Occlusion training (aka blood flow restriction or aka Kaatsu training) is an easy and safe way to rapidly increase muscle size with very light weights and inexpensive equipment.
Explain like I'm Five (ELI5)
Occlusion training is exerxising with tourniquets on your extremities (arms or legs).
Restricting the blood flow return from a limb traps metabolites (lactate and hydrogen ions) within the muscle tissue. Metabolites are waste by-products from muscular work.
The blood flow restriction also creates an oxygen debt. The muscles are forced to work in an oxygen poor environment.
The restriction also causes intense pooling and saturation of blood within the muscle, increasing capillary perfusion. It's the biggest pump you've ever had!
All this simply means an icreased stress on the muscle. Stress leads to adaptation. In this case the adaptation is mostly size and a little strength.
An alternate hypothesis: Some researchers believe the reason occlusion training works is due to an increase in muscular activation. Restricting blood, oxygen and metabolites makes the lifting more difficult. Because it is more difficult, the nervous system recruits more motor units to complete the lift. increased motor unit recruitment means more muscular activation means more growth.
Occlusion training is great for injuries, the elderly and the fatigued
Very light weight can be used so its ideal for injured athletes and very weak old people. Also, if you're totally fatigued from training hard, but you still want to get some work in, using light weight with occlusion can help you get that extra credit done with minimal risk for injury.
6.6% size increase in quads
This study, in The Journal of Strength and Conditioning Research, participants with an average age of 64 were divided. Those who used occlusion, lifted weight that was only 20-30% of their one rep max (very light weight).
Those who did not use occlusion, lifted weight that was 70-80% of their one rep max (moderately heavy).
The non-occluded (heavy) group made 7.9% growth in quads and the occluded (light) group made a 6.6% growth gain.
Not much strength increase
The non-occluded (heavy) participants made 54% increase in leg press strength, whereas the occluded (light) group only saw a 17% increase.
So, occlusion can't replace hard, heavy work when it comes to strength, obviously. But it comes pretty damn close for hypertrophic gains, and it does it with barely any weight. You're more likely to injure yourself driving to the gym than you are lifting 20% of your one rep max. For this reason, I love adding occlusion to my hard, heavy strength training. Bigger muscles have more potential for strength, and they look good too.
I've seen some really expensive high-tech bands designed specifically for occlusion training. This $2,800 set even has a hand held, touch screen. These devices look really cool and I'd love to try them out...but i'm still not un-poor. I use red Voodoo floss bands, because they're $25 and have a secondary function for mobility work. Click here for a video demonstration.
I suspect the high priced sets have a function to control tension, which my voodoo floss bands do not have. This is a nice feature, but it's not necessary. I've been using voodoo floss bands for several years and I've learned the tricks to wrapping for a good set.
How to wrap Voodoo Occlusion bands
Not too loose: Wrap the bands around the proximal end (near torso) of your limb. Be sure to wrap tight enough that the blood flow return to the torso is restricted. Your veins should bulge and your limb should swell and turn red.
Not too tight: Be sure not to wrap too tight. You don't want to completely cut blood flow off...just restrict it. Wrapping too tight will stop blood flow off from entering the limb. This hurts and defeats the purpose. Your limb will turn pale if you've wrapped too tight.
Wrap with equal tension from the first wrap to the last wrap. Don't start very tight and end very loose, or visa versa. Wrapping evenly enables us to easily and quickly decrease the tension slightly by unwrapping once or twice.
Go light: Use weight that is only 20% of your one repetition maximum. If you can curl 100 lb dumbbells, use only 20's. You will understand why once you try. It hurts.
Sets/Reps/Rest: After reading the research, I chose to go with 4 cluster sets of 30, 15, 15, 15 reps. I rest about 30-45 seconds between each set. Your arms and legs should be screaming by the end of the first set. Be sure to fully relax your limbs between sets and allow blood to swell into the limb.
Movements: This is really the only time I do isolated movements like curls and leg extensions. Be sure to move through the full range of motion (no half reps) to achieve a big stretch of the muscle, this is basic hypertrophy stuff. Stretch = growth
Explosive Concentric / Controlled Eccentric
It's likely that increased muscular activation is the whole reason why occlusion works. A trick to get even more muscular activation is by working explosively. Lifting the weight as fast as you can will recruit more fibers. Lifting fast also helps achieve full range of motion with the contraction.
Time under tension (TUT) is strongly correlated with muscle growth, so to get the absolute max growth out of occlusion training I slowly lower the weight for 4 seconds. If I'm feeling extra masochistic, I'll hold for a 2 count at the top.
Super sets: Occasionally I will super-set opposing muscle groups (bi's/tri's or quads/hammys), to save time. The benefit is that the bands dont need to be removed to work opposing muscle groups.
Add these to the end of your strength training:
Occlusion training did not replace any of my heavy strength training. It's more of an addition to the real hard work I put in. I peform 2-3 sets per week (only one per session), always at the end of training. It's like the icing on top of the cake. It's a great way to waste your muscle in just a few minutes before calling it quits. Nothing should replace good old fashion heavy lifting though.
My arms grew 1/4 of an inch in the first three weeks. My legs grew as well but I didn't measure so I'm unsure of how much. Unfortunately, the rapid growth rate decreased drastically after the third week. My tolerance for the pain of this training increased significantly.
What the science says
I've included some links below for your reading pleasure.