Extended Abstract
Introduction
Patellofemoral pain syndrome (PFPS) is among the common causes of anterior knee pain in adolescents and adults under 60 years of age. PFPS can arise as a result of multiple factors, including structural and kinematic issues, such as an imbalance between the vastus medialis and vastus lateralis muscles, patellar malalignment, and an excessively large Q-angle. One factor contributing to PFPS that has garnered increasing attention from researchers is abnormal femoral kinematics, which alters the mechanics of the patellofemoral joint. For instance, 30 degrees of internal femoral rotation can increase contact pressure within the patellofemoral joint. Additionally, if the activity of the vastus medialis muscle is greater than that of the vastus lateralis, or if the onset of vastus medialis muscle activity is delayed, the patellar gliding movement may become abnormal, leading to anterior knee pain. Reduced knee flexion in women with PFPS is a compensatory strategy to alleviate pain, which disrupts shock absorption mechanisms in the lower extremity and may consequently culminate in an increased vertical ground reaction force. Therefore, a direct relationship appears to exist between pain and the magnitude of the vertical ground reaction force loading.
The rationale for focusing on closed kinetic chain exercises for the improvement of PFPS lies in the fact that these exercises induce simultaneous contraction of agonist and antagonist muscles. Furthermore, these exercises are more effective in restoring the strength of the quadriceps femoris muscle compared to open kinetic chain exercises. In closed kinetic chain exercises, resistance is applied simultaneously to both proximal and distal regions, while the distal segment of the upper and lower extremities remains in a fixed position.
This study was conducted to determine the effect of closed kinetic chain exercises on changes in plantar foot pressure dynamics in women with PFPS.
Methods
This quasi-experimental study was conducted on 30 female university students aged 20 to 35 years, divided into two groups of 15: One group diagnosed with PFPS and a healthy control group.
The inclusion criteria for the PFPS group included having anterior knee joint and retropatellar pain for at least two months and a maximum of one year during activities such as ascending and descending stairs, sitting, and prolonged walksing. The inclusion criterion for the control group was the absence of pain and discomfort in the patellofemoral joint. Pain intensity in the PFPS group was deemed significant if it exceeded 3 on the Visual Analog Scale (VAS).
A foot scanner was positioned along a ten-meter walkway in the laboratory. Dynamic plantar pressure data were recorded using Rsscan software at a sampling frequency of 300 Hz.
To evaluate the effects of eight weeks of training in two groups, assessments were conducted using two running protocols at slow and fast speeds, with each test repeated three times. Running trials were repeated if balance was lost, if the subject’s foot was positioned outside the designated area of the foot scanner, or if speed control was compromised. Data on plantar pressure variables were extracted during running at both slow and fast speeds. The stance phase of running was defined based on the heel-to-toe contact pattern with the ground. The mean score of the three running trials at both slow and fast speeds was used for statistical analysis. Plantar pressure variables were evaluated in three categories: Force variables, pressure at ten foot points, and center of pressure (COP) displacement in three regions. The ten foot regions included the hallux, the second to fifth toes, and the first to fifth metatarsal bones. COP displacement was assessed in the mediolateral (COPx) and anteroposterior (COPy) directions. A cutoff frequency of 20 Hz was applied to smooth the ground reaction force data. To normalize the ground reaction force data, the aforementioned values were divided by body weight (bw) and multiplied by one hundred.
Following the baseline measurement of plantar foot pressure variables, closed kinetic chain exercises were administered to two groups: Individuals with PFPS and healthy controls. The intervention lasted for eight weeks, with three sessions per week, resulting in a total of 24 sessions. The closed kinetic chain exercises encompassed the conventional squat, ball squat, wall squat, conventional lunge, isometric leg press, hip bridge, and the toe point-flex exercise (simultaneous dorsiflexion and plantarflexion of the foot with an extended instep, performed in a seated position with the lower limbs extended).
For individuals with PFPS, limitations were imposed on the execution of squats. Immediately after the eight-week exercise intervention, the measurement of plantar foot pressure variables was repeated in a post-test phase.
Results
There was no statistically significant difference in peak forces in the plantar foot pressure variables during slow-speed running between the experimental and healthy groups. A statistically significant difference was found in peak forces at the second metatarsal during fast-speed running (P<0.041). In the PFPS group, peak forces at the first toe significantly decreased in the post-test phase during slow-speed running (P<0.001). In the PFPS group, the maximum time to reach peak force significantly increased in the post-test (P<0.027). In the healthy group, peak forces at the first toe significantly decreased in the post-test phase during slow-speed running (P<0.001). A statistically significant decrease was found in peak forces in the external heel force in the healthy group during fast-speed running (P<0.001). Additionally, there was a significant decrease in peak forces at the fifth metatarsal bone in the healthy group during fast-speed running (P<0.001).
Statistically significant differences were found in the COP displacement for plantar pressure variables before and after closed kinetic chain exercises during slow-speed running between the two studied groups at the second metatarsal bone (P<0.016) and in the mediolateral COP displacement (P<0.022). A statistically significant difference was observed at the first toe during fast-speed running (P<0.006). In the healthy group, there was a statistically significant decrease in the COP displacement at the first toe in the post-test phase (P<0.003). Furthermore, the healthy group showed a statistically significant increase in the anteroposterior COP displacement in the post-test phase (P<0.001). There was a statistically significant decrease in the mediolateral COP displacement in the PFPS group during fast-speed running in the post-test phase (P<0.001). In the healthy group, a statistically significant decrease was observed in the anteroposterior and mediolateral COP displacement during fast-speed running in the post-test phase (P<0.001). A statistically significant decrease was found in the COP displacement at the first toe during slow-speed running in the post-test phase in the PFPS group (P<0.002). In the healthy group, a statistically significant decrease was observed in the COP displacement at the midfoot during slow-speed running in the post-test phase (P<0.001). Additionally, a statistically significant decrease was found in the anteroposterior COP displacement and the mediolateral COP displacement in both study groups during slow-speed running in the post-test phase (P<0.001).
Conclusion
In light of the findings of this study, the implementation of an eight-week closed kinetic chain exercise program resulted in a statistically significant reduction in plantar foot pressure variables within the group with PFPS.
Ethical Statement
The current study was approved by the Research Ethics Committee of Mohaghegh Ardabili University (IR.UMA.REC.1402.066).
Funding
This article has been extracted from Leila Sabouri master’s thesis in Sport Biomechanics at the Faculty of Psychology and Educational Sciences, University of Mohaghegh Ardabili.
Conflicts of Interest
No conflicts of interest.
Acknowledgement
We would like to thank all subjects participating in this study, as well as to the esteemed authorities of the Health Center at Mohaghegh Ardabili University, for their cooperation in the execution of this research.

Key Message: Closed kinetic chain exercises in individuals with PFPS, with a greater reduction and impact on the COP displacement variables in healthy women and those with PFPS, can be beneficial in mitigating the complications arising from PFPS and the occurrence of lower extremity injuries during running in both groups.