The trajectory of an athlete’s career follows a parabolic arc: a fairly steep rise as the body matures and skills are acquired, a peak, and then a slower, flatter decline as ability fades. But what causes this peak and decline? Obviously it has to do with physical attributes like speed and power, but what about the deep, underlying aspects of performance?
The consistency of this rise-peak-decline pattern is striking, even across very different sports. For nearly every major sport, the age of peak performance is in the range of 22-30, and some interesting trends emerge when you look at sport type in relation to an athlete’s peak age. The age at which performance tends to peak across sports seems to mirror the continuum from purely explosive, athletic sports to slower, more skill-based sports, with explosive sports peaking earlier. Further, even within sports that combine different abilities, explosive abilities (e.g. base stealing in baseball) tend to peak earlier than more cognitive, skill-based abilities (e.g. drawing walks in baseball).
* For baseball, a number of studies, using different methods, have pegged peak age between 27-29. (Link)
* For Tennis, peak age has been pegged between the early 20′s and 25. (Link)
* For basketball, peak age has been found to be at 27 for all positions, with different positions showing different patterns of decline. (Link)
* For Track and Field, peak sprinting age has been found to be in the lower-mid twenties, with endurance events having older peak ages. (Link)
* For golf, athletes have broader peaks–between 25-35, with slower declines. (Link)
* For football, running backs and receivers peak around 27, with running backs showing sharper fall-offs than receivers. Quarterbacks have a broader peak between 25-35. (Link)
So why do athletes decline? One place where we might look for an explanation is in myelin integrity. Myelin is a fatty sheath that insulates the axon of the neuron, the long portion of the neuron that conducts the electrical signal when a neuron “fires”. This sheath acts like an electrical insulator, and allows the axon to conduct a signal much faster than an unmyelinated axon. Myelin is what gets called “white matter” when we’re talking about the brain (as opposed to “gray matter”, which is mostly composed of neuronal cell bodies). Neuroplastic changes in white matter have been observed in musicians and other categories of experts–it’s as if repetition and practice cause the laying down of additional layers of this myelinated insulation–so it isn’t too great of a leap to anticipate that highly trained athletes might exhibit differences in myelination and white matter when compared to the general population.
Given that myelin is associated both with expertise and with the ultra-fast conduction of nerve signals, it seems logical to explore whether the degeneration of myelin might be associated with the decline that we see in athletes’ performance. Myelin integrity also exhibits a parabolic trajectory with age, and the breakdown of myelin is associated with slower nerve conduction and cognitive and physical decline. But while this seems like a plausible explanation, studies have shown that myelin integrity actually peaks around age 40. In a study by George Bartzokis at UC San Diego, a range of subjects were tested on a very simple but common neurological test, finger-tapping speed. Maximal finger tapping speed requires high-frequency action potential bursts and is associated with myelin integrity. The study results found that myelin integrity, as measured by brain imaging techniques, and finger-tapping speed closely mirror each other, and peaked around age 39. The study’s authors concluded that “The results suggest that in this very healthy male sample, maximum motor speed requiring high-frequency [Action Potential] burst may depend on brain myelin integrity.”
Interestingly though, even in the most skill-based sport, golf, performance decline begins before 39, the age at which studies suggest that myelin integrity peaks. Decline in every sport happens while myelin integrity, and thus the quality of the signals sent through the brain and body, should still be improving. So, again, why the decline? We will look at a couple other explanations in our next post.