One of the first indications that truly discerns the elite from the non-elite is response to exercise. You hear it from the trainer usually when the horse has its first work over 5 furlongs (1000m) in around a minute. Top trainers say that this distance is, for whatever reason, the 'gold standard' in terms of sorting out what each horse is made of. It is not so much the time of the work over the distance itself, but more-so the response to this work with the elite horses post-work recovery and appetite and demeanor the following days, separating them out from the others. It now seems that this intuitive 'feel' that a trainer has in terms of response to exercise is the result of significant genetic changes with the exercise itself determining much of this.
The genetic basis for response to exercise is becoming a lot clearer as scientists work to discover the genes, gene-gene, and gene-environment (epigenetic) interactions which control the genes responsible for angiogenesis, fatty acid oxidation, oxidative phosphorylation, mitochondrial biogenesis and muscle fibre type composition. One important epigenetic signature in exercise response is DNA methylation which can suppress the expression of a gene. Generally, it was thought that this DNA methylation was quite stable but a new study, published in Cell Metabolism, has found that exercise itself can alter the methylation pattern, thereby changing gene activity. The study (in humans) found that, after exercise, the DNA methylation of certain genes that are involved in mitochondrial function and ‘fuel usage’ decreased. The consequence of this is that 'the suppressor' was lessened and the activity of (most of) these genes significantly increased. The effects of this change were however transient, as the DNA methylation pattern was restored after 48 hours and the authors of the paper are not exactly sure how this all works other than to suggest that the increased calcium release during exercise might be relevant.