1. Introduction
Many physical activities are accompanied with injury. For many professional and non-professional athletes, the occurrence of these injuries are already accepted to participate in sports and championship activities [
1]. Each injury not only is accompanied with pain and incapability, but also holds the athlete back from sport fields and can impose direct and indirect costs on the athlete and the sport club
[2,
3].
Studies indicate that most of sport associated injuries relate to the lower limbs
[4]. Athletes who participate in volleyball, basketball, handball and soccer should suddenly change their movement directions during a sport game, or rapidly reduce their speed, or perform jumping, leaping, landing and sudden stops, that make them more susceptible to lower limb injury compared to other sports [
5-8]. Therefore, prevention of injury to the joints of lower limbs in these sports seems necessary. One of the most important risk factors for knee and ankle injury is impaired postural control and balance. Postural control and balance are the most important abilities of athletes.
Accordingly, it is a determining indicator in examining the functional ability of athletes [
9]. For this reason, prescribing exercises to improve postural control and the balance of lower limb joints are necessary to prevent injury and better function of the athlete. Conventional exercise programs to prevent and rehabilitate injuries include strength exercises, balance exercises, core stability, and plyometric exercises [
10-13]. Because sports like basketball, volleyball, soccer and handball require jumping and landing, hopping exercises can be suitable for these athletes. Hopping exercises are considered as plyometric and among basic and fundamental motor skills that are low-cost and trainable. In addition, they can be employed in sport programs as part of the workout schedule [
10].
The effect of hopping exercises on improvement of the static and dynamic balance of athletes and non-athletes have been reported in domestic and foreign studies. For example, Karimizadeh et al. (2012) assessed the effect of hopping exercises on the dynamic balance of athletes with functional instability in their ankles. They reported that hopping exercises significantly increase the distance of the reach of the participants in each of the 8 directions of the Star Excursion Balance Test [
10]. However, researchers believe that in the event of an injury, the entire body should be considered as a system that the defect in each part of it can affect the function of other parts [
14].
Camerford and Mottram indicated that the stability of core parts of the body is imperative for safe and efficient movement of the limbs and especially the lower limbs. In fact, the trunk and core parts of the body should be sufficiently stable to have efficient lower limb functional movements with minimal injury [
15]. In addition, the effect of core stability exercises on improving the balance of athletes has been reported by researchers [
16,
17]. Suspension exercises with TRX is a new functional exercise method by which hundreds of different types of exercises can be performed. It uses the force of gravity or body weight with 2 rope-like levers for different purposes. It has recently drawn the attention of people attending sports and exercise. Studies show that the unique feature of TRX exercises, compared to other exercise methods, is to activate the body’s core stabilizing muscles by changing the body position, in the upper and lower limb movements [
18].
Other researchers also referred to the high electrical activity of the core stabilizing muscles when performing movements like plank exercises on unstable surfaces such as TRX, compared to stable surfaces like the ground [
19,
20]. Moreover, in some studies, TRX has been considered a destabilizing device that besides core stability exercises, it can be used to design all types of balance, neural and muscular exercises [
19-22]. Literature review revealed that core stabilizing muscles have a significant effect on improving the athletes balance, and TRX exercises largely emphasizes on improving the function of core stabilizing muscles.
The effectiveness of hopping exercises has already been reported for improving athlete balance; however, this effectiveness has not been compared with other exercise methods. Therefore, the present study aimed to compare the effects of hopping and TRX exercises on the static and dynamic balance of male college athletes.
2. Materials and Methods
This was a quasi-experimental study with pretest, posttest design, and two experimental (TRX and hopping exercises) and one control groups. The statistical population of this study consisted of college athletes engaged in volleyball, basketball, soccer and handball, among whom 36 athletes were selected purposefully according to the research inclusion and exclusion criteria. Then, they were randomly divided into a control group and two experimental groups (hopping and TRX exercises). The inclusion criteria consisted of athletes aged 20 to 28 years, practiced at least 3 years in volleyball, basketball, soccer, or handball, could perform 5 squats in 5 seconds with 60% of the body weight (as a precondition for entering to hopping exercises) [
23], lacked any pathologic symptoms and history of fracture, operation, or joint illnesses in the lower limbs or spine within the past 5 years [
24,
25].
The exclusion criteria were pain in any part of the body during the performance of test in a way that the athlete would not be able to cooperate [
25] and more than 2 absences from the exercise sessions [
26]. After the research samples were selected based on inclusion and exclusion criteria, they were randomly divided into three groups: 1. Hopping exercises (n=12) with an Mean±SD age of 25.22±2.32 years, height 176.10±0.13 cm, body weight 71.85±5.15 kg, and body mass index 21.98±1.19 kg/m2; 2. TRX exercise group (n=12) with the Mean±SD age of 26.79±1.84 years, height 177±6.38 cm, body weight 72.70±6.31 kg, and body mass index 22.42±1.19 kg/m2; and 3. The control group (n=12) with an Mean±SD age of 24.85±3.26 year, height 174.72±5.95 cm, body weight 67.18±11.42 kg and body mass index 22.92±2.34 kg/m2.
For pretest measurements, the research samples were invited to the sports hall according to the specified timetable. Subsequently, the initial information form was completed by each athlete and anthropometric measurements (weight, height, waist and hip circumference) of each person were obtained. Then, measurements related to the static and dynamic balance of the participants were collected. For measuring the static and dynamic balance, the Biodex Balance System was used. This system consists of a moving circle plate to station the participant (balance meter plate), a monitor, and an electronic processor (Figure 1).
In this research, the dynamic balance of athletes was assessed at instability level 4 (great instability) and the static balance was assessed at a static level and only by the overall indicator. The lower values on the balance system, denotes better athlete balance and vice versa. After completing pretest measurements, the experimental group performed TRX and hopping exercises for 4 weeks, 3 sessions per week, under the supervision of the researcher (Appendix 1, 2, 3, and 4).
The control group was asked not to do any special sports activities during the study period and only perform their usual daily activities. A training session was held to familiarize the experimental groups’ samples with the method of performing TRX and hopping exercises, prior to the onset of exercises. TRX and hopping exercise session comprised an initial 10-min warm-up followed by 30 to 40 min of selected TRX and hopping exercises under the supervision of the researcher. All of the movements that were performed in TRX exercises were based on related references and articles published in the field of suspension TRX exercises [
27,
28].
The researcher has also designed the protocol for TRX suspension exercises, based on 1-year coaching experience in this field. TRX exercises included exercises for the lower limbs as well as the plyometric and balance basis, so that it could be compared with hopping exercises, and also the volume and intensity of both exercises were matched by the researcher in accordance with the principles of FITT (frequency, intensity, time spent and type of exercise) and then confirmed by a specialist physician. Next, the descriptive statistical tests of mean and standard deviation were used to describe the data, and the paired t test was used to compare the intra-group results.
The Analysis of Covariance (ANCOVA) was used to compare inter-group variables. All statistical analyses were performed at the significance level of 0.05 using SPSS. To determine the normality of data, the Shapiro-Wilk statistical test was used which confirmed the normal distribution of data.
3. Results
A significance level was considered in all tests (P≤0.05) (Table 1). The results of paired t test showed a significant difference between the pretest and posttest in the static and dynamic balance of athletes in the exercise groups of TRX and hopping, in a way that the balance fluctuations in the posttest in these two groups reduced after 4 weeks of exercise, compared to the pretest (P≤0.05). This result indicates a significant improvement in the static and dynamic balance in both groups; however, no significant difference was seen in those variables, among the control group members (P>0.05).
ANCOVA was applied to compare the difference among 3 groups in the static and dynamic balance scores. The obtained results are reported in Table 2 which indicate a significant difference among 3 study groups in terms of the dynamic and static balance of the athletes in the posttest (P≤0.05), after controlling the effect of pretest results (covariate). Therefore, the Bonferroni post-hoc test was used to examine the inter-group difference (Table 2).
The results of Bonferroni post-hoc test indicate no significant differences between the TRX exercise and hopping groups (P=1.00) in the dynamic balance test. However, a significant difference was found between the control group and the hopping group (P=0.001) as well as the control group and the TRX group (P=0.001).In addition, in the static balance test, there was no significant difference between the TRX and hopping groups
(P=0.56); however, the differences between the control and hopping groups (P=0.001) as well as the control group and TRX group (P=0.001) were significant.
4. Discussion
The present study aimed to compare the effect of 4 weeks of suspension exercise with TRX and hoping exercise on some risk factors for the lower limbs injury in male college athletes. The static, dynamic balance test, and stability limits in the two exercise groups showed significant improvement, compared to the control group (P<0.05). However, there was no significant differences between the effect of hopping and TRX exercises on the static and dynamic balance of athletes (P>0.05).
Hobscher et al. in a review study of balance and neuromuscular exercises concluded that the balance and neuromuscular exercises improve the neuromuscular connection and by reducing the delay in proprioceptive sensory function, the acute injuries in ankle and knee areas reduce significantly. Such exercises could be performed to improve the balance of athletes due to better neuromuscular coordination and increased coordination of vision, vestibular, and proprioceptive systems. Therefore, the exercises designed in this study, may be able to improve the balance by improving the efficiency of sensory receptors and neuromuscular facility, while improving the proprioceptive sense of the joints [
29]. Figure 2 by Joseffine Kee et al. shows the contribution of various exercises in improving the proprioceptive sense.
Only in dynamic conditions, all 4 muscular receptors are activated and the proprioceptive sense is strengthened.
Considering the previous studies, exercises with traction-contraction mechanism can improve and change the start of muscular activity and may also indirectly affect the feed-forward. This mechanism is considered in the treatment and prevention of lower limb injuries [
30]. According to the study findings, these exercises improve the static and dynamic balance and the limits of athlete stability. Designing an exercise program to strengthen balance and ameliorate posture fluctuation is an appropriate tool for preventing injury and a safer and quicker method for the athletes to recover from injuries.
The athletes who participated in this study were selected from the field of basketball, volleyball, football and handball. In these sports, zigzag movements and cutting, jumping, and landing maneuvers are risk factors for many lower limb non-contact injuries. Thus, the hopping and TRX exercise programs that require both legs and single-leg jumping and landing, as well as cutting maneuvers and zigzag movements without the loss of balance with high agility and speed in the frontal and sagittal directions, can improve the balance function in these athletes [
31].
One of the most important characteristics of suspension exercises is the proper activation of the core stabilizing muscles in all movements performed with TRX [
32]. Research results have supported a direct connection between the core stabilizing muscles and the ability to maintain balance [
33]. In fact, TRX exercises not only strengthen the body main motional muscles, but also strengthen the core stabilizing muscles by performing a functional activity [
34]. It can be concluded that both exercises can have a desirable effect on the static and dynamic balance of athletes.
In conclusion, employing these exercises with our study designed protocol may be a safer and more suitable way for beginner athletes. They can learn the correct technique of performing the movements with fewer mistakes in the exercise. They can also diversify their exercises to prevent their bodies get used to boring exercises which is one of the principles in exercise design. These types of exercises can also be used alongside other exercise protocols.
The effect of hopping exercise in improving the static and dynamic balance of athletes and non-athletes have been reported in domestic and foreign studies; however, we are still witnessing injuries of the lower limbs in these athletes. On the other hand, the core stabilizing muscles have a significant effect on improvement of athletes’ balance. In this regard, TRX exercises emphasizes on improving the function of core stabilizing muscles. The effectiveness of hopping exercise on improvement of athletes balance has been already reported; however, this effectiveness has not been compared with other exercise methods.
Considering the results of this study, both hopping and TRX exercises have significant impacts on the static and dynamic balance of athletes, and both of these exercises can be used by athletes engaged in basketball, volleyball, football, and handball. However, in the discourse on prevention of sports injuries, final decision in rejecting or accepting TRX exercises cannot be made due to limited studies in this regard, and further studies should be conducted.
Ethical Considerations
Compliance with ethical guidelines
All ethical principles were considered in this article. The participants were informed about the purpose of the research and its implementation stages; They were also assured about the confidentiality of their information; Moreover, They were allowed to leave the study whenever they wish, and if desired, the results of the research would be available to them. The consent form for voluntary and informed participation in the research was signed by participants.
Funding
This study is part of the curriculum of studies of sports pathology and corrective movements at the University of Tehran. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflict of interest
The authors certify that they have no affiliation with or involvement in any organization or entity with any financial interest, or non-financial interest in the subject matter or materials dismissed in this manuscript.
Acknowledgments
Authors of this study hereby express their gratitude to all those who assisted in conducting this study.
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