Sprint for one minute, then jog for one minute. Repeat the sequence, lowering the time to 45 seconds, then 30 seconds, then 15 seconds. Do it again, this time starting at two minutes. Swim two fast laps freestyle, then swim one lap underwater. Repeat five times. Sprint up a flight of stairs. At the top, do one set of 10 squats. Jog back down, then sprint back to the top. Do one set of 10 box jumps. Repeat the sequence three times. Put two hula-hoops on the ground, about a metre away from each other. Jump into one hoop, landing on one leg. Bend your knee slightly to stabilise yourself. Jump into the second hoop, this time landing on your other leg. That’s one rep. Do 20.