I think the "changes our DNA" is far fetched, but the link between exercise and the neurochemistry in the brain has been proved by multiple studies.
I've mentioned here before, but John J. Ratey recently wrote the excellent Spark: The Revolutionary New Science of Exercise and the Brain[1], where he explains in colorful details what happens in (and to) the brain when you exercise.
A technically more correct way of putting it might have been "alters our gene expression", but that isn't as grabby-- not to mention the additional buzzkill that gene expression constantly changes throughout the body due to a plethora of factors, whether you exercise or not.
This is interesting research, for sure, but the headline's claim that it "changes our DNA" is misleading. The genes are not changed, only markers that have unknown effects on their expression. Learning more about the mechanisms of how DNA interacts with our body is certainly exciting, but the implication of the headline is that our actual genetic code is being tweaked, which is not true at all.
Going to play devil's advocate: the epigenome is changed in methylation, as explained in the article, and for a NYTimes article title, "changes our DNA" is going to be much more comprehensible to the general public than "changes our epigenome". "Tweaked" is actually a very good word for what happens--none of the base pairs are rewritten, but epigenetic changes can significantly affect the organism, even to the point of being passed on to offspring.[1]
Indeed. Given that this research showed these particular studied effects were specific to particular muscles that were being exercised, it seems unlikely to transfer through entirely different set of cells and into offspring.
In fact, my uneducated first guess would be that the different methylation patterns are related to the actual buildup in strength, which itself would require some way of coding for the expression of certain genes differently in one set of muscle cells than in another.
From what I remember of cell biology, expression is so key that some biologists argue DNA & DNA expression are of equal consequence and perhaps even meaningless without the other. Is a gene in your DNA that is never expressed really part of your genotype?
Yes, because it can be expressed in future generations. Re-used or re-purposed in future environments. Non-expression of a gene that's detrimental in the current environment can itself be useful to the survival of the gene until it can become useful.
I've mentioned here before, but John J. Ratey recently wrote the excellent Spark: The Revolutionary New Science of Exercise and the Brain[1], where he explains in colorful details what happens in (and to) the brain when you exercise.
[1] http://www.amazon.com/Spark-Revolutionary-Science-Exercise-B...