Toe Orientation Alters Load Distribution and Coordination Patterns during Badminton Lunge Landing

Technical Summary: Toe Orientation Alters Load Distribution and Coordination Patterns during Badminton Lunge Landing

Problem Statement
Badminton involves frequent, high-intensity multidirectional movements that impose substantial mechanical loads on the lower extremities, leading to a high incidence of non-contact injuries. The forward lunge is a primary mechanically demanding task, generating impact loads of approximately 2.5 times body weight. While foot orientation at initial contact is known to influence lower-limb biomechanics, existing literature presents conflicting findings regarding the effects of toe rotation (e.g., toe-in vs. toe-out) on joint loading and injury risk. Furthermore, previous studies have largely focused on isolated joint-level kinematics or kinetics, with limited understanding of how temporal coordination across the lower-limb kinetic chain influences the internal mechanical environment of the knee joint. Specifically, the relationship between inter-joint coordination, center of mass (COM) dynamics, and tissue-level stress responses under different toe orientations remains unclear.

Methodology
This study employed a multi-scale approach combining experimental biomechanics, cross-correlation analysis, and subject-specific finite element analysis (FEA) to investigate these interactions.

• Participants and Protocol: Thirty male recreational badminton players performed right-leg lunge landings under two randomized conditions: 20° toe-in orientation (TIO) and 20° toe-out orientation (TOO). Kinematic and kinetic data were captured using a 10-camera motion capture system (200 Hz) and force plates (1000 Hz).
• Data Processing: Kinematic and kinetic data were processed using OpenSim 4.5.2 to calculate joint angles, moments, and reaction forces. Data were normalized to body weight and the contact phase (0–100%).
• Coordination Analysis: Cross-correlation analysis was performed to quantify the temporal coupling strength and time lag between key variables, including COM displacement, ankle/knee angles, joint reaction forces, and shear forces.
• Finite Element Analysis (FEA): Eight participants underwent CT and MRI scanning to reconstruct high-fidelity 3D models of the knee joint (including bones, cartilage, menisci, and ligaments). These models were subjected to the mean peak contact forces derived from the experimental trials for both TIO and TOO conditions. The models utilized linear elastic material properties and frictionless contact definitions to simulate intra-articular stress distributions.
• Statistical Analysis: Differences in discrete variables were assessed using one-way repeated-measures ANOVA, while time-series data were analyzed using Statistical Parametric Mapping (SPM). Cross-correlation coefficients were transformed using Fisher's z-transformation for comparison.

Key Contributions
The study advances the field by integrating three distinct analytical scales:

1. Kinetic Chain Coordination: It quantifies the temporal coupling between ankle motion, knee loading, and global COM dynamics, moving beyond isolated joint analysis.
2. Tissue-Level Stress Mapping: It utilizes subject-specific FEA to visualize how different landing strategies alter stress distribution within specific knee structures (ligaments, menisci, cartilage).
3. Mechanistic Linkage: It establishes a cross-scale link demonstrating how macro-level coordination patterns (observed via cross-correlation) correspond to micro-level mechanical environments (observed via FEA).

Results

• Kinematics and Kinetics: Compared to TOO, TIO landings resulted in significantly greater ankle dorsiflexion and eversion angles. TIO also produced higher ankle and knee joint reaction forces, particularly during the late landing phase (94–100%). Conversely, TOO landings exhibited greater knee abduction angles and higher initial ground reaction forces (0–5%).
• COM Dynamics: TIO was associated with greater sagittal-plane COM displacement, while TOO resulted in greater coronal-plane COM displacement.
• Coordination Patterns: Cross-correlation analysis revealed significant differences in coupling strength. For instance, the coupling between ankle dorsiflexion and knee shear forces was stronger under TIO, whereas ankle-knee coordination was more pronounced under TOO.
• FEA Stress Distribution: The FEA results indicated that TIO led to higher peak von Mises stresses and more concentrated stress distributions across all evaluated knee tissues (ACL, PCL, MCL, LCL, menisci, and tibial cartilage), particularly in the medial compartment. In contrast, TOO resulted in lower peak stresses and a more uniform, distributed stress pattern across the joint structures.

Significance and Claims
The paper concludes that toe orientation markedly modulates kinetic chain coordination and knee stress during badminton lunge landings. The authors claim that TIO promotes a localized, load-bearing strategy that concentrates mechanical demand on the knee joint and increases concurrent loading across multiple tissues. In contrast, TOO facilitates a distributed load-sharing strategy through joint alignment and inter-joint coordination, resulting in reduced stress concentration within knee tissues.

The authors suggest that these findings provide a biomechanical basis for optimizing landing techniques, potentially offering a strategy for injury risk reduction by promoting load redistribution. However, the paper maintains a modest stance regarding clinical application, explicitly stating that the study does not establish physiological injury thresholds. Therefore, the observed stress differences are interpreted as relative differences in acute mechanical demand rather than direct evidence of increased injury risk. The study emphasizes that foot landing posture influences knee loading through its effect on the broader kinetic chain coordination rather than acting as an isolated local factor.