Core Activation Patterns Across Different Figure Skating Jumps

Technical Summary: Core Activation Patterns Across Different Figure Skating Jumps

Problem Statement
While recent advancements in sports science have shifted toward objective quantification of figure skating jumps using wearable sensors (IMUs, accelerometers) and high-speed motion analysis, the specific role of the trunk musculature in maintaining a rigid rotational axis remains underexplored. Previous research has predominantly focused on lower-limb kinematics and explosive power. However, successfully executing multi-rotational jumps requires vast control over the body's central axis during the flight phase to minimize the moment of inertia. There is a lack of direct electromyography (EMG) quantification of core muscle activation patterns across different jump types (Axel, Salchow, Loop) and difficulty levels (single/double vs. triple), particularly regarding the timing, symmetry, and intensity of abdominal muscle recruitment during preparation, flight, and landing phases.

Methodology
The study employed a synchronized multimodal sensor framework to monitor 12 adolescent female figure skaters. The experimental setup included:

• Sensors: A torso-mounted accelerometer (ACC) and two skate-mounted Inertial Measurement Units (IMUs) to track flight time and rotation speed. Surface EMG sensors were placed bilaterally on the m. obliquus externus abdominis and m. rectus abdominis (with a reference electrode at C7), recorded at 1000 Hz.
• Task: Participants performed six distinct jump types: Single/Double Axel (1A/2A), Double/Triple Salchow (2S/3S), and Double/Triple Loop (2LO/3LO). All jumps were executed with counter-clockwise rotation.
• Data Processing: Takeoff and landing were detected primarily via IMU and ACC data. EMG signals were segmented into three phases: preparation (0.5s pre-takeoff), flight, and landing (0.5s post-landing). Signals were normalized to the percentage of inter-trial maximum (%ITM) to allow cross-subject comparison.
• Metrics: The analysis calculated Peak Inter-Trial Maximum (PITM), Integrated ITM (IITM), and a Co-contraction Index (CCI) to evaluate bilateral symmetry and muscular tension.

Key Contributions

1. Dataset Creation: The authors generated a publicly available figure skating dataset containing annotated recordings from 12 adolescent female participants, including 2 or 4 EMG channels and ACC data, distinguishing six jump types with synchronized IMU data.
2. Phase Segmentation Framework: The study established a methodology for creating jump phase annotations through multimodal data analysis, synchronizing takeoff/landing detection with core muscle EMG data.
3. Quantitative EMG Evaluation: The paper provides a quantitative assessment of activation levels, timing, and muscular symmetry of the right and left core muscles across the three execution phases for six different jump types.
4. Kinematic Correlation: It offers a comparative analysis of airtime and rotation speed across the six jump types, correlating these kinematic baselines with neuromuscular profiles.

Results

• Bilateral Asymmetry and Phase Shift: A consistent pattern of lateralization was observed. During the preparation phase, there was a pronounced right-side dominance in the m. obliquus externus (eccentric loading). Conversely, during the flight phase, dominance shifted to the left side (concentric contraction) to maintain the rotational axis.
• Muscle Function Differentiation: The m. obliquus externus acted as the primary engine for rotational control, exhibiting higher activation levels than the m. rectus abdominis. The rectus muscle functioned primarily as a central sagittal stabilizer, showing high bilateral symmetry during the flight phase, particularly in multi-rotational jumps.
• Intensity vs. Duration: Triple jumps (3S, 3LO) exhibited significantly higher integrated ITM (muscular tension) in the oblique muscles compared to their double-jump counterparts, despite minimal differences in airtime (e.g., 0.50s for 2LO vs. 0.53s for 3LO). This indicates that increased rotational velocity (up to ≈1570 °/s) necessitates higher muscular tension rather than longer flight duration.
• Landing Mechanics: The landing phase was characterized by a powerful bracing mechanism. Co-contraction indices (CCI) exceeded 80% in high-rotation jumps (e.g., 88.2% for 3LO), indicating a massive simultaneous contraction of core components to stabilize the vertical axis against impact forces.
• Takeoff Mechanics: Axels (forward takeoff) required balanced bracing strategies, whereas edge jumps (Salchow/Loop, backward takeoff) showed stronger bilateral asymmetries and higher overall activation to initiate rotation.

Significance and Claims
The authors claim that this study provides an objective framework for evaluating jump technique and optimizing strength training in competitive figure skating. By synthesizing findings from lower-limb kinematics with direct core quantification, the research bridges a gap in understanding the neuromuscular mechanisms of the trunk. The study posits that the core musculature acts as a dynamic compensator, shifting activation timing based on the specific mechanical requirements of the jump (torque generation in preparation vs. rigid bracing in landing).

The paper modestly frames these findings as a pilot study limited to adolescent female athletes, acknowledging that physiological differences may affect generalizability to male or elite adult skaters. It also notes limitations regarding the focus on superficial abdominal muscles (excluding deep stabilizers and the erector spinae) and potential signal artifacts from the cold rink environment. However, the authors assert that the identified patterns—specifically the shift from right-side dominance to left-side dominance and the intensity-based scaling for triple jumps—offer new insights into the biomechanics of figure skating that can inform future training and injury prevention strategies.