Patellofemoral pain syndrome (PFPS) is a common cause of anterior knee pain. Quadriceps muscle strengthening is an important part of treatment of this condition, but this strengthening is often painful to perform. This study aimed to compare the effects of quadriceps strengthening at low intensity with blood flow restriction (BFR) to quadriceps strengthening at high intensity in individuals with patellofemoral pain (PFP). Furthermore, to examine whether patients who experienced PFP on resisted knee extension had greater change in pain and quadriceps strength from BFR than from high intensity quadriceps strengthening.
METHODS (WHAT THEY DID):
79 participants were randomly allocated to either tradi- tional quadriceps strength training (with placebo BFR) or low-load BFR training. Both groups performed 8 weeks of leg press and leg extensions 3 times per week, the traditional group at 70% of 1 repetition maximum (1RM) (3 x 7-10 reps), and the BFR group at 30% of 1RM (1 x 30 reps, then 3 x 15 reps, with 30 seconds rest be- tween sets). The authors examined improvements in pain during functional activities (squatting, stairs, sitting), quadriceps muscle strength (isometric knee ex- tensor torque, in Nm) and quadriceps muscle size (quadriceps muscle thickness, in cm).
RESULTS/WHAT THEY FOUND:
The BFR group had a 93% greater reduction in pain with activities of daily living (p=0.02) than the traditional group. Participants with painful resisted knee exten- sion (n=39) had greater increases in knee extensor torque with BFR than traditional training (p<0.01). Otherwise, no between-group differences were found for pain related to function, knee extensor torque, or quadriceps thickness. Finally, no difference in global perceived change in pain was found between groups at 6 months.
LIMITATIONS/THINGS TO KEEP IN MIND:
In this study, if pain during performance of exercises was reported to be greater than 2/10 on the visual analogue scale the load was reduced by 20%. This reduction in load may have reduced the load to less than 70% 1RM for many subjects in the traditional quadriceps strengthening group, resulting in submaximal quadriceps strength gains.
Furthermore, participants in the BFR group had significantly more pain with daily activity than the traditional quadriceps strengthening group at baseline. This means that there was greater potential for pain reduction in the BFR group, which reduces confidence that the results in this study are due to intervention rather than baseline differences. Finally, while no differences were found in quadriceps muscle size, it is possible that the 8 week study duration was insufficient to identify detectable changes in muscle size.
Reducing pain, improving function and increasing quadriceps strength are fundamental goals of PFP rehabilitation. This study shows that both traditional quadriceps strengthening and BFR training can be used to reduce pain from PFP and increase quadriceps strength. Unfortunately however, many people with PFP find heavy strength training for the quadriceps painful to perform. This often means that they avoid quadriceps resistance training altogether, which further perpetuates the issue as quadriceps weakness can contribute to PFP. This is where the real clinical implications of this study shine through, as it shows that BFR training is an effective alternative to traditional quadriceps strengthening for people with PFP who have poor tolerance to heavy resistance training.
BFR training can be performed using any exercise that targets the desired muscle group. For example, squats, leg press and leg extensions are all valid exercises for the quadriceps musculature. To perform BFR training for the quadriceps, a cuff or wrap should be tied around the proximal thigh to a perceived tightness of 7/10, and loads of 20-30% 1RM should be used with high repetitions (>15) and short rest periods (< 1 minute). BFR training has been shown to produce similar amounts of muscle growth to traditional resistance training, and so is a great technique to use with patients who are unable to train with heavy loads but would benefit from developing muscle size and strength, such as those post ACL reconstruction, post muscle strain, and also tendinopathy patients.