Week four opens by upgrading the oldest circuit in the book. Day 22 is Day 3's exact lineup - high knees, march steps, climbers, slow climbers - with every interval now at 30 seconds, looped non-stop for 3, 5 or 7 rounds. No rest between exercises, none between loops, and no more short sprints to hide inside.
The 10/20 gear-change structure is gone; in its place sit four equal 30-second gears that blur the line between sprint and cruise. Thirty seconds of climbers cannot be attacked the way ten could - it has to be paced, sustained, survived - and the march steps and slow climbers that used to be recovery now run long enough to become work in their own right. Two minutes per loop, entirely unbroken: this is the endurance version of a circuit you first met as a sprint drill.
Open each 30-second interval at a pace you can defend to its end - the final ten seconds are where the interval actually lives. March steps stay tall and driven. Keep the hips low through both climber speeds, and make the slow climbers full and deliberate: long knee drives, no shrinking range as the loops stack up.
On Day 3 this circuit dealt in ten-second problems - now every problem runs thirty seconds and the only answer is still 'keep moving'.
Make it Harder: Drive the knees all the way to the chest on every fast climber.
Make it Easier: Return to Day 3's clock - 10-second sprints, 20-second cruises - and keep the loops non-stop.
