Effect of Blood Flow Restriction Training on Functional and Self-Reported Outcomes in Runners with Patellofemoral Pain

Patellofemoral pain is a common, chronic musculoskeletal condition, presenting as pain around or behind the patella during patellofemoral joint loading activities, such as squatting, stair ambulation, and running. Patellofemoral pain affects a large proportion of the population, especially runners, and tends to persist in about 50% of the cases. Females are nearly twice as likely to sustain certain running-related injuries as compared to males, with patellofemoral pain being the most commonly reported running-related injury. Patellofemoral pain has often been associated with weakness of the quadriceps and hip musculature, as well as altered knee and hip biomechanics during running. The current clinical practice guidelines recommends combining hip and knee exercises, in preference to knee exercises alone, to reduce pain and improve function. However, quadriceps strengthening exercises are thought to increase load through the patellofemoral joint which may aggravate symptoms. In addition, patellofemoral pain has been associated with increased patellofemoral joint stress with previous studies showing a direct relationship between a greater knee flexion angle and a longer step length leading to greater patellofemoral joint stress. Therefore, a strong clinical need remains to evaluate conservative treatment options within this cohort. The American College of Sports Medicine recommends loads of 60-85% of the maximum load a person can lift (1 RM)to develop muscular strength. For many patients with patellofemoral pain, the joint loads from high-load resistance training can cause symptoms to flare, with increased pain and joint discomfort. As a result, patients are often advised to reduce their resistance to a level that does not provoke symptoms. However, this low-load resistance training may not maximize muscular strength gains. Therefore, there is a significant unresolved challenge to designing an effective treatment targeting muscular strength with resistance training loads necessary for improvements in muscular strength. Blood flow restriction training (BFRT) is a promising alternative treatment to safely improve muscular strength. By applying a pressurized cuff around the thigh, arterial blood flow is reduced leading to an accumulation of metabolites. This exercise-induced metabolic stress promotes adaptation of the muscle and allows low-load resistance training (20-30% of 1RM) to induce the same training benefits as traditional high-load resistance training (60-85% of 1RM). This training method has been successfully used in healthy populations to elicit equivalent and/or greater strength gains than traditional forms of exercise. While BFRT treatment holds great promise in addressing muscular strength deficits, the benefits for runners with patellofemoral pain are unknown. In addition, the benefits of muscular strength proximal to the pressurized cuff, such as increased hip muscle strength, is not well understood. This highlights the need for detailed assessments of BFRT’s impact on improving distal and proximal muscular strength, improving running biomechanics, and subsequent running ability within this cohort. Therefore, the overarching hypothesis of our study is that low-load resistance training with BFRT is more effective than low-load resistance training without BFRT for improving quadriceps and hip strength and knee and hip running biomechanics. This in turn leading to improved pain, knee function, and running ability in runners with patellofemoral pain.