Exercise only preserves the muscles you actually use
It was great to see the big response to the MRI pics I posted a couple of days ago showing the well-preserved leg muscles of a 70-year-old triathlete. Very striking stuff. But let me now offer the following caveat:
This is a figure from a new study from the University of Western Ontario, just posted at Medicine & Science in Sports & Exercise. They analyzed the biceps brachii (arm muscles) of nine young runners (average age 27), nine old non-runners (70), and nine lifelong masters runners (67). They measured the number of functional motor units (i.e. group of muscle fibres activated by a single motor neuron), which typically declines with age. As you can see, the two old groups were pretty much the same, far below the young group.
In contrast, the same researchers studied leg muscles (tibialis anterior) in a similar group of volunteers last year (as I blogged about here) — in that case, the older runners did preserve the number of motor units. What this tells us is that exercise, on its own, doesn’t preserve all the muscles in your body: in the words of the researchers, there’s no “whole body neuroprotective effect,” or at least none that shows up in this relatively small study. It just preserves the muscles you’re using on a regular basis. So that’s still good news for triathletes, but maybe not as good for runners and cyclists!