Improving peak finger flexor force at reduced loads: Finger training with blood flow restriction


You don't have to look far in the sports literature to hear about blood flow restriction training. As the name implies it's a way to manipulate the body's circulatory flow that has been shown to re-create the stimulus of high-intensity training with loads as low as 20-50% 1-repetition max.  As a student, I was exposed to BFR through the rehabilitation literature performed with the original system, the Kaatsu system. For the last couple of years, I've been using blood flow restriction training in my clinic on clients who are injured and could not sustain, for a period of time, a normal high-intensity loading program. With good clinical success, supported by literature reviews, I've been able to reduce pain, maintain muscle mass, and keep athletes motivated while being sidelined. In most papers on BFR, or occlusion training, there is usually a comparison between three groups, a normal high-intensity group, a low load with blood flow restriction group (LLBFR), and low load without blood flow restriction group (LL). The majority of which demonstrated that low load with blood flow restriction is as useful at maintaining strength and muscle size as the high-intensity loading group. Over the last 10 years, there has been mounting interest in the use of BFR in non-injured athletic populations. That is the basis of this investigation.

 Mechanisms review:

 Without going into too much detail it's safe to say that with over 400 published peer-reviewed journal articles since 2010, blood flow restriction training is something worth paying attention to. The physiologic effects can be complex with some theoretical speculation in the literature but the principle is relatively simple. By using a specific pneumatic cuff placed around a proximal limb we can restrict a percentage (20-90%) of the arterial inflow while fully occluding the venous outflow to working muscle. It's very important to note that even under these restricted conditions we still get blood flow to and from the working muscle. The skeletal muscle pump is how we get blood from the deep veins back to the heart and this mechanism does not stop with blood flow restriction training but simply slows it down to make athletes reach their O2 saturation quickly.  The primary goal is reducing oxygen availability to a specific type of muscle fibre so the remaining fibers which do not use oxygen pick up the work. By limiting the oxygen availability, and accumulating acidic byproducts, the smaller fibres (Type I and IIa) cannot perform work efficiently. The muscular work in subsequent sets then is picked up by the largest fibres (TypeIIx) of working muscle. Once we’ve created this chemical absence of homeostasis we then get a large influx of sensory information sent back to the brain which is responsible for creating the increased hormonal profile we see with BFR training. All of this can be done at percentages as low, or even lower in some cases, as 20% of an athletes 1-reptition maximum. The graph provided by Loenneke shows this mechanism clearly.


 A few things to note regarding the rationale with this research and the intervention itself. There are only a few ways that we can enhance muscular recruitment and hypertrophy. Recruitment is all about training your muscle groups to use a higher percentage of the largest fibres for a specific activity than they did previously. Hypertrophy is all about increasing the actual size of those muscle fibres and their ability to grow (side-to-side, and their individual diameter) within a muscle group.  There are two ways we can optimize these mechanisms with training. We can exercise at a very high intensity (85-90% with low velocity) for a set number of repetitions (5-7) or we can exercise at a moderate intensity (70-85% with moderate velocity) to muscular failure. In the high-intensity loading state, we choose a load that is so high we have to rely on more fibres, the TypeIIx fibres, to move the heavy load. Conversely, in the high-volume state we create a level of fatigue over the working sets where we slowly recruit larger and larger motor units with all the work. The downside of using either of these approaches is the time it takes to recover from that high intensity muscular work. The fatigue and protein fibre breakdown that accompanies high intensity and moderate loading to failure is significant and reduces overall training frequency. Therein lies the real appeal of using BFR to train the forearms and finger flexors within an athletes training cycle and season. We can still reach muscular failure however we are doing so at an intensity that reduces the protein breakdown that accompanies high intensity loading while still benefiting from the hormonal profile as if we were. This has been documented in the BFR literature many times over.




Research protocol:

 To date, there has been no research performed on the use of blood flow restriction training as a mechanism to enhance finger flexor strength. In addition to this article, there will be a paper submitted as a retrospective analysis on this study to a peer-reviewed journal. The study design was based on other blood flow restriction studies which were aimed at measuring improvements in peak muscle strength.  In general, most BFR papers study a specific exercise or muscle group at intensities approximately 20-50% of an athletes 1-repetition max. They usually compare a low load BFR group to a low load non-BFR group as well as a regular high-intensity group. In this case, we only used the former two, low load with BFR (LLBFR) and a low load non-BFR group (LL). My goal was to run approximately 8-10 athletes through a specific hangboard protocol I created to assess the plausibility, safety, methodology, and subjective response of this as a training tool for non-injured healthy climbers. Until this study, I had only performed this same protocol on myself during multiple cycles (3-4 weeks) with no noted downside. So, my hypothesis was that using a low load BFR finger training protocol I would be able to track a statistically significant improvement in peak finger force over 10 sessions.

 I used a random selection of climbers from the Salt Lake City area who were free of a current finger injury, who had a finger training history of at least 2 years and were able to perform 10 training sessions at 2 per week for 5 weeks. It was quite helpful that I had a wide range of climbing skill levels and training history from 5.10 sport climbers to V13 boulderers.

 What I did was assign one group to the BFR protocol consisting of bilateral restriction at 200-250mmHg on the Bstrong BFR bands (which is approximately 20-50% arterial occlusion pressure), and one group with bilateral restriction with 5mmHg added pressure. For the control group, the low pressure created a slight pressure to mimic the idea that there was adequate pressure to create the BFR stimulus. This likely created some abnormality in blood flow but nowhere near the extent of the BFR group.  As already mentioned, most BFR papers use a percentage of (20-50%) of an athletes 1-repetition maximum to assign training loads. It has been my experience testing athletes fingers that body weight is approximately 40-60% of their maximum intensity when using both arms. So, for this study I did not individualize the protocol for the hang portion. I only manipulated the load to the fingers before the body weight hang.  I did this intentionally so as to make it simple for climbers to use as a training tool on the road or at their house. I made the assumption that the edge size would approximate the appropriate intensity and percentage max for each individual so long as they came into the hang with pumped forearms.


The warm-up was standardized so as to reduce the likelihood that any participant was either more or less prepared for the intervention as compared to their peers. The following was the general warm-up we used.

Warm-up (specific part 1)

(1) 4-finger pocket pull-up (large pocket) 3 x 5 at body weight

(2) Open hand small edge hang 7:3 x 5 (2 minute rest)

(3) Half crimp medium edge hang 7:3x5 (2 minute rest)

(4) Concentric pull-up with 30% added weight 2 x 3 with 20s. rest between sets

(5) 4-finger pocket hang with same weight added 5x1 with 60s. rest between

(6) Half crimp small edge at body weight 5x1 with 60s. rest between

 Warm-up (specific part 2)

(1) Hang position seated with 50% effort x 1 each edge (19mm, 12.7mm) with 60s. rest between)

(2) Hang position seated with 80% effort x 1 each edge (19mm, 12.7mm) with 60s. rest between)

 I need to make a note regarding the pressure used in this particular investigation. I used a type of BFR product that is elastic and contains multiple chambers instead of a classic blood pressure cuff which only has one chamber. It is a more comfortable (physically on the limb, not metabolically) product for the overhead work of hanging from one's fingers. I have used pneumatic single chamber systems (classic BP cuff) on myself for this same protocol to check that the stimulus was similar in intensity (7 out of 10 discomfort). It is important to note that the pressure used in this research (200-250 mmHg) on my multi-chambered system would occlude arterial blood flow at 100% on a single-chambered system, which is not advised. I have calculated that 200-250mmHg on the product I use is approximately equal to 75-100mmHg on a blood pressure cuff (which is approximately 30-40% arterial occlusion pressure for the males and 40-60% for the females).

Exercise intervention:

Once bands were in place on the arm (below the deltoid and at the upper margin of the biceps brachii) on both arms each group performed the same exercise intervention. The groups used a tension climbing flashboard (upside down) and performed finger curls with added weight from full extension into a fully flexed position (as if they were moving into a full crimp) on the 19mm edge. They were to perform 15-repetitions to complete muscular failure. This ranged in weight per individual from around 35-90 lbs depending on the group assigned. These were performed with a loading pin with weights connected to the sling below while they were standing and curling upward. Upon completion of fatigue at 15-repetitions they immediately set the board down and walked over to the tension hangboard and performed a half-crimp 7-second hang on the smallest edge possible. Most performed this on the 30, 25, or 20mm edge size however there were a few participants who could perform their sets on the 10mm edge. The wide range in external load with the finger curls came from whether an athlete was in the BFR group or the control group. The BFR group participants had a much smaller weight than the non-BFR (LL) group.

 Upon completion of the hanging portion of the program, they would take a strict 30-second rest. Once the rest (arms at the side in a standing position) was finished they performed the same finger curl protocol with either the addition or reduction of weight so they could hit that 15-repetition number to muscular failure. They performed this for 12 sets total, which took approximately 15 minutes. For the remaining 5-minutes, I had the participants leave the bands on and keep the pump in their arms until 20-minutes was over. The same protocol was used on the BFR control group (LL) however they were using a much larger weight on the finger curls (60-90lbs) to reach muscular failure with the same interset rest period.

Pre and post intervention testing:

 For both groups, we did a maximum effort half crimp peak and average finger force test (lbs) on both the 19 and 13mm edge size. I gave the participants 3 trials each with 2-3 minutes rest between, and kept the highest peak value. These were all performed in a seated position with the hips blocked (via squat rack pin with yoga pad around the bar) with both arms overhead at 110- 120-degrees of elbow flexion. The participants were queued to bring on the force slowly for 1 second then really bear down at max effort for another 2-4 seconds. As soon as the peak force was hit and a plateau demonstrated they were told to stop pulling. The average force was taken over the entire time the athlete started their pull until a plateau was reached and they were told to stop. With a sample rate of 250ms there was approximately 20 force readouts in that timeframe to calculate the average. Each athlete was told to come fresh to the pre and post testing session with at least 2-days of rest before. Each participant was tested in the same room, with the same board, same prototype custom strain gauge by Exsurgo Technologies, same chalk, and the same level of emotional support.


Results and discussion:

As you can see from the graphs (table 1) below participants 1-4 were the BFR group (LLBFR) and participants 5-8 were the control or apparent BFR group (LL). The graphs below show a side-by-side analysis of the pre and post-test peak force and the pre and post-test average force for both edge sizes. If you recall each effort was sustained until a peak plateau was reached, likely between 3-5 seconds upon which the athlete released tension. So, the averages could be less consistent a measure than the peak measure, however, they do demonstrate an overall increase in force impulse (force sum over time).


19mm graph.png
13mm graph.png

Table 1

 Table 2 represents each participants pre and post test peak and average force on both edge sizes. It also provides a column for the peak and average force difference (change after the intervention) for each participant.  Looking at the far right of the data table (table 2) you can see the two primary measures representing each group (LLBFR and LL) at each respective edge size. The mean (average) difference in peak force between each group (pre and post intervention) as well as the difference in the average force of each group. On the 19mm edge size, the average difference in peak force over a 5-week training cycle was 90.7lbs for the BFR group (LLBFR) and 20.2lbs for the control group (LL). The BFR fingerboard group had a 4.5 times improvement in peak finger force over the control on the same edge size and a 3.15 times improvement in average force produced. When looking at the data on the 13mm edge size the improvement was less dramatic with an average difference in peak finger force being 30.8lbs (LLBFR), which is 2.07 times that of the control group (LL) and 1.9 times improvement for average force produced. 

group data.png

Table 2

 As mentioned previously, the graphs demonstrate less dramatic improvements in peak finger force on the smaller edge size (13mm). I hypothesize this comes from the inability of many participants to hang off their body weight fully pumped on the smaller edge sizes. Only 25% (6 of 8) of the participants were able to perform over 60-percent of their hang sets on a 15mm or smaller edge size, where most participants were spending their time hanging on the 30, 25, and 20mm edges. That being said, I would also predict that doing regular max weighted hangs (with added weight to failure) on a larger edge size (20mm is the most commonly used) would not be predictive for improved performance on a smaller edge size. This comes from the specific motor unit recruitment that happens by training at a specific edge size.

force difference graph.png




 Given that most research investigations report an improvement in muscular strength and hypertrophy with low load blood flow restriction training, it is feasible that these same principles can be applied to the finger flexors of climbers. This comes at a much-desired drop in tensile stress to the pulley system of the fingers. In addition to reducing stress to the finger flexors of climbers, we can still train specifically on a fingerboard to improve aerobic capacity, muscular recruitment, local energy storage, and capillary networks in the muscle groups specific to climbing performance. These are some additional improvements noted in the BFR literature not tested in this particular study but have been demonstrated elsewhere. What I have done in this paper is document that in a 5-week time frame with blood flow restriction training at submaximal loads I can improve peak and average finger flexor force with no noted downside.

As I’ve mentioned previously, I do not believe BFR finger training is a complete replacement for high-intensity finger training. It’s largest use to date has been on injured or elderly populations. Both of which would not be able to tolerate higher intensity loads. That being said, BFR is now being investigated in athletic populations as a means to augment regular training loads to reduce overloading and injury.  There have been multiple papers in which BFR was used side-by-side regular high resistance training as a mechanism to augment strength, power, and aerobic capacity which reduced the frequency of high intensity loading. We’ve known for quite a while that high-intensity loading is necessary for long term soft tissue adaptation and tendon density. But if we can find the right balance between “enough” soft tissue strain using high loads and learn to manage metabolic stressors (muscle recruitment and energy system utilization) with something like BFR we might find something we’ve always wanted, the same amount of training with less injury risk.

 For the future:

 The next thing that needs to be investigated in regards to rock climbing performance and blood flow restriction is the comparison between a LLBFR group and a regular high intensity loading group. In addition to peak and average finger flexor force we would use more pre and post-test metrics (alactic power output for 10-seconds, anaerobic capacity for 30-seconds, and rates of force development) which would provide better insights into the mechanisms and adaptation resulting from each intervention. I have performed some of these metrics on local group of climbers using BFR which will be the topic of the next paper. To date, this is the first investigation which measured peak and average finger flexor force both before and after an intervention of blood flow restriction training for the finger flexors of climbers. Any questions regarding the protocol, equipment used, safety, or to learn more about blood flow restriction you can contact me directly. Trainingbeta, as gracious as they are for publishing this article, is not responsible for the contents of this article and are mine solely. I do advise people get educated about using blood flow restriction prior to trying this on yourself. Your risks and liability are your own after reading this paper.

 Tyler Nelson DC, MS, CSCS

Camp4 Human Performance


Tyler Nelson