The relatively small sample size (11) and uncertainty around what "3 weeks of increasingly strenuous exercise" consists of, makes the results hard to interpret. OTOH, weekly muscle biopsies is a fairly invasive stab (ahem) at getting solid data.<p>It is possible that this ends up as more evidence for HIIT[0] as a sweet-spot for exercise, if the 'vigor' alluded to exceeds that of a HIIT regimen.<p>Could be especially important if there turns out to be a firm limit on exercising more beyond which you get <i>worse</i> results (and not just for other measures like health outcomes or joint damage, but for an individual's primary goal).<p>[0] High Intensity Interval Training