The Influence of Neuromuscular Training on Whole-body Movement Strategies and Knee Mechanics During Change-of-direction Tasks in Sports Science Students
Condition: Anterior Cruciate Ligament Injuries
MeSH terms: Anterior Cruciate Ligament Injuries
Study type: Interventional

Summary: 
      Background

      Knee injuries are common during sports that require fast change-of-direction (COD) movements
      such as sidestepping and pivoting during soccer, basketball, handball, and related sports.
      COD movements expose the knee joint to large external forces, particularly if players show a
      poor COD technique such as lateral trunk lean towards the plant foot or a strong knee valgus
      of the cutting leg. Larger external forces and moments that act on the knee joint are
      expected to result in larger strain of the anterior cruciate ligament (ACL) and thus a higher
      risk of ACL rupture. Consequently, during sports like soccer and basketball, many non-contact
      ACL injuries occur during COD tasks. While neuromuscular training (NMT) programs have been
      developed to effectively reduce the risk of sports injury including ACL tears, ACL injury
      rates have not declined in the last years. One of the reasons for this paradox may be that
      many NMT programs such as the FIFA11+ program, which were developed to protect from injury do
      not actually improve COD movement strategies. It may be assumed that FIFA11+ does reduce the
      overall risk of sports injury through general improvements in strength and balance as well as
      safer jump landing technique but not through safer COD technique. Further, if training
      interventions were successful in reducing 'high-risk' movement patterns and in developing
      knee-stabilizing muscle synergies during COD movements, it remains unclear whether the
      improved movement strategy, e.g. the reduction in external knee valgus moments, actually
      corresponds to reduced ACL strain. In consequence, there is the need for a comprehensive
      investigation to determine whether a NMT program focused on improving COD technique will
      improve COD movement and muscle activation strategies and whether these improvements are
      correlated with estimated ACL strain.

      A second reason for the paradox may be that current experimental protocols to investigate COD
      movement strategies in the laboratory are not a good indicator for actual player behavior on
      the field thus masking potential benefits of NMT on lateral movements. Therefore, the sports
      injury prevention community should aim to move the assessment of COD movement strategy onto
      the playing field and into a more realistic playing environment while characterizing the
      kinematics and kinetics of sidestepping based on wearable sensors. In consequence, novel
      analytical frameworks based on wearables need to be developed, which can capture full-body
      kinematics and the underlying forces during COD movements on the playing field. In the long
      run, such systems could facilitate real-time feedback with respect to COD technique on the
      playing field and thus enhance motor learning of the players as well as characterize
      real-world player agility.

      Research objectives & hypotheses

      Objective 1: To determine the effect of an 8-week NMT and COD technique modification
      intervention (multidirection training, MD) on 1) COD movement strategies as characterized by
      the lateral trunk angle and knee valgus moment and 2) estimated ACL strain during 45- and
      135-degree COD movements in comparison to an 8-week NMT and linear sprint training
      intervention (linear sprint training, LS) in sports science students.

      Hypothesis 1: There will be a larger reduction in lateral trunk angle and knee valgus moment
      and an associated reduction in ACL strain in the MD group compared to the LS group following
      the 8-week intervention, which will be retained four weeks later.

      Objective 2: To determine the effect of an 8-week NMT and COD technique modification
      intervention on leg muscle synergies as characterized by the number of muscles and the
      structure of the synergy vector for each identified muscle synergy in comparison to an 8-week
      NMT and linear sprint training intervention in sports science students.

      Hypothesis 2: One or multiple muscle synergy vectors will show an increased contribution of
      hip abductor muscle activity in the MD group following training and there will be a lower
      number of activated muscles per identified synergy, i.e. a more selective muscle activation
      in comparison to the LS group. These improvements will be retained four weeks later.

      Objective 3: To determine the validity of an analysis framework to estimate COD movement
      strategy (lateral trunk angle, foot progression angle, knee valgus moment) and ACL strain
      based solely on inertial motion capture data in comparison to the gold-standard of 3D optimal
      motion capture.
    

Detailed description: 
      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.
    

Intervention name(s): FIFA11+ and multidirectional training (MD); FIFA11+ and linear sprint training (MD)
Intervention type(s): Behavioral; Behavioral
Intervention description(s): This intervention initially contains a shortened version of the FIFA11+ injury prevention program including running (straight, hip out, hip in, jump-run-ups), strengthening (planks, squats, nordic hamstring curls), and single-leg balance exercises. The initial part is followed by COD technique modification training, which contains exercises aimed at improving COD technique (safer and more effective body re-direction, use of penultimate step, avoiding knee valgus) and COD braking and re-acceleration impulse.
The duration of each training session is 25-30 minutes. The training is carried out twice per week under supervision with supervisors providing feedback to participants regarding their COD technique. Participants are encouraged to complete a third training session in their own time.; This intervention initially contains a shortened version of the FIFA11+ injury prevention program including running (straight, hip out, hip in, jump-run-ups), strengthening (planks, squats, nordic hamstring curls), and single-leg balance exercises. The initial part is followed by a linear sprint training, which contains exercises aimed at improving sprint technique (e.g. sagittal arm and leg movement, trunk lean), use of the stretch-shortening cycle, leg stiffness and propulsive impulse .
The duration of each training session is 25-30 minutes. The training is carried out twice per week under supervision with supervisors providing feedback to participants regarding their sprinting technique. Participants are encouraged to complete a third training session in their own time.
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Intervention model description: Participants will be assigned to multidirectional training group (MD) or a linear sprint training group (LS) in a quasi-randomized way. Both groups will complete an 8-week training program and will complete baseline, follow-up, and retention testing (4 weeks post follow-up).
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: electromyography; inertial measurement unit; neuromuscular training; muscle activity; muscle synergy; sidestepping movement; side-cutting movement