The Influence of Neuromuscular Training on Whole-body Movement Strategies and Knee Mechanics During Change-of-direction Tasks in Sports Science Students

Study design and participants

This is a quasi-randomized trial to investigate the effects of effects of two neuromuscular training interventions (multidirectional vs. linear sprint training) on COD movement strategies in sports science students and in parallel to develop a methodological framework for field-based COD movement assessments. This trial will be registered with ClinicalTrials.gov after ethical approval has been granted. An a-priori sample size estimation was conducted based on a previous non-randomized controlled trial reporting a strong, beneficial effect of a 6-week COD technique modification on the Cutting Movement Assessment Score (CMAS), a qualitative screening tool to quantify biomechanical and neuromuscular deficits during COD tasks [significant group x time interaction, Cohen's f2 = 0.63 (right leg) - 1.00 (left leg)]. With an a-priori significance level of alpha = 0.05 and a desired power of 0.8, the minimum required sample size was estimated in G*Power v3.1.9.7 as only N = 8 (n = 4 in each training group). One concern with this previous study is, however, that CMAS raters were not blinded to group assignment leading to a potential systematic bias and overestimated effect size. A second concern is that the CMAS, which combines multiple biomechanical and neuromuscular deficits (e.g. knee valgus, lateral trunk flexion, hip internal rotation) into one aggregate score may show a larger effect compared to the analysis of single biomechanical variables (e.g. knee abduction moment) like in the current study. Based on these considerations the required sample size of N = 40 sports science students (n = 20 for the MD and LS) was selected. With an expected drop-out rate of 25%, this sample of at least N = 30 participants will enable to detect moderate to strong interaction effects (Cohen's f2 > 0.3) with a power of at least 0.8.

Experimental protocol

All participants will take part in a first familiarization session (WN 40) to practice the execution of the COD task and receive information about the content and goals of the training intervention. Baseline testing (WN 40-41), follow-up testing (WN 49-50), and retention testing (WN2-4, 2022) will be conducted in the laboratory Pulverturm at the ISW Innsbruck and will follow the same testing protocol. Participants will be equipped with 47 retroreflective markers for 3D motion analysis (extended full-body PlugIn Gait model, 10 cameras, 200 Hz) and 14 sensors for combined measurements of surface electromyography (sEMG, 2000 Hz) and inertial segment data (200 Hz) (Noraxon Ultium, Noraxon Inc., Scottsdale, AZ, USA) of the right leg. Afterwards, the participants will be asked to warm-up on a stationary bike for five minutes followed by the initial running exercises of the FIFA11+ program. Maximum voluntary contractions (MVCs) will be obtained for ankle plantarflexion/dorsiflexion, knee flexion/extension, hip extension/flexion, and hip abduction according to standardized manual tests. IMU position and orientation with respect to the participants' anatomy will be determined based on images and calibration movements taken before the start of the measurements. After four successful practice trials, participants will be asked to complete 10 COD movements with a 45-degree cutting angle (COD45) and 10 COD movements with a 135-degree cutting angle (COD135) always planting and cutting with the right foot on a ground-embedded force plate (1000 Hz, Kistler, Winterthur, Switzerland). The approach and exit speed for each COD movement will be controlled to approximately 4.5 m/s (COD45) and 4 m/s (COD135) as measured by optical timing gates placed within the approach and exit zones (Witty, Microgate, Bolzano, Italy). Rest periods of one minute in between trials and five minutes in between blocks (COD45 vs. COD135) will avoid accumulation of neuromuscular fatigue.

Data analysis

Using the 3D marker trajectories and force data as inputs (optimal motion capture, OMC, model), full-body kinematics, 3D joint moments, muscle forces, and ACL strain will be estimated using inverse kinematics and EMG-informed optimization procedures in OpenSim (v.4.2) combined with FE simulations.

Using only the inertial sensor data as inputs (inertial motion capture, IMC, model), full-body kinematics, 3D joint moments, muscle forces, and ACL strain will be estimated using an IMU-tracking and optimal control algorithm combined with FE simulations. This latter approach is novel and is currently being developed.

The muscle activation pattern of the right leg will be further analyzed via a muscle synergy analysis [one muscle synergy model for each testing time point (baseline, follow-up 1, follow-up 2] and quantified according to its muscle synergy vectors and synergy activation profiles. Specifically, the number of muscles per synergy vector and the shape of the muscle synergy vectors will serve as additional dependent variables.

Statistics

Objective 1 \& 2: Effects of the NMT and COD technique modification intervention on the kinematic, kinetic (OMC model), and EMG-related outcome variables will be tested according to a repeated measures ANOVA with the between-subject factor 'group' (MD vs. LS) and the within-subject factor 'time point' (baseline, follow-up, retention). The null hypothesis H1 will be rejected if there is a significant interaction effect 'group x time point' at an a-priori significance level of alpha = 0.05. Interaction effects, i.e. effect modification, due to the participants' sex or potential other covariates (e.g. baseline COD performance) will be explored in additional three-way repeated measures ANOVAs. Post-hoc testing will investigate changes in dependent variables between time points for each group.

Objective 3: The validity of the IMC model will be determined based on Bland \& Altman limits of agreement to estimate the systematic bias and random error of the IMC model-based dependent variables in comparison to the OMC model-based variables. The IMC model will be called valid if the limits of agreement are smaller than the observed changes in the corresponding variables between baseline and follow-up testing in the intervention group.

Ethical considerations / risk-benefit analysis / insurance information

All participants will be sports science students and thus frequently encounter the injury risks associated with multi-directional sports. Therefore, the risk of injury for participants in this study will be no higher than in their everyday life. In the rare case that a participant sustains an injury during this study, he/she will be covered by accident insurance provided to all University of Innsbruck students. Furthermore, all participants will benefit from participating in the current study given that the FIFA11+ NMT program, which is part of the training in both training groups, has been shown to effectively reduce the risk of sports injury. Overall, the benefits of this study outweigh the risks.