EFFECTS OF PLYOMETRIC TRAINING WITH RESISTANCE BANDS ON NEUROMUSCULAR CHARACTERISTICS IN JUNIOR TENNIS PLAYERS

Dario Novak, Bruno Urisk, Iva Lončar, Filip Sinković

University of Zagreb, Faculty of Kinesiology, Zagreb, Croatia

CORRESPONDING AUTHOR:

Dario Novak

Horvaćanski zavoj 15, 10000 Zagreb, Croatia

+385994455699

dario.novak@kif.hr

ABSTRACT

The purpose of this study is to investigate the effect of 6-weeks (conducted twice per week for a total of 12 sessions) of plyometric training with resistance bands on different neuromuscular characteristics among the sample of junior tennis players. Thirty top junior tennis players between the ages of 12 and 14 years (age 13.5±1.8 years, weight 51.3±12.5 kg, height 162.7±12.6 cm) were allocated to either the control group (standard in-season regimen) (CG; n = 15) or the experimental group, which received additional plyometric training with resistance bands (TG; n = 15). Pre- and post- tests included: anthropometric measures; squat jump (SJ); vertical countermovement jump (CMJ); single leg vertical countermovement jump (1-leg CMJ); vertical countermovement jump with arm swing (CMJA); 7 jumps from the feet (7jumps); standing long jump (SLJ); triple jump (TJ); 20 m sprint time (with 5, 10 and 20 m splits); generic CODS (20Y test and T-test) and reactive agility test. After the training intervention, the TG showed significant (p < .05) improvements in the first step quickness, acceleration, speed, as well as generic CODS performance, with percentages of change and effect sizes ranging from 3.6% to 10.5% and 0.5 (moderate) to 1.7 (large), respectively. No significant changes were observed in the CG after the training intervention. Our findings provide useful information for coaches to create a wide range of tennis-specific situations to develop a proper performance, especially for their player’s neuromuscular fitness.

 INTRODUCTION

Speed-explosive properties are speed, agility and explosive power, and they represent a set of motor skills very important for success in tennis. These abilities are treated jointly, due to several common characteristics: they use the same energy resources, similarly stimulate the nervous system, have common factors on which the level of a particular ability depends and meet the same prerequisites for intensive training of a particular motor ability (Milanović et al., 2014). Also, it is considered that athletes with more pronounced speed-explosive properties find it easier to control their body in urgent training and competition situations, which greatly contributes to the game, but also to the prevention of injuries (Trecroci et al., 2016). Athletes as well as their coaches are trying to find new ways to improve certain motor skills, and thus improve results in certain sports. This includes the method of plyometrics as one of the most effective methods for the development of different types of explosive power and can be explained as any type of training in which eccentric - concentric muscle work occurs (Čanaki & Birkić, 2009). Many studies agree that plyometrics involves specific exercises that cause significant stretching of a muscle that is under eccentric contraction and is followed by strong concentric contraction (Davies, Riemann & Manske, 2015; Fernadez et al., 2016; Salonikidis & Zafeiridis, 2008). Such a mechanism serves to develop a strong movement in a short period of time. Also, a very significant element of the plyometric system is the reactive ability of the apparatus to move. By this is meant the summary contribution of the muscle stretching reflex, with the muscle contracting strongly immediately after stretching (Kirit & Arslan, 2019). Due to all the above, the influence of plyometric training on motor skills and on biomechanical and physiological parameters in tennis is increasingly being researched. A review of the literature shows that the use of plyometric training in everyday tennis training significantly affects agility, more precisely, better results are achieved in agility tests (T-test, 505 test) (Fernadez et al., 2016) and in the sidestep test (Miller et al., 2006). Also, the application of combined plyometric and tennis training showed an improvement in speed, more precisely a 20m sprint (Fernadez et al., 2016) and 12m sprint (Salonikidis & Zafeiridis, 2008). In addition to agility and speed, combined plyometric and tennis training affect jumping where significantly better results have been found in broad jump and countermovement jump (Fernadez et al., 2016). Also, using a combination of plyometric and tennis training, an improvement in tennis player strength was found in the upper extremities (Fernadez et al., 2016) as well as in the lower extremities and service speed which is a very important component of tennis success (Salonikidis & Zafeiridis, 2008). Using additional plyometric training 2-3 times a week with daily tennis training can significantly affect jumping where it is seen how to achieve better results in long jump and triple jump (Smajic et al., 2015) as well as in vertical jumps (Mohanta, Kalra & Pawaria, 2019). However, no studies have simultaneously examined the contribution of the plyometric training with bands on different neuromuscular factors. Accordingly, in the present study, we investigated the effects of plyometric training with resistance WearBands™ bands on neuromuscular characteristics among a sample of junior tennis players.

METHODS

Design and participants

Thirty top junior tennis players between the ages of 12 and 14 years (age 13.5±1.8 years, weight 51.3±12.5 kg, height 162.7±12.6 cm) were allocated to either the control group (standard in-season regimen) (CG; n = 15) or the experimental group, which received an additional plyometric training with resistance bands (TG; n = 15). All of the participants have from 6 to 8 hours of tennis training per week and during the training program, strength training was prohibited. Physical tests were carried out before and after the training period, including anthropometric measures, squat jump (SJ); vertical countermovement jump (CMJ); vertical countermovement jump with arm swing (CMJA); 7 jumps from the feet (7jumps); standing long jump (SLJ); triple jump (TJ); 20 m sprint time (with 5, 10 and 20 m splits); generic CODS (20Y test and T-test) and reactive agility test.

Measures

A week before starting with the training program initial tests were provided on each subject on the same day. Each subject was tested in the same order and recorded with the same equipment by the same investigators. There were three of investigators and each of them was charged for the specific group of tests. For body height, arm span, arm length, leg length and foot length was used anthropometry, and for the body mass, body mass index (BMI) and % body fat we have incorporated a bioelectrical impedance analyser (HBF-500, Kyoto, Japan). Time completing the 20 m straight line dash with 5m, 10 m and 20m sprint time as well as generic CODS (20Y test and T-test) were measured with Powertimer Newtest system (Oulu, Finska). Reactive agility test in sagittal plane was tested with Wireless Training Timer SEM Witty (Microgate, Bolzano, Italia). For measuring standing long jump and single leg triple hop we used tape measure and for the squat jump (SJ); vertical countermovement jump (CMJ); vertical countermovement jump with arm swing (CMJA); 7 jumps from the feet (7jumps) we used Microgate Optogait system (Microgate, Bolzano, Italia).

Training program

Since the subjects are young athletes the training program needed to be adapted to their age and abilities. The 6-week plyometric training is composed of low and moderate levels of plyometric exercises (Table 1). It includes different kinds of vertical, horizontal, and lateral jumps and hops that are scheduled in each training. Since the fact that elastic bands are used, only lower body exercises are included in the program. Table 1 shows the training schedule that is described by the numbers of week, names of the exercises, numbers of sets and repetitions and the rest period. Subjects mostly performed 3 to 4 sets of 4 to 6 exercises with 5 to 10 repetitions with maximum intensity. Depending on exercise, rest period was between 15 and 60 seconds between sets and 60 to 120 seconds between the exercises. Duration of the training was between 30 and 45 minutes including warm up period and was led by a certified strength and conditioning coach. The multi-patented WearBands™ Dynamic Gravitational Resistance Training System applies gravitational, multi-planar, multi-directional resistance during sport-specific movement at or near full-speed. By applying multi-planar resistance, the system allows the athlete to maintain his or her normal center of gravity while amplifying neuromuscular stimulation during sport-specific movement. Unlike more traditional “bungee” resistance systems, which apply mostly single plane, single direction sheer resistance, WearBands™ improves force production into and through the ground during any movement in any direction. This unique ability allows sport-specific change of direction training (in any direction), as well as aiding first-step quickness, acceleration and speed development. The system’s neuromuscular stimulation and feedback also aids an athlete’s reactive ability. By allowing an athlete to move in any direction at any speed with little or no restrictions, while simultaneously amplifying neuromuscular stimulation, the athlete can train precise sports-specific movement in a way not before possible.

Table 1. Six – weeks plyometric training program

Statistics

Data were expressed as mean ± SD. Differences between training and control group were assessed using the unpaired sample t-test. Within-group differences between pre-test and post-test results were assessed using the paired sample t-test. Effect sizes (Cohen’s d) were calculated for each dependent variable. The thresholds for effect size statistics were as follows: trivial (< 0.35), small (0.35–0.80), moderate (≥0.80–1.5), or large (> 1.5). Statistical analyses were performed with SPSS software version 17.0 (SPSS, Inc., Chicago, IL, USA). The level of statistical significance was set at p ≤ 0.05.

RESULTS

Table 2. Individual characteristics of the players. Data and means (±SD)

Table 2 illustrates individual characteristics of the players in both training and control group. Data were expressed as mean ± SD. It shows that the groups had similar characteristics in regards with their age (CG: 13.3 ± 2.0 vs TG:  12.8 ± 1.7), height (CG: 164.3 ± 13.1 vs TG:  161.2 ± 12.2), weight (CG: 51.8 ± 11.5 vs TG:  50.9 ± 13.5), tennis practice (CG: 4.3 ± 2.2 vs TG:  4.1 ± 2.4), weekly tennis training (CG: 4.4 ± 3.1 vs TG:  4.5 ± 3.3) and weekly conditioning (CG: 2.0 ± 1.4 vs TG:  2.1 ± 1.3).

Table 3. Mean (±SD) between pre-test and post-test measurements for the control and training groups.

CMJ = countermovement jump, SJ = squat jump, LJ = long jump, SLTH = single leg triple hop, WS-S = Witty Sem sagital plane; * significant (p < 0.05) differences between training and control group; # significant (p < 0.05) differences between pre- and post-test

Mean (±SD) between pre-test and post-test measurements for the control and training groups were presented in Table 3. No significant differences between CG and TG group were observed before the training intervention (p < 0.05). In terms of within-group comparisons, the TG showed significant (p < 0.05) improvements in the first step quickness (1.83 ± 0.1 vs 1.71 ± 0.1), acceleration (2.85 ± 0.2 vs 2.58 ± 0.1), speed (4.56 ± 0.4 vs 4.18 ± 0.2), as well as generic CODS performance (T-test: 12.4 ± 1.1 vs 11.8 ± 0.9  and 20-yard:  5.7 ± 0.4 vs 5.5 ± 0.4 ) with percentages of change and effect sizes ranging from 3.6% to 10.5% and 0.5 (moderate) to 1.7 (large), respectively. No significant changes were observed in the CG after the training intervention.

DISCUSSION AND CONCLUSIONS

This study aimed to investigate the effect of the plyometric training with resistance bands on different neuromuscular characteristics among the sample of junior tennis players. We can conclude that the plyometric training with resistance bands significantly increased the first step quickness, acceleration, speed, as well as generic CODS performance over the regular strength and conditioning training alone.

The First Step Quickness, Acceleration and Speed

In the sport of tennis, players must be able to react as fast as possible to actions performed by the opponent, where reaction time, initial acceleration, and agility play an important role (Reid et al., 2013; Fernadez et al., 2016). The game is characterized by high-intensity efforts in terms of the first step quickness, acceleration and speed. The first step quickness is one of the most important factors in order for the player to reach an effective hitting position (Dobos, et al., 2021). However, the ability to accelerate within a short distance are both essential requirements for handling the ball correctly to successfully solve the game situations (Kovalchik & Reid, 2017; Dobos, et al., 2021). Initial acceleration can be referred to as the first 10 m and 20m of a sprint (Fernadez et al., 2016). The results of our study show that the experimental program positively effects all the speed components in horizontal direction among the sample of young tennis players. Our results of improvements in the first step quickness, acceleration and speed performance after plyometric training are supported by several studies conducted on tennis players (Salonikidis & Zafeiridis, 2008; Fernandez et al., 2016; Mohanta et al., 2019). Therefore, regarding the significant improvement in the sprint of 5, 10 and 20 meters as a result of applied plyometric training with resistance bands training, and the fact that the first step quickness, acceleration and speed are highly important for the success in the tennis match (Dobos, et al., 2021), we may emphasize that plyometric training with resistance bands training could be observed as a useful training program aimed at improvement of these capacities in youth tennis players. We can hypothesize that in our study improvements occurred due to reactive strength and powerful push-off of legs.

Lower Body Explosive Power

The results of the research indicate that there were no significant changes in the results of tests for estimating the explosive power of the lower extremities in the horizontal and vertical components of jumping. It can be concluded that plyometric training with elastic resistance does not affect the improvement of performance in explosively strong properties of horizontal and vertical type. It is to be assumed that plyometric training with resistance bands emphasizes eccentric stimuli with an emphasis on performance speed, but not a pronounced force in the performance of tasks, especially in the sample of young tennis players. This is one of the first studies to conduct plyometric training with resistance bands, therefore comparisons are difficult since previous studies were focused exclusively on plyometric training conducted mostly with mature players (Salonikidis & Zafeiridis, 2008; Fernandez et al., 2016). For example, Salonikidis and Zafeiridis (2008) reported a significant improvement in drop jump (DJ; 15%) and lower extremity maximum isometric force (11%) after 8 weeks of training. One of the few studies of the impact of plymetric training for physical abilities in young tennis players was from Fernadez et al. (2016). They showed how plyometric training seems to be an appropriate stimulus for improving physical qualities in tennis players. It demonstrates the importance of specific power training for enhancing the explosive actions of tennis players (Fernadez et al., 2016). Similar findings were established by Markovic and Mikulic (2010) that plyometric training could increase horizontal jumping performance by 1.4% to 7%, however with less improvement than vertical jumping (Markovic & Mikulic, 2010). It is possible that the contents of the plymetric program of this study did not significantly emphasize the maximum vertical component of the performance. Also, results might be explained by having a combination of lateral, horizontal, and vertical direction drills, in contrast to previous studies, in which the amount of vertical direction drills was higher (Ozbar, Ates & Agopyan, 2014).

Change of Direction Speed and Reactive Agility

In our study, significant improvements were also recorded in generic CODS performance (measured by T-test and 20-yard agility test) after plyometric training with resistance bands. Tennis is an extremely dynamic sport in which players perform 300–500 high intensity efforts during a best of three sets match (Fernandez, Mendez-Villanueva & Pluim, 2006). Therefore, CODS is considered as one of the key performances in tennis. CODS comprises of the acceleration phase, deceleration phase, change of direction, and reacceleration in the other direction (Falch, Rædergård & van den Tillaar, 2019). Our results of improvements in CODS performance after plyometric training are supported by several studies conducted on tennis players (Fernandez et al., 2016; Fernandez et al., 2018; Mohanta et al., 2019). In other studies, young tennis players also showed significant improvements in the tests of generic CODS after multiple weeks of neuromuscular training (Barber-Westin, Hermeto & Noyes, 2015; Barber-Westin, Hermeto & Noyes, 2010; Bashir et al., 2019; Yildiz, Pinar & Gelen, 2018). In accordance with results on sport-specific CODS, plyometric training with resistance bands did cause the improvement for tennis-specific reactive agility. However, a limited number of studies evaluated the effects of training on sport-specific reactive agility performance, measured by sport-specific tests (Salonikidis & Zafeiridis, 2008). For example, Trecroci et al. (2016) investigated the effect of speed, agility and quickness training on reactive agility in soccer players (Trecroci et al., 2016). Players significantly improved agility performance by 4.2%, but the authors suggest that improvement occurred due to improvements recorded in the speed over 5 meters and not due to faster decision-making ability (Trecroci et al., 2016). There are few studies that use tests to assess the reactive component of agility. In one such study, the authors conclude that plyometric training improved fitness characteristics that rely more on reactive strength and powerful push-off of legs such as, lateral reaction time, 4-m lateral and forward sprints, drop jump and maximal force (Salonikidis & Zafeiridis, 2008). We can hypothesize that in our study CODS improvements occurred due to the advances in technique, and the fact that the experimental program involved multi-directional movements.

This study has a number of limitations, which will be discussed below. Firstly, the subjects involved in this study were selected youth tennis players in a very sensitive and crucial developmental phase. Secondly, we did not evaluate the biological age of the participants, which is known to influence neuromuscular performance; and thirdly, we did not have the possibility to look at the mental and physical fatigue that may have occurred during the testing process; therefore, it could have potentially affected the most effective movement execution.

In summary, the present study suggests that there is a positive effect of the plyometric training with resistance bands mostly on horizontal components of explosive power, but not on vertical components of neuromuscular characteristics in junior tennis players’ players. Our findings provide useful information for coaches to create a wide range of tennis-specific situations to develop a proper performance, especially for their player’s neuromuscular fitness. Additional studies are needed to identify interventions that can increase sport-specific neuromuscular fitness with the ultimate goal of achieving better performance.

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