Blood flow restriction training: feel the pressure

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). 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 strength.

What is blood flow restriction training?

Blood flow restriction training is achieved through the use of inflatable pressurized 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 standardized recommendations for the applications of BFR during LIRT. However, it is important that an evidence-based, 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).

Physiology of BFR training

The mechanisms underpinning the hypertrophic and strength adaptations are yet to be fully determined. Research theorizes 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 — 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.
  • 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. 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. 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.
• 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.

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 postoperatively. 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 the healing of an injured structure. For example, following 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 utilized BFR in a rehabilitation-based setting. Two of the studies are case studies only. 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 reconstruction. 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 the 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

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). Safe application using the Sports Rehabilitation Tourniquet (SRT), which is an inflatable cuff of pressures between 90-150mmHg (ideally > 120mmHg). 

Correct application of the SRT

 

Training protocol

A typical protocol used in the literature whilst performing BFR with LIRT is 1 set of 30 repetitions, followed by three sets of 15 repetitions with 30-60 seconds of rest at a load of 20-30% 1RM. 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, it’s important to progress with caution, and the protocol may be as little as three 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 athlete’s training regime. For example, if they complete HIRT three 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

When utilizing LITR with BFR, it is important to cause metabolic stress whilst training; therefore, short rest periods are key. Sets do not have to be performed to muscular fatigue. 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

Safety considerations

The use of BFR and LITR has been shown in research to be a safe training modality. 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. Its 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 tools that can be used for injured athletes in the 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 returning to play.