Blood flow restriction training: feel the pressure

Luke Heath looks at the evidence for blood flow restriction training; does it benefit athletes who require rapid post-injury rehab and if so, how should it be performed

Introduction

An inevitable consequence of lower limb injuries is muscle atrophy and weakness. Rehabilitation therapists and coaches want to find ways to limit this from happening, so an athlete’s recovery is speedy, safe and injury recurrence is prevented.

A traditional method of training athletes to increase muscle size and strength is high intensity resistance training (HIRT) with multiple sets of 5-12 repetitions at loadings greater than 70% of a single repetition maximum (1RM)¹. However, following an injury or surgery, it may not be possible to perform HIRT. Indeed, it may even further damage healing tissue and therefore cannot be performed at all. By contrast, low intensity resistance training (LIRT) at reduced intensities (20-50% 1RM) in conjunction with blood flow restriction (BFR) has been shown in research to be effective at increasing muscular hypertrophy and strength².

Figure 1: Blood flow restriction training

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What is blood flow restriction training?

Blood flow restriction training is achieved through the use of inflatable pressurised cuffs or tourniquets around a limb (proximal to the muscle being trained), which limits blood delivery to and from the contracting muscles (see figure 1) . Currently there are no standardised recommendations for the applications of BFR during LIRT³. However, it is important that an evidencebased, safe approach is used when applying BFR during resistance training. This article looks at the physiological mechanisms behind BFR with LIRT, and when and how it is currently used to rehabilitate athletes at the GWS Giants football club for lower limb injuries (see box 1).

Box 1: Physiology of BFR training

The mechanisms underpinning the hypertrophic and strength adaptations are yet to be fully determined. Research theorises that metabolic stress and mechanical tension both contribute to the hypertrophic and strength adaptations when performing BFR and resistance training. Mechanical tension – This is the process by which mechanical strain is placed on muscles, which can induce muscular hypertrophy and strength. This is stimulated by HIRT. However, there is less mechanical tension on muscles whilst performing LIRT using BFR. Therefore mechanical stress appears to play a less important role in developing muscle hypertrophy and strength. However as an athlete introduces more HIRT in combination of LIRT with BFR, both mechanisms can work synergistically to increase muscle hypertrophy and strength. Metabolic stress – It has been theriosed that exercise-induced metabolic stress can induce muscular hypertrophy via various mechanisms, including elevated hormone production and increased fast twitch fibre recruitment. These mechanisms are thought to mediate muscle protein signaling and/or satellite cell proliferation, which are the basis of muscle growth. There is conflicting research on whether cell swelling, muscle damage and increased production of reactive oxygen species (ROS) play a physiological role in muscle hypertrophy and strength whilst using BFR and resistance training(4). Hormones – Metabolic stress is the accumulation of metabolites during exercise. The greater the lactate production (metabolites) during an exercise program, and the more fatiguing the exercise, the greater the growth hormone (GH) and insulin-like growth factor (IGF)-1 response – and therefore the greater the anabolic stimulus. Scott et al. (2015) showed the metabolic stress and muscle hypertrophy in a healthy population who undertook different exercise programs(3). Both programs consisted of two volume/ intensity-matched resistance exercise protocols (3-5 sets of 10 reps at 75% 1RM), with the only difference being the control group had a 30-second rest period at the midway point of each set. Results showed blood lactate concentrations (metabolic stress) to be significantly higher following the without-rest experimental group. Following 12 weeks of training, the without-rest experimental group showed significantly greater muscle crosssectional area versus the control group. With normal unrestricted blood flow, the typical workload of 3 x 10 reps of LIRT is insufficient to cause metabolic stress to cause muscular fatigue. However, the hypertrophic effects of the metabolic stress caused by HIRT have been also shown with using BFR and LIRT(5). The aim of LIRT using BFR is to therefore create a training environment where there is production of lactate, by inducing muscular fatigue. This is the metabolite that stimulates the production of GH and IGF-1(6-8). Fast twitch fibre Recruitment – The other mechanism behind muscle hypertrophy is the increased recruitment of type II muscle fibres with BFR using LIRT. The recruitment of fast twitch fibres is because of decreased oxygenation and metabolic accumulation as described above. Research has shown that there is increased activation and recruitment of type II fibres whilst using BFR and LIRT(6-8).

When is blood flow restriction training used?

Following an injury or surgery, atrophy of surrounding muscles is very common. For example, following ACL reconstruction, quadriceps muscle wasting is evident within the first week post operatively. Prevention of muscle atrophy and increases in strength is associated with greater athlete performance. It is therefore vital to restore muscular hypertrophy and strength to allow for a safer and quick return to play for an injured athlete. During the acute phases of rehab, it’s important to protect the healing tissue. HIRT, a traditional training modality for increasing muscle hypertrophy and strength may be contraindicated as it may further injure or compromise healing of an injured structure. For example, following a reactive patellar tendinopathy, the tendon cannot withstand HIRT. If the athlete is subjected to heavy resistance training, the tendon may become more painful and even further injury can occur.

There are only three studies that have utilised BFR in a rehabilitation based setting^{4 5 6}. Two of the studies are case studies only^{7 8}. One well-conducted study by Ohta et al examined a 16-week LIRT program using BFR on knee extensor and flexor strength following an ACL reconstruction⁹. Results showed strength was better maintained pre/post operation and between injured/uninjured limbs for the BFR group. The BFR group also showed a trend towards a significant increase in cross-sectional area of the knee extensors with no change in the control group.

Although there are no other high quality studies that focus on rehabilitation, there is a lot of evidence that shows BFR and LIRT can increase muscular hypertrophy and strength. Clinically, athletes with specific injuries could benefit from this type of training to accelerate their rehabilitation and return to play. The rehabilitation coordinator must liaise with the team sports physician or surgeon to get clearance to use BFR on athletes. Injuries that can benefit from LIRT using BFR are any lower limb injury (see Table 1).

Table 1: Indications for use of LIRT using BFR
Injury	Comments
Knee - ligament, meniscal, cartilage, fracture & surgery	-Ligamentous, chondral, meniscal, fractures and surgeries of these structures, will most often have loading restrictions during the acute phase of rehab. This is to ensure structures are not stressed and are protected, so they can sufficiently heal. Once the structure is safe to be loaded, the treating physician gives clearance, BFR and LIRT can commence. -ACL reconstruction – BFR can be utilized as soon as an athlete is clear to go on a bike. LITR usually commences at approximately the 4-6 week mark post-operatively. BFR and LITR can be used in the first 2-3 months where only low-load resistance training is tolerated and is indicated because the athlete is not allowed to load the in-mature graft and the knee may not be able to handle high mechanical stress. -Once the HIRT is indicated and the athlete’s knee can handle this training modality, LIRT and BFR can be used as a training adjunct on low training days or at the end of a HIRT training day for extra hypertrophy and strength gains.
Ankle - ligament, cartilage, fracture & surgery	- See first point in box above
Tendiopathy - Achilles, pattelar & quadriceps (reactive phase in particular)	-Tendinopathy occurs from a direct blow to the tendon or most commonly can occur when there is a mismatch between tendon capacity and load placed on the tendon. This occurs when there is a sudden and/or substantial change in load. -Quadriceps atrophy and thus weakness is a common presentation of patellar tendinopathies. This means the tendons are less likely to withstand the loads placed upon them. -Relative rest is the first priority to unload the reactive tendon and there should not be complete cessation of activities because this will decrease the overall capacity of the tendon. -In reactive tendons, isometric contractions with moderate-heavy loads can be effective in reducing pain. -It’s important that these exercises do not further aggravate the tendon, so care must be taken when prescribing the amount of resistance to be used. Close monitoring of how the athlete tolerates load prescription is advised. This is where utilising BFR and LIRT is indicated, as they athlete may not be able to tolerate HIRT. -The athlete will need to transition to HIRT as it creates necessary tendon stiffness – stiffness that from LIRT with BFR does not. LIRT with BFR can still be utilised during low-load training days to stimulate much-needed muscular hypertrophy.
Muscular/tendon strain - calf, quad, hamstring	-Tissue repair and protection via de-loading and/or complete rest are vital during the acute phase of a strain. The severity of the strain determines when the tissue can commence loading. Again LIRT with BFR should be the initial type of loading to restore muscle hypertrophy and strength. Once the athlete can tolerate HIRT, they should be weaned off LIRT and BFR. However they can continue to use BFR and LIRT as a training adjunct to HIRT.
Lower limb fracture - acute or chronic stress fractures & surgeries	- See first point in first box

Methods of blood flow restriction training

There are a number of variables to consider when applying BFR and using LIRT. These include: Type of cuff and occlusive pressure Training protocol Safety considerations Type of cuff and occlusive pressure Two important factors when using BFR are cuff width and cuff pressure. The cuff pressure in the literature is highly variable between studies. Moderate cuff pressures are recommended typically 1.3 times above systolic blood pressure (>120mmHg) or between resting diastolic blood pressure and systolic blood pressure (80-120mmHg)^{10 11 12}. Safe application using the Sports Rehabilitation Torniquet (SRT), which is an inflatable cuff of pressures between 90-150mmHg (ideally > 120mmHg). See this link below for correct application of the SRT: https:// www.youtube.com/watch?v=4J6KiXpl3sY

Training protocol

A typical protocol used in the literature whilst performing BFR with LIRT is 1 set of 30 repetitions, followed by 3 sets of 15 repetitions with 30-60 seconds of rest at a load of 20-30% 1RM¹³. It is important to note however that because of injury, an athlete may not be able to complete this amount of repetitions and sets, as it may induce too much mechanical stress. This may interfere with healing, re-aggravate an injury and even further injure the athlete.

Once an athlete has been cleared to commence LIRT using BFR its important to progress with caution and the protocol may be as little as 3 sets of 10-12 repetitions with a load of 20% 1RM. As the athlete improves they will be able to tolerate more repetitions, sets and loading. Once an athlete transitions from LIRT to the desired HIRT, BFR training can be used as an accessory training modality. For example, after a lower body HIRT session, some LIRT accessory lifts for quadriceps hypertrophy can be used, such as single leg squats or knee extensions with BFR.

LITR using BFR can also be used on low-load training days, when a HIRT is the main focus of the athletes training regime. For example if an athlete is to complete HIRT 3 times per week, LIRT using BFR can be utilized on two other days (see Table 2).

Table 2: Example of a training week with HIRT and LIRT using BFR
Mon	Tues	Wed	Thurs	Fri	Sat	Sun
HIRT	LIRT+BFR	HIRT	Rest Day	HIRT	LIRT+BFR	Rest Day

When utilising LITR with BFR, its important to cause metabolic stress whilst training; therefore short rest periods are key. Sets do not have to be performed to muscular fatigue¹⁴. Working to fatigue is a form of maximal training and may induce too much mechanical stress for the injury. The recommended training protocol for BFR and LIRT is shown in Table 3. The occlusion should remain on for the entirety of the sets for an exercise to allow for metabolites to accumulate.

Table 3: Training Protocol for BFR and LIRT
Load	Sets	Repetitions	Rest	Frequency
20-50% of 1RM	3-6	10-15	30-60 seconds	2-4 timers per week

Safety considerations

The use of BFR and LITR has been shown in research to be a safe training modality(12). Precautions must be taken as the use of a tourniquet presents a risk for blood clotting and venous emboli. Caution should be exercised if giving BFR training to those with compromised vascular status, or with any postoperative lower limb surgery. Tourniquet pressures recommended above using the SRT are unlikely to cause any damage to soft tissue structures under the cuff. It’s important to get clearance from a sports physician or the operating surgeon before applying BFR training, and normal safety considerations should be followed with respect to biological healing of the injury.

Summary

LIRT at reduced intensities in conjunction with BFR has been shown in research to be effective at increasing muscular hypertrophy and strength. More research needs to be done using BFR and LIRT with the injured population. Through the mechanisms described above, BFR and LIRT is a helpful training tool that can be used for injured athletes in early stages of rehabilitation, and as an accessory to HIRT. HIRT must not be forgotten, as this traditional training modality is important in building muscular strength and hypertrophy, which is vital in the later stages of rehabilitation before return to play.

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