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Immediate effects of real time feedback and kinesiotaping on kinematics and muscle activity in athletes with dynamic knee valgus - PMC

Dynamic knee valgus (DKV) is a significant risk factor for anterior cruciate ligament (ACL) injuries. Real-time feedback (RTF) and Kinesio taping (KT) are common interventions used to prevent DKV. This study aimed to compare the immediate effects of ...

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Immediate effects of real time feedback and kinesiotaping on kinematics and muscle activity in athletes with dynamic knee valgus

Taha Gheibi

Taha Gheibi

1
Masters of Sport injury and Corrective Exercise, Department of Exercise Physiology and Corrective Exercise, Faculty of Sport Sciences, Urmia University, Urmia, Iran

Find articles by
Taha Gheibi

1
,
Ebrahim Mohammad Ali Nasab Firouzjah

Ebrahim Mohammad Ali Nasab Firouzjah

2
Department of Exercise Physiology and Corrective Exercise, Faculty of Sport Sciences, Urmia University, Urmia, Iran

Find articles by
Ebrahim Mohammad Ali Nasab Firouzjah

2,
✉
,
Hadi Abbaszadeh Ghanati

Hadi Abbaszadeh Ghanati

3
Department of Biomechanics and Sports Injury, Faculty of Sport Sciences, Kharazmi University, Tehran, Iran

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Hadi Abbaszadeh Ghanati

3
,
Thomas Gus Almonroeder

Thomas Gus Almonroeder

4
Brooks College of Health Professions at Trine University, Fort Wayne, USA

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4

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Article notes

Copyright and License information

1
Masters of Sport injury and Corrective Exercise, Department of Exercise Physiology and Corrective Exercise, Faculty of Sport Sciences, Urmia University, Urmia, Iran

2
Department of Exercise Physiology and Corrective Exercise, Faculty of Sport Sciences, Urmia University, Urmia, Iran

3
Department of Biomechanics and Sports Injury, Faculty of Sport Sciences, Kharazmi University, Tehran, Iran

4
Brooks College of Health Professions at Trine University, Fort Wayne, USA

✉
Corresponding author.

Received 2025 Oct 5; Accepted 2026 Feb 23; Collection date 2026.

© The Author(s) 2026

Open Access
This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit
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.

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PMCID: PMC13057237 PMID:
41764284

Abstract

Dynamic knee valgus (DKV) is a significant risk factor for anterior cruciate ligament (ACL) injuries. Real-time feedback (RTF) and Kinesio taping (KT) are common interventions used to prevent DKV. This study aimed to compare the immediate effects of RTF, with and without KT, on the kinematics and muscle activity in athletes with dynamic knee valgus. This randomized controlled trial study included 34 male athletes aged 20–25 years with DKV (> 10°) from jumping sports (handball, basketball, and volleyball) who were randomly assigned to two groups: RTF (age 21.94 ± 2.56 years, height 184.35 ± 5.27 cm, weight 74.50 ± 6.75 kg) and RTF + KT (age 22.29 ± 1.86 years, height 183.05 ± 6.01 cm, weight 73.50 ± 5.48 kg). Dynamic knee valgus was screened using Kinovea software during a landing from a 32 cm platform. All participants performed step-down, lateral step-down, double-leg squat and single-leg squat exercises under RTF and RTF with KT conditions. All kinematics and electromyographic variables were assessed during the single-leg vertical drop jump (SL-VDJ) task. Knee flexion, hip flexion, knee valgus and ankle dorsiflexion angles were measured by an IMU system and feedforward activity of hip and knee muscles was measured by an EMG device before and after the exercise intervention. 2 × 2 mixed-model ANOVA (group: RTF, RTF + KT, time: pretest, posttest) was used for data analysis at the significance level of
p
≤ 0.05. There was a significant group-by-time interaction effect for peak knee flexion angle (F
1,32
=5.382,
p
= 0.027), gluteus medius activity (F
1,32
=5.9532,
p
= 0.004), and vastus medialis activity (F
1,32
=4.288,
p
= 0.047), with the RTF + KT group exhibiting greater pre-to-post increases in peak knee flexion, gluteus medius activity, and vastus medialis activity, compared to the RTF group. There was a significant main effect of time for peak hip flexion angle (F
1,32
=7.427,
p
= 0.010), peak knee valgus angle (F
1,32
=90.201,
p
= 0.001), peak ankle dorsiflexion angle (F
1,32
=4.211,
p
= 0.048), gluteus maximus activity (F
1,32
=17.069,
p
= 0.001), vastus lateralis activity (F
1,32
=35.908,
p
= 0.001), medial hamstring activity (F
1,32
=60.183,
p
= 0.001), and lateral hamstring activity (F
1,32
=36.983,
p
= 0.001), with both groups exhibiting similar changes over time. In summary, RTF + KT and RTF effectively altered kinematic and electromyographic ACL injury risk factors. The RTF + KT intervention demonstrated notable within-group enhancements for multiple measures, particularly in increasing knee flexion and activation of the gluteus medius and vastus medialis muscles. Consequently, while RTF alone constitutes an effective intervention, the RTF + KT combination may offer additional benefits for addressing deficits in knee flexion and specific muscle activations in athletes displaying DKV.

Keywords:
Visual feedback, Kinematics, Electromyography, Movement retraining, Motor control
Subject terms:
Anatomy, Health care, Medical research
Introduction

The anterior cruciate ligament (ACL) plays a vital role in resisting anterior tibial translation, internal-external tibial rotation, and valgus-varus movements
1
. The significance of the ACL is particularly evident in team ball sports, where non-contact ACL injuries are highly prevalent
2
. These injuries often occur during dynamic jump-landing tasks or cutting maneuvers
3
. Neuromuscular control deficits of the hip in the frontal/transverse plane can lead to medial knee collapse during hip and knee flexion, which is termed dynamic knee valgus (DKV)
4
. DKV has been frequently assessed during single-leg movements, particularly single-leg squats and landings
5
. This assessment is crucial for several reasons. Firstly, DKV during single-leg stance, often accompanied by loss of balance, is a primary pattern observed during lower extremity injuries
6
. Secondly, the majority of ACL ruptures occur during single-leg landings
7
. Thirdly, single-leg movements are more challenging in terms of skill and technique execution compared to double-leg movements, facilitating the identification of individuals at higher risk of injury
8
.

During landing, the movements of the hip, knee, and ankle contribute to the attenuation of ground reaction forces (GRF). If these components do not act synergistically, the lower extremity may lack the ability to attenuate GRFs, thereby increasing ligament stress
9
. In such instances adoption of an upright body position with minimal flexion during landing lead to elevated tensile and rotational forces on the ACL
10
. Consequently, landing with increased trunk, hip, and knee joint flexion can significantly attenuate GRFs
9
.

In addition to biomechanical factors, neuromuscular control factors also play a significant role in inducing alterations in lower extremity mechanics and kinematics
11
. Proper activation of the posterior chain muscles (including the gluteus maximus and medius, hamstrings, gastrocnemius, and soleus) is crucial for attenuating GRFs. In the absence of adequate activation of these muscles, ligaments and joints are subjected to increased stress, placing them at heightened risk of injury
12
. The gluteus maximus primarily contributes to hip extension and external rotation, playing a secondary role in frontal-plane control
13
. Premature contraction of the quadriceps muscles by the athlete and the lack of simultaneous activation of the gluteus and hamstring muscles creates a predisposition for knee collapse towards valgus
14
. This improper posture allows GRF to act in the valgus direction, increasing the risk of injury. Epidemiological studies have demonstrated that higher knee abduction torques, knee abduction angles, and vertical GRFs are predictors of ACL injury
15
. Furthermore, a more erect posture during landing, characterized by reduced hip and knee flexion, is a well-established risk factor for non-contact ACL injuries
3
,
6
.

By examining the mechanisms of ACL injury, preventive strategies should focus on increasing flexion and reducing DKV during landing
16
. One common method to prevent DKV and subsequently, ACL injury, is the use of Kinesio taping (KT)
17
. In the field of sports injury treatment and prevention, KT is emerging as a beneficial tool
18
. Based on scientific findings, KT plays a positive role in reducing pain, increasing joint range of motion, improving proprioception, and enhancing muscle activity
19
. This tape functions by stimulating cutaneous mechanoreceptors, enhancing neuromuscular activity
20
. In individuals with ACL rupture, the application of KT on the knee improves proprioception, strength, and static balance
17
,
21
. During jump landings, some studies indicate that knee KT reduces DKV
22
. In this context, a recent study, applying 75% tension KT to the knee in men, achieved a significant reduction in DKV during a jump-landing task
23
.

The use of feedback, in training or rehabilitation sessions, also enhances motor control and learning, effectively improving motor pattern retraining
24
,
25
. Real-time
24
or post-task
25
visual feedback is employed to target neuromuscular changes. Real-time feedback (RTF) enables individuals to observe their movements and make immediate biomechanical adjustments
24
. Providing RTF has the potential to be highly effective for promoting long-term movement pattern changes
24
.

While neuromuscular re-training programs for ACL injury prevention have demonstrated success in promoting “safer” movement patters, there is still a need to enhance the effectiveness of these programs
26
. Considering that these prevention programs are typically conducted over a 6 to 8-week period, identifying a method to promote immediate movement pattern retraining could represent a novel and valuable approach. Based on the aforementioned information, it can be argued that both KT and RTF are effective methods for preventing DKV and ACL injury risk factors. While RTF alone is effective for immediate biomechanical modification, the proprioceptive augmentation provided by KT may further enhance neuromuscular control and movement quality. It is hypothesized that applying KT in conjunction with RTF will potentiate its effects, leading to greater improvements in lower extremity kinematics and muscle activation patterns. This synergistic approach is proposed to offer superior immediate protection against DKV and ACL injury risk factors compared to RTF alone. Therefore, the aim of the present study is to examine the effects of RTF, with and without KT, on kinematic variables and feedforward muscle activity in male athletes with DKV.
Material and method

This research employed a randomized parallel-group quasi-experimental pre–post design. The study population comprised male recreational athletes aged 20–25 years participating in jumping sports (handball, basketball, and volleyball). The minimum sample size was determined using GPower software (version 3.1.9.2). An a priori power analysis was conducted using an F test for a repeated-measures ANOVA with a within–between interaction. The following parameters were entered: effect size f = 0.25, alpha level = 0.05, statistical power = 0.80, two groups (RTF, RTF + KT), two measurement time points (pre, post), and an assumed correlation among repeated measures of 0.60 (moderate correlation). Based on these inputs, the required total sample size was estimated to be 28 participants. Accounting for a potential 20% attrition rate, the final sample size was 34 participants, recruited through convenience sampling based on the study’s inclusion criteria.

Participants were randomly allocated to one of two groups, RTF (
n
= 17) or RTF + KT (
n
= 17), using the website
http://randomizer.org
. Concealed allocation was achieved through computer-generated blocked randomization using a random number Table (1 = RTF group, 2 = RTF + KT group). Prior to commencement, baseline data collection was conducted by a researcher not involved in recruitment or intervention delivery. Subsequently, the randomized numerical sequence was placed in opaque, sealed envelopes. An independent evaluator, unaware of the study hypotheses and methods, assessed the outcomes before and after the interventions.

Prior to participation, all individuals provided written informed consent approved by the university’s ethics committee. Furthermore, this study received ethical approval with the code IR.X.REC.1403.031 from Urmia University.

Inclusion criteria for this study were: athletes participating in jumping sports (handball, basketball, and volleyball), presence of DKV greater than 10 degrees during single-leg landing
27
, absence of trunk and lower extremity injury within the preceding 6 months, age range of 20 to 25 years, and a body mass index within the range of 18.5–25. Exclusion criteria included the presence of musculoskeletal deformities, a history of fracture or dislocation of the hip, knee, or ankle, a history of low back pain in the past year, vestibular impairment, ligamentous injuries in the lower extremities, and participation in a movement re-training program within the past year
28
.

Single leg landing test

A total of 112 potential participants were initially screened for eligibility. Following the application of predetermined inclusion and exclusion criteria, 34 eligible athletes (30.4% of the initially screened cohort) were ultimately enrolled and completed the study protocol. Prior to performing the landing tasks, the participants engaged in a 10-minute warm-up consisting of light jogging, stretching exercises, and plyometric activities. The single-leg landing test was utilized for screening DKV, employing Kinovea software (Bordeaux, France, version 0.8.15) during landing from a 32 cm platform. Individuals exhibiting DKV exceeding 10 degrees were considered susceptible to ACL injury
29
. The knee valgus angle was defined as the angle between a line from the anterior superior iliac spine to the midpoint between the femoral condyles (not the center of the patella) and a line from the midpoint between the femoral condyles to the ankle. The DKV angle was assessed as the difference between the static frame on the platform and the frame at the point of peak knee flexion during the landing task, evaluated using two-dimensional video analysis and Kinovea software.
Motion analysis system

An Inertial Movement Unit (IMU) system (APEX, Rasht, Guilan, Iran) was used to collect kinematic data during the jump-landing task at a sampling frequency of 250 Hz. Sensors were placed on the pelvis, thigh, shank, and the dorsal aspect of foot (between the first and fifth metatarsal heads). The shank sensor placement was standardized using the tibial crest as an anatomical landmark. Thigh sensors were positioned midway between the greater trochanter and the lateral femoral epicondyle, and the pelvic sensor was placed between the posterior superior iliac spines.

IMU-based joint angle estimation has been validated for various movements including squatting, jumping, and gait analysis
30
–
32
. In this study, knee flexion, hip flexion, knee valgus, and ankle dorsiflexion angles were derived from the relative orientation between adjacent IMU sensors. The moment of foot contact was determined using the accelerometer data from the IMU placed on the distal shank or foot. Ground contact was defined as the instant when the raw vertical acceleration signal exhibited a distinct peak or abrupt change exceeding a pre-set threshold, synchronized with the EMG data acquisition system for validation.
Single-leg vertical drop jump (SL-VDJ)

Participants performed a vertical jump followed by a single-leg landing on their dominant leg on the ground. Dominant leg preference was determined by asking participants which leg they preferred to land on after a jump. The SL-VDJ task involved dropping from a 10 cm box, landing on the dominant leg, immediately performing a maximal vertical jump, and landing again
33
. Trials were discarded and repeated if the participant jumped off the box instead of stepping off, if the non-landing leg contacted the ground, if they clearly lost balance, or if they fell during the test. A one-minute rest period was provided between repetitions to minimize fatigue. The peak knee valgus and flexion angles, peak hip flexion angle, and peak ankle dorsiflexion angle during this task were measured using the IMU system.
Electromyography (EMG) analysis

EMG activity was recorded using a 16-channel EMG system (Bayamed, Tehran, Iran) with a sampling frequency of 1000 Hz. Bipolar surface electrodes (SKINTACT, ECG, Austria) with an inter-electrode distance of 2 cm were utilized. Prior to application on the dominant leg, any excess hair at the electrode placement sites was shaved, and the skin was prepared with alcohol and cotton. Electrodes were positioned according to established SENIAM (Surface Electromyography for Non-Invasive Assessment of Muscles) guidelines and previous research
34
.

Maximal voluntary contraction (MVC) was assessed for the following muscles using the bipolar surface electrodes. Each MVC trial lasted 5 s, with at least 1 min of rest between trials
35
. For the gluteus maximus (Gmax), participants in a prone position with 0° hip extension and 90° knee flexion performed resisted hip extension; electrodes were placed midway between the second sacral vertebra and the greater trochanter
36
. For the gluteus medius (Gmed), in a side-lying position, participants performed resisted hip abduction; electrodes were placed at 50% of the distance from the iliac crest to the greater trochanter, oriented towards the trochanter
37
. For the medial hamstrings, electrodes were placed at the 50% midpoint of the line connecting the ischial tuberosity and the medial tibial epicondyle
38
. For the lateral hamstrings, electrodes were positioned at the 50% midpoint of the line between the ischial tuberosity and the lateral tibial epicondyle
36
. For the vastus medialis (VM), with the knee flexed at 90°, participants performed resisted knee extension; the electrode was placed at 80% of the distance from the anterior superior iliac spine to the medial joint line
37
. For the vastus lateralis (VL), with the knee flexed at 90°, participants performed resisted knee extension; the electrode was placed 10 cm superior and 7 cm lateral to the superior patellar border, angled 10° laterally
36
.
EMG data processing

Raw EMG signals were band-pass filtered using a fourth-order zero-lag Butterworth filter with a cutoff frequency range of 20 to 450 Hz
39
. Subsequently, the data were rectified and processed using a root mean square (RMS) algorithm. To normalize EMG data, MVC of each muscle was measured before the SL-DVJ test. For analysis, the average RMS of three landing trials was calculated and normalized to the average RMS of the corresponding muscle’s MVC, with the result expressed as a percentage (%MVC). Feedforward (or “preparatory”) muscle activity was determined by measuring the onset of muscle activation in the 150 ms preceding ground contact
40
. The raw EMG signal during this pre-contact interval was processed using the RMS algorithm in MATLAB (version 8.4, 2014b), yielding a value representing the average signal power and muscle activity level.
Implementation of RTF and KT methods

All participants in both groups first underwent a standardized familiarization session. Although they were already proficient in the SL-VDJ task, this session comprised a demonstration and up to five practice trials to mitigate potential learning effects and ensure consistent performance. Following familiarization, participants completed a pre-test of the SL-VDJ task with EMG electrodes and IMU sensors attached. Baseline data were recorded as the average of three successful trials. Subsequently, both the RTF + KT group and the RTF group performed four training exercises: bilateral squat, unilateral squat, forward step-down, and lateral step-down, each repeated 10 times (Fig.
1
)
41
. A two-minute rest interval was included between each exercise to prevent fatigue and ensure movement quality. The unilateral exercises were performed only on the dominant leg. Participants in the RTF + KT group performed these exercises in front of a full-length mirror (visual feedback) after KT application, receiving verbal cues from a corrective exercise specialist. The mirror featured a vertical center line, and participants were positioned so this line bisected their body. The specific verbal instruction was to focus on preventing the knee from moving inward across this body midline, thereby maintaining proper alignment
42
, and encouraging visual monitoring and control of DKV. The RTF group performed the same four training exercises with visual feedback from the mirror and verbal cues, without the application of KT. It is important to note that no feedback was provided during the SL-VDJ task for either group. The KT procedure involved applying a standard KT technique (appropriate for ACL injury prevention) to the participants’ legs. A 5 cm wide, 30 cm long I-strip of KinesioTex
®
tape (Japan) was cut and applied with 75% tension from the tibial tuberosity to over the medial and lateral femoral condyles to restrict anterior tibial translation
23
. Following the completion of the training exercises by both groups, a post-test was conducted under the same conditions as the pre-test, with all participants performing three successful trials of the SL-VDJ task.

Fig. 1.

Open in a new tab

Four training tasks: forward step-down, bilateral squat, lateral step-down and unilateral squat.
Descriptive and inferential statistics were used for the analysis of the collected data. Independent t-tests were employed to compare the demographic characteristics of the groups, and the Shapiro-Wilk test was used to assess normality. Mixed-model ANOVA, with a between-subjects factor of group (RTF, RTF + KT) and a within-subjects factor of time (pretest, posttest), was conducted to examine the kinematic variables and muscle activity. In cases where there as a group-by-time interaction effect, Bonferroni post hoc tests were conducted to examine pretest-posttest changes within each group. Additionally, 95% confidence intervals (95% CI) were calculated based on the adjusted mean differences between groups. To quantify effect sizes for between-group comparisons, Cohen’s d was calculated, with values of 0.2, 0.5, and 0.8 interpreted as “small,” “medium,” and “large” effect sizes, respectively. The data were analyzed using SPSS version 22 (SPSS Inc., Chicago, IL, USA), with the significance level set at
p
≤ 0.05 (95% confidence level).
Results

Examining demographic characteristics revealed no statistically significant difference in age, height, body mass, body mass index, or sport experience between the two groups (Table
1
).

Table 1.

Demographic characteristics of participants.

Characteristics

RTF (
n
= 17)

RTF + KT (
n
= 17)

P
value

Age (year)

21.94 ± 1.56

22.29 ± 1.86

0.554

Body mass (kg)

74.50 ± 6.75

73.50 ± 5.48

0.637

Height (m)

184.35 ± 5.27

183.05 ± 6.01

0.510

Body mass index (kg/m
2
)

21.88 ± 1.09

21.94 ± 1.42

0.897

Sport experience (year)

5.35 ± 1.50

6.24 ± 1.82

0.124

Open in a new tab

P value from independent T-test; significant difference (
p
< 0.05).
Kinematics

There was a significant group-by-time interaction effect for peak knee flexion (
p
= 0.027) (Table
2
; Fig.
2
). Post hoc tests indicated that the RTF (
p
= 0.001) and RTF + KT (
p
= 0.001) groups both exhibited an increase in peak knee flexion from pre-to-post. However, the RTF group only exhibited an 20.0% increase, while the RTF + KT group exhibited a 34.0% increase. There were no group-by-time interaction effects for peak hip flexion (
p
= 0.59), peak knee valgus (
p
= 0.19), or peak ankle dorsiflexion (
p
= 0.57) (Table
2
; Fig.
2
). There were significant main effects of time for peak hip flexion (
p
= 0.002), peak knee valgus (
p
= 0.001), and peak ankle dorsiflexion (
p
= 0.048), with athletes exhibiting greater hip flexion and ankle dorsiflexion, and less knee valgus, at the posttest time point (compared to pretest) (Fig.
2
). There were no significant main effects of group (
p
≥ 0.17) (Table
2
).

Table 2.

kinematics variables of athletes during single-leg vertical drop jump.

Kinematic
Variables

Group

Pretest
Mean ± SD
(95% CI)

Posttest
Mean ± SD
(95% CI)

ES
†
(CI
95%
)
% change

p
Value

Main Effect of Time

Main Effect of Group

Group × Time Interaction

Peak knee flexion (°)

RTF

50.61 ± 8.23

(46.69–54.52)

59.74 ± 7.43
¥

(56.20-63.27)

1.16

(0.43–1.89)

%20.0 ↑

F

(1,32)

= 68.435

p

= 0.001 *

F
(1,32)
= 1.543

p
= 0.223

F
(1,32)
= 5.389

p

= 0.027*

RTF + KT

50.26 ± 8.10

(46.41–54.11)

66.60 ± 11.02
¥, a

(61.36–71.83)

1.69

(0.90–2.47)

%34.0 ↑

Peak hip flexion (°)

RTF

41.75 ± 6.73

(38.55–44.94)

49.03 ± 9.29
¥

(44.61–53.44)

0.89

(0.19–1.60)

%20.0 ↑

F

(1,32)

= 11.921

p

= 0.002*

F
(1,32)
= 0.651

p
= 0.426

F
(1,32)
= 0.293

p
= 0.592

RTF + KT

42.25 ± 9.55

(37.71–46.79)

52.23 ± 12.94
¥

(46.07–58.38)

0.87

(0.17–1.58)

%29.6 ↑

Peak knee valgus (°)

RTF

13.53 ± 4.15

(11.55–15.50)

5.61 ± 3.12
¥

(4.12–7.09)

-2.15

(-3.00 - -1.31)

%55.1 ↓

F

(1,32)

= 118.332

p

= 0.001 *

F
(1,32)
= 1.142

p
= 0.293

F
(1,32)
= 1.774

p
= 0.192

RTF + KT

13.74 ± 3.79

(11.93–15.54)

3.60 ± 2.48
¥, a

(2.42–4.77)

-3.16

(-4.17 - -2.15)

%71.7 ↓

Peak ankle dorsiflexion (°)

RTF

18.52 ± 3.55

(16.83–20.20)

19.77 ± 4.44

(17.65–21.88)

0.31

(-0.36-0.98)

%12.2 ↑

F

(1,32)

= 4.211

p

= 0.048 *

F
(1,32)
= 1.966

p
= 0.171

F
(1,32)
= 0.337

p
= 0.566

RTF + KT

19.10 ± 3.42

(17.47–20.72)

21.81 ± 5.29
¥

(19.29–24.32)

0.60

(-0.07-1.29)

%16.8 ↑

Open in a new tab

Abbreviations: Results are presented as mean ± SD and 95% confidence interval (CI: lower bound upper bound); *, statistically significant difference (
p
< 0.05); ¥, pretest to posttest significant difference; †, effect size; £, large Cohen’s d effect size (0.8); results of Bonferroni post hoc test: a = significant difference between RTF and RTF + KT.
Fig. 2.

Open in a new tab

Changes in peak knee flexion (top-left), peak hip flexion (top-right), peak knee valgus angles (bottom-left), and peak ankle dorsiflexion (bottom-right) for RTF and RTF + KT groups.
Feedforward muscle activity

There were group-by-time interaction effects for Gmed (
p
= 0.004) and Vmed (
p
= 0.047) feedforward activity (Table
3
; Fig.
3
). Post hoc tests indicated that the RTF and RTF + KT groups both exhibited an increase in Gmed (RTF:
p
= 0.009; RTF + KT:
p
= 0.001) and Vmed (RTF:
p
= 0.001; RTF + KT:
p
= 0.001) activity from pretest to posttest. However, the changes in Gmed and Vmed muscle activity were greater for the RTF + KT group (Gmed % change = 69.0%; Vmed % change = 42.2%), compared to the RTF group (Gmed % change = 26.0%; Vmed % change = 26.4%). There were no group-by-time interaction effects for Gmax (
p
= 0.73), Vlat (
p
= 0.82), Mham (
p
= 0.42), or Lham (
p
= 0.26) (Table
3
; Fig.
3
). There were significant main effects of time for Gmax (
p
= 0.001), Vlat (
p
= 0.001), Mham (
p
= 0.001), and Lham (
p
= 0.001), with athletes exhibiting greater feedback forward muscle activity at the posttest time point (compared to pretest) (Fig.
3
). There were no significant main effects of group (
p
≥ 0.08) (Table
3
).

Table 3.

EMG variables of athletes during single-leg vertical drop jump.

Group

Pretest
Mean ± SD
(95% CI)

Posttest
Mean ± SD
(95% CI)

ES
†
(CI
95%
)
% change

p
Value

Main Effect of Time

Main Effect of Group

Group × Time Interaction

Gmax (mvc %)

RTF

27.38 ± 7.02

(24.04–30.71)

32.33 ± 9.82
¥

(27.66–36.99)

0.58

(-0.10-1.26)

%20.0 ↑

F

(1,32)

= 17.069

p

= 0.001 *

F
(1,32)
= 0.419

p
= 0.522

F
(1,32)
= 0.122

p
= 0.729

RTF + KT

28.87 ± 6.91

(25.58–32.15)

34.73 ± 12.64
¥

(28.72–40.73)

0.57

(-0.11-1.26)

%19.2 ↑

Gmed (mvc %)

RTF

26.05 ± 5.18

(23.58–28.51)

32.03 ± 8.25
¥

(28.10-35.95)

0.86

(0.16–1.57)

%26.0 ↑

F

(1,32)

= 49.346

p

= 0.001*

F
(1,32)
= 1.156

p
= 0.290

F

(1,32)

= 9.532

p

= 0.004*

RTF + KT

24.00 ± 6.97

(20.68–27.31)

39.36 ± 11.79
¥, a

(33.75–44.96)

1.58

(0.81–2.35)

%69.0 ↑

Vmed (mvc %)

RTF

42.00 ± 7.80

(38.92–45.70)

52.42 ± 8.41
¥

(48.42–56.41)

1.28

(0.54–2.02)

%26.4 ↑

F

(1,32)

= 88.311

p

= 0.001*

F
(1,32)
= 0.402

p
= 0.530

F

(1,32)

= 4.288

p

= 0.047*

RTF + KT

40.99 ± 8.73

(36.84–45.14)

57.29 ± 13.27
¥

(5.98–63.59)

1.45

(0.69–2.20)

%42.2 ↑

Vlat (mvc %)

RTF

67.73 ± 10.90

(62.54–72.91)

56.72 ± 12.54
¥

(50.75–62.68)

-0.93

(-1.64 - -0.22)

%15.8 ↓

F

(1,32)

= 35.908

p

= 0.001*

F
(1,32)
= 0.224

p
= 0.639

F
(1,32)
= 0.050

p
= 0.824

RTF + KT

66.45 ± 12.84

(60.34–72.55)

54.58 ± 11.31
¥

(49.20-59.95)

-0.98

(-1.69 - -0.26)

%16.2 ↓

Mham (mvc %)

RTF

36.40 ± 10.00

(31.64–41.15)

53.09 ± 12.89
¥

(46.96–59.21)

1.44

(0.69–2.20)

%53.2 ↑

F

(1,32)

= 60.183

p

= 0.001*

F
(1,32)
= 1.424

p
= 0.241

F
(1,32)
= 0.664

p
= 0.421

RTF + KT

37.56 ± 7.51

(33.99–41.13)

58.17 ± 10.27
¥

(53.28–63.05)

2.29

(1.42–3.15)

%61.7 ↑

Lham (mvc %)

RTF

61.40 ± 13.33

(55.06–67.73)

48.26 ± 11.71
¥

(42.69–53.82)

-1.04

(-1.76 - -0.33)

%17.0 ↓

F

(1,32)

= 36.983

p

= 0.001*

F
(1,32)
= 3.264

p
= 0.080

F
(1,32)
= 1.320

p
= 0.259

RTF + KT

59.56 ± 10.40

(54.61–64.50)

40.30 ± 8.25
¥, a

(36.37–44.22)

-2.05

(-2.88 - -1.22)

%31.1 ↓

Open in a new tab

Abbreviations: Gmax: gluteus maximus, Gmed: gluteus medius, Vmed: vastus medialis, Vlat: vastus lateralis, Mham: medial hamstring, Lham: lateral hamstring. Results are presented as mean ± SD and 95% confidence interval (CI: lower bound, upper bound); *, statistically significant difference (
p
< 0.05); ¥, pretest to posttest significant difference; †, effect size; £, large Cohen’s d effect size (0.8); results of Bonferroni post hoc test: a = significant difference between RTF and RTF + KT.
Fig. 3.

Open in a new tab

Changes in Gmax (top-left), Gmed (top-right), Vmed (middle-left), Vlat (middle-right), Mham (bottom-left), and Lham (bottom-right) activity for RTF and RTF + KT groups.
Discussion

The aim of the present study is to examine the effects of RTF, with and without KT, on kinematic variables and feedforward muscle activity in male athletes with DKV. Our findings indicate that the addition of KT enhanced the effects of RTF, as athletes exhibited greater increases in knee flexion, Gmed activity, and Vmed activity during a SL-VDJ when KT was included during training (based on the group-by-time interaction effects). RTF also led to increases in hip flexion, ankle dorsiflexion, Gmax activity, Vlat activity, Mham activity, and Lham activity, as well as a reduction in knee valgus; however, the addition of KT did not enhance these effects (based on the main effects of time, without group-by-time interaction effects). These findings suggest that RTF is effective for immediately altering SL-VDJ landing kinematics and feedforward muscle activity, and that the addition of KT can selectively augment these effects for specific outcomes, namely peak knee flexion angle and the feedforward activation of the gluteus medius and vastus medialis muscles.

Kinematics

The present study revealed significant within-group increases from pretest to posttest in peak knee and hip flexion angles in both groups. However, a significant group-by-time interaction was observed for peak knee flexion, with the RTF + KT group demonstrating a greater pretest-posttest increase in peak knee flexion, compared to the RTF group. These findings align with Herman et al.
43
regarding the integration of feedback-based exercises with resistance training. Additionally, the results support the effectiveness of feedback exercises in reducing ACL injury risk factors, consistent with the studies by Shams et al.
44
and Abbaszadeh Ghanati et al.
28
, but contrast with the findings of López et al.
45
.

Motion analysis in the sagittal plane during landing is particularly critical for ACL injury risk. Increased anterior tibial shear force, primarily generated in the sagittal plane, elevates stress on the ACL, thereby raising injury susceptibility
46
. Previous studies have demonstrated that reduced knee and hip flexion angles in the sagittal plane lead to greater impact forces on the knee, consequently increasing ACL injury risk
47
–
50
. Research has also established a direct relationship between knee and hip flexion angles during the landing phase and GRF
51
. Pollard et al. further demonstrated that changes in joint angles and moments at the knee and hip are strongly associated with ACL loading. Reduced knee and hip flexion angles increase extension moments at these joints, significantly amplifying tensile forces on the ACL
52
.

These findings indicate that improper landing technique and reduced lower-limb joint flexion are key factors in elevating ACL injury risk
53
. In the present study, the RTF + KT group demonstrated a greater increase in knee flexion post-intervention compared to the RTF group. These results suggest that combining RTF + KT appears particularly effective in increasing peak knee flexion during a single-leg jump-landing task. This improvement in knee flexion during jump-landing represents a significant finding for knee injury prevention, especially regarding ACL injuries. Reduced knee flexion during landing leads to inadequate shock absorption at the knee joint, substantially increasing ACL injury risk
54
. Since greater knee and hip flexion angles in the sagittal plane play a crucial role in shock absorption and lower limb protection during landing
55
, movement training using specific, targeted strategies to improve landing technique should be considered an effective preventive approach for reducing ACL injury risk. These exercises, by improving movement patterns and enhancing the body’s shock absorption capacity, can significantly decrease the likelihood of ACL injuries.

The RTF + KT and RTF groups showed similar reductions in peak knee valgus angles following the intervention (no group-by-time interaction effect, main effect of time). Individuals with hip internal rotation and valgus knee alignment demonstrate greater knee valgus angles during jump-landing tasks compared to those with normal lower extremity alignment
56
. DKV increases frontal plane motion and elevates loading on the lateral knee compartment. Preventing this motion requires activation of hip abductor and external rotator muscles to control excessive knee movement
57
. The current findings align with Abbaszadeh Ghanati et al.‘s study
58
regarding the effectiveness of external focus feedback strategies in improving knee abduction angles. Our RTF intervention produced significant reductions in peak knee valgus angles from pretest to posttest. These results indicate that RTF may be effective for modifying movement patterns and reducing knee injury risk, particularly ACL injuries.

Restricted ankle dorsiflexion flexibility, particularly with the knee extended, is associated with increased ACL injury risk
59
,
60
. Studies demonstrate that individuals with limited ankle flexibility tend to land with reduced knee flexion angles, thereby increasing ACL loading
59
. As a modifiable risk factor, ankle dorsiflexion plays a crucial preventive role - being both easily measurable and trainable
61
. Research further links restricted ankle mobility with increased medial knee displacement during drop-jump tasks
60
. Interestingly, inclined surface training with plantarflexed ankle positioning has shown potential for improving dorsiflexion range and reducing aberrant knee kinematics
62
. The present study observed increased maximum ankle dorsiflexion angles in both intervention groups post-training (main effect of time).
Muscle activity

All EMG variables demonstrated significant pretest-to-posttest increases in both intervention groups, indicating improved neuromuscular activation following training. Significant group-by-time interaction effects were observed for gluteus medius and vastus medialis activity, with the RTF + KT group exhibiting greater pretest-to-posttest increases compared with the RTF group. These findings suggest that the addition of KT may augment the effects of RTF for enhancing activation of specific hip and knee stabilizing muscles.

Both interventions significantly increased gluteus maximus and gluteus medius activity relative to baseline, demonstrating their effectiveness for improving proximal muscle activation. Although both groups improved, descriptive effect sizes and percentage changes were larger in the RTF + KT group. Strengthening of the gluteus maximus (hip external rotator) and gluteus medius (hip abductor) is considered critical for lower-limb control and prevention of excessive DKV
63
,
64
. While some studies emphasize the role of hip external rotators in controlling knee abduction
13
, others highlight the importance of hip abductors during landing
65
. The present findings support existing evidence that enhanced gluteal activation contributes to improved lower-extremity biomechanics and may reduce ACL loading by limiting valgus collapse
64
.

Both the RTF and RTF + KT interventions resulted in significant within-group improvements in feedforward activation of the medial and lateral hamstrings and vastus medialis and lateralis muscles. A significant group-by-time interaction was observed only for lateral hamstring feedforward activity, indicating a greater pretest-to-posttest increase in the RTF + KT group. Quadriceps and hamstrings are estimated to contribute approximately 13.6% and 18.1%, respectively, to frontal-plane motion control, and improvements in their activation have been shown to reduce landing-phase joint torques
66
. Reduced hamstring activation may compromise joint stability and increase anterior tibial shear forces, particularly when accompanied by elevated quadriceps activity, thereby increasing ACL loading
67
. In contrast, appropriate quadriceps-hamstrings co-contraction enhances tibial stability and mitigates ACL stress. Enhanced medial hamstring activation during high-risk landing tasks may therefore represent a protective neuromuscular adaptation that limits excessive dynamic valgus and rotational loading of the ACL
68
.
Limitations

Since the present study was conducted on male athletes (due to greater accessibility to this population), future research could investigate these effects in females, untrained individuals, and other demographic groups. According to previous research, females demonstrate different responses to motor learning strategies—particularly those involving visual feedback—within ACL injury prevention programs. Therefore, the current protocol could be applied to female athletes or conducted with both male and female participants to explore potential sex-related differences in intervention outcomes. Additionally, since kinematic and electromyographic risk factors were assessed only during the single-leg vertical drop jump task, further studies are needed to evaluate these variables during other dynamic tasks such as various jump-landings and cutting maneuvers. Comparing results across multiple movement tasks would help identify the most effective training interventions for reducing injury risk. Finally, the focus on immediate outcomes necessitates future research with extended follow-up periods to evaluate the retention of improvements over time.
Conclusion

In summary, both RTF and RTF + KT effectively reduced biomechanical risk factors associated with ACL injury. Although the RTF + KT group demonstrated greater within-group improvements across several variables, its added impact was primarily focused on enhancing knee flexion angle, along with increasing the activity of the gluteus medius and vastus medialis muscles. Therefore, while RTF serves as a core effective intervention, the combined RTF + KT approach is recommended for the targeted enhancement of these specific parameters in athletes with DKV.
Acknowledgements

The authors would like to thank all participants in the collaboration to make this study.
Abbreviations

KT

Kinesio taping

DKV

Dynamic knee valgus

RTF

Real-time feedback

ACL

Anterior cruciate ligament

Author contributions

RH: Investigation, Conceptualization, Methodology, Data capture, Data analysis.EM: Writing- Original draft preparation, Data curation, Conceptualization, Scientific editing.HA: Writing- Original draft preparation, Investigation, Data capture, Date analysis.TG: Writing- Original draft preparation, investigation, Data analysis, Scientific editing.
Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
Declarations

Competing interests

The authors declare no competing interests.
Ethics approval and informed consent to participate

All experimental protocols of this study were carried out following Declaration Helsinki and were approved by the Ethics Committee of Urmia University (Approval No. IR.X.REC.1403.031). All subjects provided written information informed consent prior to participation in the study.
Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

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</reference>

<statements>
1. | Measured Biomechanical Variable | Pre-Intervention Baseline (Mean \(\pm\) SD) [49] | Post-Intervention RTF (Mean \(\pm\) SD) [49] | Effect Size (Cohen’s \(d\)) [49] | Kinematic Percentage Change [49] | Statistical Significance (\(p\)-value) [49] | | --- | --- | --- | --- | --- | --- | | **Peak Knee Valgus Angle (\(^\circ\))** | \(13.53^\circ \pm 4.15^\circ\) | \(5.61^\circ \pm 3.12^\circ\) | \(-2.15\) | **\(55.1\%\) Reduction** | \(p = 0.001\) [cite: 49] | | **Peak Knee Flexion Angle (\(^\circ\))** | \(50.61^\circ \pm 8.23^\circ\) | \(59.74^\circ \pm 7.43^\circ\) | \(+1.16\) | **\(20.0\%\) Increase** | \(p = 0.001\) [cite: 49] | | **Peak Hip Flexion Angle (\(^\circ\))** | \(41.75^\circ \pm 6.73^\circ\) | \(49.03^\circ \pm 9.29^\circ\) | \(+0.89\) | **\(20.0\%\) Increase** | \(p = 0.002\) [cite: 49] | | **Peak Ankle Dorsiflexion (\(^\circ\))** | \(18.52^\circ \pm 3.55^\circ\) | \(19.77^\circ \pm 4.44^\circ\) | \(+0.31\) | **\(12.2\%\) Increase** | \(p = 0.048\) [cite: 49] |
2. Deploying real-time biofeedback (RTF) using computer vision and inertial sensors produced significant biomechanical improvements in high-risk movement patterns [49].
3. Peak knee valgus angles decreased by 55.1%, reducing frontal-plane ligament strain [49].
4. These kinematic adaptations confirm that real-time multimodal biofeedback can alter high-risk motor habits, demonstrating the clinical and preventive value of sports ITS implementations [49].
</statements>

Begin the assessment now. Output only the JSON list, without any conversational text or explanations.