There is a difference between 20 rep squats and 20 rep Breathing squats. Each version can be a killer but the 20 rep Breathing squats can also be a force of pure will power. I continued to do this system, from time to time, when getting ready for football season over the years. Great for ultra stamina (endurance and strength). Was 16 the first time beginning this type of training.
Geo did the 20 rep version in the clip. A tribute to the over the hill, or under the wave, USN veterans all over the world. Geo be the man. And the terror of the 78 and any beer bar in Oceanside/Carlsbad.
The idea is to load to your usual 10 rep max in the squat. Start by taking 3 deep and full upper chest breaths before every beginning rep. This can be accomplished for the first 5 to 6 reps at first. From this point you are going to need more deep breaths between every rep. When the 20th breath is reached you should be sucking in air in great masses. Probably up to 8 or 10 breathes, gasping for air. Might take between 3 to 5 (or more) minutes to complete the 20 reps. Here is where the pure strength of will and mind focus comes in.
Best to use a crampted/cam'ed squating bar, if anyone can find one now days. Easier on the traps and shoulder when squating. If using a regular Olympic bar, a pad/towel, etc under the traps/shoulder can help greatly.
Every workout you must add a 5 to 10 lb's to the bar. That is the point of this type of exercise, it is progressive from workout to workout. The body is trained to adapted to a newer workload each workout. Program is usually for twice a week. One set should do it. A few have done two sets a workout. Some old BB'ing vet told me, when I first started, if I can do 2 sets of breathing squats, the first one was not hard enough. One set, done right, you should be praying for death, it can be that hard. Not a program for most people anyway.
After all the sets are done take a light BB/DB and do 20 rep pullovers (working on the stretch). If you are young enough (anything under 24 to 25 years old..mean average) the cartilage between the ribs is still elastic enough to stretch. Which in return can expand the rib box to a lasting increase in chest size. That's the theory anyway. Have witnessed 2 to 3 inch increases on the total chest measurement for some. Only other exercise done along with this are moderate weight BB rows and benches, for regular reps of 8-10 for 2 sets each.
Have been 20 rep breathing squat programs, in the past, that only require your own bwt weight on the bar. So if you weighted 180, for example, that would be all the weight that is require for the program. Been told it is the massive amounts of oxygen taken in to the lungs and in return, to the blood stream that makes the difference in a 20 rep (or more) breathing type of program. And it's ability to build muscle.
All in all, a 20 rep breathing squat program is another version of Rest-Pause training. Which is very effective when wanting to add muscle mass a strength . Good Luck.
Side Bar: if not use to this type of training, the whole rib box may ache , like nothing else, for days. This is from the expanding of the rib box through deep breathing and stretch.