People with PFP are less physically active than healthy controls, with regard to both steps per day and minutes of mild, moderate, and intense activity. Increases in activity-related pain may cause patients to modify their lower extremity function during tasks associated with physical activity.
By Neal R. Glaviano, PhD, AT, ATC; Andrea Baellow, MS; and Susan Saliba, PhD, MPT, Med
It is widely accepted that engaging in regular physical activity is beneficial for promoting and maintaining overall physical health and reducing the risk of chronic disease and premature death. The American College of Sports Medicine and the Centers for Disease Control and Prevention have published guidelines on physical activity and public health that have been endorsed by the American Heart Association.1,2 Healthcare professionals involved in testing and prescribing exercise accept these guidelines as preventive measures.
Recommendations are that healthy adults, 18 to 65 years old, engage in a minimum of 30 minutes of moderate-intensity aerobic physical activity 5 days a week or a minimum of 20 minutes of vigorous-intensity aerobic activity 3 days a week, with an overall minimum of 10,000 steps per day.1 Recommendations also are available for increasing muscle strength and endurance to promote and maintain good health and physical independence.1
The benefits of participating in aerobic and muscle-strengthening physical activities are vast. They include promoting and maintaining skeletal health and reducing the risk of premature chronic health conditions, including thromboembolic stroke, hypertension, type 2 diabetes mellitus, obesity, many cancers, anxiety, and depression.1 Engaging in extra weight-bearing activities and higher-impact activities such as stair climbing or jogging can further promote and maintain skeletal health.
These recommendations become problematic, however, in populations of patients who may be refraining from or limiting physical activity because of chronic pain.
The impact of patellofemoral pain
Patellofemoral pain (PFP) is a chronic condition described as generalized anterior knee pain during a multitude of activities, typically becoming worse with prolonged activity.3,4 Activities that induce or exacerbate pain include, but are not limited to, walking, jogging, squatting, lunging, kneeling, prolonged sitting, and walking up and down stairs.5-8 Many of these activities are the same as those recommended by the American College of Sports Medicine as ways to promote physical health and reduce the risk of morbidity. The situation is problematic and paradoxical: People who have a chronic condition—specifically, PFP—are limited in their ability to engage in activities to benefit their overall health.
As many as 74% of adults with PFP decrease their activity level or stop activities altogether because of pain.9 Rathleff and colleagues10 also identified similar trends within an adolescent population: 71% of adolescents with PFP reduced or stopped sports participation and decreased their leisure time each week, compared to both healthy controls and adolescents with other types of knee pain.
These results are concerning. People with PFP have pain and symptoms for many years following their initial diagnosis,10,11 and current conservative treatments are not always successful in producing positive long-term outcomes.12 People with PFP who are unable to complete the recommended amount of physical activity because of pain are at serious risk of poor overall health and morbidity.
Study and findings: General discussion
We designed a study to objectively evaluate physical activity levels in people with PFP and compare those levels to physical activity levels in people without PFP. We also analyzed our findings to determine if a relationship exists between activity level and any of three subjective measures:
- worse knee pain over the past 72 hours, based on a visual analog scale (W-VAS)
- subjective function, based on the Anterior Knee Pain Scale
- fear avoidance belief, based on the Fear Avoidance Belief Questionnaire physical activity subsection.
We enrolled 40 total participants: 20 people with PFP (15 females, 5 males; median age, 22.2 [±2.6] years) and 20 healthy controls (15 females, 5 males; median age, 20.8 [±1.8] years). Participants completed the three subjective questionnaires and wore a wireless monitor over a 2-week period to collect data on daily activity level, which was assessed by both steps per day and minutes of mild, moderate, and high activity per day.
We found that people with PFP are less physically active than healthy controls. Those with PFP took 3400 fewer steps and completed almost 1 hour less of physical activity each day over the 2-week period. This hour of physical activity can be further broken down to 40 fewer minutes of mild activity, 4 fewer minutes of moderate activity, and 10 fewer minutes of high physical activity (Figure 1, page 18).
Among study participants with PFP, we also identified a positive relationship between physical activity, defined by steps per day, and the Anterior Knee Pain Scale. This finding suggests that people with better subjective function are also more active. We saw a negative relationship between steps per day and the W-VAS and Fear Avoidance Belief Questionnaire; participants with a greater level of pain were less likely to be active, and those with more fear avoidance beliefs completed fewer steps per day.
There were no relationships between the subjective scales and minutes of mild, moderate, or high activity. There were also no relationships between physical activity levels and subjective function among healthy controls.
The physical activity-pain relationship in people with PFP
The etiology of PFP is unknown, but it has long been proposed that one cause is increased stress on the patellofemoral joint. Excessive physical activity might result in repetitive stress that exceeds the joint’s ability to accommodate the load.13
There has been a recent increase in research evaluating physical activity in patients with PFP to gain a greater understanding of the role of activity in the pathology of PFP and its influence on the individual.10,14,15 Briani et al reported that women with PFP who were more physically active also reported a greater level of pain (both self-reported pain for the previous month and current pain level assessed in a laboratory setting).14 An intense level of physical activity predicted almost one third of PFP cases, whereas a moderate level of physical activity predicted only 1% of cases.15
These findings are different from those of our study, which found that greater knee pain in the previous 72 hours was associated with less activity over the subsequent 2-week period. Although there are methodological differences between the studies,14,15 it is important to consider that the directional relationship between activity and pain is unknown. It is plausible that people experiencing a greater level of pain might modify their activities to minimize subsequent pain. Within our study, we did find that elevated fear avoidance beliefs were also evident in patients who had a greater level of pain and a lower level of physical activity.
Knee pain associated with an increase in activity provides some support for the theory that repetitive loading may be a factor that contributes to the presentation of pain in these patients. We have data (in review) suggesting that less active women with PFP have altered frontal-plane kinematics during common physical activity tasks, such as running, squatting, and stair ambulation. These subjects presented with greater hip adduction and knee abduction, which has been linked to a greater level of pain and lower subjective function.16,17 If these women participate in physical activity, therefore, altered mechanics might be responsible for increased pain. This becomes a challenging “catch-22” for PFP patients: The prospect that increased physical activity will result in knee pain is as problematic as the prospect of physical inactivity, which can lead to decreased health-related quality of life18 and increased risk of a myriad of health conditions.19-22
Because a relationship exists between the level of physical activity and pain, it is important to evaluate the consequences of pain during functional activities. Self-reported pain has been studied during specific functional tasks in patients with PFP,5,16,23-25 but the effect of pain on neuromuscular measures during commonly performed physical activity tasks also must be evaluated.
Bazett-Jones and co-workers26 reported that increasing knee pain with repetitive single-leg squats was associated with a decrease in hip extensor strength and altered hip mechanics during running. Greuel and colleagues27 also found that increased pain has an influence on running mechanics, specifically at the knee. Changes in lower-extremity function do appear to be relative to the magnitude of pain reported by patients; Ott and colleagues28 found that women with PFP who reported more knee pain following aerobic exercise had a greater reduction in quadriceps activity than women who did not have pain following aerobic activity and healthy controls.
The findings of Briani et al14 also support this change in quadriceps function, as PFP patients who were more active and experiencing a greater pain level had a delay in quadriceps activation during stair ambulation. These changes in neuromuscular function have been hypothesized to be a compensatory strategy to reduce loading on the knee; however, given the chronicity of PFP, it is unknown how modifications in lower-extremity mechanics contribute to long-term joint health and the potential risk of additional pathology.
Employing interventions that decrease pain and improve individual impairments for the patient is vital.29 Emerging evidence suggests that subgrouping patients with PFP may provide a more targeted intervention and improve outcomes, as opposed to treating all PFP patients the same way.30 One of the challenges with PFP is the heterogeneous presentation of symptoms and pain-provoking tasks from one patient to the next. This complicates the clinician’s ability to prescribe recommendations for physical activity while minimizing pain.
To the best of our knowledge, no published studies have evaluated the effect of an intervention program specifically targeting physical activity levels for PFP patients. However, a recent treatment paradigm, RISK (Reduce overall load, Improve capacity to attenuate loads, Shift loads, Keep adapting to the runner’s goals and capacity), has been proposed for treating runners with PFP.31 Although this treatment approach currently focuses on runners, the concepts behind it provide strong recommendations for treating other PFP patients who have modified their activity level because of pain.
Reduction of load. Because pain contributes to altered lower-extremity mechanics, it is important to employ proper pain management early to prevent potential consequences. Reducing the load is a common treatment for patients in whom PFP has been diagnosed; a study in the United Kingdom of physiotherapists’ management strategies for PFP found that a large number recommend that their patients not participate in recreational or sporting activities if they experience any knee pain.32 This concept is also supported by Dye and co-workers,33 who propose that tissue homeostasis of the patellofemoral joint is essential for patients with PFP. Patients must stay within their “envelop of function,” Dye advised, by minimizing activities that lead to increased pain and symptoms.33
Strength training. It is important, after reducing load, to progress to a strength-training program to improve the capacity to attenuate the load on the knee joint. Both hip-focused and knee-focused strength-training programs have produced positive short-term outcomes with regard to both pain and subjective function.34-37
Shifting the load during common pain-provoking tasks should be the next step. Gait retraining has produced positive improvements in running mechanics for patients with PFP, with short-term retention of beneficial improvements.38 Salsich et al39 also identified improvements in lower-extremity movement and control following a task-specific movement training program. This experience provides support for individualizing treatment for PFP patients, based on functional impairments that may prevent them from being physically active.
Adaptation. The final step in the RISK paradigm is to have the patient adapt to specific goals, which requires identification of the types of physical activity in which the patient aims to participate. As recommended by Barton,31 this step should include communication between patient and clinician, and should be adjusted as symptoms and physical activity goals change.
People with PFP are less physically active than healthy controls, in regard to both steps per day and minutes of mild, moderate, and intense activity. Clinicians should be aware that increases in the activity level of patients with PFP may be accompanied by worsening knee pain, which may result in modifications to lower-extremity function during tasks often associated with physical activity. Assessing activity level and pain may provide valuable information when evaluating and treating patients with PFP. Additional research in understanding activity modification within this population is warranted.
Neal R. Glaviano, PhD, AT, ATC, is Assistant Professor in the School of Exercise and Rehabilitation Sciences, University of Toledo, Ohio. Andrea Baellow, MS, is a doctoral student and Susan Saliba, PhD, MPT, MEd, is Professor, both in the Department of Kinesiology at the University of Virginia, Charlottesville.
- Haskell WL, Lee IM, Pate RR, et al. Physical activity and public health: updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Med Sci Sports Exerc 2007;39(8):1423-1434.
- American College of Sports Medicine Position Stand. The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults. Med Sci Sports Exerc 1998;30(6):975-991.
- Devereaux MD, Lachmann SM. Patello-femoral arthralgia in athletes attending a Sports Injury Clinic. Br J Sports Med 1984;18(1):18-21.
- Crossley KM, Stefanik JJ, Selfe J, et al. 2016 Patellofemoral pain consensus statement from the 4th International Patellofemoral Pain Research Retreat, Manchester. Part 1: Terminology, definitions, clinical examination, natural history, patellofemoral osteoarthritis and patient-reported outcome measures. Br J Sports Med 2016;50(14):839-843.
- Willson JD, Binder-Macleod S, Davis IS. Lower extremity jumping mechanics of female athletes with and without patellofemoral pain before and after exertion. Am J Sports Med 2008;36(8):1587-1596.
- Willson JD, Davis IS. Lower extremity mechanics of females with and without patellofemoral pain across activities with progressively greater task demands. Clin Biomech 2008;23(2):203-211.
- Herrington L. Knee valgus angle during single leg squat and landing in patellofemoral pain patients and controls. Knee 2014;21(2):514-517.
- Bolgla LA, Malone TR, Umberger BR, Uhl TL. Hip strength and hip and knee kinematics during stair descent in females with and without patellofemoral pain syndrome. J Orthop Sports Phys Ther 2008;38(1):12-18.
- Blond L, Hansen L. Patellofemoral pain syndrome in athletes: a 5.7-year retrospective follow-up study of 250 athletes. Acta Orthop Belg 1998;64(4):393-400.
- Rathleff MS, Rathleff CR, Olesen JL, et al. Is knee pain during adolescence a self-limiting condition? Prognosis of patellofemoral pain and other types of knee pain. Am J Sports Med 2016;44(5):1165-1171.
- Stathopulu E, Baildam E. Anterior knee pain: a long-term follow-up. Rheumatology 2003;42(2):380-382.
- Lankhorst NE, van Middelkoop M, Crossley KM, et al. Factors that predict a poor outcome 5-8 years after the diagnosis of patellofemoral pain: a multicentre observational analysis. Br J Sports Med 2016;50(14)881-886 .
- Milgrom C, Finestone A, Eldad A, Shlamkovitch N. Patellofemoral pain caused by overactivity. A prospective study of risk factors in infantry recruits. J Bone Joint Surg Am 1991;73(7):1041-1043.
- Briani RV, de Oliveira Silva D, Pazzinatto MF, et al. Delayed onset of electromyographic activity of the vastus medialis relative to the vastus lateralis may be related to physical activity levels in females with patellofemoral pain. J Electromyogr Kinesiol 2016;26:137-142.
- Briani RV, Pazzinatto MF, De Oliveira Silva D, Azevedo FM. Different pain responses to distinct levels of physical activity in women with patellofemoral pain. Braz J Phys Ther 2017;21(2):138-143.
- Ferrari D, Briani RV, de Oliveira Silva D, et al. Higher pain level and lower functional capacity are associated with the number of altered kinematics in women with patellofemoral pain. Gait Posture 2017 July 10. [Epub ahead of print]
- Nakagawa TH, Serrao FV, Maciel CD, Powers CM. Hip and knee kinematics are associated with pain and self-reported functional status in males and females with patellofemoral pain. Int J Sports Med 2013;34(11):997-1002.
- Anokye NK, Trueman P, Green C, et al. Physical activity and health related quality of life. BMC Public Health 2012;12:624.
- Oguma Y, Shinoda-Tagawa T. Physical activity decreases cardiovascular disease risk in women: review and meta-analysis. Am J Prev Med 2004;26(5):407-418.
- Calton BA, Lacey JV Jr, Schatzkin A, et al. Physical activity and the risk of colon cancer among women: a prospective cohort study (United States). Int J Cancer 2006;119(2):385-391.
- LaMonte MJ, Blair SN, Church TS. Physical activity and diabetes prevention. J Appl Physiol 2005;99(3):1205-1213.
- Kyu HH, Bachman VF, Alexander LT, et al. Physical activity and risk of breast cancer, colon cancer, diabetes, ischemic heart disease, and ischemic stroke events: systematic review and dose-response meta-analysis for the Global Burden of Disease Study 2013. BMJ 2016;354:i3857.
- Ferber R, Kendall KD, Farr L. Changes in knee biomechanics after a hip-abductor strengthening protocol for runners with patellofemoral pain syndrome. J Athl Train 2011;46(2):142-149.
- Glaviano NR, Huntsman S, Dembeck A, et al. Improvements in kinematics, muscle activity and pain during functional tasks in females with patellofemoral pain following a single patterned electrical stimulation treatment. Clin Biomech 2015;32:20-27.
- Graci V, Salsich GB. Trunk and lower extremity segment kinematics and their relationship to pain following movement instruction during a single-leg squat in females with dynamic knee valgus and patellofemoral pain. J Sci Med Sport 2015;18(3):343-347.
- Bazett-Jones DM, Huddleston W, Cobb S, et al. Acute responses of strength and running mechanics to increasing and decreasing pain in patients with patellofemoral pain. J Athl Train 2017;52(5):411-421.
- Greuel HH, Liu A, Jones RK. How does pain influence running in individuals with patellofemoral pain? Gait Posture 2017;57:143.
- Ott B, Cosby NL, Grindstaff TL, Hart JM. Hip and knee muscle function following aerobic exercise in individuals with patellofemoral pain syndrome. J Electromyogr Kinesiol 2011;21(4):631-637.
- Glaviano NR, Saliba S. Impairment based rehabilitation for patellofemoral pain patients. Phys Sportsmed 2016;44(3):311-323.
- Selfe J, Janssen J, Callaghan M, et al. Are there three main subgroups within the patellofemoral pain population? A detailed characterisation study of 127 patients to help develop targeted intervention (TIPPs). Br J Sports Med 2016;50(14):873-880.
- Barton C. Managing RISK when treating the injured runner with running retraining, load management and exercise therapy. Phys Ther Sport 2017 October 4. [Epub ahead of print]
- Smith BE, Hendrick P, Bateman M, et al. Current management strategies for patellofemoral pain: an online survey of 99 practising UK physiotherapists. BMC Musculoskelet Disord 2017;18(1):181.
- Dye SF, Staubli HU, Biedert RM, Vaupel GL. The mosaic of pathophysiology causing patellofemoral pain: Therapeutic Implications. Oper Tech Sports Med 1999;7(2):45-54.
- Ferber R, Bolgla L, Earl-Boehm JE, et al. Strengthening of the hip and core versus knee muscles for the treatment of patellofemoral pain: a multicenter randomized controlled trial. J Athl Train 2015;50(4):366-377.
- Hamstra-Wright KL, Aydemir B, Earl-Boehm J, et al. Patient-reported outcomes remain improved 6-months post patellofemoral pain rehabilitation. J Sport Rehabil 2016:1-27.
- Piva SR, Goodnite EA, Childs JD. Strength around the hip and flexibility of soft tissues in individuals with and without patellofemoral pain syndrome. J Orthop Sports Phys Ther 2005;35(12):793-801.
- Khayambashi K, Mohammadkhani Z, Ghaznavi K, et al. The effects of isolated hip abductor and external rotator muscle strengthening on pain, health status, and hip strength in females with patellofemoral pain: a randomized controlled trial. J Orthop Sports Phys Ther 2012;42(1):22-29.
- Noehren B, Scholz J, Davis I. The effect of real-time gait retraining on hip kinematics, pain and function in subjects with patellofemoral pain syndrome. Br J Sports Med 2011;45(9):691-696.
- Salsich GB, Yemm B, Steger-May K, et al. A feasibility study of a novel, task-specific movement training intervention for women with patellofemoral pain. Clin Rehabil 2017 July 1. [Epub ahead of print]