Immediate Effects of Valgus Control Feedback and Differential Learning Strategies on Feedforward Muscle Activity of the Lower Limbs in Female Athletes with Dynamic Knee Valgus

Introduction

Anterior Cruciate Ligament (ACL) injuries are highly prevalent in sports, with approximately 91% of these injuries occurring during athletic activities [1]. Dynamic knee valgus (DKV) is considered as a significant risk factor for ACL injuries. DKV is a multiplanar lower extremity movement pattern characterized by hip adduction and internal rotation, knee abduction, anterior tibial translation, tibial external rotation, and foot inversion [2]. This movement pattern may increase mechanical stress on the knee joint and surrounding structures, thereby increasing the risk of both acute and chronic musculoskeletal injuries, particularly non-contact ACL tears.

Injury prevention strategies should focus on increasing knee flexion angle and decreasing knee valgus angle during landing. One common strategy for preventing ACL injuries and for improving lower extremity alignment, especially knee valgus, is the use of motor control strategies and feedback-based training instructions. Visual feedback has been employed to target neuromuscular changes in real-time or post-task. Real-time feedback allows individuals to observe their movements and make immediate biomechanical adjustments. Another effective strategy to prevent DKV is Differential Learning (DL) method. This method emphasizes movement variability and motor adaptation rather than repetitive movement execution. Methods that incorporate practice variability facilitate motor adaptability, as such variability increases the number of degrees of freedom involved in motor control, ultimately leading to improved performance and reduced injury risk.

Neuromuscular training programs have been shown to reduce ACL injury risk by up to 50% in men and 67% in women [22]. However, there is still no consensus on the optimal approach. Given that these programs typically last 6 to 8 weeks, the development of quicker intervention methods for ACL injury prevention is a crucial step. Since both valgus-control feedback (VCF) and DL methods have been proposed as rapid and effective methods for preventing ACL injuries, a direct comparison of these two approaches may help identify a more effective intervention strategy for injury prevention and optimize injury prevention programs. Based on the above, the aim of this study was to investigate the immediate effects of VCF and DL on feedforward muscle activity of the lower limbs in female athletes with DKV.

Material and methods

This study employed a quasi-experimental, pre-test post-test design to evaluate the effects of the intervention. The study population consisted of female recreational athletes (aged 20-25 years) participating in jumping sports (handball, basketball, and volleyball) in Tehran. Sample size calculation was performed using G*Power (version 3.1.9.2) based on a two-way repeated measures ANOVA with an effect size of 0.25, alpha level of 0.05, power of 0.80, and two measurement points, resulting in a required sample size of 28 participants. Considering a 20% dropout rate, 34 participants were recruited and randomly assigned to two groups: VCF strategy group (n=17) and DL strategy group (n=17).

Kinovea software was used to screen for DKV during a 32 cm drop landing. Individuals with a DKV angle greater than 10 degrees were considered at risk for ACL injury. Muscle activity was recorded using a 32-channel electromyography system (TeleMyo DTS, Noraxon Inc., Scottsdale, USA) with a sampling frequency of 2000 Hz. The raw electromyographic signals were filtered using a fourth-order zero-lag Butterworth filter with a band-pass range of 20–450 Hz.

All participants in both groups performed a pre-test of the Single leg drop vertical jump (SL-DVJ) task while wearing the electrodes sensors. After three successful and acceptable trials of the SL-DVJ task, the pre-test data for both groups were recorded. Subsequently, participants in both groups immediately performed four exercise tasks: double-leg squats, single-leg squats, single-leg step-downs, and lateral step-downs. Participants repeated each exercise ten times. Participants in the VCF group performed all four exercises in front of a full-length mirror and were instructed by a corrective exercise specialist to prevent their knees from moving towards the midline of the body by visually monitoring their knee valgus alignment [1]. Participants in the DL group were engaged in a structured training process characterized by non-repetitive practice attempts, consistent with DL principles. No augmented feedback was given to the participants in the DL group. Prior to each training session, the trainer designed a diverse set of task variations for each of the four designated exercises [3]. After completing the exercise sets, both groups performed a post-test under the same conditions as the pre-test, completing three successful trials of the SL-DVJ task.

In the data processing procedure, we used Excel 2019 and MATLAB (version 8.4, 2014b). statistical indicators were examined at a significant level 0.05, using SPSS software, version 22.

Results: A significant group × time interaction effect was observed for the feedforward activity of the gluteus medius (F 2،33 = 6.308, p = 0.017) and medial hamstring (F2, 33 = 6.095, p = 0.019) muscles (p < 0.05). The main effect of time was significant for all study variables. A significant main effect of group was also found for the gluteus medius (F2, 33 = 5.032, p = 0.032) and medial hamstring (F2, 33 = 9.680, p = 0.004) muscles. Furthermore, significant between-group differences were identified between the VCF and DL groups in the feedforward activity of the gluteus medius (p = 0.012) and medial hamstring (p = 0.002) muscles. Post hoc Bonferroni analysis demonstrated that both the VCF and DL groups showed significant increases in the feedforward activity of the gluteus maximus (p = 0.014, p = 0.002, respectively), gluteus medius (p = 0.005, p = 0.001, respectively), vastus medialis (p = 0.011, p = 0.001, respectively), and medial hamstring (p = 0.025, p = 0.001, respectively). Moreover, both groups exhibited significant reductions in the feedforward activity of the vastus lateralis (p = 0.002, p = 0.001, respectively) and lateral hamstring (p = 0.003, p = 0.001, respectively).

Conclusion: Both the VCF and DL approaches were effective in modifying neuromuscular variables associated with ACL injury risk. However, the DL group demonstrated greater improvements in feedforward muscle activity of the gluteus medius and medial hamstring compared with the VCF group. These findings suggest that incorporating movement variability and task-specific modifications may enhance neuromuscular control in female athletes with DKV.