Comparison of the DNS-Based Developmental Exercise and Single Leg Squat Exercise on Quadriceps Muscle Activation in Fencers

This study aims to compare the effects of three exercises-single-leg decline squat, single-leg decline squat with core activation, and Dynamic Neuromuscular Stabilization (DNS)-based half high kneeling exercise-on quadriceps muscle activity in fencers. Fencing involves asymmetric movements that demand high neuromuscular coordination, strength, and power, particularly in the lower extremities. The lunge, a key movement, relies on horizontal peak velocity influenced by back leg extensor strength and power. Lumbopelvic stability is crucial for injury prevention and performance enhancement, as it stabilizes the body against external stresses and optimizes joint function.DNS, grounded in neurodevelopmental kinesiology, focuses on activating the integrated spinal stabilization system (ISSS), which includes intersegmental spinal muscles, deep neck flexors, diaphragm, abdominal wall, and pelvic floor muscles. This approach integrates optimal breathing patterns, improves movement quality, and ensures functional joint centration to maximize strength efficiency and minimize mechanical stress.The protocol involves electromyographic (EMG) assessment of the vastus medialis obliquus (VMO), vastus lateralis (VL), and rectus femoris (RF) muscles on the dominant side during the exercises. Participants, aged 18-24 years with at least 5 years of fencing experience and no recent knee injuries or DNS training, undergo assessments in a controlled laboratory setting.Surface EMG is recorded using an eight-channel system (Noraxon, USA) with a sampling frequency of 1500 Hz. Electrode placement follows SENIAM recommendations: VMO at 80% of the distance between the anterior border of the medial collateral ligament and the superior anterior iliac spine; VL at two-thirds along the line from the anterior superior iliac spine to the lateral patella edge; RF at the midpoint between the anterior superior iliac spine and the upper patella edge. Skin preparation ensures impedance below 2 kΩ. Maximum voluntary isometric contraction (MVIC) testing normalizes EMG data, performed seated with hips at 90° and knees at 60° flexion, involving three 5-second maximal contractions with 30-second rests.Exercises are randomized and performed with a metronome at 60 beats per minute to standardize 3-second concentric, isometric, and eccentric phases per repetition. Three trials per exercise are conducted, with 30-second rests between trials. Single-leg decline squat: Performed on a 25° decline board, dominant leg only, to 60° knee flexion, with an adjustable mechanical device for depth control.

Single-leg decline squat with core activation: Identical to the above, plus abdominal bracing to enhance trunk stability, mimicking ISSS activation.

DNS-based half high kneeling: Involves forward leg at 90° hip/knee flexion with slight abduction/external rotation, contralateral knee on ground; posterior shift maintains ISSS activation, neutral pelvis, and spinal alignment, with tactile cues from the investigator.

All EMG data will be stored for offline processing. Raw EMG signals will be filtered using appropriate band-pass filters to remove movement artifacts and high-frequency noise. The filtered EMG signals will then be rectified and smoothed (for example, by calculating the root mean square over a defined moving window). For each participant, normalized EMG amplitude (%MVIC) for each muscle and each exercise will be calculated by averaging across the repetitions and across the predefined movement cycle. These normalized values for vastus medialis, vastus lateralis, and rectus femoris will form the basis of the primary analyses comparing the three exercises.

Planned statistical analyses will use within-subject methods appropriate for repeated measures (for example, repeated-measures ANOVA or non-parametric equivalents, depending on data distribution). Assumptions of the selected statistical tests (such as normality) will be checked, and corrections will be applied as needed. The comparisons of interest will focus on differences in normalized quadriceps muscle activity between the three exercises for each of the recorded muscles. Effect sizes and confidence intervals may be calculated to describe the magnitude and precision of differences. No interim analyses or long-term follow-up are planned, as this is a single-session study.