The Influence of Functional Rehabilitation Braces with Resistance on Joint Coordination and ACL Force in Martial Artists Following ACL Reconstruction

Abstract

Objective: The resistive knee orthosis, as a novel rehabilitation device, is designed to provide resistance to joint movement during continuous walking, thereby enhancing the postoperative recovery effect. This study aims to explore the impact of such orthoses on the joint coordination patterns of martial artists after anterior cruciate ligament (ACL) reconstruction. Methods: A total of 44 martial artists who underwent ACL reconstruction were recruited and divided into an experimental group (EG, n = 22, using resistive braces) and a control group (CG, n = 22, using conventional braces). Assessments were conducted preoperatively (T0) and at 15 days (T1), 30 days (T2), and 60 days (T3) postoperatively. The changes in joint coordination patterns during the gait cycle were analyzed, and the ACL force was estimated using a musculoskeletal model. Results: At T2 and T3, compared with the CG, the EG exhibited a significantly larger peak knee flexion angle (p < 0.05). At T3, the EG showed higher hip–ankle in-phase coordination (p < 0.05), increased proximal hip–knee coordination (p < 0.05), and decreased knee–ankle anti-phase coordination (p < 0.05). In addition, the ACL force in the EG was significantly lower. Conclusions: The resistive knee orthosis can effectively improve the joint coordination of martial artists after ACL reconstruction and reduce the ACL force.

1. Introduction

Anterior cruciate ligament (ACL) injuries are a common type of knee injury among athletes and the general population. Approximately 350,000 people undergo ACL reconstructive surgery in the United States each year, a number that reflects the high prevalence of ACL injuries and their profound impact on patients’ quality of life [1,2]. Despite significant advances in techniques and postoperative rehabilitation methods for ACL reconstruction surgery, many studies have shown that postoperative patients continue to face long-term functional problems, particularly in terms of postural control and knee stability [3,4,5]. These problems are prevalent in ACL reconstruction patients and are often associated with inadequate postoperative recovery. For this reason, early and effective rehabilitation interventions have become particularly important, especially personalized and scientific recovery strategies starting from the second postoperative day, to reduce the risk of limited joint function and secondary injuries [6].

Chinese Wushu, as a traditional sport with comprehensive and complex movements, has a high risk of injury, especially ACL injury, due to its high intensity and rapid movement style [7]. Wushu athletes often face violent rotations, sharp stops, and sudden changes in direction during training and competition, which increase the probability of ACL injuries [8]. ACL injuries not only affect the athletes’ performance in competition, but also may bring about long-term athletic dysfunction, especially after reconstructive surgeries, where the recovery process is more critical. If the recovery strategy is appropriate, it can effectively promote the stability and motor function of the knee joint and enable athletes to return to training and competition earlier, thus reducing the loss of athletic ability and its impact on their careers [9]. Therefore, exploring effective rehabilitation methods is particularly important for martial arts athletes.

The restoration of complete knee range of motion is considered an important goal in rehabilitation after ACL reconstruction. In recent years, with the continuous improvement of surgical techniques, modern ACL reconstruction surgeries have been able to achieve knee stability earlier and effectively reduce postoperative discomfort [10]. However, despite surgical repair of structural damage, postoperative patients may still face knee instability and functional deficits, which are often closely related to early rehabilitation measures [11]. In order to promote the early return of patients to normal activities, knee supports are widely used in the rehabilitation process. In clinical practice, knee supports are usually classified into preventive, rehabilitative, and functional supports based on functional needs. Studies have shown that functional braces, especially personalized braces for post-ACL reconstruction, can effectively provide stabilizing support and promote range of motion and stability of the knee joint to a certain extent [12,13].

In addition to the assistance of knee braces, resistance training has been widely used in the rehabilitation process after ACL reconstruction as an effective means of recovery. Resistance training helps to restore the strength, stability, and motor function of the knee joint, and studies have shown that resistance training can significantly improve knee function and reduce postoperative complications [14]. However, in the early postoperative phase, it is often difficult to apply sufficient loads to achieve significant improvements with traditional resistance training due to the trauma associated with surgery and its effects on the knee joint. To better address this issue, recent studies have begun to explore the application of sustained mild resistance through functional tasks, such as gait, to help patients gradually regain knee function and reduce the incidence of postoperative complications [15]. This new resistance training strategy is expected to provide a more nuanced and controlled rehabilitation pathway during recovery.

Based on this concept of resistance training, the study of functional rehabilitation supports for knee resistance has received extensive attention in recent years. Such supports help to restore a more normal walking pattern and improve the symmetry of the joint’s moment and range of motion by providing appropriate resistance to knee motion [16]. For example, it has been shown that these braces are effective in increasing the peak flexion angle of the knee, thereby improving the functional performance of the knee [17]. However, despite the significant effect of such supports on postoperative recovery, their potential role in joint coordination has not been fully explored. Joint coordination refers to the precise coordination of multiple joints during movement, which can reflect the functional recovery of the knee after ACL reconstruction and is closely related to the long-term stability of the knee [18]. Therefore, exploring the effects of knee resistance braces on joint coordination holds great research value.

This study aimed to investigate the effect of a knee resistance functional rehabilitation brace on joint coordination after ACL reconstruction. By analyzing the joint movement parameters under different brace conditions, it explored whether these braces are effective in improving joint coordination, thereby promoting the recovery of patients undergoing ACL reconstruction. In addition, the study incorporated neural network modeling to predict ACL loading through simple biomechanical indicators, such as joint angle and coordination, thus providing new ideas and methods for real-time, non-invasive monitoring of ACL loading. This study not only contributes to an in-depth understanding of the role of knee braces in recovery after ACL reconstruction, but also provides a new technical path for ACL load monitoring and prediction, which is of great significance in guiding clinical rehabilitation practice. This study was approved by the Ethics Committee of Guangzhou University.

2. Methods

2.1. Participants

This study adopted a prospective cohort study approach and included 44 martial arts athletes aged between 18 and 30 years who underwent anterior cruciate ligament (ACL) reconstruction surgery as the research subjects (see

Table 1. Demographic information of the participants.

	Experimental Group (n = 22)	Control Group (n = 22)
Gender	50% female	50% female
Age (years)	26.4 ± 6.3	27.3 ± 5.9
Height (cm)	170.7 ± 7.9	171.3 ± 8.1
Weight (kg)	66.2 ± 8.7	67.1 ± 8.5
Training Experience (years)	12.1 ± 5.9	13.3 ± 6.7
Muscle Diameter—Rectus Femoris (cm)	2.1 ± 0.9	2.2 ± 0.8
Muscle Diameter—Vastus Lateralis (cm)	1.6 ± 0.2	1.7 ± 0.3
Muscle Diameter—Vastus Medialis (cm)	1.3 ± 0.3	1.4 ± 0.4

). The inclusion criteria were as follows: unilateral isolated ACL rupture, the surgical method was autologous double-bundle semitendinosus and gracilis tendon reconstruction of ACL, the patients could actively cooperate to complete various tests and follow-up during the research period after the operation, they had full active knee joint range of motion, and there were no joint locking and knee joint swelling phenomena.

The exclusion criteria included the following: combined with other severe knee joint injuries, such as meniscus tears, collateral ligament injuries, etc.; suffering from systemic diseases that affect motor function, such as neurological diseases, severe cardiovascular diseases, etc.; and a history of bilateral knee surgery intervention in the past.

In terms of sample size calculation, G power software 3.1 was used to conduct a priori power analysis. The significance level was set at α = 0.05, the power was set at 80%, and the effect size was set at 0.2. The analysis showed that at least 20 subjects were required in each group, and the sample size of this study met the minimum requirements.

2.2. Study Design

Using the random number table method, the 44 recruited martial arts athletes were randomly and evenly divided into an experimental group (EG) and a control group (CG), with 22 subjects in each group. The experimental group used a resistive knee brace (RehaBrace, FGP S.R.L., Dossobuono, Italy), which could generate a force of 2.5 kg; the control group used a traditional functional brace with a range of motion of 0–120 degrees (DA334-7, Shaanxi, China). In the first 15 days after the operation, both the EG and CG patients locked the brace in full knee extension, and the brace was unlocked 15 days after the operation to carry out range-of-motion training (see Figure 1).

2.3. Rehabilitation Program

All subjects received a standardized physical therapy program and a standardized walking treatment.

• Standardized Physical Therapy Program: Conducted 5 times a week for 8 consecutive weeks. The specific content covers passive joint movement training, straight-leg raising training, quadriceps femoris electrical stimulation treatment, and knee joint range-of-motion restoration training.
• Standardized Walking Program: Conducted 2–3 times a week, spanning from the 3rd to the 8th week, for a total of 6 weeks. Walk on a treadmill at a speed of 1 m/s, rest for 2 min after every 3 min of walking, and complete 6 rounds in total. Warm up the knee joints for 5 min before walking, and take appropriate rest after the end. The total duration of each session was 40 min (see Figure 2).

2.4. Evaluation Time Points

• Pre-operation (T0): Before the operation, baseline data were comprehensively collected from all subjects, including basic physical indicators (height, weight, BMI, etc.), knee joint function evaluation, and joint range-of-motion measurement.
• 15 days after operation (T1): Evaluation of changes in knee joint range of motion. At the same time, a comprehensive joint coordination assessment was carried out on the subjects.
• 30 days after operation (T2): Evaluation of changes in knee joint range of motion was carried out again.
• 60 days after operation (T3): Evaluation of changes in knee joint range of motion. At the same time, a comprehensive joint coordination assessment was carried out on the subjects, and the joint forces and ACL forces were estimated with the help of a musculoskeletal model.

2.5. Data Collection and Analysis

2.5.1. Knee Joint Range-of-Motion Measurement

A high-precision electrogoniometer was used to measure the knee joint range of motion of the subjects during natural gait walking. During the measurement, the electrogoniometer was accurately placed on the knee joint of the lower limb under study, ensuring that the two sensors of the electrogoniometer were strictly aligned with the axes of the thigh and the calf to ensure that the measurement data could accurately reflect the knee joint angle. Based on the ground reaction force (GRF) data obtained from the force platform, the state of the knee joint at the initial stage of gait was deeply analyzed. When the GRF reached 10 N, the time point was accurately determined as the heel contact time on the force platform.

2.5.2. Joint Coordination Analysis

A three-dimensional motion capture system (Qualisys system) was used to collect the kinematic data of the lower limb joints of the subjects during natural gait walking. The system is equipped with 8 infrared cameras, and the sampling frequency is 200 Hz. In total, 48 reflective markers were precisely pasted on the skin of the subjects. The pasting positions include the left and right acromioclavicular joints, iliac crests, greater trochanters, medial and lateral epicondyles of the knee joint, medial and lateral malleoli, and the first and fifth metatarsal heads. In addition, there are the anterior superior iliac spine, posterior superior iliac spine, a rigid plate with four markers connected to the thoracic spine, bilateral thighs, and the lower legs with elastic Velcro straps, as well as three marker-rigid plates connected to the heels. The kinematic data reduction was calculated using Visual 3D software (https://www.visual-3d.com/ (accessed on 30 March 2025)). The original kinematic and kinetic data were filtered using a fourth-order, zero-lag recursive Butterworth filter with a cut-off frequency of 20 Hz. Using the angle–angle diagram to construct the vector of the angle between any two segments in the time series, the coupling angle was accurately calculated. The coupling angle is the angle of this vector relative to the horizontal line, ranging from 0° to 360°. Based on the improved vector coding technology, the changes in joint coordination during the gait cycle were deeply analyzed, specifically including the coordination between the hip–knee joint, hip–ankle joint, and knee–ankle joint (see Figure 3) [18].

Classification of Coordination Modes (Figure 4):

• In-Phase Coordination: When the coupling angle is in the range of 22.5° to 67.5° or 202.5° to 247.5°, it indicates that the two segments rotate synchronously in the same direction.
• Antiphase Coordination: When the coupling angle is in the range of 112.5° to 157.5° or 292.5° to 337.5°, it indicates that the two segments rotate in opposite directions.
• Proximal Phase Coordination: When the coupling angle is in the range of 157.5° to 202.5° or 337.5° to 360°, it indicates that the movement mainly occurs in the proximal segment.
• Distal Phase Coordination: When the coupling angle is in the range of 67.5° to 112.5° or 247.5° to 292.5°, it indicates that the movement mainly occurs in the distal segment.

2.5.3. Musculoskeletal Model

A Kistler three-dimensional force platform was used to synchronously collect the ground reaction force (GRF) at a frequency of 1000 Hz, and kinetic data reduction was carried out using Visual 3D software. The musculoskeletal modeling in OpenSim (Simtk.org) software was used to generate the motion files and meet the subject scaling requirements. A general musculoskeletal model with 23 degrees of freedom (DOF) driven by 92 Hill-type muscle–tendon units was constructed, and it was scaled according to the anthropometric data of each subject to make the model highly match the physical characteristics of the subjects. The model was optimized using the Residual Reduction Algorithm (RRA), and its mass properties and kinematic parameters were finely adjusted. The Computed Muscle Control (CMC) algorithm was used to determine muscle excitation, and a forward dynamic simulation of the participants’ landing kinematics was carried out. Joint reaction force (JRF) analysis was carried out in OpenSim to obtain the net knee joint JRFs. Finally, the muscle forces and knee joint JRFs obtained were input into the sagittal plane knee joint model developed by Kernozek and Ragan to accurately calculate the ACL force (F_ACL).

The specific process is as follows (Figure 5) [19]:

1.

Calculation of Tibiofemoral Contact Force (F_tf)

$$F_{\parallel }=F_{tf}\cdot \cos {\phi }_{tf}-F_{pat}\cdot \cos {\phi }_{pat}-F_{ham}\cdot \cos {\phi }_{ham}-F_{gas}$$

Parameter Explanation:

$F_{\parallel }$: Net axial force.

F_tf: Tibiofemoral contact force, which is the solution target of this formula.

φ_tf: Tibial posterior slope angle. According to previous literature, it is set to 8.5°.

F_pat: The sum of all quadriceps muscle strength estimates.

φ_pat: The tendon angle of the patellar tendon force (quadriceps) depending on the knee flexion angle.

F_ham: The sum of all hamstring muscle strength estimates.

φ_ham: The tendon angle of the hamstring depending on the knee flexion angle.

F_gas: The sum of the medial and lateral gastrocnemius muscle strength estimates.

2.

Calculation of the Anterior–Posterior Shear Force on the Knee Ligament (F_ligament)

$$F_{AP}=F_{tf}\cdot \sin {\phi }_{tf}+F_{pat}\cdot \sin {\phi }_{\mathit{pat}}-F_{\mathit{ham}}\cdot \sin {\phi }_{\mathit{ham}}+F_{\mathit{ligament}}$$

Parameter Explanation:

F_AP: Net anterior–posterior (AP) shear force.

F_ligament: The anterior–posterior shear force on the knee ligament, which is the solution target of this formula.

3.

Calculation of ACL Force (F_ACL)

$$F_{ACL}=N\left(F_{100N}+F_0\left({\theta }_{\mathit{knee}}\right)\right)$$

Parameter Explanation:

N: Proportional coefficient.

F_100N: The ACL force reported when a 100 N anterior tibial force is applied and the corresponding knee joint angle is θ_knee.

F₀: The ACL force reported when no anterior tibial force is applied and the corresponding knee joint angle is θ_knee.

θ_knee: Knee joint angle.

2.6. Statistical Analysis

The Shapiro–Wilk test was used for the normality analysis of the data. A mixed-design analysis of variance (ANOVA) was performed on the knee joint range of motion to evaluate the main effects of time (T0, T1, T2, and T3), group (CG × EG), and their interaction (time × group). The post hoc analysis adopted the Bonferroni correction method. Due to the limitations imposed by ethical and health-first principles, only the joint coordination at T1 and T3 as well as the anterior cruciate ligament (ACL) load at T3 were available for analysis. Therefore, due to the non-normal distribution of the data, non-parametric testing (Mann–Whitney U) was employed to analyze joint coordination. Additionally, a T-test was utilized to compare the differences in ACL between the different groups. Statistical analysis was carried out using SPSS (version 21.0, IBM, Chicago, IL, USA), and the significance level of α was set at 0.05.

3. Results

Table 2. Influence of different knee braces on the maximum range of motion during the knee support phase.

	EG	CG	p	ES	Group × Time
T0	45.6 ± 6.9	43.2 ± 6.2	1.000	0.063	p = 0.005 ES = 0.275
T1	13.2 ± 8.8	16.1 ± 9.0	0.297	0.026
T2	34.4 ± 6.6	25.4 ± 7.4	0.000	0.292
T3	47.1 ± 7.3	37.7 ± 8.8	0.001	0.253
p	0.000	0.000
ES	0.830	0.775

and Figure 6 illustrate the impact of different knee braces on the maximum range of motion of the knee joint. The research findings indicate a significant interaction effect between the group and time (F = 5.063, p = 0.005, ES = 0.275). The analysis of the simple effects of the group shows that at time point T2, the experimental group (EG) is significantly higher than the control group (CG) (p = 0.000, ES = 0.292), and at time point T3, EG is also significantly higher than CG (p = 0.001, ES = 0.253). The analysis of the simple effects of time reveals that for both EG and CG, compared with T0, there are significant differences in the joint range of motion at time points T1 and T2 (p < 0.05). However, the difference between T0 and T3 is not significant (p > 0.05).

The results of

Table 3. Influence of different knee braces on lower limb joint coordination at time point T1.

	In-Phase	Antiphase	Proximal Phase	Distal Phase
Hip–ankle
CG	14.55 ± 10.31	25.51 ± 5.68	39.74 ± 12.53	20.20 ± 9.99
EG	15.32 ± 10.52	23.43 ± 5.18	39.51 ± 14.84	22.74 ± 9.88
p	0.705	0.060	0.423	0.862
Hip–knee
CG	25.77 ± 11.63	17.70 ± 5.72	14.47 ± 5.58	42.02 ± 15.84
EG	26.64 ± 11.43	17.74 ± 5.85	14.67 ± 6.63	40.95 ± 15.73
p	0.728	0.537	0.492	0.587
Knee–ankle
CG	4.34 ± 3.65	13.27 ± 5.89	58.66 ± 9.37	23.73 ± 12.64
EG	3.41 ± 2.64	14.43 ± 5.79	59.95 ± 8.29	22.21 ± 12.39
p	0.160	0.926	0.979	0.467

demonstrate that at time point T1, there are no significant differences in joint coordination across all joints between the two groups. At T3, compared with CG, EG exhibits higher hip–ankle in-phase coordination (p = 0.013), increased proximal hip–knee coordination (p < 0.001), and reduced knee–ankle anti-phase coordination (p = 0.028) (see

Table 4. Influence of different knee braces on lower limb joint coordination at time point T3.

	In-Phase	Antiphase	Proximal Phase	Distal Phase
Hip–ankle
CG	24.63 ± 10.12	15.85 ± 5.35	39.96 ± 6.98	19.56 ± 10.76
EG	31.51 ± 6.13	15.25 ± 5.72	38.63 ± 6.69	14.61 ± 10.72
p	0.013	0.292	0.202	0.483
Hip–knee
CG	38.89 ± 12.35	7.69 ± 4.64	4.44 ± 2.85	48.98 ± 16.48
EG	39.77 ± 10.51	6.79 ± 4.49	7.26 ± 1.47	46.18 ± 15.70
p	0.164	0.958	<0.001	0.968
Knee–ankle
CG	3.26 ± 2.91	14.25 ± 5.75	79.28 ± 8.17	3.21 ± 2.33
EG	3.93 ± 2.96	9.16 ± 5.76	83.27 ± 9.15	3.64 ± 2.53
p	0.280	0.015	0.096	0.236

and Figure 7).

The results of

Table 5. Comparison of ACL forces between different groups.

	EG	CG	t	p	ES
FACL	0.51 ± 0.13	0.63 ± 0.17	−2.24	0.030	0.69

Note: The F_ACL was standardized according to the body weight (BW) of the subjects.

show that compared with CG, EG experiences a smaller ACL force during walking at T4 (t = −2.24, p = 0.030, ES = 0.69).

4. Discussion

4.1. Analysis of ACL Recovery

The key finding of this study suggests that the use of a knee brace with resistance has a significant positive impact on rehabilitation after anterior cruciate ligament (ACL) reconstruction, particularly in terms of knee flexion range. Compared with the control group, the experimental group had a greater maximum joint range of motion during the knee support phase, especially during the longer postoperative recovery phase, suggesting that the knee brace with resistance was effective in promoting the recovery of knee range of motion. This improvement may be attributed to the controlled yet progressive resistance, which allows for graded rehabilitation intensity, thereby optimizing tissue adaptation without overloading healing structures—a critical factor in moderate to severe ACL injuries [20]. Compared with the results of previous studies, the present study provides more significant supporting evidence. It has been noted that although ordinary knee braces are helpful for recovery after ACL, their effect is more limited, especially in the longer-term recovery process, where they fail to significantly improve the joint range of motion [21]. This discrepancy may stem from differences in rehabilitation intensity, as traditional braces provide passive support rather than active resistance-based stimulation, which is particularly beneficial for patients with higher baseline impairment levels [22].

In this study, the knee brace with resistance showed significant advantages at the T2 and T3 moments, and especially at the T3 moment, the knee range of motion of the experimental group was significantly higher than that of the control group, which is consistent with the findings of previous studies. However, previous studies have usually failed to observe such a significant difference, especially at the time point after one month postoperatively [23]. One possible explanation is that earlier research often included heterogeneous patient populations with varying injury severity, whereas our study’s protocol emphasized controlled resistance progression, which may have amplified functional gains in patients with more pronounced initial deficits. The results of the present study suggest that the band resistance knee brace was able to perform better one month postoperatively, contributing to accelerated recovery of joint function, especially in terms of the ability to flex the knee [24]. This improved effect may be related to the design principle of the resisted brace, which strengthens the muscles around the knee joint by providing moderate resistance, which in turn helps to restore joint stability and range of motion [25]. Notably, the resistance levels in our study were tailored to individual tolerance, ensuring that rehabilitation intensity aligned with tissue healing stages—an approach that may explain the superior outcomes compared to fixed-support bracing in prior work [26].

4.2. Joint Coordination Analysis

Our findings revealed that while no significant differences existed in joint coordination between the experimental (EG) and control groups (CG) at T1, the EG demonstrated superior hip–ankle isotropic coordination, stronger proximal hip–knee coordination, and reduced knee–ankle inversion coordination at T3, indicating the positive effect of resistance-enhanced bracing on joint coordination. This improvement was particularly evident in patients with moderate to severe ACL injuries [27], where progressive resistance provided optimal rehabilitation intensity to restore neuromuscular control without compromising healing tissues. The observed transition to more isotropic and proximal movement patterns with reduced inversion coordination suggests improved force transmission and movement synergy, with the resistance brace effectively addressing the coordination deficits typically seen in higher-grade ACL injuries [28]. The significant reduction in knee–ankle inversion coordination points to enhanced gait mechanics and joint stability [29], which are crucial for postoperative rehabilitation, particularly for cases requiring higher rehabilitation intensity due to greater initial impairment [30]. While previous studies have shown that resisted bracing improves knee-specific motor control [31], our study extends these findings by demonstrating comprehensive lower-limb coordination benefits, a critical advancement given that most prior research failed to account for injury severity when assessing coordination outcomes [32]. Importantly, unlike earlier studies that used restrictive rigid braces [33]—which may artificially alter coordination patterns [34] and are particularly unsuitable for patients with severe injuries requiring progressive mobility—our matched-mobility design isolated the specific effects of resistance. This methodological refinement explains why we detected coordination improvements where previous studies using conventional bracing protocols did not [35], particularly in the crucial 2-month postoperative window when rehabilitation intensity needs to be carefully calibrated to injury recovery status. Our findings not only validate the clinical utility of resistance bracing but also highlight its particular value for patients with greater baseline impairment who require graduated, intensity-adjusted rehabilitation approaches.

In addition, the choice of time point also appears to be particularly important. Previous studies have mostly assessed joint coordination at the T0 time point, the early stage after surgery, when patients are more affected by joint injuries, and it may be difficult to accurately differentiate the effects of the intervention. Instead, we chose to assess joint coordination at T1 and compare the results with those at T3, which provided more convincing data to support the study. At T1, there was no significant difference in joint coordination between the intervention and control groups, suggesting that joint coordination may be affected by both injury and rehabilitation during the initial postoperative rehabilitation phase. In contrast, at T4, after two months of intervention, the experimental group showed a significant improvement in joint coordination, further demonstrating the facilitating effect of the knee brace and its increased resistance on the recovery of joint coordination. Our study reveals the significant impact of knee braces with resistance on joint coordination recovery. Specifically, the experimental group appeared to have better joint coordination within 2 months postoperatively, especially in terms of improvement in isotropic coordination, proximal coordination, and reduction in reverse coordination, which provides strong support for functional rehabilitation after ACL reconstruction. This finding provides a new theoretical basis for the clinical application of knee braces, as well as new perspectives and ideas for future related research.

4.3. Force Simulation

The results of this study demonstrated that the functional rehabilitation brace with resistance significantly reduced ACL forces in martial arts athletes’ post-reconstruction, with the experimental group (EG) showing markedly decreased ACL loading during walking at T4 compared to the controls (CG). This protective effect was particularly pronounced in athletes with high-grade ACL injuries [36], where the progressive resistance provided optimal rehabilitation intensity to restore joint stability without compromising graft healing. The skeletal muscle model analysis confirmed the brace’s effectiveness in reducing ACL forces under controlled conditions, with greater force reduction observed in cases of more severe initial ligament damage [37], suggesting that the resistance brace’s load-modulating capacity is particularly beneficial for high-intensity rehabilitation protocols. These improvements likely stem from enhanced joint coordination and stability, as the resistance brace promotes more controlled movement patterns while allowing graded return to functional activity–a critical advantage over traditional braces that often fail to provide this intensity progression, especially for athletes requiring sport-specific rehabilitation [38]. Our findings align with previous research showing that functional braces reduce ACL loading [39], but importantly extend these observations by demonstrating that resistance bracing offers superior protection during dynamic movements, particularly during the critical return-to-sport phase when rehabilitation intensity must be carefully matched to tissue healing status [40]. While conventional braces primarily limit excessive motion [41], our resistance brace actively enhances neuromuscular control, making it especially valuable for patients with greater baseline impairment who require both protection and progressive challenge during rehabilitation. This study provides compelling evidence that resistance bracing represents an important advancement in ACL rehabilitation, particularly for high-demand athletes, where precise control of rehabilitation intensity is crucial for successful return to pre-injury performance levels.

Research recommendation: Future research could further explore how to optimize the skeletal muscle model to improve the simulation accuracy of ACL forces, especially under more complex movement patterns and a wider range of individual difference conditions.

5. Conclusions

This study demonstrated that a knee brace with resistance significantly facilitated the recovery of knee flexion range and joint coordination during rehabilitation after anterior cruciate ligament (ACL) reconstruction. In particular, during the longer postoperative recovery phase, the experimental group demonstrated greater knee range of motion and better joint coordination with the use of a band resistance brace, especially in terms of a significant reduction in knee–ankle reverse coordination, optimizing force transmission and joint stability. These findings emphasize the potential of resistance-bearing braces in accelerating functional recovery of the knee.