Very true and I didn’t clarify that I was coming from the standpoint that arterial and venous issues are not infrequently hand-in-hand (my bad for not clarifying).
Some people are now using 100% occlusion (may not be true 100%) though, so your point about proper use definitely comes into play. The cuff itself obviously has no clue what it’s occluding.
Sorry! That’s the unfortunate part of the TR forum — random spit take boobytraps! It’s happened to me! 
False:
Blood flow restriction reduces arterial blood flow to working muscles while also occluding venous return.
(https://www.frontiersin.org/articles/10.3389/fphys.2019.00810/full)
Blood flow restriction (BFR) is a training method partially restricting arterial inflow and fully restricting venous outflow in working musculature during exercise.
When the cuff is inflated, there is gradual mechanical compression of the vasculature underneath the cuff, resulting in partial restriction of arterial blood flow to structures distal to the cuff
(Blood Flow Restriction Exercise: Considerations of Methodology, Application, and Safety - PMC)
I guess this is why BFR/occlusion “training” is dangerous for the medically/professionally unsupervised general populace — too much easily accessible forum babble.
Yes, studies have shown that BFR training might be “safe” for CAD patients (Blood Flow Restriction Resistance Exercise Improves Muscle Strength and Hemodynamics, but Not Vascular Function in Coronary Artery Disease Patients: A Pilot Randomized Controlled Trial - PMC), but to say it has no effect on arterial flow is flat out incorrect.
Science > bros.
If you think I am advocating Bros > Science, I would suggest you are misinterpreting my posts.
However, you have spent a good deal of time claiming BFR is dangerous and broscience and just cited at least one study that clearly states there was benefit to it.
I would also note that your first link was using much higher pressures than my understanding is recommended for BFR (partial to complete occlusion…it also notes pressure up to 300mmHG, which is a LOT of pressure and would be quite painful for those using those pressures).
Again, I am not advocating for or against BFR, especially as it pertains to endurance training. There is clearly evidence to indicate that it is of benefit in some cases.
Lie any new, emerging protocol, there is still much to be learned.
Y’all do realize that it is common to completely block blood flow to muscles for well over an during surgery? Skeletal muscle ain’t like the heart; it doesn’t need a continuous supply of oxygen to survive.
In my job we are taught that a tourniquet, placed as tight as possible, can be applied for 3-4 hours without the risk of causing further damage and/or losing the limb. Of course this is to prevent bleeding out and not the same thing, but interesting nonetheless 
.
Good article. Thanks for posting that. There is a ton of good info in there regarding it’s proper use and results. It’s pretty much a meta analysis that covers almost every concern that has been listed in this discussion to date.
I was surprised to see there’s also been significant research with aerobic exercise (running & cycling) as opposed to mostly resistance exercise (weight lifting.)
If you’re interested in BFR, that looks to be the most comprehensive research article I’ve seen to date - and yes, you are correct that they state that arterial blood flow is restricted as well for what it’s worth.
Where did you get taught that? 3-4 hours is way too long for a tourniquet. Anything over 2 is questionable. This study (Tourniquet time affects postoperative complications after knee arthroplasty - PMC) showed anything over 100 minutes had complications post-surgery. I’d double check that info. We have an alarm that goes off at 90 minutes of tourniquet time and I’ve never seen any longer being used (N=1 obviously).
And of course, muscles aren’t contracting during surgery. Then again, even if they were the ischemia would result in such rapid fatigue that it would have limited impact on the length of the harm-free time.
I suppose you could also point to diving mammals as an example of how well muscle can tolerate lack of oxygen delivery.
That could be considered a total ischemic environment and can be observed naturally in active powerlifters (and even higher pressures!!!).
Ischemic preconditioning (heart) has and is used with CAD/CVD patients, both pre and post-op to good effect, allowing a greater HR range for exercise. As well, if the diseased patient can’t exercise, BFR training (essentially ischemic preconditioning) can be used to elicit exercise-like benefits without taxing the heart.
As long as I can exercise there is zero reason for me to undertake BFR. 
Do these diving mammals have the same physiology as diving humans? 
Paging Dr. Moreau…Paging Dr. Moreau…
From over the last decade working with top tier tactical and combat medics. I will take their real life experience over a medical study 20 years ago of knee arthroplasties in a bloodless environment. Of course we’re comparing apples and oranges here, saving lives in a blood involved field versus a “bloodless field” per the study. That being said per the study:
“It is generally recommended that the use of tourniquet should be limited to two hours due to the risk complications, however, that these complications are mostly minor and of a short-term nature and that there are no contraindications to longer tourniquet time when necessary.”
When the options are death or damage from a tourniquet, I would hope they choose keeping the tourniquet on longer. I don’t think many soldiers are going to be picky when they’re losing massive amounts of blood.
And the study was from 2013 so not too old. Regardless, as I think we’re veering off topic, I’d be interested to see some long term studies on this. Plus I don’t think these products are meant to stay on that long.
I might be missing something, but are there any studies that suggest doing 2-4 hours of BFR for endurance training? From personal experience, if you can mentally tolerate any longer than 20 minutes of BFR while cycling, you are a beast!
It seems that there are quite a few misconceptions of how BFR is used, beyond gym bros strapping up their arms and flexing in mirror. I’m not a medical expert by any means, but I’ve given BFR a shot with the help of physical therapists that specialize in BFR, so I’ll summarize my n=1 experience with a few key points that I’ve learned along the way:
BFR is safe, given you have cuffs that measure occlusion pressure and you have measured what your personal 100% limb occlusion pressure (LOP) is. Establishing an accurate LOP from the beginning is also important because it ensures consistency from session to session and basically sets up your “training zones” in terms of % of LOP.
BFR is not the same as a tourniquet that completely occludes blood flow. BFR training zones are based on your personal LOP, which can be measured using a doppler device such as the Edan SD3 Vascular Doppler. For the BFR cycling intvervals that I was prescribed by my PT, the cuff pressure ranged from 60 - 80% of LOP depending on the workout.
BFR training sessions are short. The BFR cycling workouts I was prescribed were always under 30 minutes long, and included no more than 20 minutes of working intervals.
BFR sessions are hard! There were a few 20 minute interval sessions that I mentally caved on because of the discomfort. Think of the feeling in your legs at the end of a 105% FTP interval, but extend that feeling for 15 more minutes… all the while, your HR is only 135 bpm… and you’re only pushing 120 watts
BFR isn’t a replacement for volume. This is probably obvious, but BFR isn’t intended to replace long rides or sweetspot/threshold/vo2 workouts. From my understanding, BFR may provide some of the same benefits as a VO2 or threshold workout, but in less time and with less stress on your body.
Here’s what my PT had to say regarding the training benefits to expect from BFR:
“VO2Max is a 3 tier system: Lung, Heart/Circulatory, Muscle. Many athletes once they reach a higher level of performance don’t have a respiratory limitation, instead they have a physiological limitation in the muscle capability to maintain work capacity. That’s were BFR excels. It can increase formation of new vessels (leading to greater oxygen delivery), it increases mitochondrial ability to utilize oxygen for energy production, it changes perception of fatigue (though Afferent fibers communicating with the CNS). Putting all the pieces together, it makes it an incredible tool.”
To summarize my n=1 experience with BFR and cycling, I can’t say for sure if (and by how much) it improved my performance on the bike. I followed a BFR cycling program of 2-3 workouts per week for a couple months at the beginning of 2019. During that program, the interval duration and occlusion pressure were increased incrementally, similar to the type of progression you see in TR’s programs. At the end of that time, I had a small increase in FTP (and some noticeably more vascular quads!) Hard to say how much performance improvement was attributed to BFR as opposed to my regular TR workouts.
This year I don’t intend to do any BFR training since I would rather spend that extra training time on the bike (without cuffs) or improving my strength in the gym.
To wrap this up, I wouldn’t write off BFR for cycling as pseudoscience or as dangerous. At the same time, it seems be in its infancy for use in endurance training and needs more established research and training protocols to prove its effectiveness for cyclists that already have a decent level of fitness.
I just skimmed through this whole post, and I must be missing something. I just stumbled onto BFR/Occlusion training on the recommendation from a highly experienced Orthopedic surgeon friend of mine who specializes in total joint replacements. He’s recently done some investigation of the science, and spoke directly with Jim Stray-Gundersen, MD, CMO/co-founder & developer, B Strong about the clinical protocols and scientific evidence for BFR training efficacy as he is rehabbing his own broken ankle.
From my understanding, this form of training could be [less] damaging, given the lower physiological stress/damage to the muscles targeted. I.e. significantly lower loads, but forcing the cells to deal with the overload of metabolic byproduct that can’t be cleared because of the veinous flow restriction. As I understand it, the overload/pooling of the metabolic byproduct is believed to prompt the adaptive signaling. I.e. you get the same effect of overloading the muscle with lactate to stimulate the adaptive processes, without the higher stress required without BFR–muscles recover faster, with less micro tearing/damage, but the signal is potentially just as strong.
I watched some very informative YouTube videos that went through the science and hit on some of the history of BFR training. In particular, there was one titled “Symposium: Blood flow restricted exercise in…” by Sports Kongres that went through a ton of scientific studies along a few different applications. I was Zwifting at the time, so didn’t take it all in, but that and whatever auto-played afterwards seemed to sell me on the concept. This form of training has a ton of application and science in the construct of rehabilitative therapies, and has been used by Olympic athletes and teams. And, apparently the history of its use has been quite long in Japan without significant risks.
@Mikael_Eriksson interviewed Brendan Scott, PhD on episode #87 in December 2017 on his “That Triathlon Show”, which was also pretty informative too. That Triathlon Show: Blood Flow Restriction training with Brendan Scott | EP#87 I wish he’d revisit this topic, as he is clearly science based and the timing of his show at Christmas time in 2017 may have missed many people’s radar.
Based on my cursory review of evidenced based material I could find on YouTube, and the fact that it was good enough for the doctor to use on himself, I was sold and ordered by B Strong Training System yesterday. I do want to see more science on the endurance side for BFR, but I am thinking this could be a very effective way to sustain/build strength and muscle mass via weight-lifting without exacting an overly burdensome recovery process that detracts from my ability to train on the bike…this is where I think the real gains could be made.
@Nate_Pearson and @chad have said many times on the TR podcast that the toll of weightlifting comes at the expense of on the bike training. I’d be keen to get their take on this as a potential easy get for those of us who want to focus on the bike, but still maintain/get some strength training benefits.
I am frankly stunned that I have not stumbled on this sooner…?
Showed up in my news feed this morning:
https://www.engadget.com/2020/01/05/smarttools-smartcuffs-blood-flow-restriction-training/
^^ This. Imagine getting many of the benefits of weight training but not having to try to figure out where to fit it into your overall training schedule.
Apparently your PT never studied exercise physiology. While the central circulation is the primary limiter of VO2max in everyone, that is especially true in endurance trained individuals. Conversely, their exercise capacity is even less limited by peripheral factors. Both of these are of course due to the fact that peripheral adaptations to training are much greater in magnitude than central adaptations.
I know a guy who put a clothespin “somewhere” once. I didn’t like it. I mean he didn’t like it.