All training sessions were supervised by a certified Sportsmetrics instructor and a tennis professional certified by the United States Professional Tennis Association. The instructors kept written records of all exercises performed by each athlete for each training session. There were 3 sessions conducted per week (Monday, Wednesday, Friday) for 6 weeks. Each session lasted 1.5 hours. During the jump training and speed and agility drills, players were encouraged to maintain a neutral alignment by reinforcing the knees and ankles to be placed hip distance apart with exaggerated knee and hip flexion on landing from a jump, decelerating, and cutting. The trainers and tennis professionals gave constant feedback on body mechanics during all training drills. Instructional terms and cues such as “land softly,” “ keep your knees and feet directly under hips,” and “bend your knees deeper” were repeatedly used to aid in the education process. Proper stroke instruction and footwork were also continually emphasized. Strength training placed an emphasis on hamstring, quadriceps, gastrocnemius, soleus, hip flexion and abduction, and core to aid in proper lower extremity alignment and muscle recruitment patterns. Upper body strengthening was accomplished with a medicine ball, hand weights, and body exercises such as wall push-ups and seated press-ups. Core strengthening involved a series of exercises, beginning with 150 repetitions and progressing up to 300 repetitions. Static flexibility exercises were performed at the end of each training session.
All data were normally distributed (Kolmogorov-Smirnov test), and therefore, a 2-tailed paired t-test was used to detect differences for each test between the pretrain and posttrain periods. Effect sizes were calculated and interpreted according to Cohen's standards (4). A level of p ≤ 0.05 was considered to be statistically significant.
No athlete sustained an injury or developed an overuse syndrome as a result of the training program. All athletes completed at least 14 of the 18 training sessions; 3 players completed 14 sessions, 2 completed 15 sessions, 4 completed 16 sessions, 3 completed 17 sessions, and 3 completed 18 sessions.
Upon completion of training, statistically significant improvements were found for the baseline forehand and backhand tests, the service line test, the 1-court suicide, the 2-court suicide, the abdominal endurance test, and the single-leg crossover hop for both legs (Table 2). Large effect sizes were noted for the majority of these tests, except the single-leg hop.
Highly significant improvements were noted for both baseline tests, because 67% improved the forehand test score and 80% improved the backhand score. In the service line test, all but 1 player improved. In the 1-court suicide run, all players improved, and in the 2-court suicide, all but 1 player improved their time to complete the test. The greatest average percent improvement was noted in the abdominal endurance test (76%), with all but 2 players demonstrating better times.
Normal limb symmetry (≥85%) was detected in the single-leg triple crossover hop in 87% during both test sessions. A mean improvement of 36 cm was detected in both legs (p ≤ 0.05). Normal limb symmetry was recorded in the single-leg hop test in 87% of the players during the pretrain test and in 93% at the posttrain test. The mean distance hopped did not significantly improve between test sessions. Sixty-seven percent of the players did show some improvement in the distance hopped on the right leg, whereas 47% had improvement in the left leg.
Tennis is a demanding sport for the competitive athlete because it requires a combination of technique, speed, agility, explosive power, and aerobic conditioning along with the ability to react and anticipate quickly and cope with fatigue and pressure throughout a match (11,43). These attributes have been demonstrated to correlate with tournament performance in elite players (24,45). Our training program is unique in that it comprises a blend of neuromuscular training and sport-specific enhancement tasks to specifically improve dynamic balance, agility, speed, and strength. We were unable to find a similar multiweek program designed specifically for adolescent competitive female and male tennis players in the literature to compare our results to, because most studies provide a single-time physiological profile of players (1,7,9,13,18,35,36,48).
The neuromuscular training principles and exercises chosen for this study were derived from a previously published training program (3,16,17) that was shown to be effective in improving neuromuscular indices and reducing the risk of noncontact knee ligament injuries in adolescent athletes. Our program requires a dedicated tennis professional who understands the basis for the neuromuscular training elements to instill them into the tennis-specific drills, along with proper stroke and footwork instruction. Supervision of training of competitive tennis players is essential for continued improvement in both the physical and mental aspects of the game. Kovacs et al. (29) found that just a 5-week period of unsupervised tennis training resulted in significant reductions in speed, power, and aerobic capacity in collegiate nationally ranked players.
Core stability and strength are required for trunk rotation that occurs during the serve and groundstrokes, especially the open-stance forehand (23). These elements play an integral role in tennis performance and are well-established requirements in tennis conditioning programs (8,44). The combination of trunk rotation and upper limb drive (shoulder internal rotation, elbow extension, wrist flexion) are crucial components that help bring about optimal racquet speed and position at ball impact (30). Ellenbecker and Roetert (8) established an isokinetic profile of trunk rotation strength in 109 elite male and female tennis players aged 11-54 years. The men had symmetrical strength between the forehand and backhand directions, and the women had only small (4-8%) differences in strength between these directions. The authors suggested that core-stabilization programs should focus on both directions of trunk rotation to enhance muscle strength and balance. Our program incorporated numerous drills and exercises to improve core strength and stability in both directions, such as twisting lunges with a medicine ball and exaggerated forehand and backhand medicine ball throws. Abdominal exercises on mats were performed at the end of the training sessions, beginning with 150 repetitions the first week and progressing up to 300 repetitions, using a variety of exercises. The training program appeared effective, because all but 2 players improved in the abdominal endurance test.
Although the program included upper body strength exercises, it is recommended that players perform additional upper body strength training either during the program sessions or on opposite days that training is conducted. It is also suggested that this training program be conducted during a 6-week time period in which the player is not peaking for important tournaments or school competition. In this manner, the player focuses on the goals of the program and will be less likely to miss training sessions because of travel or tournament scheduling conflicts.
There are many tests that are available to determine alterations in neuromuscular indices. We choose a small battery of tests to measure lower limb symmetry and balance, agility and speed, and abdominal endurance. We avoided previously described tests that required equipment not normally available in tennis facilities or that required advanced medical knowledge. For instance, the United States Tennis Association has a testing protocol in which many of the tests require a physical therapist or athletic trainer to perform with tools such as a goniometer, blood pressure cuff, grip-strength dynamometer, and skinfold calipers (44). The tests described in our study can be performed by any individual without the need for expensive equipment. Our future assessments will include the low-cost, established multistage fitness test to determine VO2max (31,41) and medicine ball throws to assess upper body strength (44). Girard and Millet (13) conducted a study on elite male tennis players aged 13.6 ± 1.4 years and found asymmetry between the strength of both upper and lower limbs. The authors suggested the importance of continual monitoring these factors during puberty and modification of training to reduce these imbalances and the risk of injuries. Kovacs et al. (29) also recommended that coaches assess on a regular basis strength, speed, agility, and aerobic capacity of elite players to ensure better compliance with training programs.
We videotaped the single-leg hop tests to show the athlete and parents the player's body position on landing to determine if they had adequate control of the core, upper extremity, and lower extremity. We found subjectively that only approximately one-third of the players were able to maintain an adequate body position on landing before training (Figure 5). The others demonstrated noteworthy medial-lateral displacement at the knee joint, along with poor upper body control and posture. Some athletes had exaggerated trunk flexion that affected their ability to hold the landing position. Twenty percent of the players were unable to hold the landing and fell to the ground (Figure 5C). After training, marked subjective improvements were noted in the neuromuscular control on landing in all but 2 of the players. The improved technique translated into superior confidence and significant increases in the distance hopped in the triple crossover hop. We believe this test provides a measure of dynamic balance in addition to limb symmetry, more so than the single hop for distance task. There was no significant improvement in the single hop for distance test for either the right or left limb, which could have been because the training program did not include single-hop training. The only single-leg exercise was the triple hop, which was done during weeks 3-4. Still, we believe that these single-leg hop functional tests are valuable in detecting lower limb asymmetry that typically would not be depicted by the other testing procedures.
Unfortunately, tennis is associated with a unique profile of injuries because of its demands and the tremendous range of age and skill level of players. To date, there have been no published injury prevention training programs designed specifically for this sport. In a review of 119 articles, Pluim et al. (39) concluded, “we were unable to identify measures proven to prevent tennis injuries.” Kibler and Safran (21) noted that specific alterations in mechanics, such as incomplete flexion of the knee (less than 10°) in the cocking phase of the serve, increased loads in the shoulder and elbow by 23 and 27%, respectively. Overuse injuries are common, including patellofemoral pain syndromes, patellar tendinitis, bursitis, Achilles tendinitis, plantar fasciitis, rotator cuff inflammation, lateral epicondylitis, and medial epicondylitis. In a study of 4 United States National Association national junior tournaments, the incidence of medical withdrawals was calculated to be 11.7 per 1,000 athletic exposures in the 14 and under age group, which increased to 20.6 in the 16 and under group and 22.7 in the 18 and under group (20). Our future goals are to determine if this program is effective in reducing injuries in junior tennis players and to assess if a difference exists between genders in changes in neuromuscular indices after training.
There exists a tremendous array of tennis instructional materials, from books to videotapes to online sources. Although many of these resources provide sound advice based on medical and research experience, it is difficult to find a specific training protocol in which the exercise progression is provided in detail and is based on a program proven to improve neuromuscular indices in young athletes. Therefore, our purpose was to develop a tennis-specific training program for competitive junior players that implemented the essential components of Sportsmetrics and added exercises and drills designed to improve dynamic balance, agility, speed, and strength. The results of this study show that this program is feasible, low in cost, and appears to be effective in improving the majority of neuromuscular indices tested. One limitation is that there was no control or comparison group in this investigation, which will be included in future studies.
We devised a 6-week training program for competitive junior tennis players. The program is unique in that it incorporates jump training and other drills from a previously published training program reported to improve neuromuscular indices and reduce the risk of knee ligament injuries in adolescent athletes. The supervised training sessions are conducted 3 times a week for 1.5 hours per session. The program includes a dynamic warm-up, plyometric and jump training, strength training (lower extremity, upper extremity, core), tennis-specific drills, and flexibility. This program is low in cost and appears to be effective in improving speed, agility, abdominal endurance, and single-leg function and balance in young tennis players. All training and testing procedures are performed on the tennis court, and we recommend that this program be conducted during a time period in which the player is not peaking for important tournaments or school competition. Further research is required to determine if this training program can reduce the incidence of injuries in tennis players.
The authors would like to thank Gateway Golf and Country Club, Fort Myers, Florida.
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