Myelin Decay in Brain Slows Athletes

(October 19, 2008) - There isn't any middle-aged athlete alive, even a weekend ones, who doesn't know about losing a step with age. It's more than just achy joints and arthritis, researchers say. It's because in middle age, we begin to lose myelin - the fatty sheath of "insulation" that coats our nerve axons and allows for fast signaling bursts in our brains. (Read about "The Brain")

Researchers compared how quickly a group of males ranging in age from 23 to 80 could perform a motor task and then correlated their performances to their brains' myelin integrity. The researchers found a striking correlation between the speed of the task and the integrity of myelination over the range of ages. Put another way, after middle age, we start to lose the battle to repair the myelin in our brain, and our motor and cognitive functions begin a long, slow downhill slide.

The myelination of brain circuits follows an inverted U-shaped trajectory, peaking in middle age. Dr. George Bartzokis, the study leader and others have long argued that brain aging may be primarily related to the process of myelin breakdown.

"Studies have shown us that as we age, myelin breakdown and repair is continually occurring over the brain's entire 'neural network,'" said Bartzokis. "But in older age, we begin losing the repair battle. That means the average performance of the networks gradually declines with age at an accelerating rate."

In the study, each of the 72 participants had a magnetic resonance imaging (link to x02) scan that measured the myelin integrity in the vulnerable wiring of their brain's frontal lobes. The maximum finger-tapping speed (the number of taps over a period of 10 seconds) was measured just before the MRI measure was obtained.

The results supported what the researcher had suspected, that finger-tapping speed and myelin integrity measurements were correlated and "had lifespan trajectories that were virtually indistinguishable," according to Bartzokis. They both peaked at 39 years of age and declined with an accelerating trajectory thereafter.

"Beginning in middle age," he said, "the process of age-related myelin breakdown slowly erodes myelin's ability to support the very highest frequency bursts. That may well be why, besides achy joints and arthritis (Read about "Arthritis & Rheumatic Diseases"), even the fittest athletes retire and all older people move slower than they did when they were younger."