Blood flow restriction training is quickly becoming a standard of practice in the orthopedic and sports physical therapy realm. In this post I will highlight a recent study examining the effect of low-load BFR vs. high-load traditional resistance training on the Achilles tendon. Following a quick highlight of the study including its purpose, methods, results, and the conclusions made, I’ll offer some insights on this study and its applicability to clinical practice. This post is simply to bring attention to a recent study and is not meant to replace detailed reading and consumption of the article. Please see the reference at the bottom of this page to read the article yourself (it is available for public access).
Research Article: Low-load blood flow restriction training induces similar morphological and mechanical Achilles tendon adaptations compared with high-load resistance training (Centner et al.)
Purpose: The authors note that the effects of BFR on muscles is well documented. However, there is a lack of research investigating BFR’s effect on tendons. Shedding light in this area can help to provide a rationale as to why BFR may be useful in the treatment of tendinopathic conditions.
Study Methods:
The study looked to investigate the mechanical and morphological changes in the Achilles tendon in response to either low low BFR training or traditional resistance training. Both training regimens were administered 3x/week for 14 weeks. The low-load BFR training group worked at intensities of 20-35% 1RM. The traditional resistance training group administered exercises at 70-85% 1RM consistent with guidelines for hypertrophy training. Key measurements included mechanical and material properties of the tendon, muscle/tendon cross-sectional area, and isometric strength. A control group was included in the study design and remained inactive for the entirety of the 14 weeks.
See table 1 below summarizing the exercise parameters for the two groups.
| Low-Load BFR Group | High-Intensity Traditional Resistance Training Group | |
| Frequency | 3x/week | 3x/week |
| Exercises: | 1 standing, 1 sitting calf raise exercise | 1 standing, 1 sitting calf raise exercise |
| Dosage: | 4 sets with reps of 30/15/15/15 at 20-35% 1RM | 3 sets 6-12 reps at 70-85% 1RM |
| Rest Breaks | 1 min. between sets (cuff remained inflated), 3 min. between sets (cuff deflated) | 1 min. between sets, 3 min. between exercises |
| Cuff Pressure: | 50% LOP | n/a |
Results:
Similar increases in Achilles tendon CSA were found in both the low-load BFR and high-load training groups.
Similar increases in Achilles tendon stiffness (tendon mechanical properties) were found between the groups.
No significant effect was noted in Young’s modulus (tendon material properties) in both groups following the 14 weeks of training.
Both groups demonstrated significant increases in gastrocnemius muscle CSA compared to the control group.
Both groups demonstrated significant increases in maximal isometric strength compared to the control group.
Study Strengths/Weakness:
The strengths of this study include that there were blind assessors, a control group, control for lifestyle factors, and appropriately progressed training loads consistent with standard practice.
One weakness of the study includes the validity of ultrasound in assessing muscle/tendon cross-sectional area.
Key takeaway: “The overall findings revealed that, despite a much smaller training load, LL BFR caused adaptations in Achilles tendon CSA and mechanical properties as well as in muscle mass and strength compared to HL.” [1]
Discussion:
This study was able to demonstrate that LL-BFR can be a potent stimulus to achieve positive changes in myotendinous hypertrophy and mechanical properties with significantly less training load than previously documented. This is in contrast to other studies observing the effect of LL BFR on patellar tendon that failed to produce a significant increase in tendon hypertrophy. However, these differences may be due to methodological differences between these studies.
This study is unable to answer the question of how much the hypoxic environment contributes to the observed hypertrophic changes in the Achilles tendon. To assess this, the authors would need a separate control group undergoing LL resistance training without the addition of BFR.
In terms of clinical applicability there is much to discuss. These interventions are logical for patients undergoing rehabilitation for tendinous conditions (surgical tendon repair, conservative rehabilitation following acute tendinous injury, or tendinopathic conditions).
This study confirms previous findings suggesting that to induce tendon mechanical changes cyclic mechanical loading must occur for >12 weeks. I think a nice addition to this study would have been to observe tendon CSA and properties at multiple time points throughout the 14 weeks of training. Multiple data points might have shed some light on the “minimal effective dose” of mechanical loading to induce positive changes in myotendinous properties.
However, when considering patients rehabilitating with tendinopathy this study highlights the importance of emphasizing function over structural improvements as part of the short-term (and long-term) therapeutic goals. Practically, most patients will not be able to attend therapy 3x/week for 14+ weeks. It is important to progress them back to some form of their prior activity and modify as needed as soon as safely possible to increase patient compliance to a tendon loading program.
This study also highlights the importance of establishing a detailed progressive tendon loading program as part of a home exercise program. This will assist in achieving the appropriate loading frequency known to result in increases in tendon mechanical properties.
When high intensity loading is contraindicated (early phase tendon repairs or patients with highly sensitized tendinopathy) it may be beneficial to initiate BFR as soon as possible to reduce the effects of atrophy, increase patient compliance to the program, create value for rehabilitation visits, and increase patient confidence.
Conclusion:
This study establishes treatment validity for low-load BFR in treating tendon conditions. Further research is needed to corroborate these findings and to investigate the role of the BFR induced hypoxic environment associated with BFR training.
Based on this study, it is appropriate to utilize BFR in treating patients with tendinous conditions. However, clinicians must still have consideration for training frequency, cost effectiveness, prognosis, patient education, and short- and long-term goals to ensure maximal outcomes for patients.
References:
[1] Centner C, Lauber B, Seynnes OR, Jerger S, Sohnius T, Gollhofer A, König D. Low-load blood flow restriction training induces similar morphological and mechanical Achilles tendon adaptations compared with high-load resistance training. J Appl Physiol (1985). 2019 Dec 1;127(6):1660-1667. doi: 10.1152/japplphysiol.00602.2019. Epub 2019 Nov 14. PMID: 31725362.
