Comparison of Knee Strengthening Combined With Hip or Ankle Joint Exercises on Clinical Symptoms, Sports Performance and Soft Tissue Structure in Women With Patellofemoral Pain Syndrome
Phase: NA
Conditions: Patellofemoral Pain Syndrome, Anterior Knee Pain, Exercise Therapy
Sponsor: Kaohsiung Medical University Chung-Ho Memorial Hospital

 
 
 
 
 
Knee Strengthening With Hip vs. Ankle Exercises in 
Women With Patellofemoral Pain Syndrome 
 
 
 
 
 
 
 
 
 
 
 
 
September 25, 2025

 
 
Abstract 
1 
Purpose: This study compared the effects of knee strengthening combined with either hip or ankle 
2 
joint exercises on dynamic knee valgus (DKV), visual analogue scale (VAS) scores during activity, 
3 
tendon stiffness, muscle structure, ankle range of motion, and muscle strength in women with anterior 
4 
knee pain. Methods: Forty-five female recreational athletes aged 20–40 with anterior knee pain were 
5 
randomly assigned to three groups: hip + knee exercises (HK group, n = 15), ankle + knee exercises 
6 
(AK group, n = 15), and stretching alone (control group, n = 15). The HK and AK groups received 
7 
supervised telehealth-based exercise sessions (30 minutes/day, 3 times/week for 8 weeks), while the 
8 
control group received only an educational pamphlet. Assessments were conducted at baseline, 4 
9 
weeks, and 8 weeks.  
10 
 
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Key Words: (1) Dynamic alignment (2) Tele-rehabilitation (3) Pain modulation (4) Muscle strength.
12 

 
 
Introduction 
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Anterior knee pain refers to clinical symptoms of pain around the patella that occur during 
14 
activities such as squatting, running, and climbing stairs due to increased pressure on the 
15 
patellofemoral joint. Anterior knee pain is a non-contact knee injury, typically characterized by a 
16 
gradual onset of pain around the knee joint that is not related to trauma. Additionally, the pain tends to 
17 
worsen with increased activity, leading to limitations in movement and reduced exercise performance 
18 
(1, 2). Statistics show that this condition accounts for 25-40% of all knee injuries, with a significantly 
19 
higher prevalence in women than in men (3). This may be related to anatomical differences, 
20 
particularly the larger knee valgus angle in women. Additionally, characteristics such as muscle 
21 
strength and muscle coordination in women may also contribute to greater knee joint instability, 
22 
further increasing the risk of anterior knee pain, impacting quality of life, and raising healthcare costs 
23 
(4-6). 
24 
Treating anterior knee pain is particularly challenging because multiple factors cause it. There is 
25 
currently no consensus on treatment strategies, but scholars generally agree that the primary causes of 
26 
anterior knee pain include increased dynamic knee valgus (DKV) angle, weakness in the knee and hip 
27 
muscles, and poor landing mechanics (7-9). Although the pain associated with anterior knee pain 
28 
primarily occurs in the anterior knee, the underlying causes are not limited to the knee joint but also 
29 
involve the hip and ankle joints. Therefore, treatment strategies need to be multifaceted, such as 
30 
combining hip and quadriceps strengthening, foot and ankle mobility exercises, movement retraining, 
31 

 
 
and patient education, which together target both proximal and distal factors contributing to 
32 
patellofemoral pain (10-14). 
33 
Recent studies have shown that hip muscle control and ankle dorsiflexion range of motion 
34 
(ROM) influence the DKV angle during weight-bearing activities (15). In the top-down kinetic chain 
35 
theory, the hip abductor and external rotator muscles eccentrically contract to control hip adduction 
36 
and internal rotation (16). When these muscles are weak, poor neuromuscular control during 
37 
weight-bearing activities can lead to increased femoral adduction and internal rotation, increasing the 
38 
lateral force on the patellofemoral joint (17, 18). This results in excessive load on the patellar tendon 
39 
and facet joints, which is a key factor in anterior knee pain development (19-21). Numerous studies 
40 
have demonstrated that weakness in the hip abductor and external rotator muscles can lead to patellar 
41 
rotation and instability (19, 20). In research by Ferber and colleagues, a three-week hip abduction 
42 
muscle training program for anterior knee pain patients alleviated knee pain and increased knee 
43 
stability more quickly than the group that only received knee joint training (22). Furthermore, 
44 
randomized controlled trials have shown that quadriceps training combined with hip abduction and 
45 
external rotation muscle training is more effective in reducing knee pain than quadriceps training 
46 
alone (23, 24). The existing evidence suggests that training both the hip and knee joint muscles is 
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more effective than training the hip muscles alone. Additionally, hip muscle training alone is slightly 
48 
more effective than knee joint training alone (25). Therefore, studies recommend incorporating hip 
49 
muscle training into the training programs for anterior knee pain patients (21, 26, 27). 
50 

 
 
On the other hand, in the bottom-up kinetic chain theory (2), ankle dorsiflexion ROM and the 
51 
strength of the ankle plantar flexor muscles play crucial roles in absorbing ground reaction forces 
52 
during landing (28, 29). When ankle dorsiflexion is restricted, patients may compensate for the 
53 
sagittal plane movement deficiencies by increasing the coronal plane movement (30). In other words, 
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when ankle joint angles are limited, the knee joint may increase the DKV angle as a compensatory 
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strategy, leading to a stiffer landing strategy that increases the knee joint's exposure to greater ground 
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reaction forces during weight-bearing, thereby increasing the risk of anterior knee pain (31, 32). In a 
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proper landing process, the forefoot hits the ground, followed by the eccentric contraction of the 
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plantar flexor muscles to assist in ankle dorsiflexion. Thus, the eccentric contraction capacity of the 
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posterior lower leg muscles also plays a crucial role during weight-bearing (33). In other words, 
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restricted ankle dorsiflexion can affect the entire lower limb kinetic chain, increasing the risk of 
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anterior knee pain. 
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In daily life or sports environments, single-leg landing is a common movement in many jumping 
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activities. During landing, if the ankle dorsiflexion angle is restricted, the forward glide of the tibia is 
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reduced, requiring compensatory hip adduction and internal rotation (34). This movement pattern in a 
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closed kinetic chain leads to dynamic knee valgus, increases friction along the patellar tracking path, 
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reduces the lower limb's shock absorption capacity, and subjects the patellar tendon to greater ground 
67 
reaction forces, leading to anterior knee pain (35). Therefore, the single-leg landing test (SLL) is 
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often used to assess lower limb dynamic alignment and evaluate the DKV angle. Compared to 
69 

 
 
single-leg squat tests or step-down tests, the SLL better reflects the actual lower limb alignment 
70 
during athletic movements (36).  
71 
A literature review reveals that only one study has shown that a single session of ankle joint 
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exercise intervention and relaxation can effectively increase ankle dorsiflexion ROM and reduce 
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DKV (37). However, the cases in that study did not involve anterior knee pain, and the intervention 
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was limited to single-session immediate effect. Currently, there is a lack of high-level evidence in the 
75 
literature to demonstrate that improving the muscle strength around the hip joint and the mobility of 
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the ankle joint can reduce DKV and thereby alleviate the clinical symptoms of anterior knee pain. 
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Notably, there is only one study that specifically explores the relationship between ankle joint 
78 
interventions, DKV, and anterior knee pain, and this study only examines the effects immediately 
79 
postintervention (31). More importantly, as mentioned earlier, most assessments focus on changes in 
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pain and biomechanics. To date, no studies have investigated the long-term effects of exercise 
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interventions on the structural changes in the hip, knee, and ankle soft tissues or explored the potential 
82 
mechanisms of recovery. 
83 
Telemedicine is a simple rehabilitation method that overcomes spatial limitations. Particularly 
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during the COVID-19 pandemic, to reduce the risk of face-to-face transmission, many patients were 
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unable to continue their rehabilitation at hospitals (38). As a result, telemedicine became an 
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alternative solution, allowing patients to continue their rehabilitation. Telemedicine not only 
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effectively reduces treatment costs but also improves patient adherence to treatment (39, 40). 
88 
Telehealth-delivered physical therapy, including telerehabilitation, has been shown in randomized 
89 

 
 
trials to be as effective as face-to-face care for musculoskeletal conditions—yielding comparable 
90 
improvements in pain, physical function, and quality of life—while systematic reviews report similar 
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outcomes across a broad range of conditions such as low back pain and knee osteoarthritis (41). These 
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findings demonstrate that physical therapy programs can be effectively and successfully administered 
93 
via telehealth in musculoskeletal populations (42, 43). Although some literature indicates that 
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telemedicine is effective in alleviating pain and improving knee function in anterior knee pain 
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patients, there is still a lack of high-level evidence to support this, and most studies have focused 
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solely on clinical symptoms (44). Therefore, this study adopted 8 weeks of telemedicine as an 
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intervention strategy to further understand the benefits of combining hip or ankle joint exercises on 
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exercise performance, clinical symptoms, and tissue structure in female patients with anterior knee 
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pain. We hypothesized that 8 weeks of telehealth-based supervised exercise, both the hip and ankle, 
100 
coupled with knee strengthening, would effectively improve DKV and pain in women with anterior 
101 
knee pain, and both groups would provide comparable benefits. 
102 
 
103 
Methods 
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All participants provided written informed consent for this study, which was approved by the 
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Institutional Review Board of Kaohsiung Medical University Chung-Ho Memorial Hospital 
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(Approval Number: KMUIRB-E(I)-20220334). Before the formal trial begins, the examiners 
107 
received comprehensive testing training. Each participant will also be familiarized with all 
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experimental procedures and testing items. 
109 

 
 
 
110 
Participants 
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A total of 45 female recreational athletes with anterior knee pain were recruited. We only 
112 
included females in the current study due to their approximately twice the risk of anterior knee pain 
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compared to males (3). Cases were required to be evaluated by orthopedic or sports medicine 
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physicians to confirm the diagnosis of anterior knee pain. To exclude the possibility of joint 
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degeneration, the participants' age was restricted to 20-40 years. Recreational athletes were defined as 
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individuals who participate in aerobic exercise or physical activities at least three times per week for 
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a minimum of 30 minutes per session. Inclusion Criteria: (1) Female recreational athletes aged 20-40 
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years who engage in regular exercise; (2) Experiencing pain in the anterior or surrounding patella 
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during at least two or more of the following activities: walking, running, jumping, kneeling, squatting, 
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climbing stairs, or prolonged sitting; (3) A pain index of 3 or higher on the Numeric Pain Rating Scale 
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(NPRS) and symptoms persisting for at least 3 months; (4) Knee pain unrelated to trauma. Exclusion 
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Criteria: (1) Inability to operate a smartphone or computer; (2) History of fractures or surgeries 
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involving the hip, knee, ankle, or foot; (3) History of meniscus, knee ligament injuries, or ankle 
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sprains within the last six months; (4) Knee ligament laxity, inflammation, swelling, patellar 
125 
dislocation, or subluxation; (5) Cognitive impairment or inability to follow simple instructions; (6) 
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History of cardiovascular or neurological disorders; (7) Advised by a physician to avoid exercise. Use 
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of over-the-counter pain medication was not an exclusion criterion. Participants were instructed to 
128 
maintain their usual medication habits and to refrain from initiating new oral analgesics for knee pain 
129 

 
 
during the intervention period. At baseline, no participants reported regular use of oral analgesics for 
130 
anterior knee pain, and no changes in medication use were reported during the study. 
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Experimental Procedure and Random Grouping 
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A single-blinded randomized controlled trial was conducted, in which outcome assessors were 
134 
blinded to group allocation to reduce the risk of bias. Upon arrival at the research laboratory, 
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participants first performed a simple warm-up (5 minutes of cycling) before immediately undergoing 
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pre-tests. The measurements were conducted in the following order: pain index assessment, patellar 
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tendon stiffness measurement, ultrasound examination, ankle joint ROM measurement, DKV angle 
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measurement, and maximum muscle strength measurement. After completing the pre-test (T0), 
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participants randomly drew a numbered card from an opaque box to determine their group 
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assignment for the subsequent 8-week exercise intervention: Group A (ankle + knee joint exercise 
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group, AK), Group B (hip + knee joint exercise group, HK), or Group C (stretching group). After 
142 
grouping, participants were immediately instructed on and performed the assigned exercise 
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intervention once. Following three training sessions per week, post-tests (same as pre-tests) were 
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conducted at the 4th week (T1) and the 8th week (T2) (Figure 1). Throughout the exercise training 
145 
period, participants were guided and monitored by a professionally trained physical therapist. 
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Interventions 
148 

 
 
Participants in the hip + knee joint exercise group (HK group) and the ankle + knee joint exercise 
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group (AK group) received one-on-one exercise instruction from a physical therapist with a 
150 
background in sports medicine. The exercise training goals for the HK group included strengthening 
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the knee extensors (Figure 2(a) Primarily targets the quadriceps (knee extensors), improving knee 
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extension strength and stability 2(b) Also strengthens the quadriceps, with greater isolation of the 
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knee extensors compared to (a), focusing on controlled terminal knee extension 2(c) Works 
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the quadriceps, gluteal muscles, and to some extent the hamstrings, emphasizing closed-chain 
155 
strengthening and functional loading of the lower limb, while also training postural control), hip 
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external rotators (Figure 3(a) Strengthens the hip abductors (particularly gluteus medius) while 
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promoting pelvic stability during lateral movement 3(b) Activates the gluteus maximus and posterior 
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chain muscles, with added hip abductor engagement from the resistance band 3(c) Specifically targets 
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the hip external rotators (gluteus medius, gluteus minimus, piriformis) to improve control of hip 
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rotation and reduce dynamic knee valgus 3(d) A progression of (a) that increases challenge to the hip 
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abductors and lateral stabilizers, requiring greater control at the knee and ankle 3(e) Glute bridge with 
162 
one leg raised using a resistance band – An advanced form of (b), training unilateral gluteal and core 
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strength, while also engaging hip abductors and extensors for pelvic stabilization 3(f) Isolates 
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the gluteus medius and hip abductors, critical for controlling frontal-plane motion and stabilizing the 
165 
pelvis during single-leg tasks), and hip abductors (Figure 3). For the AK group, the training goals 
166 
included strengthening the knee extensors (Figure 2), ankle dorsiflexors (Figure 4(a) Strengthens 
167 
the ankle plantarflexors (gastrocnemius, soleus), improving calf strength and lower-limb push-off 
168 

 
 
power 4(b) A progression of (a) that further develops plantarflexor strength and enhances ankle 
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stability and balance under unilateral loading 4(c) Increases ankle dorsiflexion ROM by mobilizing 
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the talocrural joint, improving tibial forward glide during weight-bearing 4(d) Strengthens 
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the dorsiflexor muscles (tibialis anterior, extensor digitorum longus), enhancing control of foot 
172 
clearance during gait and landing 4(e) Stretches the gastrocnemius–soleus complex, improving ankle 
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flexibility and reducing compensatory movement patterns), and plantar flexors (Figure 4), as well as 
174 
performing ankle joint self-mobilization and stretching exercises (Figure 4). The therapist ensured 
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that the participants were familiar with and correctly performing the exercises before they left. At the 
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end of the session, participants were provided with a home exercise demonstration handout to be 
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performed three times per week for eight weeks. The handout included precautions to take during 
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exercise, guidelines for managing exercise injuries, and a contact number for consultation. 
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Home exercise training was remotely supervised. During the home exercise period, participants 
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engaged in moderate-intensity exercise (rate of perceived exertion, RPE, 12-14) three times per week. 
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Each exercise was performed in two sets, with each set consisting of 10-15 repetitions according to 
182 
the training plan, and the total exercise time was approximately 30-45 minutes. The therapist used 
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communication software to supervise participants one-on-one remotely, guided them through the 
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exercises, monitored their RPE, and provided individualized, gradual adjustments as needed. The 
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therapist also corrected participants' posture and movements if necessary and adjusted the length or 
186 
resistance of the resistance bands to increase or decrease exercise intensity based on the participants' 
187 
abilities. 
188 

 
 
Participants in the stretching group received a knee exercise handout and were instructed on 
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quadriceps and hamstring stretching exercises at baseline. Unlike the HK and AK groups, no remote 
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supervision, monitoring, or follow-up was conducted for the stretching group. This group functioned 
191 
as the unsupervised control condition. 
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Outcome measures 
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Primary Outcome (DKV) 
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The Single Leg Landing Task (SLL) was used to measure the DKV angle during single-leg landing. 
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The participant stood on a 30 cm box and first bent the non-testing leg's knee to approximately 90 
197 
degrees. After stabilizing, the participant jumped forward with the testing leg to a target 10 cm away 
198 
from the box, maintaining balance for five seconds upon landing. During the test, the non-testing leg 
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was not allowed to touch the ground, the participant was instructed to keep their eyes looking forward, 
200 
and both arms were crossed over the chest to minimize the influence of arm movement. The entire 
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sequence was repeated twice, and video recordings were made using a smartphone (45). Image 
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Analysis: Before recording, markers were placed on the midpoint of the knee joint (midpoint of the 
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line connecting the medial and lateral femoral condyles), the midpoint of the ankle joint (midpoint of 
204 
the line connecting the medial and lateral malleoli), both anterior superior iliac spines (ASIS), and the 
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midpoint of the line connecting the ASIS and the knee joint. A smartphone camera was positioned 2 
206 
meters in front of the participant to record the video. The video was then analyzed using Kinovea 
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software version 0.8.27 (https://www.kinovea.org/download.html) to measure the two-dimensional 
208 

 
 
frontal plane projection angle (FPPA). The knee valgus angle was calculated by subtracting the 
209 
obtained angle from 180 (the larger the value, the greater the knee valgus angle). The sequence was 
210 
repeated twice, and the average value was taken.  
211 
Secondary outcomes 
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Numeric Pain Rating Scale (NPRS): The NPRS is an 11-point scale where 0 indicates no pain 
213 
and 10 indicates the worst pain imaginable. Participants were asked to rate their perceived pain both 
214 
at rest and during weight-bearing in a lunge position (46, 47). 
215 
Patellar Tendon Stiffness Measurement: The stiffness of the patellar tendon was assessed using a 
216 
handheld device (MyotonPRO; Tallinn, Estonia). Participants were seated at the edge of a bed with 
217 
their knees bent at 90°. The tension was measured 3 cm below the apex of the patella, with the 
218 
assessment repeated three times. The average value was taken as the patellar tendon stiffness (48). 
219 
Muscle structure: A portable ultrasound device (Linear wireless probe LU700L VET) was used 
220 
to assess the structure of the gastrocnemius and gluteus medius muscles in a resting state. Ultrasound 
221 
images were used to record muscle thickness (MT) and pennation angle (PA). The pennation angle 
222 
was defined as the angle between the deep fascia and muscle fibers. Muscle thickness was defined as 
223 
the length of a perpendicular line drawn from the origin of the muscle fibers at the deep fascia to the 
224 
superficial fascia, based on the pennation angle (49). Gastrocnemius: Participants lay prone on a bed 
225 
with a towel placed under the knee to flex it to 20°-30°, and the ankle was fixed at 90° using a 
226 
goniometer. The ultrasound probe was placed parallel to the gastrocnemius muscle fibers, and the 
227 
scanning depth was adjusted to 6.3 mm to display both the deep and superficial fascia. The pennation 
228 

 
 
angle was defined as the angle between the deep fascia and muscle fibers. Muscle thickness was 
229 
measured as the length of a perpendicular line drawn from the origin of the muscle fibers at the deep 
230 
fascia to the superficial fascia (49). Gluteus Medius: Participants lay on their side, with the test leg on 
231 
top, and the hip and knee joints in a neutral position. The ultrasound probe was placed between the 
232 
iliac crest and the greater trochanter, parallel to the gluteus medius muscle fibers. The greater 
233 
trochanter was positioned in the lower right third of the image as a landmark to increase measurement 
234 
consistency, with the gluteus medius centered in the image for recording (50). 
235 
Ankle Joint ROM: Since patients with anterior knee pain often experience knee pain during 
236 
weight-bearing activities, this study used a weight-bearing lunge test to measure the active 
237 
dorsiflexion angle of the ankle during weight-bearing. A measuring tape was placed on the floor, with 
238 
the participant's heel and second toe aligned with the tape. The participant started with their toes 10 
239 
cm from the wall, touching the wall with the knee while keeping the heel on the ground. The heel 
240 
must maintain contact with the floor. If the participant could easily touch the wall or could not reach it, 
241 
the distance was adjusted by 1 cm increments, gradually adjusting the distance forward or backward 
242 
according to the participant's ability until they could no longer keep the heel fully in contact with the 
243 
ground. At the maximum angle, a goniometer was used for measurement, with the fixed arm placed 
244 
flat on the ground and the movable arm aligned with the line connecting the lateral malleolus and the 
245 
head of the fibula. The test was repeated twice, and the average value was recorded (51). 
246 
Maximum Voluntary Isometric Strength: A handheld dynamometer (MicroFET3; Hoggan 
247 
Scientific LLC, USA) was used to measure the maximum isometric strength of the hip abductors, 
248 

 
 
knee extensors, ankle dorsiflexors, and ankle plantar flexors. Each test was repeated twice, and the 
249 
average value was recorded (52). 
250 
 
251 
Statistics 
252 
The sample size for this experiment was estimated using G*Power and calculated using the priori 
253 
sample size for Repeated Measures ANOVA. The effect size (ES) was set at f = 0.45, with an alpha 
254 
value of 0.05 and a power of 80%. Based on the above calculations, the required sample size was 36 
255 
participants. Considering a potential 10% dropout rate, 40 eligible participants were to be recruited. 
256 
However, to increase the statistical power, the final target was to recruit 45 participants. 
257 
Data processing and analysis were conducted using SPSS 20.0 for Windows statistical software. 
258 
The significance level for all data was set at p < 0.05, and all numerical data were presented as mean 
259 
± standard deviation. The Shapiro–Wilk test was used to determine the normality of the data 
260 
distribution. If the data were normally distributed, a two-way ANOVA with repeated measures was 
261 
used to analyze the 3 group factors (hip + knee group, hip + ankle group, stretching group) x 3 time 
262 
factors (pre-test, week 4, post-test) to first examine the significance of the interaction effect. If the 
263 
interaction effect was significant, indicating that the group and testing time factors influenced each 
264 
other, a simple main effect test and Bonferroni post hoc comparisons were performed. A One-way 
265 
ANOVA analysis was used to compare intra-group differences before the intervention, followed by 
266 
Bonferroni post hoc comparisons. Training adherence was calculated using the formula: (actual 
267 

 
 
training sessions/24) * 100%. Test-retest reliability was verified using the Intraclass Correlation 
268 
Coefficient (ICC) to ensure the consistency of all measurements.  
269