Virtual reality and functional training effect on contractile properties of lower leg muscles and postural stability

Background and purpose. Tensiomyography is a noninvasive and reliable method to identify the differences in skeletal muscle responses. Poor lower leg muscles cause poor postural stability, leading to the risk of injury in athletes. The study aims to investigate the aftereffect of a six-week virtual reality environment and functional training program on the contractile properties of lower-leg muscles and postural stability index. Material and methods . A comparative pre-test and post-test study design was selected for this study. Twenty-four male athletes were taken part in the study. The participants were randomly divided into a virtual reality intervention-training group (n=12) or a functional training group (n=12). The virtual reality environment training was provided using the CAREN integrated virtual reality system with a D-flow application from Motek. Functional training for static and dynamic postural stability was performed with various open and closed-eye exercises in the physical therapy lab. The contractile properties of lower-leg muscles were measured using tensiomyography. The postural stability index was assessed using a stadiometer. The assessments were performed before and after six weeks of training. A paired sample t-test was used to determine differences between pretest and posttest intervention outcome measures, and sample t-test was also applied to determine differences between groups after six weeks of training. Results . Results indicated significant differences between pretest and posttest measurement in virtual reality training group for displacement (t=2.81, p=.043), (t=-6.92, p=<.001) in gastrocnemius lateral and medial muscle respectively, and sustain time (t=2.29, p=.042) in souls muscle. The postural stability with close eye was significant (t=2.61, p=.024). The functional training group showed significant differences for sustain time (t=-18.86, p=<.001) in gastrocnemius lateral, and relaxation time (=3.24, p=.008), delay time (t=3.07, p=.011), and sustain time (t=-19.74, p=<.001) in gastrocnemius medial, and sustain time (t=3.17, p=.009) in souls muscle. The postural stability was having insignificant differences. Conclusion . The virtual reality environment and functional training, help to improve performance, and tensiomyography could be used to assess and evaluate the parameters that could be helpful for optimizing training load in the performance enhancement process of athletes.


Introduction
The contractile properties of muscle can be determined by Tensiomyography (TMG) by applying an electric stimulus [1].TMG is a simple, noninvasive method for measuring skeletal muscle contractile parameters using a linear displacement sensor [2].TMG can serve as a viable option by measuring several parameters [3].The measurement of muscle contraction time (Tc) and muscle displacement (Dm) can be gained quickly and with minimal input from participants [4].The mechanical adaptation of muscles was determined through TMG with endurance [5] and strength [1] training.The differences in muscle properties between gender in resistance-trained individual were explained to athletes for better performance [6].TMG can be distinguished between different muscles as the effect of the different training programs with its parameters.Many studies have been conducted with TMG to focus on the rehabilitation process and quantification of the muscles' response to training load and injury prevention.Muscle stiffness, weak contraction speed, and muscle belly displacement are some causes of injury in athletes [7].
The functional deficit of lower-leg muscle is an identified factor related to weak postural stability and injury risks [8][9].The functional impairment of the lower leg muscle is one of the main causes to enhance injury risk [10].The stable posture induced by strong muscle activation reduces the degree of freedom [9].The weak lower-leg muscles have deficits in postural stability.Maintaining proper posture is a difficult endeavor that requires the coordination of multiple sensory and motor systems.The visual, vestibular, and somatosensory mechanoreceptors deliver proprioceptive impulses to the central nervous system for processing [11][12][13].A good posture stability is essential for athletic and daily living activities.Among the numerous activities (sudden running, jumps, stops, direction changes, dodges) requiring stable postural control [13].Posture stability is essential to a person's well-being since it reduces the chance of injury during everyday activities and improves athletic performance [8].
Athletes typically utilize balance training to enhance their performance and prevent the atrophy of their calf muscles and other components of their core and postural stability.The investigation of muscle strength and stability following two diverse training methods is essential for shedding light on the mechanisms through which some training methods may be effective.The goal of this study is to investigate the effect of functional training in a virtual reality environment on the lower leg muscles and the dynamic postural stability of athletes.

Design
A comparative pre-test and post-test study design was selected to achieve the objective of this study.This study was conducted in accordance with the Declaration of the Principles of Helsinki.The approval was obtained from the Deanship of Scientific Research.All participants signed informed consent.

Setting
The study was conducted in the laboratory of the Physical Therapy Department, College of Applied Medical Sciences, Imam Abdulrahman bin Faisal University, Dammam, Saudi Arabia

Sample Size calculation
The sample size is calculated using http:// sample size.net/correlation-samplesize/ Data from (López-de-Celis C. et al., 2020) [14] were used to calculate the sample size.The total number of participants was 24 subjects.A virtual reality intervention-training group (n=12) and a functional training group (n=12).The total sample size =24 α (two-tailed) = 0.05 -Threshold probability for rejecting the null hypothesis.Type I error rate.β=0.05 -Probability of failing to reject the null hypothesis under the alternative hypothesis.Type II error rate.

Participants
In this study, the only participants were male athletes who competed at the national level.Participants came from a variety of sporting clubs located in the eastern region, and they were selected at random.Participants were not allowed to take part in the study if they had any ailment affecting their musculoskeletal, neurological, or systemic health, or if they were taking any medication that could have an impact on testing or intervention.

Tensiomyography (TMG):
The contractile properties of the lower-leg muscle as lateralis and medialis gastrocnemius, and soleus muscles were measured using TMG (TMG-BMC Ltd., Ljubljana, Slovenia) at the beginning and end of the six-week training program.
Stadiometer: The postural stability test was conducted before and after completing the sixweek training program.The postural stability index was measured using a stabilometer Prokin 252 (TecnoBody, Italy) with a single leg test.The test was performed using eyes open and closed eyes with 20 stability levels, and a 30-second rest interval was given between each trial.

Procedure
On arrival at the physical therapy lab, before completing the consent form, participants were asked to read the comprehensive protocol and procedures outlined for the study.The participants' agreement was obtained before collecting data on a variety of demographic factors.Participants were randomly assigned to either the functional training group or the virtual reality intervention training group by drawing names out of a box.Participants in the VR intervention group had six weeks of CRANE instruction, with three 45-minute sessions each week.Participants walk or balance themselves on a moving treadmill while tackling a variety of mental or physical challenges in a series of immersive apps like "Endless Road," "Forest Road," "Boat Sailing," and "Mountain Patrol," among others.The functional training group also undergoes non-virtual realitytraining sessions for 45 minutes three times per week for six weeks.The session includes different static and dynamic postural stability exercises with open and closed eyes, such as jumping over the soft and hard surfaces, anteroposterior, mediolateral, diagonal, and horizontal jumps, jump over the S, Z, and W course lines.Specific researchers supervised all training sessions.Before and after completing six weeks of training sessions, all participants were tested for contractile properties of their lower-leg muscle and postural stability.The non-invasive tensiomyography method assessed the contractile properties of lower-leg muscles.The measurement of the gastrocnemius lateralis, medialis, and souls muscle for the dominant leg were taken in the prone lying position, and the knee angle was set at 50 of flexion.Foam pads were used to support the leg.The measurement was taken with a specific electrical stimulator and a sensor tip with prefixed tension; it was placed upon the muscle belly.The contractile properties of the lower-leg muscles were analyzed during twitch contraction evoked by individual maximal electrical stimulators over the muscle belly of one-millisecond intervals.The electric current gradually increased by 20 mA per stimulation.There was a 10-second interval between each stimulation to reduce the fatigue effects.The utmost response was succeeded at approximately 100 mA.

Statistical Analysis
The Shapiro-Wilk test was conducted to determine the normal distribution of data.Descriptive statistics were calculated for the contractile properties and postural stability index, including mean and standard deviation.A paired sample t-test was used to determine the main effects of the virtual reality environment and functional training interventions on measuring of TMG parameters of gastrocnemius lateral, gastrocnemius medial, and souls muscle and postural stability index for the pretest and posttest.Sample t-test was also conducted to determine after intervention between virtual reality environment and functional training interventions groups.The α (twotailed) level was set at 0.05 level.The IBM SPSS v-21 was used for data analysis.

Results
To achieve the objective of the study, normality of contractile properties of muscle's pretest and post test data were checked for virtual reality environment and functional training interventions groups.It was found that data were normally distributed as indicated in Table 1.Thus, parametric tests were used for comparisons between pretest and posttest for gastrocnemius lateral, gastrocnemius medial, and souls muscle's contractile properties and postural stability (Table 2-4).While study results focus on the pretest and posttest mean values, it was indicated that there was improvement in the muscle contractile properties and postural stability.But these changes/differences were statistically no significant.
Table 2 indicated that there were no significant differences between pretest and posttest measurement of contractile properties of muscle except Dm for gastrocnemius lateral muscle (t=2.81,p=.043), gastrocnemius medial (t=-6.92,p=<.001), and TS for souls muscle (t=2.29,p=.042).The postural stability was significant (t=2.61,p=.024) with close eye measurement.Whereas open eye measurement was insignificant (t=.726, p=.483) in virtual reality training group.
Table 3 revealed that there were no significant differences between pretest and posttest measurement of muscle contractile properties for functional training group except Ts (t=-18.86,p=<.001) for gastrocnemius lateral, Tr (=3.24, p=.008), Td (t=3.07,p=.011), Ts (t=-19.74,p=<.001) for gastrocnemius medial, and Ts (t=3.17,p=.009) for souls muscle).The postural stability was also having insignificant differences in pretest and posttest during open eyes and close eye measurement for functional training group.Regarding the contractile properties of muscles, few studies have been conducted on professional and elite athletes from specific sports.The muscle contractile properties in professional soccer players have changed as the effect of training and competition.The soccer players were evaluated after ten weeks of strength and speed training, which showed that Tc, Td, and Dm decreased severely [15].Professional volleyball female players have indicated substantial improvement after four-month physical conditioning and training [16].A study on basketball players showed that parameter Tc positively and moderately correlated with external load measured and accelerometry.At the same time, Dm and Tc do not vary significantly.Authors also suggested that the TMG parameters change significantly, while the relative load increase by 13% between weeks [17].Dm and Tc have been the most thoroughly evaluated parameters for professional soccer players using TMG.Flexibility and contractile properties of lower extremities have a positive correlation between Dm and flexibility (r=.516, p<.001), no significant relationship was found between Tc and flexibility, and nor with Tc and Dm of lower extremity muscle [18].Dm and Tc are modified throughout the season due to different training loads and competition [15].Dm was measured lower after high-load resistance exercise compared to high-volume training workload [19].While Tc was longer, Dm tended to decrease following six days of high-intensity interval training [14].The negative correlations were shown between Dm, Td, Vd, and power (r=-0.75,r=-0.61, and r=-0.75, respectively) for the rugby players.These negative correlations were not statistically significant between power developed in the test and muscles' contractile properties [20].The Dm values observed in the calf muscles confirmed that soccer players had less stiff muscles than the general population [21].A study of elite Brazilian soccer players showed similar values of Dm and Tc between left and right leg muscles [22].Alvarez-Diaz et al. demonstrated that Spanish soccer players showed lateral symmetry in the leg muscles compared to Dm and Tc values for both the left and right foot [7].There were many sports where the muscles' contractile properties were measured for the left and right sides.In relation to Dm and Tc, insignificant differences were found in the lower extremity's muscles to the left and right feet for professional cyclists [17].No significant differences were found in the left and right feet muscle contractile properties during the three periods of the training session for professional soccer players [23].In short, the results of this study showed that the values of TMG parameters in athletes are different from the previously investigated in the recreational and low-active population [21][22][23].The results established positive correlations between the pretest and posttest for some TMG parameters.
No statistically significant differences between the pretest and posttest were seen using virtual reality-based serious games training for fifteen sessions, each session consists of forty-five minutes and five times per week improve functional mobility, gait speed, lower limb muscular strength and postural outcomes [29].Kanyilmaz et al. conducted a virtual reality-based exercise program and conventional exercises program for 30 minutes a day, 5 sessions per week, 15 sessions in total for 3 weeks duration.The findings revealed that virtual reality based vestibular rehabilitation exercises were more benefited than conventional vestibular rehabilitation exercises programs.The improvement was seen in postural stability test, Berg Balance test and Time Up & Go Test [30].However, it is feasible that statistical differences were observed between pre and posttest outcome measures due to altering the balance strategies as the effect of intervention training.

Conclusion
In summary, this study has provided insight into the lower leg muscles' contractile properties in athletes.It could be concluded that lower leg contractile properties of muscles and the postural stability of athletes are affected by the type of training program.The current study findings were statistically significant but mean scores showed positive differences.The study indicates that virtual reality environment training and functional training effect on the muscle contractile properties and postural stability in athletes.Tensiomyographical measurement might be used as means to evaluators performance among general and spots population.However, new studies are needed with the increased sample size, different study designs, different training protocols, and specific sports disciplines that might be helpful to optimize and modify the training load in the performance enhancement process for the different athletes.
The participants were instructed to perform a 20-minute warmup and stretching exercises before the test.Participants can run a two-minute trial on the balance platform to become familiar with the device's functionality.Prokin (version 4.8.7) was Health, sport, rehabilitation Health, sport, rehabilitation Здоров'я, спорт, реабілітація Здоров'я, спорт, реабілітація Здоровье, спорт, реабилитация Здоровье, спорт, реабилитация 2024 10(2) used, and the equilibrium management test was chosen to determine the stability index.The pressure level of the stabilometer platform was set to difficulty level 20 (out of 40).The body sensor was attached to the chest, and the participant stood on the platform with a single leg, eyes open.The test was performed according to the company's open and closed-eyes instructions.
in the stability index in the open eyes and closed-eye tests.The result indicates that the virtual reality and functional training program had no differential effects on the measured stability index for the left and right feet.However, the improvement can be seen as the effect of the intervention-training program.Regarding athletes, some studies have indicated that during training sessions and competitions, athletes should develop abilities that require dynamic balance control while kicking, passing, dribbling, and carrying the ball [24].Grancher et al. indicated that traditional balance-training programs three times per week for four weeks showed only a small to moderate effect on postural stability [25].Faigenbaum et al. found a specific improvement in postural stability after six weeks, five times per week, and after ten-minute rope balancing training provided [26].Mahjur and Norasteh revealed that a home-based specific and comprehensive balance-training for three times a week for ten weeks significantly enhance postural stability and functional status [27].Donatoni da Silve et al. reported that Pilates training twice weekly for the duration of six week (1-hour Session) with a supplementary home program improved postural stability, mobility, functional mobility, and spatiotemporal parameters of gait in healthy adults [28].Pournajaf et al. revealed that balance training Health, sport, rehabilitation Health, sport, rehabilitation Здоров'я, спорт, реабілітація Здоров'я, спорт, реабілітація Здоровье, спорт, реабилитация Здоровье, спорт, реабилитация 2024 10(2)

Table 4
revealed that there were no significant differences between virtual reality training group and functional training group in posttest measurement of muscle contractile properties except Tr (t=--2814, p=.010) for gastrocnemius medial muscle.The postural stability has significant differences between virtual reality training group and functional training group during open eye (t=4.12,p=.000) and close eye (t=6.87,p=.000) measurements.

Table 1
Normality (Shapiro-Wilk) test for contractile properties of muscles and stability index between virtual reality and functional training group

Table 2
Pretest and posttest statistical difference of muscle contractile properties and postural stability for virtual reality training group

Table 3
Pretest and posttest statistical difference of muscle contractile properties and postural stability for functional training group

Table 4
Posttest statistical comparison between both groups for muscle contractile properties and postural stability.68 in virtual reality training group.The significant differences was also existed between pretest and posttest measurement of sustain time in gastrocnemius lateral.The relaxation time, delay time and sustain time in gastrocnemius medial, and sustain time in souls muscle.The postural stability was also having insignificant differences in pretest and posttest during open eyes and close eye measurement for functional training group.Significant differences between virtual reality training group and functional training group were existed in sustain time in gastrocnemius medial muscle.The postural stability has significant differences between virtual reality training group and functional training group during open eye and close eye measurements.