Brain – Not Lungs – Spurs Body Towards Physical Limits

New information suggests that your brain – not your body – determines your body’s physical limit during sustained physical exercise.

Since the twenties scientists have believed that VO2 max, the maximum amount of oxygen that you’re able to deliver to your muscles during hard exercise, determines your physical limits. Now, a new study claims that your VO2 max isn’t really a maximum at all. Furthermore, your heart and lungs don’t call the shots – your brain does.

In the decades since, VO2max was introduced it has become the industry standard for evaluating aerobic fitness. Researchers measure it using an incremental test to a subjects exhaustion. Once they’re unable to continue on the treadmill or bike it’s determined that they have reached a plateau in oxygen consumption shortly before failure.

Experts argue about where the oxygen consumption peaks – whether the heart can’t pump more blood, the muscles can’t absorb more oxygen from the blood, or the lungs can’t extract more oxygen from the air.

But the new theory, proposed by physiologist and author Tim Noakes, suggests that the limit comes from the brain, which proactively prevents athletes from reaching these physical limits to avoid catastrophic, event fatal, outcomes.

Last month’s issue of the British Journal of Sports Medicine contained eight different studies that, in various ways, offered support for Dr. Noakes’s questioning of the standard incremental VO2max test. In one study, volunteers were separated into incremental and decremental tests. Volunteers who were in the decremental exercise had a brief warm-up before the decremental test ramped immediately to a speed higher than the maximum speed reached in their previous incremental test. After about a minute – just before the subjects were about to fall off the back of the treadmill – the speed was decreased by one kilometre an hour. This process was repeated over and over, with the speed being lowered just before the subjects reached failure.

VO2 max scores were the same among participants in the incremental test, but participants in the decremental group, increased their V02 max scores by an average of 4.4 per cent. These results suggest that participants were able to transport more oxygen to their muscles due to the altered test structure – not due to a plateau in the functioning of the heart, lungs or muscles.

Researchers suggested that since the decremental subjects knew that their would become progressively easier, their brains would be less likely to pre-emptively slow their efforts to prevent over-exhaustion. They also noted that “since emotional stress can affect blood flow and metabolism, that knowledge alone could alter [the study participants’] physiological response to exercise.”

This new research raises questions about the physical limitations we encounter during hard exercise – and suggests that knowing your oxygen capacity is less important “than believing that you can go a little faster or a little farther.”

Source: The Globe and Mail, “The brain’s the boss when it comes to oxygen uptake”