I'll summarize as best I can from my readings.
Basically athletes perform one set of twenty reps for 15-20 different exercises. The program generally proceeds from multi-joint exercises to single joint exercises and, as described in the book features lots of simple, single joint exercises that we would never use at MBSC.
However, that does not take away from the concept of a higher volume, lower intensity phase as a change up. It is important to note that , as with any programming concept, you can feel free to interpret the idea in your environment.
For us at MBSC, I like the 1x20 as a change up for athletes that we have year round.
In a twelve week off-season program 1x20 is not a great fit but, for athletes we have year round it can be a great change of pace.
First let me start out and say that, at least according to what I have read, 1x20 is a bit of a misnomer. Athletes only do 1x20 in week 1 of the program and, over a three week phase the program is actually 20-14-10 or 20-14-8.
If you are a percentage person (and for simplicity sake, I am) we did:
60% in week 1
68% in week 2
78 percent in week 3.
( PS- yes, I know this isn't perfect but, trust me and try it.)
We also had to figure out how an idea like 1x20 fits for power exercises ( Olympic lifts where we'd never do 20 reps), bodyweight exercises like chin-ups, and unilateral exercises.
Our solutions were as follows.
Olympic lifts- instead of 1x20 we start with 4x5 for a total of twenty reps of, in our case, hang clean.
Chinups- the goal is 20 reps in as few sets as possible. We push for a max set on set 1 and then, fill in the rest.
Unilateral Exercises- for unilateral exercise we will do 10 reps on each side in phase 1. I'm just not a fan from a time or technique standpoint of sets of 20 for unilateral exercises.
Below is a sample program we used with our middles school group. Note that warm-up sets have been added for exercises that require them.