The Effects of Fatigue on the Lower Limb Biomechanics of Amateur Athletes during a Y-Balance Test

-Balance Test (YBT) is a reliable tool for assessing the dynamic balance of athletes' lower limbs. This study aimed to compare the effects of the YBT on lower limb biomechanics before and after fatigue. Sixteen adult male recreational athletes were recruited for the study, and motion capture in combination with a force plate was used to collect kinematic, dynamics, and center of pressure (COP) data of the dominant leg during YBT testing before and after fatigue. Based on the research ndings, there were signi cant statistical differences in the distances reached during the YBT in three directions before and after fatigue. After fatigue, there is a signi cant decrease in the ROM of the hip and knee joints in all three directions. Also, there is a signi cant increase in hip joint torque in

after fatigue. Based on the research ndings, there were signi cant statistical differences in the distances reached during the YBT in three directions before and after fatigue. After fatigue, there is a signi cant decrease in the ROM of the hip and knee joints in all three directions. Also, there is a signi cant increase in hip joint torque in the anterior- and posterior-lateral directions, while a signi cant decrease in hip and ankle joint torque is observed in the posterior-medial direction. Moreover, there is an increasing trend in positive and negative joint work for the hip, knee, and ankle joints in all three directions after fatigue. The range of COP displacement also increases following fatigue. The decline in YBT scores demonstrates the detrimental impact of fatigue on the dynamic balance of the lower limbs of adult male amateur athletes. We hope that these results can provide information for athletes and coaches to better understand the effects of fatigue on the dynamic balance of lower limbs, so as to carry out targeted lower limb balance training and prevent sports injuries. Keywords:Y Balance Test; fatigue; lower extremity; kinematic; dynamics 1. Introduction Balance is a critical component of athletic performance and injury prevention for athletes, and a lack of balance is closely associated with an increased risk of lower limb injuries [1]. Therefore, balance is of utmost importance for athletes, as it signi cantly impacts the quality of their training and competitive performances [2]. Balance, as an ability, has been de ned as comprising two conditions, static and dynamic balance. Static balance refers to the ability of the human body to maintain posture or stability and to control its center of gravity in a relatively stationary state [3–5]. Dynamic balance refers to the ability of the human body to automatically adjust and maintain posture and control balance when moving or being subjected to external forces [6]. Since most sports are performed under dynamic conditions, dynamic balance is one of the most important factors in uencing daily activities and sports performance. There are several eld tests that exist to obtain data of the

the ability of the human body to automatically adjust and maintain posture and control balance when moving or being subjected to external forces [6]. Since most sports are performed under dynamic conditions, dynamic balance is one of the most important factors in uencing daily activities and sports performance. There are several eld tests that exist to obtain data of the dynamic balance of an athlete, and the Y-Balance test (YBT) is one of the most widely accepted methods for assessing dynamic postural stability [7–9]. It is a cost-effective and commonly used objective Healthcare2023,11, 2565.

Healthcare2023,11, 2565 2 of 13 measurement method for assessing lower extremity dynamic balance, functional symmetry, and stability [9–12]. The YBT can evaluate an individual's performance in terms of muscle coordination, stability, and symmetry in three directions: anterior (A), posterolateral (PL), and posteromedial (PM). In the YBT, participants are required to maintain single-leg balance while reaching as far as possible with the other leg in three different directions. By observing the maximum reach distances in three directions and the degree of COP displacement, we can make a reasonable assessment of athletes' dynamic balance capabilities [13]. Achieving balance requires the coordinated integration of sensory inputs, central processing, and motor control. Visual acuity, vestibular organs, the nervous system, muscle strength, and proprioception all play crucial roles in maintaining body balance [14–16]. Among these factors, the activity of the lower limb muscles is particularly critical for sustaining dynamic balance in athletes. Previous studies have shown that muscle fatigue is an important in uencing factor in sports injuries and is also involved in decreases in dynamic balance ability [16–18]. Muscle fatigue refers to a decline in the ability of muscles to maintain or produce the expected force. Traditionally, muscle fatigue has been de ned as a reduction in maximal strength or power induced by exercise [19]. Rose et al. [20] found signi cant differences in balance levels between fatigued and non-fatigued states among athletes. Both local and whole-body fatigue can result in de- creased postural control performance, manifested as increased postural sway, which in turn disrupts the body's balance and stability [21]. Previous studies have indicated that maximal anaerobic fatigue has a negative impact on athletes' YBT scores [22]. Nader Abdelkader et al. [23] found that inducing fatigue during YBT measurements has inconsistent effects on the dynamic balance among different athletic populations. Following fatigue, the dynamic balance of professional athletes is better than that of amateur athletes. In the professional athletic population, a study by Ross Armstrong et al. [24] found that professional dancers' YBT performances were not affected by fatigue induced by aerobic tness testing (DATF). However, in the recreational sports population, Majid et

the dynamic balance among different athletic populations. Following fatigue, the dynamic balance of professional athletes is better than that of amateur athletes. In the professional athletic population, a study by Ross Armstrong et al. [24] found that professional dancers' YBT performances were not affected by fatigue induced by aerobic tness testing (DATF). However, in the recreational sports population, Majid et al. [25] discovered that fatigue decreased all functional test scores and lower limb muscle activity levels in amateur athletes during the YBT. The ndings demonstrated a signi cant impact of fatigue on dynamic balance in amateur athletes. Currently, several studies have investigated the impact of lower limb fatigue on athletes' balance abilities. However, there was a relative lack of speci c research focusing on the changes in lower limb biomechanical parameters during the YBT in athletes. Therefore, the main objective of this study was to explore the biomechanical variations in the dominant supporting leg of adult recreational athletes during the YBT process, before and after inducing muscular fatigue. We hypothesized that fatigue would signi cantly in uence the biomechanical characteristics of the lower limbs, particularly leading to increased hip and knee joint torques and increased work for the supporting leg. Additionally, we posited that fatigue might have also increased the length of the COP path of the lower extremities. 2. Materials and Methods 2.1. Participants Effect sizes were calculated from previous research with methods that closely resem- bled this study [26]. Based on the a priori sample size calculation conducted using G*Power 3.1.7 [27], a minimum sample size of 16 participants was required to detect signi cant differences in YBT before and after fatigue (power: 0.8, effect size: 0.80, = 0.05, and = 0.2). In this study, we recruited 16 recreational athletes (22 1.8 yrs, 179.8 3.4 cm, and 78.6 6.9 kg) from the School of Physical Education at Ningbo University. These partici- pants engaged in at least 1–2 h of physical exercise daily and had a history of regular sports training for at least 6 years, with 2–3 exercise sessions per week. To ensure the accuracy of the research

recreational athletes (22 1.8 yrs, 179.8 3.4 cm, and 78.6 6.9 kg) from the School of Physical Education at Ningbo University. These partici- pants engaged in at least 1–2 h of physical exercise daily and had a history of regular sports training for at least 6 years, with 2–3 exercise sessions per week. To ensure the accuracy of the research results, we excluded individuals with a history of neurological or muscular diseases, lower limb fractures or surgeries within the past six months, and ankle sprains within the last year. All tests were conducted in the laboratory of the Faculty of Sports

Healthcare2023,11, 2565 3 of 13 Science at Ningbo University. Prior to the study, the participants were provided with de- tailed information about the entire experimental procedure and all signed informed consent forms. The Ethics Committee of the Ningbo University Research Institute approved the study (RAGH202305013005.2), which was performed in accordance with the Declaration of Helsinki [28]. 2.2. Experimental Design Before the formal experiment, participants underwent a 5 min warm-up activity on a motorized treadmill. Participants were tested before and after performing the fatigue protocol. Before the measurement, the participants were familiarized with YBT by prac- ticing the test on their dominant limb (determined by asking the participants which leg they would use to kick a ball). The YBT was conducted on a force plate, and black tape was used to mark the Y-shaped test positions on the force plate. The standing leg remained on the force plate during the whole task while the other leg performed error-free maximum arrival movements along the calibrated black tape in all three directions. The maximum distances reached in the anterior, posteromedial, and posterolateral directions related to the stance leg were recorded using a tape measure [29]. During the test, the participants kept their hands on their waists, and each direction was repeated three times with a 10 s rest in between each trial (Figure). After completing the fatigue protocol, the same testing procedures were repeated [25,30].Healthcare 2023, 11, x FOR PEER REVIEW 3 of 13 In this study, we recruited 16 recreational athletes (22 ± 1.8 yrs, 179.8 ± 3.4 cm, and 78.6 ± 6.9 kg) from the School of Physical Education at Ningbo University. These partici- pants engaged in at least 1–2 h of physical exercise daily and had a history of regular sports training for at least 6 years, with 2–3 exercise sessions per week. To ensure the ac- curacy of the research results, we excluded individuals with a history of neurological or muscular diseases, lower limb fractures or surgeries within the past six months, and ankle sprains within the last year. All tests were conducted in the laboratory of the Faculty

sports training for at least 6 years, with 2–3 exercise sessions per week. To ensure the ac- curacy of the research results, we excluded individuals with a history of neurological or muscular diseases, lower limb fractures or surgeries within the past six months, and ankle sprains within the last year. All tests were conducted in the laboratory of the Faculty of Sports Science at Ningbo University. Prior to the study, the participants were provided with detailed information about the entire experimental procedure and all signed in- formed consent forms. The Ethics Committee of the Ningbo University Research Institute approved the study (RAGH202305013005.2), which was performed in accordance with the Declaration of Helsinki [28]. 2.2. Experimental Design Before the formal experiment, participants underwent a 5 min warm-up activity on a motorized treadmill. Participants were tested before and after performing the fatigue pro- tocol. Before the measurement, the participants were familiarized with YBT by practicing the test on their dominant limb (determined by asking the participants which leg they would use to kick a ball). The YBT was conducted on a force plate, and black tape was used to mark the Y-shaped test positions on the force plate. The standing leg remained on the force plate during the whole task while the other leg performed error-free maximum arrival movements along the calibrated black tape in all three directions. The maximum distances reached in the anterior, posteromedial, and posterolateral directions related to the stance leg were recorded using a tape measure [29]. During the test, the participants kept their hands on their waists, and each direction was repeated three times with a 10 s rest in between each trial (Figure 1). After completing the fatigue protocol, the same test- ing procedures were repeated [25,30]. If the following situations occurred during the testing process, the participants needed to complete the test again: (1) the supporting leg deviates from the central area of the YBT system; (2) the heel of the supporting leg is off the ground; (3) instability of the center of gravity, leading to the reaching leg touching the ground; (4) the reaching

[25,30]. If the following situations occurred during the testing process, the participants needed to complete the test again: (1) the supporting leg deviates from the central area of the YBT system; (2) the heel of the supporting leg is off the ground; (3) instability of the center of gravity, leading to the reaching leg touching the ground; (4) the reaching leg cannot return smoothly to the starting position; (5) the participant puts their body weight on the reaching leg during maximum reach; (6) and significant swinging of the upper limbs during the test. If the test was abandoned, a new round of testing was conducted until the participant completed three successful trials in each direction [30]. Figure 1. (1) The participants performing the Y-Balance test. (A) Participant demonstrating the Y- Balance Test in the anterior direction. (B) Participant demonstrating the Y-Balance Test in the pos- terolateral direction. (C) Participant demonstrating the Y-Balance Test in the posteromedial direc- tion. (2) A flow chart was created to outline the data collection and processing. 2.3. Fatigue Protocol Figure 1. (1) The participants performing the Y-Balance test. (A) Participant demonstrating the Y-Balance Test in the anterior direction. (B) Participant demonstrating the Y-Balance Test in the posterolateral direction. (C) Participant demonstrating the Y-Balance Test in the posteromedial direction. (2) A ow chart was created to outline the data collection and processing. If the following situations occurred during the testing process, the participants needed to complete the test again: (1) the supporting leg deviates from the central area of the YBT system; (2) the heel of the supporting leg is off the ground; (3) instability of the center of gravity, leading to the reaching leg touching the ground; (4) the reaching leg cannot return smoothly to the starting position; (5) the participant puts their body weight on the reaching leg during maximum reach; (6) and signi cant swinging of the upper limbs during the test. If the test was abandoned, a new round of testing was conducted until the participant completed three successful trials in each direction [30]. 2.3. Fatigue Protocol To induce fatigue, participants were

the starting position; (5) the participant puts their body weight on the reaching leg during maximum reach; (6) and signi cant swinging of the upper limbs during the test. If the test was abandoned, a new round of testing was conducted until the participant completed three successful trials in each direction [30]. 2.3. Fatigue Protocol To induce fatigue, participants were asked to perform squatting until exhaustion at a controlled pace of 2 s per squat. Participants were instructed to perform the following steps: Start with fully extended knees, standing upright, arms akimbo. Then, bend the knees to approximately 130 for the squatting motion and then extend the knee to the starting position for under 2 s. A metronome was used to give feedback to the participants and ensure the pace of squatting [31,32]. During the implementation of the fatigue protocol, participants' heart rates and Rating of Perceived Exertion on the Borg Scale (6–20 scale) were recorded. The fatigue protocol was stopped when all of the following criteria were

Healthcare2023,11, 2565 4 of 13 met: 1. The participant's heart rate exceeded 90% of their age-calculated maximum heart rate (HRmax = 220). 2. The participant was unable to maintain the original squat frequency. 3. The Borg Scale rating exceeded RPE > 17 (very hard) [33]. In our study, each partici- pant performed a minimum of 50 squats [34]. To ensure that participants were still in a fatigued state, the YBT was immediately repeated after nishing the squats. The fatigue protocol used focused on muscle fatigue in the lower limbs, and the motions of the squat in the fatigue protocol were similar to those of supporting the leg on the dominant side during YBT. 2.4. Instruments During the testing process, a total of 38 optical markers with a diameter of 14 mm were used. These markers were attached to the anatomical locations of the participants based on the Gait2392 muscle-skeletal model, and the same operator consistently placed the markers. The movement trajectories of the markers were recorded using an eight-camera Vicon motion capture system (Vicon Metrics Ltd., Oxford, UK) at a sampling frequency of 1000 frames per second [35,36]. Ground reaction forces and COP measurements were obtained using an embedded Kistler force platform (Kistler Force Platform System 92-81B, Winterthur, Switzerland) xed in the center of the oor, with a sampling frequency of 200 Hz[37]. Before each experiment, the cameras and laboratory setup were calibrated to ensure stable marker trajectories and minimize noise interference. All participants were instructed to wear standardized tight shorts and were barefoot during the testing process. 2.5. Data Processing and Analysis The standardization of YBT scores was calculated by dividing each reach distance by the participant's leg length and multiplying it by 100 [22]. To optimize the model for individual segment lengths, a static standing pose was recorded before recording marker displacements during YBT. The marker trajectories were smoothed with a 12 Hz low-pass Butterworth lter [38]. The angular displacement of the joints was calculated for each stride using inverse kinematics in Opensim (SimTK v. 4.0.1). The standard inverse dynamics method was utilized to calculate the joint movements,

for individual segment lengths, a static standing pose was recorded before recording marker displacements during YBT. The marker trajectories were smoothed with a 12 Hz low-pass Butterworth lter [38]. The angular displacement of the joints was calculated for each stride using inverse kinematics in Opensim (SimTK v. 4.0.1). The standard inverse dynamics method was utilized to calculate the joint movements, and the joint work was computed based on both inverse kinematics and inverse dynamics. All joint dynamics data were normalized by the participant's body weight [39]. Subsequently, the kinematic and dynamics parameters of the joints were normalized into 101 data points. COP path, distance, and the area of the circle, which contains 95% of the data, were calcu- lated from the force plate data using a custom-written Matlab script [38]. The kinematic and dynamics data sets were time-normalized to the stance phase (0–100%) for each participant, allowing for time-series comparisons. The dynamics variables were normalized to body weight, and the COP was adjusted for leg length to minimize the in uence of height [40]. 2.6. Statistical Analysis The experimental data were processed using SPSS 26.0 software (IBM, Armonk, NY, USA). The Shapiro–Wilk test was applied to ensure the normality of the data. Paired-sample t-tests were used to compare the kinematic, dynamics, and COP activities of the supporting leg before and after fatigue. A signi cance level ofp 0.05 was considered statistically signi cant. The data are presented as mean values standard deviation [25]. 3. Results 3.1. Score of the YBT Before and after fatigue, the scores of the YBT in three directions are shown in Table.

This study investigates the impact of fatigue on lower limb biomechanics in amateur athletes during the Y-Balance Test.