One of the huge advantages of Blood Flow Restriction (BFR) for rehab professionals is the ability to achieve similar muscle changes to heavy load training but with much lower loads. This has a clear benefit when working with someone who isn’t able to tolerate higher intensity exercise. But one important question to ask is: Does BFR truly replace the importance of mechanical loading?
The short answer is "No." While BFR is great for reducing the load needed to achieve fatigue and stimulate an anabolic effect, one must still achieve a session volume (weight x total reps performed) similar to that of heavy load training. And while the ability to lift light has inherent appeal, there is likely a floor beyond which you cannot continue to reduce load and expect equivalent outcomes. Let’s examine how this might look at different percentages of an individual’s one rep max (1RM).
15% 1RM
The BFR evidence is quite limited when it comes to the investigation of loads that do not meet the standard of 20-40% 1RM set out by the methodology paper spearheaded by Dr. Stephen Patterson. (Patterson et al. 2019) On the whole, the exercise physiology literature is far more robust regarding very light loads such as 15% 1RM. Generally it would indicate that one’s training status will interact strongly with the need for external load. Put simply, the more resistance trained the individual, the more load will matter. Regardless of training status, as loads dip below 30% 1RM, they seem to have a lesser effect on force production as an outcome than hypertrophy. (Schoenfeld et al. 2021)
Jessee et al used an 8 week training period to tease out the effect of 15% 1RM knee extensions with BFR at different pressures vs both a load matched free flow control or 70% 1RM. (Jessee et al. 2018) BFR was performed at either 40% LOP or 80% LOP. All groups performed 4 sets to failure to ensure equal effort across groups. Following 16 sessions, muscle thickness increased in all groups with no difference between groups. However, only the 70% 1RM group demonstrated a significant increase in 1RM strength.
Similarly, Buckner et al used the same methods to examine the effects of 16 sessions of biceps curls. (Buckner et al. 2020) Since it’s generally accepted that higher relative pressures are necessary in the lower extremities, this allows for the examination of whether or not the magnitude of pressure might augment the effect of the very light load. Following the eight-week training period, each condition increased muscle thickness, however the 70% load condition produced significantly greater changes in muscle thickness. When looking at changes in strength, only the 70% condition had an increase in 1RM strength. Given the suboptimal muscle changes with very low loads the authors concluded, "Blood flow restriction [even with high pressures] cannot be used to compensate for an insufficient external load."
The research tends to suggest that very low loads create minimal or at least a suboptimal muscle response and we shouldn’t train with them for an extended period. However, this doesn’t mean there isn’t a benefit to using them in rehab. Clinically, this can be beneficial when trying to progress someone from a passive protocol into resistance exercise or when acclimating the individual to BFR. Effort (proximity to failure) is still king when it comes to muscle growth. This highlights the importance of adding exercise volume and/or cuff pressure when mechanical loading is at its lowest. Focusing on these targets instead of an arbitrary number of reps likely gives us the best chance of ensuring progress when the load is inadequate.
20% 1RM
A training load set to 20% of the individuals 1RM appears to be the lower threshold to produce similar muscle adaptations to heavy load training. One of the early projects looking at the physiologic effects of low load BFR training was done by Laurentino et al. (Laurentino et al. 2012) In this project, the authors had individuals perform knee extensions for eight weeks separated into a high load condition at 80% 1RM and two low load conditions at 20% 1RM; one with BFR at 80% LOP and the other without BFR. Following sixteen sessions, the high load group and BFR group had significantly greater improvements in knee extension 1RM strength and CSA compared to the traditional low load group.
More recently Biazon et al conducted a 10 week training study comparing heavy load with and without BFR to low load with BFR. (Biazon et al. 2019) The set/rep scheme was 80% 1RM for 3x10 for both heavy load conditions and 20% 1RM for 3x20 in the low load group. Following the 5thweek, an additional set was added to each condition. Pressure was set to 60% LOP for both BFR conditions. Following the 10 weeks of training, all groups significantly increased their 1RM compared to baseline with no difference between groups. Muscle CSA measurements also significantly increased for all conditions with no difference between groups. The results from this paper indicate a load of 20% with BFR is just as effective as training at heavy load and there seems to be no additional benefit to performing BFR with heavy load.
Collectively, and in agreement with Patterson 2019, these papers indicate a load of 20% 1RM should be the targeted entry point to BFR resistance exercise with a tourniquet pressure in the lower extremity that is relatively high, between 60-80% LOP.
30% 1RM
A training load of 30% 1RM with BFR has generally been considered the preferred training load to produce similar muscle changes to heavy load training. For instance, in an 8 week study Kim et al separated individuals into three conditions. (Kim et al. 2017) There was a training group who completed 24 sessions and had each arm randomized to either 75% 1RM biceps curls or 30% 1RM biceps curls with BFR at 50% LOP. The training conditions were compared to a non exercising control group. Following the training period, there were significant increases in muscle thickness for both training conditions with no difference between conditions. Additionally, 1RM strength significantly increased in both training conditions.
In a more clinically relevant example, Hughes et al enrolled individuals coming off a recent ACLr into performing a structured PT program with the addition of a leg press exercise. (Hughes et al. 2019) The two training conditions for the leg press were 30% 1RM with BFR at 80% LOP or 70% 1RM to target traditional heavy load. Following the 8-week training period, both conditions had a significant increase in muscle fiber thickness and pennation angle as well as 10RM leg press strength, with no difference between groups. In another clinical example, Dr. Noyes et al looked at the effect of BFR amongst those with chronic strength loss following a variety of knee surgeries.(Noyes et al. 2021) On average, subjects had a 43% deficit in quadriceps strength at 8 months post-op and had completed 5 months of structured PT. Individuals initially performed 9 sessions of BFR resistance exercise at 25-35% 1RM with pressures ranging from 60-80% LOP. The authors noted higher pressures were used with lower loads and a lower pressure if the individual was able to perform the exercises in the higher load range. Following the initial 9 sessions, the individuals were encouraged to perform an additional 9 sessions. After 9 sessions, 69% of the patients had a 10% or greater increase in MVIC (isometric strength). Following 18 sessions, 86% of the patients had a 20% or greater increase in quadriceps MVIC.
30% of an individual’s 1 RM has been one of the most common target intensities for BFR studies. It appears to be an adequate training load to create a similar response to traditional heavy load training but may still require a fairly high cuff pressure like 60-80% LOP in the LE to ensure that effect.
40% 1RM or more
Recently Alan Kacin’s group did a follow up to their initial ACL prehab paper where they took 18 individuals who were scheduled to have an ACLr and divided them into a BFR group or a sham-BFR group.(Kacin et al. 2021) Over a 3-week period, individuals performed 9 sessions of knee extensions and hamstring curls loaded to ~40% 1RM for 4 sets to failure. The BFR group used a pressure of 150mmHg with a wide tourniquet (13.5 cm). Following the prehab period, the BFR group significantly improved isokinetic strength at 60 degrees/sec by 14% and improved quadriceps CSA by 4.9% while the sham group had no change from baseline.
Lixandrão et al conducted a longer-term knee extension study looking at the effect of two different loads at two different percentages of LOP and compared those to a high load group exercising at 80% 1RM. (Lixandrão et al. 2015) The BFR groups trained at 20% and 40% 1RM with 40% LOP and 80% LOP for each loading condition. The set/rep scheme was 2-3 sets of 15 for the BFR conditions and 3 sets of 10 for the 80% load group (which creates significant volume differences). Following the 12-week training period, muscle CSA significantly increased in all groups except the 20% 1RM/40% LOP group. The greatest increases came from the 40% load groups (regardless of pressure) and 80% 1RM. The results in CSA indicate when the load is low one needs to keep a high pressure, but as the load is increased towards a moderate load the pressure can be decreased. There were similar increases in strength amongst all BFR conditions, which were significantly lower than the change in 1RM strength in the 80% 1RM group. One should consider these results with caution as the volume of work was not close to being equated nor did the low load groups demonstrate a high amount of effort.
Moderate loads such as 40% 1RM with BFR can be utilized to progress exercise intensity when the individual would be unable to tolerate high intensity training. From the available data, when training at this intensity a lower pressure of 40-50% LOP could be utilized.
Manipulating the set/rep scheme to produce a similar exercise volume as high load training is a great strategy. For example, 30/15/15/15 with 30% 1RM, 25/15/15 at 40% 1RM, 15/15/15 with 50% 1RM, and 10/10/10 at 75% 1RM would all produce a similar training volume (weight x reps).
Takeaways
BFR reduces but it doesn’t replace the importance of load. Very low loads can be effectively used to improve tolerance and slow down the loss of muscle during the very acute phases of rehab (check out our blog on Anabolic Resistance or our podcast on preventing muscle atrophy for more on this). However, to achieve similar results to high load resistance training while using BFR, it looks like we need a training load of 20% 1RM or above and to use a relatively high pressure (60-80% LOP in the lower extremity or 50% LOP in the upper extremity) when at that 20% intensity. As the loading increases, the cuff pressure can likely come down. The individual’s strength should continuously be monitored and the training loads adjusted/progressed to reflect their change in strength. This can be accomplished by formally determining an individual’s maximal strength or multi-repetition max every 4 weeks and progressing their working weight after the individual is able to complete the prescribed sets and reps. If we can account for these within session targets of effort, load, and cuff pressure, then we should see consistent effects from our use of BFR.
References:
1. Patterson, S. D., Hughes, L., Warmington, S., Burr, J., Scott, B. R., Owens, J., Abe, T., Nielsen, J. L., Libardi, C. A., Laurentino, G., Neto, G. R., Brandner, C., Martin-Hernandez, J., & Loenneke, J. (2019). Blood Flow Restriction Exercise: Considerations of Methodology, Application, and Safety. Frontiers in Physiology, 10, 533.
2. Schoenfeld, B. J., Grgic, J., Van Every, D. W., & Plotkin, D. L. (2021). Loading Recommendations for Muscle Strength, Hypertrophy, and Local Endurance: A Re-Examination of the Repetition Continuum. Sports (Basel, Switzerland), 9(2). https://doi.org/10.3390/sports9020032
3. Jessee MB, Buckner SL, Mouser JG, et al. Muscle Adaptations to High-Load Training and Very Low-Load Training With and Without Blood Flow Restriction. Front Physiol. 2018;9:1448.
4. Buckner SL, Jessee MB, Dankel SJ, et al. Blood flow restriction does not augment low force contractions taken to or near task failure. EJSS . 2020;20(5):650-659.
5. Laurentino GC, Ugrinowitsch C, Roschel H, et al. Strength training with blood flow restriction diminishes myostatin gene expression. Med Sci Sports Exerc. 2012;44(3):406-412.
6. Biazon TMPC, Ugrinowitsch C, Soligon SD, et al. The Association Between Muscle Deoxygenation and Muscle Hypertrophy to Blood Flow Restricted Training Performed at High and Low Loads. Front Physiol. 2019;10:446.
7. Kim D, Loenneke JP, Ye X, et al. Low-load resistance training with low relative pressure produces muscular changes similar to high-load resistance training. Muscle Nerve. 2017;56(6):E126-E133.
8. Hughes L, Rosenblatt B, Haddad F, et al. Comparing the Effectiveness of Blood Flow Restriction and Traditional Heavy Load Resistance Training in the Post-Surgery Rehabilitation of Anterior Cruciate Ligament Reconstruction Patients: A UK National Health Service Randomised Controlled Trial. Sports Med. Published online July 12, 2019. doi:10.1007/s40279-019-01137-2
9. Noyes FR, Barber-Westin S, Sipes L. Blood Flow Restriction Training Can Improve Peak Torque Strength in Chronic Atrophic Postoperative Quadriceps and Hamstrings Muscles. Arthroscopy. 2021;0(0). doi:10.1016/j.arthro.2021.03.040
10. Cook S, Cleary C. Progression of Blood Flow Restricted Resistance Training in Older Adults at Risk of Mobility Limitations. Front Physiol. 2019;10:738.
11. Kacin A, Drobnič M, Marš T, et al. Functional and Molecular Adaptations of Quadriceps and Hamstring Muscles to Blood Flow Restricted Training in Patients with ACL Rupture. Scand J Med Sci Sports. Published online April 10, 2021. doi:10.1111/sms.13968
12. Lixandrão ME, Ugrinowitsch C, Laurentino G, et al. Effects of exercise intensity and occlusion pressure after 12 weeks of resistance training with blood-flow restriction. Eur J Appl Physiol. 2015;115(12):2471-2480.
