Neuromuscular Mechanisms and Clinical Utility of Blood Flow Restriction Therapy

Lower extremity muscle weakness is a major, and potentially costly, concern for many load-restricted patient populations (e.g., elderly individuals, post-surgical patients, etc.). If left untreated, prolonged deficits in muscle function can lead to a variety of negative health outcomes including altered biomechanics, increased risk for injury, and decreased patient reported quality of life. To overcome this problem, low load exercise with blood flow restriction therapy (LL-BFRT) has been suggested as an alternative treatment approach for improving muscle strength when high load resistance exercise may be unachievable or contraindicated. However, to determine the potential benefits and clinical utility of LL-BFRT, we must investigate the underlying neuromuscular mechanisms and overall effects of LL-BFRT in healthy and clinical populations.

Therefore, the purpose of manuscript I was to determine the effects of LL-BFRT on motor unit recruitment and motor unit behavior compared to standard LL exercise without BFRT in healthy adults. In this study, compared to LL exercise without BFRT, we identified that exercising under BFRT increased overall motor unit recruitment and altered motor unit behavior of the vastus lateralis and significantly increased participant’s rating of perceived exertion. These results indicate that LL-BFRT may be an effective method for increasing muscle activation and perceived exercise difficulty without increasing load and mechanical tension during exercise.

The purpose of manuscript II was to examine the effects of LL-BFRT on muscle strength and limb symmetry in patients with quadriceps strength deficits following anterior cruciate ligament reconstruction (ACLR) compared to a true control condition. We identified that female patients treated with LL-BFRT experienced significant improvements in isokinetic quadriceps strength and limb symmetry at 90 º/s when controlling for baseline values. However, no significant between group differences were found for isokinetic or isometric quadriceps strength and limb symmetry at 180 º/s and 90 º of knee flexion, respectively. These results provide preliminary evidence to support the utilization of LL-BFRT for improving quadriceps strength in patients with lingering strength deficits after undergoing ACLR and traditional post-surgical rehabilitation programs.

Lastly, the purpose of manuscript III was to examine the effects of LL-BFRT on patient reported outcome measures (PROMS) in patients with quadriceps strength deficits following ACLR compared to a true control condition. We found that compared to a control condition, female patients treated with LL-BFRT reported significant improvements in the overall condition of their injured limb as well as noteworthy decreases in knee-related pain and fear of reinjury and increases in psychological readiness, subjective reported knee function, and knee-related quality of life. Therefore, the results of this exploratory study suggest that LL-BFRT may be an effective treatment intervention for improving various psychological components of recovery in patients with significant quadriceps strength deficits following ACLR.

By utilizing novel sEMG technology we were able to quantify changes in motor unit recruitment and behavior during LL-BFRT to provide support for one of the primary proposed mechanisms of this complementary treatment intervention. Additionally, through pilot testing we were able to preliminarily explore both the physiological (i.e., strength and limb symmetry) and psychological responses to LL-BFRT in patients with persistent quadriceps strength deficits following ACLR. These studies have provided foundational evidence to support the neuromuscular mechanisms of LL-BFRT and have also provided clinicians and researchers with suggestive evidence to promote the usage and investigation of LL-BFRT as a multifunctional intervention to combat physiological and psychological deficits in patients recovering from ACLR.