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Background. Patellofemoral pain (PFP) is one of the most common causes of knee pain in recreational runners and is exacerbated by activities that load the patellofemoral joint. Although biomechanical differences between running surfaces and elevation profiles have been documented, the influence of terrain type and training load on PFP in non-professional runners remains poorly defined.
Objective. To examine the association between predominant training terrain and the presence of PFP in non-professional runners, and to describe its functional severity. Secondarily, to analyze the relationship between terrain exposure, elevation, training load and volume with PFP, as well as the potential influence of previous knee history and footwear rotation.
Methods. An observational, analytical, cross-sectional study conducted through an online survey targeting recreational runners. The primary outcome will be the presence of patellofemoral pain, defined according to the 2016 International Consensus, and functional severity will be assessed using the Spanish-validated Kujala Anterior Knee Pain Scale. Exposures will include the percentage of kilometers run on each terrain type, positive and negative elevation gain, internal load (session rating of perceived exertion × duration), training volume, and running pace. Potential confounders will include age, sex, body mass index, running experience, training frequency, previous knee history, lower-limb strength, accumulated elevation gain, and footwear rotation. Descriptive analyses and logistic regression models will be performed to identify independent associations.
Expected results. To estimate the prevalence of PFP in recreational runners, identify terrain- and load-related factors associated with its occurrence, and define a predictive model to inform prevention strategies and training planning.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Observational group | Non-professional / recreational adult runners who train regularly and perform the majority of their training on asphalt, trail, or mountain terrain. |
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| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| Runner sample | Other | Runners with lower or different exposure to these factors: other predominant terrain types (e.g., asphalt or trail), lower accumulated elevation gain, and/or lower levels of internal load and training volume. |
| Measure | Description | Time Frame |
|---|---|---|
| Measurement of patellofemoral pain over the previous three months. | This variable will be defined according to the International Consensus on Patellofemoral Pain. Participants will be classified as positive cases if they report anterior or retropatellar knee pain in the previous three months, exacerbated by at least one weight-bearing, knee-flexion activity (e.g., running, stair ambulation, slopes, or squatting), with a duration of ≥4 weeks or ≥2 episodes during that period | Screening visit |
| Measure | Description | Time Frame |
|---|---|---|
| Measurement of functional severity of patellofemoral pain | Functional severity will be assessed using the Spanish-validated version of the Kujala Anterior Knee Pain Scale. This is a condition-specific 13-item questionnaire that evaluates functional limitations, symptoms, and the ability to perform knee-loading activities. Total scores range from 0 to 100, with higher scores indicating better function and, therefore, lower severity. |
| Measure | Description | Time Frame |
|---|---|---|
| Measurement of age | This potential confounding or moderating variable will be measured in years. | Screening visit |
| Measurement of gender | This potential confounding or moderating variable will be recorded as a dichotomous variable (female/male). |
Inclusion Criteria:
Exclusion Criteria:
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Adult non-professional / recreational runners who train regularly and perform the majority of their training on asphalt, trail, or mountain terrain.
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| Name | Affiliation | Role |
|---|---|---|
| Rubén Cuesta-Barriuso, PhD | Universidad de Oviedo | Principal Investigator |
| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| Universidad de Oviedo | Oviedo | Principality of Asturias | 33006 | Spain |
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| ID | Term |
|---|---|
| D046788 | Patellofemoral Pain Syndrome |
| D009043 | Motor Activity |
| ID | Term |
|---|---|
| D007592 | Joint Diseases |
| D009140 | Musculoskeletal Diseases |
| D001519 | Behavior |
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| Screening visit |
| Measurement of terrain exposure (previous 3 months) | This variable will capture the type of terrain on which the runner habitually trains (asphalt, trail, and mountain). Participants will report the approximate percentage of total kilometers completed on asphalt, trail, and mountain terrain over the previous three months. | Screening visit |
| Measurement of weekly positive and negative elevation gain | This variable will be recorded as an average value (meters per week, or normalized as meters per 10 km), given that eccentric loading and patellofemoral joint stress increase substantially during prolonged downhill running. | Screening visit |
| Measurement of the percentage of downhill kilometers | If mountain terrain is predominant, an additional item will be included to capture the percentage of kilometers run on downhills with a gradient ≥6%. | Screening visit |
| Measurement of training intensity and internal load (previous 4 weeks) | Training intensity will be assessed using Foster's session Rating of Perceived Exertion (sRPE), based on the Borg CR-10 scale (0-10). Participants will report their mean perceived exertion for each session type (e.g., easy runs, intervals, hill sessions) over the previous four weeks. Weekly internal load will be calculated by multiplying the sRPE value by session duration (minutes). | Screening visit |
| Measurement of training volume over the previous 4 weeks | This variable will include weekly running distance (kilometers), training frequency (number of sessions per week), and session duration (minutes per session). | Screening visit |
| Measurement of mean running pace over the previous 4 weeks | This variable will be recorded as minutes per kilometer (min/km). | Screening visit |
| Screening visit |
| Measurement of body mass index | This potential confounding or moderating variable will be calculated as kg/m². | Screening visit |
| Measurement of previous knee pain or injury | This potential confounding or moderating variable will be assessed as a dichotomous variable by asking: "Have you experienced knee pain or injury in the past 24 months?" (yes/no). | Screening visit |
| Mesurement of a running experience | This potential confounding or moderating variable will be measured as the number of years of running. | Screening visit |
| Measurement of training frequency | This potential confounding or moderating variable will be recorded as the number of training sessions per week. | Screening visit |
| Measurement of accumulated elevation gain | This potential confounding or moderating variable will be measured as the total elevation gain per week. | Screening visit |
| Measurement of lower-limb strength training | This potential confounding or moderating variable will be measured as the number of days per week dedicated to lower-limb and core strength exercises. | Screening visit |
| Measurement of footwear rotation | This potential confounding or moderating variable will be assessed as a dichotomous variable indicating the use of two or more pairs of running shoes in rotation (yes/no). | Screening visit |