory feedback sent from your muscles to your brain is not part of the equation.
A new study published in the journal Psychophysiology provides fresh evidence to support the theory that perception of effort does indeed originate in the brain. Marcora and a pair of colleagues recruited 16 healthy male volunteers and had them perform bicep curls with a light weight and a heavier weight in both non-fatigued and pre-fatigued states. While the exercises were being performed, measurements of activity in the brain’s motor cortex and the biceps muscles were taken and the subjects were asked to subjectively rate their exertion level.
Not surprisingly, the researchers found that muscle activity, brain activity, and ratings of perceived effort were greater when the subjects lifted the heavier weight. They also observed that brain activity and ratings of perceived effort were greater in the pre-fatigued state than in the non-fatigued state with both weights. Of course, one would expect that lifting a certain weight with a tired arm would feel harder than it would with a fresh arm. What’s interesting is that the brain also worked harder to lift the same weight.
With both weights and in both non-fatigued and pre-fatigued states, motor cortex activity correlated with perception of effort. When lifting the weight felt relatively easy, brain activity was relatively low. The harder the lifts felt, the more activity was observed in the motor cortex.
As scientists like to say, correlation is not causation. But the correlation that Samuele Marcora found between motor cortex activity and perceived exertion is consistent with his idea that perception of effort is awareness of brain activity rather than sensations collected from the muscles, and he has further experiments planned to seal his argument.
If Marcora’s theory is correct there will be some interesting practical applications for runners. For example, if it’s true that fatigue comes from brain activity instead of muscle activity, it should be possible to induce fatigue just by thinking about running. And if this is true, then it may be possible for runners to increase their fatigue resistance (i.e. fitness) through visualization exercises, which may serve as a complement to physical training or even as a substitute during periods of injury. Already studies have shown that imagined strength training increases muscle strength.
When Keanu Reeves’ character returned to reality from the Matrix and started running around after bad guys, he might have noticed that he felt surprisingly fit. If he did, it was thanks to all of the running around he had previously done inside the Matrix—that is, in his mind.
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