What factors are involved in hamstrings injury?
Hamstrings injury is the most frequent muscle injury in sports that require high speeds, such as football, rugby or American football.
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BFR (BFR) has emerged in recent years as a popular method for increasing muscle mass. This method is now used for different situations, from those individuals who want to promote muscle hypertrophy for aesthetic purposes to those who aim to attenuate the loss of muscle mass during the recovery of an injury. Professor Jeremy Loenneke, from the University of Mississippi, is one of the leading researchers in this field, and his work has widely contributed to much of what we currently know about BFR.
– Professor Loenneke, could you briefly explain the mechanisms by which BFR promotes muscle anabolism?
I prefer to think of BFR in three separate phases. The first involves BFR applied in the absence of muscle contraction, the second is BFR in combination with low-intensity walking/cycling, and the third is BFR in combination with low load (20-30% of max) resistance exercise.
The application of BFR by itself (Phase 1) has been shown to attenuate the loss of muscle mass and strength with immobilization. In other words, some loss still occurs but not to the same extent when BFR is applied. It is important to point out that this is based on a minimal number of observations and much more work is needed to better understand if and how BFR works when applied independent of muscle contraction. One potential idea is that the application of the cuff results in an acute change in intracellular swelling that might be important for anabolism. This, however, is only an idea and requires further study.
The second and third phase involves the application of BFR with muscle contraction. When BFR is applied with low-intensity walking/cycling, there is often a small change in muscle size and strength. The magnitude of this change will likely be related to the current training status of the individual. The largest changes occur when BFR is combined with low load resistance exercise. When this is done, the change in muscle size is similar to that of traditional high load resistance exercise. Of note, while strength does increase with low load resistance exercise in combination with BFR, the change is often less than that of high load resistance exercise. The mechanism behind the changes observed has been hypothesized to include the acute change in intracellular swelling and the accumulation of metabolites around the muscle. The metabolic accumulation may provide a reason for the high levels of muscle activation observed with this form of exercise. Once the muscle is activated, the anabolic signalling cascade is likely the same as that observed with traditional high load resistance exercise.
– Which are the benefits of BFR in sports and particularly for the rehabilitation phase?
First, I would like to state that I am not a clinician. I am an academic that studies BFR. I view my role as someone who can provide information to the clinicians so that they can use that knowledge in combination with their own clinical experience/expertise.
If one considers those three phases, the application of BFR in the absence of exercise could be used in situations where an athlete is immobilized. This has some (albeit very limited) data that this may slow down the loss of muscle mass and help maintain function. If the athlete can walk/cycle at a low intensity, the application of BFR may help to enhance the exercise stimulus.
For example, there is some evidence that there are small increases in muscle size and strength when low-intensity aerobic exercise is combined with BFR. If an athlete is capable of resistance training with low loads, then this would be the phase where they would expect to see the largest changes in muscle size and strength. Other potential benefits include changes in the vascular network that might help support muscle adaptation/recovery.
Recent work has suggested that the use of BFR may help reduce pain (at least acutely) which might also be a strategy to implement prior to performing a rehabilitative exercise. A brief bout of BFR prior to the normal standard of care may help individuals have a higher quality of session of therapy. This is only an idea and requires further study.
Whether BFR can meaningfully change the tendon is uncertain. Changes at the tendon likely require a heavier load but additional research is needed.
– Is there enough evidence to affirm that BFR is safe?
I think the evidence is there so suggest that, if done appropriately, BFR can be safely applied. Two common concerns center on muscle damage and blood clotting. There is always the possibility for either occurring with regular exercise but adding BFR does not appear to add to the risk (if applied appropriately).
Two other concerns that have been raised is whether the application of BFR may exaggerate the cardiovascular response in certain populations. It is true that BFR augments the cardiovascular response to a repetition matched control but the magnitude of this change is relatively comparable to what is observed with traditional resistance exercise. Another is the impact that repeated BFR may have on the veins (more specifically the valves) given that this form of exercise causes venous pooling. Our laboratory and others have not observed negative effects on the veins following repeated use, however, this is relatively understudied and requires further research.
– Which conditions/rules should we consider to ensure the safety of BFR?
BFR should be applied based on the cuff being used and the individual to which the cuff is being applied. For example, there are cuffs made of different materials (i.e. nylon, elastic) and widths (narrow: 3cm vs. wide 20 cm). Failure to account for either one (particularly cuff width) will have a large impact on the pressure being applied. For example, the wider the cuff is, the less pressure is needed to restrict blood flow. This does not necessarily mean it is better, it is simply a reflection of how pressure is transmitted to the tissue. The other component that should be accounted for, is the individual to which the cuff is being applied. For example, those with larger limb circumferences tend to require greater pressure than those with smaller limb circumferences. If the same pressure is applied to every individual then the stimulus applied will likely be different between individuals.
Both of these factors seem to be accounted for by using what is called a “relative pressure”. For example, place whatever cuff is going to be used for BFR on the upper portion of the arm or leg. The cuff will then slowly be inflated until one finds the lowest pressure at which there is no pulse in the limb distal to the cuff. This is termed the limb occlusion pressure. A percentage of this limb occlusion pressure is then applied to the individual because the goal is partial BFR. In other words, if the limb occlusion pressure is 100 mmHg and the goal is a relative pressure of 40% then one would apply 40 mmHg during the exercise. Since the pressure will be taken on the individual’s limb with the same cuff that will be used during exercise, one accounts for both the cuff and the individual with a single measurement. For muscular adaptations, pressures between 40% and 90% of limb occlusion pressure result in similar changes. Vascular adaptations may require higher pressures (~80% of limb occlusion pressure), but more work is needed to be certain.
– How would you recommend, from a practical point of view, to implement BFR in an injured athlete?
Assuming they are not contra-indicated to this form of training, I would have them perform sets low load resistance exercise with a goal number of repetitions (30 reps for the first set, followed by 3 sets of 15 OR task failure, whichever comes first) with 30 seconds of rest between each set. I would aim for a load around 20-30% of their max and use the repetitions as a guide for load progression. If they can execute all 75 repetitions (30-15-15-15) with proper form, then I would recommend progressing the load slightly. I would set the pressure anywhere between 40-80% of their resting limb occlusion pressure (i.e. lowest pressure at which there is no flow distal to the limb).
If the athlete cannot perform low load resistance training, I would recommend low intensity walking or cycling in combination with BFR. This may help the athlete get a little more adaptation out of every step/repetition than they would get with the same exercise without BFR. Protocols typically involve slow walking (~50 m/min) or low-intensity cycling (~40% of max aerobic capacity) for around 20 minutes. I would set the pressure anywhere between 40-80% of their resting limb occlusion pressure. However, the effect of different relative pressures is largely unknown as walking/cycling is not as well studied as blood flow restricted resistance exercise. Once the athlete can perform resistance training, I would recommend progressing to that. Again, assuming the goal is to try and recover muscle size and strength.
If the athlete cannot perform any muscle contraction, I would recommend that they might want to consider inflating and deflating the cuff multiple times in the morning and the evening. There is some, albeit minimal, evidence that this may lessen the atrophy seen during unloading and may help to maintain muscle function. This protocol typically involves inflating a cuff on an individual as they sit reclined slightly with their legs out in front of the. The cuff is inflated for 5 minutes and deflated for 3 minutes. This is repeated five times in the morning and again later in the day. The pressure likely needs to be closer to 80% of limb occlusion pressure, however, the effect of different relative pressures has not been well studied with this protocol. Once an individual can perform either low intensity/load aerobic or resistance exercise, I would progress them towards that in an effort to maximize adaptation.
– Do we need expensive materials (e.g., Doppler ultrasound) to implement and control BFR?
It is not necessary to use expensive equipment in order to use BFR. We proposed a practical model of BFR within the literature approximately 10 years ago. Since then, several studies have shown that the application of knee wraps to a limb is capable of producing favorable muscle adaptation. The limitation is that the pressure applied is not known. For healthy individuals interested in muscle growth, this is probably not a large concern because a wide range of applied pressures has been shown to result in similar changes. However, in a clinical setting, it might be important to know how much blood flow is being restricted. One suggestion has been to use a perceived tightness scale of “7” out of 10. This scale was proposed to restrict venous flow but not occlude arterial inflow. The issue with this scale is that it results in a wide range of relative pressures applied. In addition, recent data from our laboratory, suggests that individuals cannot reliably set the BFR pressure using the “7” out of 10 scale. For example, a rating of “7” may produce 30% arterial occlusion pressure on one day and lead to 90% on another day. One alternative that we have been working on is the application of the cuff relative to the size of the limb. For example, pulling the cuff to a percentage of the limb circumference. When this is done, we have shown similar reductions in blood flow to that observed with more expensive equipment. This, however, has only been demonstrated at rest and we do not know if this changes with exercise.
Thank you very much for your collaboration, Prof. Loenneke. We are sure that this information will be of much help to our readers.
In addition to Dr Loenneke’s interview, we’ve also spoken to Javier Ruiz, physical trainer and rehabilitator of Barça’s basketball team, where BFR has already been implemented.
Javier, what’s your opinion about this new technique?
From our point of view, the BFR framework offers an injured athlete a fundamental advantage: that of attempting to reduce the atrophy process as far as possible during the injury period. The injured player’s functionality is altered for a specific length of time during which their physical capabilities are decreased. Training with BFR allows us to try and reduce the loss of muscle mass and functionality, which will be key, not so much in reducing recovery time, but in adding quality to the process.
BFR combined with low-intensity exercise (up to 30% of RM) allows us to generate intracellular changes as a result of the accumulation of several metabolites that generate a muscle activation similar to the work done at high intensity. This is why an athlete who is not prepared to withstand a high mechanical load (HIT work, for example), can activate a greater number of muscle fibres, thus benefiting from the metabolic change occurring from the use of BFR. This change is also responsible for activating the pituitary gland which releases GH (growth hormone), which is key to the process of synthesising collagen, as well as increasing the number of satellite cells. There is also an analgesic effect that still requires further research to determine its exact origins, but which actually takes place: the player experiences less pain when doing low-intensity exercise combined with vascular restriction. And this entails a tremendous benefit when it comes to any Return To Play (RTP) process.
It is important to take some methodological aspects into consideration. From our point of view, the process of individualisation is key: applying the correct pressure to the cuff will allow us to get the desired effects more specifically. In short, though, we can say that BFR seems to be a good tool for both rehabilitation processes and the player’s own management of the pathology as they face more and more demanding schedules. The objective is always clear: to use these anabolic effects that make it possible to give the affected structure a metabolic addition without the implicit stress of the mechanical load.
As we can see, not only does BFR have strong scientific evidence to back it up, it is also being integrated into the training of athletes at the highest level.
The Barça Innovation Hub team
An article published in The Orthopaedic Journal of Sports Medicine —in which members of the club’s medical services participated— now suggests to consider the detailed structure of the area affected, and treating the extracellular matrix as an essential player in the prognosis of the injury.