“The cyclicality of hard alternating with easy plays out not only in the day and the week but also across training cycles and even across years. Think of Olympians who take an easy year or two in their quadrennial cycles. Check that there is variety across your training at every level, from the cooldown after a hard workout to the easier year after a particularly tough season. Active recovery, both in easy workouts and in easy days, introduces variability to training. Remember Carl Foster’s finding, outlined in Chapter 4, that athletes can adapt better to a greater overall training stress when it is variable instead of monotonous. Make the easy days really easy so that the hard days can be truly hard. If you can rein in your effort on your easy days, you’ll have room to push a little faster or a little longer on your hard days, yielding a much bigger fitness reward than simply muddling through with easy days that are too hard and hard days that therefore become too slow or short.”