Effects of step length on patellofemoral joint stress in female runners with and without patellofemoral pain.
BACKGROUND
Patellofemoral pain is common among runners and is frequently attributed to increased patellofemoral joint stress. The purpose of our study was to examine the effects of changing step length during running on patellofemoral joint stress per step and stress per mile in females with and without patellofemoral pain.


METHODS
Ten female runners with patellofemoral pain and 13 healthy female runners performed running trials at 3.7m/s in three conditions: preferred step length, at least +10% step length, and at least -10% step length. Knee flexion angles and internal knee extension moments served as inputs for a biomechanical model to estimate patellofemoral joint stress per step. We also estimated total patellofemoral joint stress per mile based on the number of steps necessary to run a mile during each condition.


RESULTS
Patellofemoral joint stress per step increased 31% in the long step length condition (P<.001) and decreased 22.2% in the short step length condition (P<.001). Despite the inverse relationship between step length and number of steps required to run a mile, patellofemoral joint stress per mile increased 14% in the long step length condition (P<.001) and decreased 7.5% in the short step length condition (P<.001).


CONCLUSIONS
These results suggest a direct relationship between step length and patellofemoral joint loads. Total stress per mile experienced at the patellofemoral joint decreased with a short step length despite the greater number of steps necessary to cover this distance. These findings may have relevance with respect to both prevention and treatment of patellofemoral joint pain.
Department of Physical Therapy, East Carolina University, Greenville, NC 28734, USA. Electronic address: willsonj@ecu.edu.
John D
JD
Willson
La Crosse Institute for Movement Science, Department of Health Professions - Physical Therapy Program, University of Wisconsin - La Crosse, La Crosse, WI 54601, USA.
Ryan
R
Sharpee
Department of Physical Therapy, East Carolina University, Greenville, NC 28734, USA.
Stacey A
SA
Meardon
La Crosse Institute for Movement Science, Department of Health Professions - Physical Therapy Program, University of Wisconsin - La Crosse, La Crosse, WI 54601, USA.
Thomas W
TW
Kernozek
D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D005684:Gait / Q000502:physiology*; D006801:Humans; D057071:Patellofemoral Joint / Q000502:physiology* / Q000503:physiopathology; D046788:Patellofemoral Pain Syndrome / Q000503:physiopathology*; D012420:Running / Q000502:physiology*; D055815:Young Adult
Gait; Kinetics; Knee; Rehabilitation