Centner C, Lauber B, Seynnes OR, Jerger S, Sohnius T, et al. Low-load blood flow re-striction training induces similar morphological and mechanical Achilles tendon adap-tations compared with high-load resistance training. Journal of Applied Physiology. 2019; 127(6):1660-1667.
Abstracted by Gina Fick, PT, ScD, COMT Castle Rock, CO – Fellowship Candidate, IAOM-US Fellowship Program & Jean-Michel Brismée, PT, ScD, Fellowship Director, IAOM – US Fellowship program
Research: To investigate the effects of low load resistance training (20-35% 1 rep. max) with blood flow restriction (BFR) on in vivo Achilles tendon properties and to compare these effects with conventional high load resistance training (70-85% 1 rep. max).
Methods: 55 healthy men between the ages of 18 and 40 years participated in this study and were randomly allocated into one of the following groups: high load resistance training (70-85% 1 rep max), low load resistance training (20-35% 1 rep max) with BFR, or a control group with no training. A between-group repeated measures design was used to assess tendon properties, cross sectional area of the gastrocnemius muscle, and unilateral maximal plantar flexion torque before and after a 14-week training program of either low load resistance training with BFR or high load resistance training. The training consisted of 3 weekly sessions for 14 weeks. Training days were separated by at least 1 day of rest between 2 consecutive sessions to allow for adequate recovery. The high load protocol consisted of 3 sets of 6 to 12 repetitions of dynamic calf raises while seated and standing, with the load progressively increased every 4 weeks from 70-85% 1 rep max. Dynamic 1 rep max testing was conducted to adjust the load for the strength level of each individual. Participants in the low load BFR group performed the same exercises as the high load group but did so at 20% 1 rep max and the load was progressively increased at 5% increments every 4 weeks until 35% 1 rep. max was reached in the final 2 weeks. For each exercise, 4 sets of 30 repetitions in the first set and 15 repetitions in the remaining 3 sets were completed. During the exercise a Zimmer Biomet 12 cm wide pneumatic nylon tourniquet was proximally positioned on the participant’s thigh, and before each training session, the individual’s arterial occlusion pressure was determined in a standing position. For the training routines, the cuff pressure was set to 50% of each subject’s arterial occlusion pressure. The cuff was inflated during the training exercises, including the 60 second interest rest period. Between the two exercises, the cuff was deflated for 3 minutes. Unilateral isometric maximum voluntary contraction torque was measured at 90 degrees of plantar flexion with an ISOMED isokinetic dynamometer. Ultrasound imaging was used to measure cross-sectional area of the gastrocnemius medialis muscle as well as the cross-sectional area and stiffness of the Achilles tendon.
Results: Both high load and low load BFR training resulted in significant increases in tendon stiffness as well as tendon cross sectional area. These changes were comparable between groups. Gastrocnemius medialis cross sectional area and plantar flexor strength significantly increased in both training groups, while in the control group, no significant changes in any of the measures were observed
Conclusions: The adaptations in the Achilles tendon cross sectional area and mechanical properties as well as increases in muscle mass and strength seen following low load resistance training with partial vascular occlusion appears to be comparable to the gains seen with high load resistance training.
IAOM-US Comments: Blood flow restriction (BFR) occludes venous outflow while maintaining arterial inflow by the application of an extremity tourniquet, which reduces oxygen delivery to muscle cells during low load exercises. This anaerobic environment has been reported to promote muscle hypertrophy by initiating cell signaling and hormonal changes that stimulate protein synthesis, proliferation of myogenic satellite cells, and preferential activation and mobilization of type II muscle fibers.1,2,3 Compelling evidence continues to support the use of BFR combined with low load (20-35% 1RM) resistance exercise to enhance muscle strength and hypertrophy.4,5, Research also suggests that BFR during low intensity cardiovascular exercise can result in small but significant muscle strength and hypertrophy gains.5 BFR alone may reduce muscle atrophy during periods of unloading following an acute injury or surgery.6
Although a number of studies have demonstrated substantial increases in muscle strength and hypertrophy with low load BFR training, this study by Centner et al. seems to be the first to report on the effects of low load BFR training on human tendon properties. It is important for clinicians to understand the effects of low load BFR training on tendon properties because increases in muscle strength and hypertrophy without adaptations in tendon properties could lead to an increase in tendonrelated injuries. Results from this study by Centner indicate that a 14-week program of progressive low load BFR exercise stimulates tendon hypertrophy when compared with no exercise. Furthermore, Achilles tendon stiffness increased 40.7% in the high load training group and 36.1% in the low load BFR training group. This information is valuable and clinically relevant to patients who have suffered injuries to the gastrocnemius, soleus, Achilles, and/or plantar fascia.
In my clinical practice, I often see athletes who have running-related injuries due to decreased mechanical stiffness and load tolerance of the Achilles tendon and/or decreased strength of the gastrocnemius-soles muscle complex. When the acute to chronic training load ratio suddenly increases to the point in which the athlete’s tendon load tolerance cannot handle acute spikes in training loads, the athlete will often develop Achilles tendinopathy. For these athletes, proper load management is essential to recovery.7 Low load BFR training is an invaluable tool in these cases where athletes need to decrease pain, inflammation, and maintain muscle strength and tendon stiffness while decreasing their overall training load. I use and recommend the PTS or Personalized Tourniquet System for Personalized Blood Flow Restriction Rehabilitation (PBFR), manufactured by Delfi Medical Innovations, Inc, a world leader in tourniquet technology and safety. The PTS for PBFR device is specifically designed to safely regulate and control tourniquet pressure for PBFR applications and includes advanced personalization and safety features (Figure 1).
I work closely with these athletes and their coaches to incorporate cross training programs on the AlterG treadmill, bicycle, and/or deep-water pool running so that they can maintain cardiovascular fitness. At the same time, I implement low load BFR training two to three times per week in order to promote mechanical stiffness within the Achilles tendon as well as increase strength and muscle hypertrophy of the gastrocnemius-soleus complex (Figure 2). In this way, athletes are able to return to a baseline training level that optimizes tendon loading and tissue healing response. In my experience, when these strategies are implemented, the athlete’s overall recovery time is reduced, their performance improves, and their reinjury risk decreases.
The results from this study by Centner et al. also support the notion that athletes should participate in high intensity training programs in order to improve performance and decrease injury risk. I encourage the athletes and coaches that I work with to incorporate high intensity weight training routines into their preseason and in season training programs as a means of increasing skeletal muscle strength and tendon stiffness for overall injury prevention. These programs work well when implemented during preseason training and adjusted throughout the season to optimize performance. In summary, when loading needs to be decreased, low load BFR training is an incredible tool to decrease pain, enhance recovery, improve muscle strength and hypertrophy, and enhance tendon stiffness and cross-sectional area.
Clinicians must have the proper training to ensure they are using the BFR equipment in a safe and effective manner, and all patients should be assessed for risks and contraindications to tourniquet use prior to BFR application. Patients who may be at risk for adverse reactions are those with poor circulatory systems, obesity, diabetes, arterial calcification, sickle cell trait, severe hypertension, or renal compromise. Potential contraindications to consider prior to BFR training are venous thromboembolism, peripheral vascular compromise, sickle cell anemia, extremity infection, lymphadenectomy, cancer or tumor, extremity with dialysis access, acidosis, open fracture, increased intra-cranial pressure, vascular grafts, or medications known to increase blood clotting risk.
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