Thanks for your thoughtful responses. It does seem that the problem with all these longevity studies is that there are so many factors and so much middle ground that the conclusions are highly questionable. e.g., I also read that runners tend to spend more time sitting the rest of the time contra the guideline to get up and move every 20 minutes! I suspect that your emphasis on avoiding over-training is probably as key to overall health/longevity as it is to fitness.