Physical activity levels in individuals with and without patellofemoral pain

Accepted Manuscript Physical activity levels in individuals with and without patellofemoral pain Neal R. Glaviano, Andrea Baellow, Susan Saliba PII:

S1466-853X(17)30153-0

DOI:

10.1016/j.ptsp.2017.07.002

Reference:

YPTSP 823

To appear in:

Physical Therapy in Sport

Received Date: 13 April 2017 Revised Date:

11 July 2017

Accepted Date: 14 July 2017

Please cite this article as: Glaviano, N.R., Baellow, A., Saliba, S., Physical activity levels in individuals with and without patellofemoral pain, Physical Therapy in Sports (2017), doi: 10.1016/ j.ptsp.2017.07.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Title: Physical Activity Levels in Individuals with and without Patellofemoral Pain Authors:

Toledo, Toledo, OH, USA

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Neal R. Glaviano PhD, AT, ATC. School of Exercise and Rehabilitation, University of

University of Virginia, Charlottesville, VA, USA

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Andrea Baellow Med, ATC. Curry School of Education, Department of Kinesiology,

Susan Saliba PhD, ATC, PT. Curry School of Education, Department of Kinesiology,

Corresponding Author:

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University of Virginia, Charlottesville, VA, USA

Neal R. Glaviano, PhD, AT, ATC. Assistant Professor, School of Exercise and Rehabilitation, Mailstop 119, University of Toledo, Toledo, OH, 43606.

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[email protected] Office: (419) 530- 4501 Fax: (419) 530-2477

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Manuscript Word Count: 3,369

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Abstract

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Objectives: Patellofemoral pain (PFP) is a chronic condition that results in long-

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term subjective and objective impairments. PFP has been identified to result in

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modification in activity levels, however it is unknown the extent of activity levels in

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individuals with and without PFP.

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Design: Case-control study

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Participants: 20 individuals with PFP and 20 healthy individuals.

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Main Outcome Measures: Physical activity was assessed by steps per day, minutes of

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mild, moderate, and high activity over 14 consecutive days. Anterior Knee Pain Scale

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(AKPS), worst pain in last week (WVAS), and Fear Avoidance Belief Questionnaire

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(FABQ) were also collected. Pair t-tests were used to compare variables between groups.

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Pearson r correlations were conducted to evaluate relationships between subjective

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function and activity level.

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Results: Individuals with PFP took less steps per day (p=.004) and completed less daily

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minutes of mild activity (p=.007) and high activity (p=.012). Significant correlations

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were seen between steps per day and subjective function: AKPS (p=.002), WVAS

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(p=.016), and FABQ (p=.002) in the PFP population.

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Conclusion: Individuals with PFP are less physically active than their healthy

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counterparts in both steps per day and minutes spent conducting physical activity.

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A relationship between subjective function and physical activity exists in individuals

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with PFP.

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Keywords: Anterior knee pain, Fear avoidance, pain

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Introduction: Patellofemoral pain (PFP) is a chronic condition that affects a variety of recreational, athletic, and military populations. It accounts for over 7% of all knee

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related pathologies being treated within the United States, and prevalence ranges between

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7-28%.1 While the etiology is unknown, it has been suggested that the pain is a result of

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increased stress on the patellofemoral joint during functional tasks, such as squatting,

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stair ambulation, jogging, and prolonged sitting.2 This increased stress on the

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patellofemoral joint has been proposed to potentially lead to the development of

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patellofemoral osteoarthritis (PFOA) in this population.3

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The presence of pain is common during a variety of functional activities and the location of pain in proximity to the patella varies between individuals with PFP.4

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Prolonged pain has been identified to be present up to 16 years after initial diagnosis.5

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The influence of pain has been theorized to alter physical activity level in these

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individuals, and previous reports have observed between 71-74% of individuals with PFP

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will modify or cease activity.6 The presence of pain may also have a psychosocial

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element; such as fear or avoidance in activity in an attempt to decrease pain experienced

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during common daily activities.7 Improvements in fear avoidance has also been

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identified as a strong predictor for successful outcomes for treating PFP and accounts for

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22% of pain variance in this population. 7,8

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Investigators have also consistently observed that patients with PFP score lower

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on self-reported functional scales.7 These questionnaires assess the participant’s ability to

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perform common activities of daily living such as walking, ascending or descending

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stairs and sitting for long periods of time.9 We assume that since individuals with PFP

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often present with a variety of pain provoking activities (walking, jogging, squatting, etc.)

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that their overall physical activity levels can be directly influenced negatively. Thus, the

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pathology contributed to both functional limitations and overall physical activity levels. While individuals with PFP often present with long-term pain and functional

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limitations great enough to modify their activity and avoid pain-provoking tasks, it is

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currently unknown if differences in activity level exist between individuals with or

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without PFP during their normal daily activities. It is also unknown if the relationship of

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pain, fear-avoidance and subjective function may play on the activity level in individuals

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with PFP. Therefore, the purpose of this study is to compare activity level between

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individuals with and without PFP. We hypothesize that individuals with PFP will be less

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active than their healthy counterparts. Additionally, we hypothesized that pain and fear

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avoidance behavior will have a negative relationship on activity level while individuals

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with higher subjective function will be more active.

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Methods:

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This was a case-control study. Dependent variables were activity level, subjective function assessed by the anterior knee pain scale (AKPS), fear avoidance questionnaire

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(FABQ), and worse pain assessed by the visual analog scale (VAS). Independent

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variables were group, individuals diagnosed with PFP and healthy controls matched on

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age, mass, and sex.

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Participants:

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Study recruitment was conducted from the university setting. 40 participants

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were enrolled in the study, 20 individuals with PFP and 20 healthy individuals (15

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females and 5 males in each group). Sample size for steps per day was determined

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utilizing data from the first five PFP and five healthy participants. Mean difference of

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2,151 steps per day, with a standard deviation of 2,194 steps was calculated with an alpha

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level of 0.05, beta of 0.20, and 20% attrition rate to determine that 20 participants in each

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group were necessary for this study. Enrolled participants for both groups were between

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18-35 years old. Those in the PFP group completed a screening process to determine

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eligibility. Inclusion criteria requiring atraumatic knee pain for greater than 3 months,

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less than 85 points on the Anterior Knee Pain Scale, and pain with a minimum of 2 of the

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following tasks: jumping, kneeling, prolonged sitting, squatting, running, stair climbing,

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pressure on patella or contraction of the quadriceps.10,11 The control participants were

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selected if they had no previous history of knee injury or pain. Exclusion criteria for both

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groups included previous knee surgery, ligamentous instability, additional sources of

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anterior knee pain (patella tendinitis, patella subluxation, bursitis, etc.), history of back,

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hip, or ankle injury, neurological impairments that would affect gait. A single researcher

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(NRG) confirmed PFP diagnosis and assessed ligamentous instability and additional

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sources of knee pain to ensure participant eligibility. This study was approved by the

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University of XXXX’s Institutional Review Board, and those participants who met

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inclusion criteria enrolled in the study by completing written informed consent.

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Procedures

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Participants reported to the laboratory for a screening session to determine

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eligibility. Individuals who met the inclusion criteria were enrolled in the study.

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Anthropometric assessment (age, height, mass) and lower extremity history

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questionnaires were completed to assess duration of symptoms, previous injuries,

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subjective function (Tegner),etc. Participants were then distributed three subjective

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questionnaires for completion; the anterior knee pain scale, fear avoidance belief

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questionnaire and worst pain assessment with a VAS.

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The Anterior Knee Pain Scale is a 13-item questionnaire that evaluates subjective function during a variety of tasks that are often difficult for PFP patients. The scale is

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scored out of 100 points, with 100 indicating the absence of functional impairments

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during the tasks. It has strong reliability (ICC=0.81-0.97) and is a common assessment

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tool within the PFP population.9

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The Fear Avoidance Belief Questionnaire is a 16-item questionnaire that measures fear-avoidance beliefs in patients. The FABQ is divided into two subcategories

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based off the fear patients are experiencing; fear avoidance during work activities

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(FABQ-W) and fear avoidance during physical activity (FABQ-PA). The FABQ-W is

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scored out of 42 points, while the FABQ-PA is scored out of 24 points. Greater scores

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reflect increased subjective fear avoidance beliefs the patient is experiencing. While

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originally being for low back pain patients, the FABQ has been utilized in the PFP

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population with modifications of the physical activities listed and the word back to knee

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throughout the questionnaire.7,12 FABQ-PA was used as the measure of fear avoidance

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for this study.

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Worst pain was assessed with the visual analog scale(WVAS). A 10-cm line that

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listed “No Pain” and “Worst Pain Imaginable” was provided to the participants who were

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instructed to place one vertical mark on the worst pain they experienced in their knee

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over the last 72-hours.

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Following the completion of all questionnaires, participants were provided a FitBit Charge HR (FitBit Inc., San Francisco, CA) following enrollment into the study to

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calculate steps per day and minutes of mild, moderate and high activity levels each day.

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Standardized instructions were provided to all participants; wear the activity band on

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their non-dominant wrist at all times during the day for 2-weeks, except while showering.

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Participants were instructed not to change their normal activity levels during their

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participation in the study. Participants were provided a charging wire with a USB

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connector and were instructed to charge the unit every night and if the device battery died

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throughout the day. Participants were instructed to document when the device was not

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worn for an entire day and provide that information to the research team. All individuals

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were contacted twice a week during their study participation to monitor their adherence

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and retrieve the participant’s documentation on their adherence. The FitBit was synced

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with Bluetooth with the FitBit Connect Application. Data was synced at a minimum of

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once a week. Data was exported from the FitBit application with each participant’s

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activity levels. The intensity of physical activity is calculated by an algorithm that

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estimates metabolic equivalents, which help measures energy expenditure during activity,

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to classify mild, moderate, and high activity levels; however the algorithm is only

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available to the FitBit company.13 After two weeks, participants returned to the laboratory

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to return their FitBit devices to the research team and were released from the study.

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Statistical Analysis:

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Data was analyzed with SPSS software (v23.0, SPSS, Inc., Chicago, IL, USA).

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Dependent variables were evaluated with skewness, kurtosis and Levene’s test for normal

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distribution and variance. Paired T-tests were conducted to determine group differences

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for anthropometric data (age, height, mass), subjective function (AKPS, FABQ-PA,

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Tegner, VAS) and objective data (steps per day and mild, moderate, and high activity

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levels). Levels of activity were directly calculated by the FitBit software for active

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minutes using metabolic equivalents. Compliance was evaluated with the device’s

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application data and cross referenced with adherence logs of participants. If the device

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was not worn, the day was not included in the average calculations. Pearson r correlations

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were conducted to compare subjective and objective variables. Classification was set a

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priori as 0-0.4 (weak), 0.4-0.7 (moderate), and 0.7-1.0(strong).14 Significance was set a

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priori of α<0.05 for all statistical analysis. Magnitude of group differences were

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calculated with Cohen’s d effect sizes and 95% confidence intervals. Effect sizes were

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interpreted as <0.20, trivial; 0.20-0.49, small; 0.50-0.79, moderate; and ≥0.80, large.15

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Results:

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All 40 participants completed the 2-week duration of the study and data from all participants was included in analysis. The dependent variables presented with normality

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for skewness, kurtosis and variance. There were no statistically significant differences in

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the anthropometric values (age, mass, or height) between groups, p>0.05.(Table 1) We

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also did not find a difference in subjective activity level when assessed by the Tegner

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Activity Scale between groups, p=0.33. We found both statistically and clinically

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significant differences in the subjective function and pain, with those suffering from PFP

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presenting with lower scores of function and an increase in pain. (Table 1)

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Individuals with PFP were found to have a decrease in both steps and minutes of

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activity per day when compared to healthy counterparts. Individuals with PFP took on

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average 3,413 steps less per day than those healthy individuals, (Healthy:

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12,042.4±3,878.7steps/day, PFP: 8,629.7±1,665.3steps/day, p=0.004, and a large

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magnitude of difference was identified between groups with a Cohen’s d= 1.14 (95%

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CL=0.47, 1.81). Differences in the range of physical activity were noted between groups;

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healthy individuals walked between 5,021 and 22,629 steps per day compared to

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individuals with PFP walking between 5,956 to 14,037 steps per day. Compared to the

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recommendation of 1,000 steps per day, 75% (15/20) of healthy individuals reached this

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threshold on average each day for the two weeks, while only 20% (4/20) of PFP patients

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did. Those with PFP also completed 40 minutes less of mild activity and 10 less minutes

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of high activity per day compared to healthy individuals, both presenting with statistically

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and large clinically significant differences. (Table 1) PFP individuals completed 4 less

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minutes of moderate activity per day, which was not statistically different (Healthy:

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16.0±6.1minutes, PFP:11.6±6.7, p=0.074) but presented with a moderately clinically

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significant difference (d=0.68; 95% CL=0.05, 1.32).

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We observed a strong negative correlation between the AKPS and WVAS scores, strong negative correlations between the AKPS and FABQ and a moderate positive

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correlation in AKPS and steps per day. (Table 2). A positive correlation between pain and

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FABQ and a weak negative correlation between pain and steps per day were identified.

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(Table 2) A negative moderate correlation was also identified between FABQ and steps

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per day. (Table 2) No significant correlations between the AKPS, FABQ, WVAS or steps

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were identified in the healthy population(p>0.05). (Table 3)

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Discussion:

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When comparing physical activity between healthy and individuals with PFP, we

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observed that those with PFP completed less physical activity a day than healthy

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individuals, with both a decrease in steps per day and minutes of mild and high activity

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per day. We also observed the relationship between pain, fear-avoidance activity and

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subjective function on activity level, with significant correlations present in all four

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variables. We evaluated the number of steps per day between healthy and those with PFP

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over a 2-week period, with healthy individuals accumulating 12,042 steps per day and

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PFP taking 8,629 steps per day. 10,000 steps per day is a step-based recommendation

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from many government agencies and professional organizations in many countries.16

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Those within the PFP group were approximately 15% below that current

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recommendation. Of all PFP participants, only 20% averaged 10,000 steps per day over

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the two-week study, compared to 75% of the healthy individuals. Those with PFP took

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3,413 less steps per day, which may have significant implications on their overall health,

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as this could result in approximately 1.2 million less steps per year for those with PFP.

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Similar reductions in steps per day have also been seen in an ACL reconstruction

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population (1,611 less steps)17 and those with chronic ankle instability (2,137 less steps)18

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compared to healthy controls. However, it is difficult to make direct comparisons due to

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methodological differences between all groups.

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Those with PFP also completed 40 less minutes of mild activity, 4 less minutes of

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moderate activity and 10 less minutes of high activity per day. This reduction in activity

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levels supports previous literature that 71-74% of individuals diagnosed with PFP reduce

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or cease participant in sporting activities.6,19 This decrease in activity may be due to the

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association of altered loading on the patellofemoral joint during functional tasks and the

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presence of fear avoidance. However, the current study is unable to determine why there

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is less physical activity in this population. Minimizing tasks that load the patellofemoral

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joint may result in a decrease in pain but will also have significant implications on

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activity level. It is also unclear the influence of developing PFP has on an individual’s

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activity level, the magnitude of change, potential that decreased activity may lead to the

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development of PFP or how quickly the modifications in activity may occur. While individuals with PFP presented with a decrease in objective physical

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activity we did not see a difference between groups in subjective function. The Tegner

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was used evaluate the highest level of activity currently experienced by our participants.

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While it provides insight into their subjective level of activity, it does not take into

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consideration the duration or frequency of their involvement in those activities.

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Frequency of an activity is only listed for level 5: jogging on uneven ground at least twice

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a week and level 6: jogging 5 times a week. The remainder of levels do not provide

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duration, nor do the other examples of activities within level 5 and 6. Concerns of over

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reporting of physical activity with the Tegner have been raised, as this limitation has been

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previously identified with other subjective scales that assess physical activity.17

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A decrease in physical activity is of great concern due to the chronicity of PFP. PFP was previously theorized to be an activity-limiting condition, however current

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evidence has identified that pain and limitations are present for up to 16 years after initial

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diagnosis.5 This long-term pathology and influence on activity level has a significant

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impact on the individual’s health; as physical activity has a direct relationships with

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cardiovascular disease20, cancer21, diabetes,22 and obesity.23 This impact is magnified by

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the fact that PFP accounts for 7% of all knee pathologies for individuals seeking medical

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attention; which can escalate as a major burden on both healthcare and the monetary costs

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associated with caring for these patients.1

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We did see a relationship between pain, fear avoidance and subjective function on

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activity levels. A negative relationship was seen for both pain and fear avoidance on steps

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per day in the PFP patients. Fear avoidance and pain have been suggested to have a

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relationship; as previous authors have suggested that fear of pain may have a greater role

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on avoidance behavior than pain itself.24 We did see a strong positive relationship

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between both pain and fear avoidance in the PFP patients (r=.753, p<.001). Future

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research should also examine additional influences of psychological factors; as fear of

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movement, catastrophizing, anxiety and depression have all been found to correlate with

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pain and physical function in individuals with PFP.25 Evaluating the effect of improving

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these psychological factors on physical activity levels also warrants evaluation, as

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previous research has found that changes in fear avoidance also accounted for 45% and

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28% variance in both changes in function and pain following a rehabilitation program

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respectively.7,26

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One of the challenges with PFP is the heterogeneous presentation of symptoms between patients. While we used common screening criteria of <85 points on the AKPS

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and requiring pain with a minimum of 2 functional activities, these factors may play a

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role in our results. The type of painful activities participants were experiencing may play

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a role in their overall function and physical activity. Participants who reported increased

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pain with walking or jogging may change either activity differently than individuals who

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only have pain with jumping or prolonged sitting, which may have a larger influence on

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outcomes measures like steps per day. Future research should evaluate the influence of

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specific painful tasks and its relationship to physical activity in individuals with PFP.

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The potential for future studies should also consider the use of mixed method studies to

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gain insight into qualitative measures of fear avoidance or changes in physical activity in

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this population.

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We also found a strong negative correlation between subjective function and fear avoidance (r=-.810, p<.001). This supports previous evidence that PFP patients with

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greater functional limitations also report an increase in fear avoidance beliefs.7 It is

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currently unknown how changes in FABQ influence the AKPS during a course of a

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rehabilitation program on individuals with PFP. It has been observed that a decrease in

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FABQ following 8-weeks of rehabilitation predicts changes in subjective function when

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assessed by the Activities of Daily Living Scale.26 Individuals with PFP have also been

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documented as having a decrease in health-related quality of life compared to both

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individuals without knee injuries and other sources of knee pain.27,28 While it is not

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possible to determine causation, a decrease in physical activity and increase in fear

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avoidance may both play a role in an individual’s quality of life.

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The Fitbit Charge HR was used for this current study due to its ability to include heartrate in the calculation of mild, moderate and high activity in the participants. The

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FitBit HR estimates metabolic equivalents by using the heart rate to determine the

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intensity of the activity being conducted. FitBit devices have been identified as valid

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assessment tools for assessing activity levels and steps during free-living conditions.29-31

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While participants were instructed to continuously wear the activity band for the entire

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duration of the study, there is the potential that some variance and non-compliance was

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evident in the current study. It was possible to evaluate some non-compliance by

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accessing the FitBit application, however it is difficult to establish duration of

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compliance during the testing duration. While adherence was monitored for the duration

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of the study and patients received email reminders, this still presents as a possible

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limitation.

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The current study does present with some additional limitations. This study evaluated a sample of healthy and PFP patient’s activity level, however we did use the

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AKPS and two pain-provoking activities to be required for inclusion for the PFP group.

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Evaluating which subjective limitations participants presented with may play a role in

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their overall decreased physical activity. We also only enrolled participants with PFP

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between the ages of 18-35 years old, which decreases the generalizability to a different

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age group with PFP. Current evidence has identified similar trends in reduced activity in

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adolescents with PFP19, which warrants additional future research. The data was collected

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in the United States, which may influence the results depending on cultural differences.

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We also collected data during the fall and spring seasons, which may influence the

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results, however we did have even groups during both seasons to minimize this concern.

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The duration of collection is also a possible concern. While two-weeks also provides

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general information on activity levels in individuals, longer studies would provide

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additional insight into normal ranges and variance over time to determine a more robust

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normative database in both a healthy and pathological group. Enquiring if the activity

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over the study duration represented their usual level of activity would also have provided

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value. While this may decrease some generalizability, this study is a starting point into

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objectively assessing and evaluating activity levels in a PFP population.

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Conclusion:

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healthy counterparts. Pain, fear avoidance and subjective function were found to have a

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Individuals with PFP presented with less physical activity when compared to their

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significant relationship to the number of steps count in those with PFP. Longitudinal

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studies may be required to determine how activity level changes during both the

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progression of PFP and the role rehabilitation programs may address these impairments.

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303 Figures and Tables

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Table 1: Pain, Fear Avoidance, Subjective Function and Activity Levels between Healthy

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and Individuals with PFP

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Table 2: Correlation Coefficients Between Subjective and Objective Function and

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Activity Levels in Individuals with PFP

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Table 3: Correlation Coefficients Between Subjective and Objective Function and

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Activity Levels in Healthy Individuals

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311 References

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Selhorst M, Rice W, Degenhart T, Jackowski M, Tatman M. Evaluation of a treatment algorithm for patients with patellofemoral pain syndrome: a pilot study. Int J Sports Phys Ther. Apr 2015;10(2):178-188. Esculier JF, Roy JS, Bouyer LJ. Psychometric evidence of self-reported questionnaires for patellofemoral pain syndrome: a systematic review. Disability and rehabilitation. 2013. Glaviano NR, Saliba SA. Immediate Effect of Patterned Electrical Neuromuscular Stimulation on Pain and Muscle Activation in Individuals With Patellofemoral Pain. Journal of athletic training. 2016;51(2):118-128. 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. International Journal of Sports Medicine. 2013. van Baar ME, Dekker J, Oostendorp RA, et al. The effectiveness of exercise therapy in patients with osteoarthritis of the hip or knee: a randomized clinical trial. The Journal of rheumatology. Dec 1998;25(12):2432-2439. Middelweerd A, HP VDP, A VANH, Twisk JWR, Brug J, Te Velde SJ. A Validation Study of the Fitbit One in Daily Life Using Different Time Intervals. Med Sci Sports Exerc. Jun 2017;49(6):1270-1279. Goetschius J, Hart JM. Knee-Extension Torque Variability and Subjective Knee Function in Patients With A History of Anterior Cruciate Ligament Reconstruction. Journal of athletic training. 2015. McGough JJ, Faraone SV. Estimating the size of treatment effects: moving beyond p values. Psychiatry (Edgmont (Pa.: Township)). 2009;6(10):21-29. Tudor-Locke C, Craig CL, Brown WJ, et al. How many steps/day are enough? For adults. Int J Behav Nutr Phys Act. 2011;8:79. Bell DR, Pfeiffer KA, Cadmus-Bertram LA, et al. Objectively Measured Physical Activity in Patients After Anterior Cruciate Ligament Reconstruction. Am J Sports Med. Apr 01 2017:363546517698940. Hubbard-Turner T, Turner MJ. Physical Activity Levels in College Students With Chronic Ankle Instability. Journal of athletic training. 2015;50(7):742747. Rathleff MS, Rathleff CR, Olesen JL, Rasmussen S, Roos EM. Is Knee Pain During Adolescence a Self-limiting Condition? Prognosis of Patellofemoral Pain and Other Types of Knee Pain. Am J Sports Med. May 2016;44(5):11651171. Oguma Y, Shinoda-Tagawa T. Physical activity decreases cardiovascular disease risk in women: review and meta-analysis. Am J Prev Med. Jun 2004;26(5):407-418. Lee IM. Physical activity and cancer prevention--data from epidemiologic studies. Med Sci Sports Exerc. Nov 2003;35(11):1823-1827. LaMonte MJ, Blair SN, Church TS. Physical activity and diabetes prevention. Journal of applied physiology. Sep 2005;99(3):1205-1213. Goran MI, Reynolds KD, Lindquist CH. Role of physical activity in the prevention of obesity in children. International journal of obesity and related

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Table 1: Pain, Fear Avoidance, Subjective Function and Activity Levels between Healthy and PFP Patients

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Healthy PFP P-value Cohen’s d Effect (Mean±SD) (Mean±SD) size with 95% CI Age (years) 20.8±1.8 22.2±2.6 .054 -0.63 (-1.26, 0.01) Mass (kg) 70.1±9.9 68.6±15.4 .708 0.12 (-0.50, 0.74) Height (cm) 172.6±7.9 167.9±7.6 .062 0.61 (-0.03, 1.24) Duration of Symptoms 0.0±0.0 25.0±27.1 .001 -1.30 (-1.99, -0.62) AKPS 100.0±0.0 75.3±7.7 <.001 4.54 (3.37, 5.71) W VAS 0.0±0.0 4.4±1.9 <.001 3.28 (2.33, 4.22) FABQ 0.0±0.0 13.6±4.4 <.001 4.37 (3.23, 5.51) Tegner 6.4±1.5 6.0±1.4 .330 0.27 (-0.35, 0.90) Steps (per Day) 12,042.4±3,878.7 8,629.7±1,665.3 .004 1.14 (0.47, 1.81) Mild Activity(Min/Day) 203.7±38.7 163.3±38.1 .007 1.05 (0.39, 1.71) Moderate Activity(Min/Day) 16.0±6.1 11.6±6.7 .074 0.68 (0.05, 1.32) High Activity(Min/Day) 27.9±12.3 17.8±7.9 .012 0.97 (0.32, 1.63) KG: kilograms; cm: centimeters; AKPS: Anterior Knee Pain Scale; WVAS: Worst Visual Analog Scale; FABQ: Fear Avoidance Belief Questionnaire; Min/Day: Minutes per day

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AKPS

FABQ

r .470

p-value .002

r -.378

p-value .016

r -.481 .118

p-value .002

Duration (months) r -.155

p-value 0.514

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Table 2: Correlation Coefficients Between Subjective and Objective Function and Activity Levels in PFP Patients

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.921

-.087

.717

-.810

<.001

.753

<.001

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-.916

<.001

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.621

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AKPS: Anterior Knee Pain Scale; WVAS: Worst Visual Analog Scale; FABQ: Fear Avoidance Belief Questionnaire

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FABQ

.105

.665

W VAS

.181

.444

W VAS p-value .487

-.216

.361

r -.332

FABQ p-value .153

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Steps

r .165

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AKPS p-value .275

r .257

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Table 3: Correlation Coefficients Between Subjective and Objective Function and Activity Levels in Healthy Individuals

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AKPS: Anterior Knee Pain Scale; WVAS: Worst Visual Analog Scale; FABQ: Fear Avoidance Belief Questionnaire

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Highlights: Those with patellofemoral pain perform less physical activity than healthy controls

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Pain and fear avoidance belief have negative relationships with steps per day

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Subjective function has a positive relationship with steps per day

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Conflict of Interest: None

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Ethical Approval: Approval was provided by the Institutional Review board at the University of Virginia (UVA IRB-HSR 17909) and all subjects gave informed consent.

Funding:

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None declared

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Acknowledgements:

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None