In the sample six-month periodization program we provided in March, we had you start off with a moderately difficult Maintenance 1 period to prep for the harder efforts ahead. Now we move into three months of intense stress and recovery, beginning with the four-week Overload 1 period detailed in the chart below.

This high-intensity training block is intentionally heavy on tough threshold work (which helps to push back the point at which lactate floods the muscle) and tougher VO₂ intervals, which quickly stress the entire system and make you faster. Your threshold is the number from your March field test (outsideonline.com/fieldtest)—an estimate of your upper limit for sustained aerobic performance. Your VO₂ max—the upper limit of your oxygen-delivery system—is roughly equal to the fastest pace you would be able to sustain for six minutes.