Tennis is one of the most popular sports, with an increasing number of active players (3,22,28). Although tennis is a noncontact sport, it is associated with a number of injuries (3,7,22,30). Most injuries in tennis occurred in the lower extremities (7,30) and they were muscle strains and ligament sprains (ankle and knee) (22,34). These injuries appeared not only in adult players but also in young tennis players (34).
To prevent such injuries, rehabilitation specialists propose specific exercise programs: strengthening exercise programs to restore muscle imbalances, stretching exercise programs to decrease muscle stiffness, and balance exercises to improve proprioception (2,4,8,32). The term “proprioception” was described by Sherrington (33), as the awareness of body segment positions and orientations. Recent rehabilitation bibliography supports that balance exercise programs improve proprioception and protect athletes from forthcoming injuries effectively (4,9,16,18,24,39). Proprioceptive information from lower limbs is important in the maintenance of equilibrium in tennis due to the nature of the game. For instance, besides the neck, pressure sensation from the footpads can tell one (a) whether the weight is distributed equally between the 2 feet and (b) whether the weight is more forward or backward on the feet (11). Proprioception is even more significant for tennis because the tennis skills are composed by complex movements demanding high balance ability (20,23). Furthermore, tennis is an explosive sport, requiring multidirectional movements and short bursts of intermittent action. Physical condition in tennis is focused on explosion, speed, agility, balance, and anaerobic energy system with focus on the recovery times (27). Balance is one of the fundamental abilities that tennis players should develop to perform better the training drills and to be an effective tennis player in the court (5,6). In addition, the balance ability is required to be maintained for an extended period especially when the games last 2-3 hours.
The aim of the present study was to examine whether balance deficits appear after a regular tennis training session in elite young tennis players. The results of the present study would clarify if there is a need for tennis-specific balance exercise program to be incorporated in the regular tennis training session.
Experimental Approach to the Problem
Tennis is a demanding game based on complex motor movements and needs high level of coordination between legs, hands, and eyes. This multidirectional nature of tennis and the extended period of games (2-3 hours) necessitate balance ability even more. The present study evaluates the balance performance before and after a regular tennis training session to define the need of a tennis-specific balance exercise program.
The study was conducted on 36 elite young tennis players (age 14 ± 2 years; body mass 55 ± 6 kg; body height 165 ± 6 cm; mean ± SD) participating in the national young tennis championship and practicing tennis at least 6 years. The participants were free of injuries in the lower limbs for the past 3 years. The subjects were informed of the experimental risks and signed an informed consent document prior the investigation. The investigation was approved by the institutional review board of human subjects at which the work was conducted.
The tennis training session was 90 minutes per session, there were 4 players per court and was performed 3 times per week. During a regular training session, there was a 10-minute active warm-up, followed by drills for ground strokes, ground strokes, and volley, and at the end practicing serves and returns. During the last 20 minutes of the session, they were playing games (Table 1). The experimental protocol took place during the last week of the precompetition period, and the goal for the training session was to work primarily on the technique and tactics of the game. In the technical training session, the goals were to develop (a) basic tennis strokes, (b) control of the ball direction (crosscourt, down the line), (c) control of the depth (long, middle, short balls), and (d) control the speed of the ball. The game situation training was oriented to define player's profile (all around, aggressive baseliner, serve and volley).
The balance assessments and the dynamometric assessments were performed on a random order on 2 different days, pre and post the same tennis training session.
Balance performance was assessed before and immediately after a tennis training session (pre training and post training, respectively). The balance assessment was performed with 2 different balance boards (10) and with the Biodex Stability System (Biodex Medical Systems, Shirley, NY, USA (1,26,36)): balance board 1, with hemispherical base, and board 2, with hemicylindrical base. Board 1 allowed movement in both anteroposterior and mediolateral directions. Board 2 restricted movement according to the way it was placed: (a) in the anteroposterior direction and used as board 2a, and (b) in the mediolateral direction as board 2b. To achieve the maximum learning effect in the balance boards, the subjects practiced single-limb stance on balance boards 3 times per week, 1 week prior the beginning of the experimental protocol. In the balance board tests, the subjects maintained single-limb stance for as long as possible. Three test trials were timed on each balance board, and the best trial was considered for further analysis. In the Biodex test, the participants maintained single-limb stance for 20 seconds, with the Biodex platform set to freely move by up to 20° from level in any direction. From the variance of the platform displacement (°) in the anteroposterior and mediolateral directions from level during the test, an instability index (Ii) was computed from the Biodex system. Three test trials were carried out, and the one with the lowest Ii (best performance) was further processed. The validity of the balance tests had already been performed (10,29). In agreement with previous reports, intraclass correlation coefficient values for 2 measurements taken in the same day (p > 0.05, Student's t-test) were 0.74 for the Biodex test, 0.72 for the board 1 test, 0.78 for the board 2a test, and 0.67 for the board 2b test.
Measurements of peak isokinetic moment in the knee flexors and extensors were performed on a different day from the balance assessment pre and post training to quantify the degree of muscle fatigue induced by the tennis training session. The subjects were secured with straps on the seated position on the chair of an isokinetic dynamometer (Cybex 6000, Cybex Inc., Ronkonkoma, NY, USA) at a hip joint angle of 110° (180° is the supine position), with the dynamometer lever and knee joint axes being visually aligned. After a standardized warm-up, 3 successive cycles of maximal effort knee extension-flexion contractions were performed at 2 different angular velocities, first at 60°·s−1 and then at 180°·s−1. More than 1 angular velocity was examined to assess whether the tennis training session would affect the production of muscular force similarly in slower and faster contractions. The 2 tests were performed ∼2 minutes apart, and the 2 legs were tested ∼5 minutes apart. Visual feedback of the recorded joint moment values was provided. For each angular velocity, muscle group, and leg, the contraction with the highest peak moment value was considered for further analysis.
One-way repeated measures analysis of variance (ANOVA) was used to test the differences in balance performance between pre and post tennis training session and in isokinetic performance at the velocities examined between pre and post tennis training session. The level of statistical significance was set at p ≤ 0.05.
Repeated measures ANOVAs revealed no difference (p > 0.05) in balance performance between pre-training and post-training measures. More specifically, a tennis training session had no effect (p > 0.05) on any of the balance performance indicators examined, Biodex Stability Index: for the right (F(1,35) = 1.027, p >0.05) and left leg (F(1,35) = 1.012, p > 0.05); board 1: for the right (F(1,35) = 0.876, p > 0.05) and left leg (F(1,35) = 0.823, p > 0.05); board 2a: for the right (F(1,35) = 0.975, p > 0.05) and left leg (F(1,35) = 0.982, p > 0.05); and board 2b: for the right (F(1,35) = 0.843, p > 0.05) and left leg (F(1,35) = 0.861, p > 0.05) (Figure 1).
However, the isokinetic torque measurements after tennis training were lower (p < 0.05) than before tennis training, indicating that muscle fatigue was inflicted by the tennis training. The average torque reduction for the knee extensors and flexors ranged from 8 to 11% (Table 2).
The aim of the present study was to examine whether a tennis training session influences the player's balance performance. In the present study, the role of fatigue induced by a tennis training session was studied in an attempt to more directly relate the effect of fatigue on the tennis player's balance performance. The data analysis showed that the tennis training session did not affect significantly the tennis players' balance ability. It should be considered that the present tennis session aimed to technique improvement and tactics of the game. This could explain the present findings from the dynamometric measurements in the knee extensors and flexors muscles, which revealed a reduction in the contractile joint moment by only 8-11%. Previous studies showed that deterioration on balance ability in sedentary individuals as a result of fatigue was found after controlled repeated ankle muscle contraction, leading to complete exhaustion or joint moment reduction by at least 50% (10,21,40). It is well established that in soccer players, high incidence of injuries occurred toward the end of a soccer training session (14,15,17,19). Similar levels of knee muscle fatigue have recently been reported in response to exercise simulating the work rate of competitive soccer (31). Also, in support to our findings, regular training soccer sessions in young soccer players did not affect the balance performance, and the dynamometric measurements (10) in the knee extensor and flexor muscles revealed that soccer training session reduced the contractile joint moment by only ∼10%.
Therefore, the absence of substantial muscle fatigue after the tennis training session may justify the present finding of maintenance of balance performance. Also, the players were elite tennis players, with no prior injuries. This latter result indicates that the function of relevant systems mediating postural control, including the muscular and proprioceptive systems (10,12,17,25,35,38), is not compromised as a result of a tennis training session in trained individuals. In addition, due to the nature of the tennis games and training, players may have increased balance performance. In support to this hypothesis, a previous study (13) showed that one-leg standing balance in basketball players was positively correlated with the years of participation in basketball, they suggested that practice may induce significant adaptive effects on standing balance. In the same study, the tennis players had the best time of one-legged balancing among players of other sports.
To conclude, the present findings showed that a tennis training session did not deteriorate significantly balance performance of elite tennis players. There was a decline in balance performance, which suggests that different level of fatigue for an extended period may have influence on the balance performance, given that tennis players are accustomed to fatigue exposure for an extended period.
Although it has been shown that the onset of fatigue after a tennis training session was accompanied with a decline in tennis performance, missed strokes, and poor timing (37), relevant information is lacking as to whether fatigue may influence balance performance. The present study showed a tendency for some balance deficits after a regular tennis training session, which may be increased with higher level of fatigue, and suggests that a tennis-specific balance exercise should be included in a player's daily tennis training session to maximize performance and minimize the injury risks in tennis. The question remains as to when is the better time to perform the tennis-specific balance exercise program, before or after training.
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