There's an interesting new study on cerebral oxygenation -- the amount of oxygen reaching the brain -- in elite Kenyan runners, A Part of Hearst Digital Media Running Shoes - Gear (press release here). It's the latest in a series of studies from a collaboration between Jordan Santos-Concejero of the University of the Basque Country and Ross Tucker and his colleagues at the University of Cape Town, with additional contributions in this case from Laval and Stellenbosch.
To understand the study's significance, it's worth looking back at some previous results. Studies have found that oxygen levels in the brain drop during severe exercise, which in turn probably affects muscle recruitment and contributes to fatigue. You can think of it as a protective effect: if the brain's oxygen supply is threatened, it compromises your ability to keep pushing it into danger. Whatever the exact mechanism, the result is that when brain oxygen drops, you'll soon slow down.
In 2010, Francois Billaut (who was then at Lethbridge and is now at Laval) used near infrared spectroscopy to measure brain oxygen levels in eight Canadian and three East African runners during a self-paced 5-K time trial. Here's the key data:
In particular, look at the filled circles ([O2Hb]) showing oxy-hemoglobin, which serves here as a marker for oxygen levels in the brain. They rise after the start of the race as the brain's oxygen demands increase (neurons are firing to recruit muscle, monitor pace, etc.), then level off -- and then, in the last kilometer, decrease. The asterisks indicate a statistically significant difference compared to the midpoint of the race.
In contrast, look at the data from the new study, which put 15 Kenyans with an average half-marathon best of 1:02 through a similar 5-K time trial:
The top graph again shows oxy-hemoglobin, which increases after the start, levels off... and stays there, with no appreciable decrease at the end of the race even though the athletes were pushing as hard as they could (they were paid based on their finishing times). That's the key result of the study: elite Kenyan runners maintain steady cerebral oxygenation during an all-out time trial, which may be one of the traits that makes Kenyan runners so good. Why should Kenyans be better than Canadians at sending blood to the brain? One explanation offered by the researchers is early-life experiences, specifically prenatal exposure to altitude ("Prenatal exposure to high altitude triggers cerebral vasodilator responses at muscle and endothelium level by stimulating extensive cerebrovascular remodeling that increases wall thickness but decreases overall contractility") and lots of exercise when they were young ("the stimulation of trophic factors and neuronal growth as well as augmented cerebral circulation through increased vascularization of the brain").
Of course, there are other factors to consider: the Kenyan subjects in the new study were much faster that the Canadian subjects in the previous study. Could it be that maintenance of cerebral oxygenation is simply a trait of truly elite runners? That's an open question, but it's also one of the biggest strengths of the new study. If we want to understand what it takes to run 1:02 for a half-marathon, we have to study people who can do that. Arranging such studies is an extremely challenging task, so it's very cool to see this and other recent experiments on truly elite athletes.
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