I'd disagree slightly with your characterization of the author's findings on over-exercising; quoting from the discussion section:
"Our findings do not provide evidence for increased mortality risk with physical activity amounts as high as seven times above the current recommended target range. All cause, CVD and CHD mortality risks were lower at physical activity levels up to approximately 5–7 times the recommended level but the additional reduction in risk of mortality with engagement in activity at levels beyond the recommendations was modest and with increasing uncertainty, as reflected by the wide confidence intervals. Thus based on all of the available studies, we did not identify a higher mortality risk at any level of physical activity above the recommended level, although the lowest point estimate for all cause mortality was approximately 2000 MET min. Our analyses suggest that 10–12 hours of weekly vigorous physical activity cannot be considered harmful to longevity."
My reading is that the authors did not draw any conclusions about increased risks at higher MET levels due to the broad confidence intervals caused by the cancer risk data.
Right. I think that statement is based on Supplement eTable 5, where they analyzed numbers up to 6,000 MET-minutes/week.
Using confidence intervals in this case is a bit misleading though. What would be most useful IMO would be the prediction interval for the lowest point estimate, as that could be used to determine if individual activity amounts are appropriate.
I'd disagree slightly with your characterization of the author's findings on over-exercising; quoting from the discussion section:
"Our findings do not provide evidence for increased mortality risk with physical activity amounts as high as seven times above the current recommended target range. All cause, CVD and CHD mortality risks were lower at physical activity levels up to approximately 5–7 times the recommended level but the additional reduction in risk of mortality with engagement in activity at levels beyond the recommendations was modest and with increasing uncertainty, as reflected by the wide confidence intervals. Thus based on all of the available studies, we did not identify a higher mortality risk at any level of physical activity above the recommended level, although the lowest point estimate for all cause mortality was approximately 2000 MET min. Our analyses suggest that 10–12 hours of weekly vigorous physical activity cannot be considered harmful to longevity."
My reading is that the authors did not draw any conclusions about increased risks at higher MET levels due to the broad confidence intervals caused by the cancer risk data.