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Tuesday, June 6, 2023

Comparison of Hip and Knee Strength and Neuromuscular Activity in Participants With and Without Patellofemoral Pain Syndrome

Brent Brookbush

Brent Brookbush


Research Review: Comparison of Hip and Knee Strength and Neuromuscular Activity in Subjects With and Without Patellofemoral Pain Syndrome

By Tristan Rodik, M.AT, ATC

Edited By Brent Brookbush, DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Bolgla, L. A., Malone, T. R., Umberger, B. R., and Uhl, T. L. (2011) Comparison of hip and knee strength and neuromuscular activity in subjects with and without patellofemoral pain syndrome. The International Journal of Sports Physical Therapy, 6(4), 285-296. FULL TEXT

Why the Study is Relevant: Patellofemoral pain syndrome (PFPS) is common in active populations and has been correlated with altered lower-extremity kinematics, patellar tracking issues and decreased hip strength (1-11). This 2011 study by Bolgla et al. investigated hip strength, knee strength and muscular activity during stair climbing in participants with and without PFPS. Lower values of hip abduction and external rotation strength were observed in those with PFPS; where as vastus medialis and vastus lateralis recruitment did not significantly differ between groups. The results of this study imply that hip abductor and hip external rotator strengthening may be beneficial for those with PFPS.

Hip Abduction with Manual Resistance
Caption: Hip Abduction with Manual Resistance

Muscle testing of the hip abductors (Courtesy of the Brookbush Institute©)

Study Summary

Study DesignCross-sectional cohort design (observational research)
Level of EvidenceIII evidence from non-experimental, comparative study
Subject CharacteristicsDemographics (PFPS Group)
  • Age: 24.5 +/- 3.2 yrs
  • Gender: female
  • Number of participants: 18
  • Height: 1.7 +/- 0.1 m
  • Mass: 63.1 +/- 9.1 kg
  • Pain: 4.4 +/- 1.5 cm
  • Duration of Symptoms: 14.4 +/- 12.8 months

Demographics (Control Group)

  • Age: 23.9 +/- 2.8 yrs
  • Gender: female
  • Number of participants: 18
  • Height: 1.7 +/- 0.1 m
  • Mass: 62.1 +/- 8.5 kg

Inclusion Criteria (PFPS Group):

  • Anterior knee pain when descending stairs
  • Pain with at least two of the following:
    • stair ascent
    • squatting
    • kneeling
    • excessive sitting

  • Pain rating of a minimum of a "3'" on a 10-cm visual analog scale (VAS) in the past week.

Inclusion Criteria (Control Group):

  • No pain with the activities noted above
  • No history or diagnosis of knee or hip pathology

Exclusion Criteria (Both Groups):

  • Previous knee surgery or significant injury
  • Traumatic patellar dislocation
  • Gait affected by neurological condition
  • Previous hip surgery or significant injury
  • Pain was measured with a 10-cm VAS
  • Participants then rode a stationary bicycle for a 3-minute warmup
  • After the warm-up, participants performed isometric strength testing for the following muscle groups:
    • hip abductors
    • hip external rotators
    • knee extensors

  • For isometric strength testing, one practice trial was followed by 3 test trials
  • Participants then performed the stair stepping task:
    • 5 practice trials were allotted
    • 10 test trials were then completed, with only the last 5 recorded for data collection

  • Electromyographic (EMG) data was collected during strength testing and stair stepping.
  • 7 participants returned 5-7 days later for repeat testing to determine measurement reliability.
Data Collection and AnalysisStrength Data Collection:
  • Isometric strength testing was performed using the Commander PowerTrack II™ (J Tech Medical, Salt Lake City, UT) hand-held dynamometer
  • Peak force values were recorded as a percentage of each subject's body mass

Electromyographic Data Collection:

  • A 16-channel myosystem 1400 electromyograpy (EMG) system (Noraxon USA, Inc, Scottsdale, AZ) was used to record muscle activity
  • Electrodes were placed along the gluteus medius, vastus lateralis and vastus medialis
  • Bi-polar AgAgCl surface electrodes (Medicotest, Rolling Meadows, IL) were used for EMG input
  • EMG signals were band pass filtered using Datapac Software (Run Technologies, Mission Veijo, CA)

Statistical Analysis:

  • Independent t-tests were used to determine group differences in age, height and mass
  • Separate independent t-tests were used to determine differences in strength testing
  • 2 by 3 (group X interval) analysis of variance (ANOVA) for repeated measures on stance interval were used to identify EMG amplitude differences between gluteus medius, vastus lateralis and vastus medialis
  • 2 by 3 (group X timing differences) ANOVA for repeated measures on muscle was used to determine EMG onset timing differences
    • an independent 1-group t- test was conducted to determine if timing differences varied significantly from zero

  • Level of significance was set to p < 0.05
  • The Bonferroni post-hoc test was used to adjust the p-value to account for multiple comparisons of strength levels, as well as to determine the significance of interactions for the two-factor ANOVAs.
Outcome Measures
  • Outcomes of strength testing were expressed as a percentage of participants' body mass
  • EMG amplitude and onset timing differences between gluteus medius, vastus lateralis and vastus medialis muscles during isometric strength testing and the stair climbing task
ResultsStrength Testing
  • Participants in the PFPS group generated approximately 21% and 10% of their body mass during hip abductor and hip external rotator testing, respectively.
  • In contrast, control group participants generated approximately 28% and 13% of their body mass during hip abductor and hip external rotator testing, respectively.
  • The PFPS group generated 22% less hip abductor (p = 0.007) and 21% less hip external rotator (p = 0.001) strength compared to controls

Stair Climbing Task

  • During the loading response of the stair climbing task, participants with PFPS generated 2.1 times more gluteus medius activity (p = 0.001) and 1.3 times more vastus medialis activity (p = 0.003) compared to controls.
  • During single-leg stance, PFPS participants generated 2.4 times more gluteus medius (p = 0.002) and 1.2 times more vastus medialis (= 0.020) activity compared to controls
  • Higher activation during the loading response and single-leg stance may be due to the need for increased neuromuscular activity to complete the task
  • All participants generated similar gluteus medius and vastus medialis activity during the pre-swing phase
  • All participants revealed similar vastus lateralis activity in all phases of gait
  • No differences were identified in EMG timing parameters
Our ConclusionsThe findings suggest that PFPS may be correlated with a decrease in gluteus medius strength, but may not be correlated changes in quadriceps muscle activity. This implies that human movement professionals should add assessment and strengthening of the gluteus medius to programs intended to address PFPS and perhaps give less attention to the quadriceps.
Researchers' Conclusions

Participants with PFPS presented with hip weakness. No significant findings were reported among groups in evaluating EMG timing onset of the vastus lateralis and vastus medialis. The results of this study add to the growing body of evidence demonstrating a relationship between PFPS and hip weakness (4, 6).

The clamshell exercise for hip abductor and external rotator strengthening (Courtesy of the Brookbush Institute©)

Review and Commentary:

This study adds to a growing body of research correlating hip muscle weakness and patellofemoral pain syndrome (PFPS) (4-6). The researchers compared quadricep , hip abductor and hip external rotator strength in those with and without PFPS. Electromyographic (EMG) output and timing of the hip abductors (gluteus medius ) and the knee extensors (vastus lateralis and vastus medialis ) were also evaluated. Findings revealed that hip abduction and external rotation strength was less in the PFPS group compared to those in the control group. No timing discrepancies of the vastus lateralis and vastus medialis were observed between groups. The findings suggest human movement professionals should consider assessment of hip abduction strength in those presenting with PFPS.

This study had many methodological strengths, including:

  • Seven participants returned to the laboratory 5-7 days after the initial testing for repeat testing to assess measurement reliability. Data from repeat testing revealed acceptable reliability (ICC > 0.70)
  • Participants engaged in five practice trials prior to stair climbing testing, allowing for familiarization. After the practice trials, 10 trials were completed and only the last five trials were recorded to control for a potential learning effect.
  • The testing positions used for maximal voluntary isometric contraction (MVIC) are similar to the methods commonly used by human movement professionals, increasing study applicability.
  • Unlike prior research, this study evaluated hip abductor, external rotator and knee extensor strength, as well as hip and knee extensor onset timing within the same cohort.

Weaknesses that should be noted prior to clinical integration:

  • The stair climbing task may not be demanding enough to expose a potential quadriceps timing onset discrepancy between the vastus lateralis and vastus medialis .
  • A larger number of participants may have been helpful in determining whether the trend toward altered timing of the quadriceps muscles was significant or an anomaly.
  • The primary examiner was not blinded to each participants' condition, which may have resulted in bias.
  • Tensor fascia latae (TFL) activity was not evaluated during stair climbing and muscle strength testing. It is possible that TFL contributed to the changes noted in hip abductor strength; further research is recommended.

Why the Study is Important:

This study evaluated the isometric strength of the hip abductors, hip external rotators and knee extensors, and the activity and onset timing of the gluteus medius , vastus lateralis and vastus medialis during stair climbing. This allowed for the strength and electromyography (EMG) data to be compared. It is interesting to note that peak gluteus medius activity was higher despite less abductor strength in the PFPS group, and that despite complaints of knee pain, the PFPS group did not demonstrate significantly different knee muscle strength or activity than controls.

How the Findings Apply to Practice:

This study implies that human movement professionals should integrate gluteus medius assessment, activation and strengthening to programs intended to address PFPS, and perhaps give less attention to assessment, modalities and exercise intended to address quadriceps recruitment.

How this Study Relates to Brookbush Institute Content:

The Brookbush Institute (BI) emphasizes the importance of hip strengthening for clients presenting with patellofemoral pain syndrome; specifically, gluteus medius and gluteus maximus activation . These muscles often present as long and under-active, as noted in the predictive models of Lower Extremity Dysfunction (LED) , Lumbo-pelvic Hip Complex Dysfunction (LPHCD) , and Sacroiliac Joint Dysfunction (SIJD) . Note, the BI has always been a proponent of knee issues being a result of hip and ankle dysfunction, and changes in knee joint arthrokinematics and muscle recruitment being ancillary issues - this problem is more thoroughly discussed in the LED model article. The BI recommends addressing individual muscles before addressing inter-muscular coordination via subsystem integration to reduce the likelihood of synergistic dominance and reliance on compensatory patterns.

Functional Anatomy of the Gluteal Muscle Group:

Manual Muscle Testing of the Gluteus Medius:

Gluteus Medius Isolated Activation:

Side-lying Gluteus Medius Exercises:

Gluteus Medius Reactive Integration Exercises:

Gluteus Medius Reactive Integration Side-stepping Progressions:

Gluteus Medius Reactive Integration Side-stepping Progressions (Part II):

Gluteus Medius Reactive Integration Side-hopping Progressions:

Recommended Readings:

  1. Gluteus Medius Activation
  2. Gluteal Strengthening Progression Considerations
  3. Overhead Squat Assessment Solutions Table - Sign Clusters and Compensation Patterns


  1. Dos Reis, A. C., Correa, J. C. F., Bley, A. S., Rabelo, N. D. D. A., Fukuda, T. Y., and Lucareli, P. R. G. (2015) Kinematic and kinetic analysis of the single-leg triple hop test in women with and without patellofemoral pain. Journal of Orthopaedic and Sports Physical Therapy, 45(10), 799-807
  2. Noehren B., Hamill, J., and Davis, I. (2013) Prospective evidence for a hip etiology in patellofemoral pain. Medicine and Science in Sports and Exercise, 45(6), 1120-1124
  3. Noehren, B., Scholz, J., and Davis, I. (2011) The effects of real-time gait retraining on hip kinematics, pain, and function in subjects with patellofemoral pain syndrome. British Journal of Sports Medicine, 45, 691-696
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  5. Ramskov, D., Barton, C., Nielson, R. O., and Rasmussen, S. (2015) High eccentric hip abduction strength reduces the risk of developing patellofemoral pain among novice runners initiating a self-structured running program: a 1-year observational study. Journal of Orthopaedic and Sports Physical Therapy, 45(3), 153-161
  6. Ireland, M. L., Wilson, J. D., Ballantyne, B. T., and Davis I. M. (2003) Hip strength in females with and without patellofemoral pain. Journal of Orthopaedic and Sports Physical Therapy, 33, 671-676
  7. Fulkerson, J. P. (2002) Diagnosis and treatment of patients with patellofemoral pain syndrome. The American Journal of Sports Medicine, 30(3), 447-456
  8. Cowan, S. M., Bennell, K. L., Crossley, K. M., Hodges, P. W., and McConnell, J. (2002) Physical therapy alters recruitment of the vasti in patellofemoral pain syndrome. Medicine and Science in Sports and Exercise, 34(12), 1879-1885
  9. Boling, M. C., Bolgla, L. A., Mattacola, C. G., Uhl, T. L., and Hosey, R. G. (2006) Outcomes of a weight-bearing rehabilitation program for patients diagnosed with patellofemoral pain syndrome. Archives of Physical Medicine and Rehabilitation, 87(11), 1428-1435
  10. Brindle, T. J., Mattacola, C. G., and McCrory, J. L. (2003) Electromyographic changes in the gluteus medius during stair ascent and descent in subjects with anterior knee pain. Knee Surgery, Sports Traumatology, Arthroscopy, 11, 244-251
  11. Sheehy, P., Burdett, R. G., Irrgang, J. J., and Van Swearingen, J. (1998) An electromyographic study of vastus medialis oblique and vastus lateralis activity while ascending and descending stairs. Journal of Orthopaedic and Sports Physical Therapy, 27(6), 423-429

© 2017 Brent Brookbush

Questions, comments, and criticisms are welcomed and encouraged.