Effects of different lunge exercises on lower limb mechanics and muscle activation in patellofemoral pain syndrome patients

Abstract

BACKGROUND: Lunge exercises are often used in strengthening programs for patellofemoral pain syndrome and have been shown to help strengthen the quadriceps. However, limited data exist to evaluate the effects of lunge exercises with medial or lateral resistance on patellofemoral joint stress and lower limb muscle activation. OBJECTIVE: To compare the effect of three lunge exercises (traditional lunge, lunge with hip adduction resistance, and lunge with hip abduction resistance) on lower limb muscle activation and patellofemoral joint stress in subjects with patellofemoral pain syndrome and health control group. METHODS: Totally 29 subjects with patellofemoral pain syndrome and 29 healthy subjects completed three different lunge exercises. Lower limb dynamics and electromyography data were simultaneously acquired using an infrared motion capture system, a three-dimensional force table, and a surface electromyography analyzer. A mixed-design analysis of variance was used to determine the effects of group and exercise on patellofemoral joint stress and lower limb muscle activation characteristics during different lunge exercises. RESULTS AND CONCLUSION: (1) During the squatting phase, the vastus lateralis muscle activation was significantly lower in both groups during the lunge exercises with hip adduction (P < 0.05), while the vastus medialis/vastus lateralis activation ratio was significantly increased in the healthy group (P < 0.05). In the patellofemoral pain syndrome group, the gluteus medius activation was significantly increased (P < 0.05) and the peak patellofemoral joint stress was significantly reduced (P < 0.05) during the lunge with hip abduction. (2) During the pushing phase, the vastus lateralis activation was significantly lower in both groups during the lunge with hip abduction (P < 0.05), and the patellofemoral pain syndrome group showed significantly reduced peak patellofemoral joint stress (P < 0.05) and enhanced gluteus medius activation (P < 0.05). In the healthy group, the vastus medialis/vastus lateralis activation ratio was significantly increased during the lunge with hip adduction (P < 0.05), and the patellofemoral pain syndrome group had significantly lower peak patellofemoral joint stress than the healthy group (P < 0.05). (3) These findings suggest that traditional lunge can be one of the preferred training methods for strengthening the quadriceps in the early rehabilitation of patellofemoral pain syndrome. Lunge exercises with lateral adduction/abduction resistance have advantages in improving vastus medialis/vastus lateralis activation imbalance, strengthening gluteus medius activation, and reducing patellofemoral joint stress during squatting, which may help rebuild neuromuscular control of the lower limb kinetic chain in the later rehabilitation stage. For patients with patellofemoral pain syndrome, lunge with lateral abduction resistance is more recommended to alleviate pain and improve function.

1. Introduction

Patellofemoral pain syndrome (PFPS) is a common musculoskeletal disorder characterized by anterior knee pain, which is aggravated during activities involving knee flexion such as squatting, kneeling, stair climbing, and prolonged sitting. PFPS not only affects athletic performance and daily activities but may also progress to patellofemoral osteoarthritis. The pathogenesis of PFPS is associated with abnormal patellar tracking and increased patellofemoral joint stress due to altered lower limb mechanics. The stability of the patellofemoral joint relies on dynamic soft tissue support, particularly the balance between the vastus medialis (VM) and vastus lateralis (VL). However, patients with PFPS often exhibit quadriceps muscle imbalance, with insufficient VM force to counteract VL pull, leading to lateral patellar displacement and abnormal joint contact pressure. Additionally, weakened hip abductor and external rotator muscles may cause compensatory femoral internal rotation, reducing patellofemoral contact area and increasing joint stress. Therefore, rehabilitation for PFPS should focus on strengthening the VM to correct quadriceps imbalance and enhancing hip muscle strength to improve lower limb kinetic chain function.

Lunge exercises are commonly used in PFPS rehabilitation as they effectively activate the quadriceps and hip muscles through multi-joint proprioceptive and muscle co-activation. However, traditional lunges have limitations: as knee flexion angle increases, patellofemoral joint stress significantly rises, and due to the activation inertia of the VM, isolated quadriceps strengthening may not effectively correct muscle imbalance. In contrast, lunge exercises with lateral resistance introduce dynamic knee instability, posing a greater challenge to balance and potentially altering lower limb muscle activation and patellofemoral joint loading. Previous studies on squats combined with hip adduction have shown that hip adduction can stretch VM muscle fibers, improve length-tension relationship, and enhance contractile force, thereby selectively activating the VM. Therefore, this study aimed to compare the effects of three lunge exercises (traditional lunge, lunge with hip adduction resistance, and lunge with hip abduction resistance) on lower limb muscle activation and patellofemoral joint stress in individuals with PFPS and healthy controls.