Kris Stallenberg 45-min Z5 (VO2 Max) Medium #04 This session uses two blocks of short, intense micro-intervals to accumulate significant time at VO2 max without the sustained fatigue of longer efforts. These 'short-shorts' are highly effective for boosting aerobic capacity and improving your ability to recover quickly from repeated hard efforts. It's a perfect workout for criterium or cyclocross simulation. bike