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1 Word count: 3324 Tennis: Physiology, Training, Injuries A. Therminarias, Laboratoire de Physiologie, Faculté de Médecine de Grenoble, 38.700 La Tronche, France. Tennis is a racket sport enjoyed by all standards and age, all over the world. It may be practiced as a recreational activity as well as in competition at different levels. Success at any level requires technical training and skill. Moreover, to be competitive the elite players must possess specific capacities related to biomechanical and physiological characteristics of this game. Physiology Physiological knowledge of tennis comes essentially from studies of players' physical characteristics, analysis of the type of activity and observation of physiological responses obtained on court . Physical Characteristics Males and females whose exclusive mode of regular exercise is tennis displayed usually a lower relative body 2 fat and a higher aerobic power ( V O2max) than a sedentary population of the same age and sex. Thus, young elite athletes were seen to have V O2max values close to 55 ml.kg-1.min-1 for females and 65 for males. They also display an above average maximal alactic power (forcevelocity tests, 40-meter sprint) (1). Moreover, compared to an untrained population, competitor players possess a higher grip strength in the preferred hand (6), a greater isokinetic strength for shoulder internal rotation and extension, wrist flexion and extension and forearm pronation (4). They may also have stronger lower limb muscles such as knee extensors and flexors. Moreover young elite players may be tighter in some movements such as shoulder internal rotation and more flexible in other movements such as shoulder external rotation (3). On the other hand, they have superior agility scores for specific tests requiring sudden changes of direction and body position while running at top speed in a small area (1). They tend to have better simple and complex reflex response time than the average (8). . . Analysis Of The Activity Tennis is an intermittent activity characterized by short bouts of high exercise intensity interspaced with periods of rest or moderate intensity. During a match, the game may last less than half an hour and up to several hours. One rally may last one stroke and 1.5 seconds or several tens of strokes and several minutes. More usually, 3 it lasts from 6 to 12 seconds with approximately 18 seconds of rest or moderate intensity between rallies. This rest time may reach up to 90 seconds, every odd game, when the players change sides. Thus, the total time of intense activity constitutes in average 25% of the total game time (2,5,10). However, this duration varies considerably according to the players' standard, style and sex. It is also influenced by factors such as the court surface, being generally longer on clay than on grass surfaces. During a rally the activity is characterized by quick bursts of running, often at top speed, with sudden changes in direction and position to correctly place the body in accordance with the stroke being executed . The execution needs specific changes in position of body segments organized in a particular time and space sequence. The ensemble requires a rapid target detection, a short reaction time and a large visual-motor coordination. Physiological Responses "On-Court" Cardiovascular involvement. The heart rate (HR) variations monitored during matches reflects the intermittent nature of the activity (2,5,10). During or immediately after a rally, HR may reach values close to the maximum HR (HRmax), decreasing more or less between each rally and much more when the players change sides. In skilled players, during a singles match, after the initial 5-6 minutes of play, mean HR may rise up to 80-85% of the HRmax and be maintained throughout the match. Simultaneously, the systolic blood pressure rises. 4 Exceptionally, in middle-aged subjects involved in a long and strenuous match, meanHR may progressively increase up to HRmax (10) outlining the cardiac strain and thus the cardio-vascular risks sometimes inherent to this activity. During doubles tennis competition mean HR reaches considerably lower values. Metabolic requirements. The mean HR measurements suggest a relatively high level of oxygen consumption. However, the discontinuity of the activity and factors such as emotional stress, use of arms, and hot conditions may overvalue the HR response. The oxygen consumption measured in male competitors on-court ranged from 24-28 ml.kg1 .min-1 accounting for approximately 50% of their maximal aerobic power (5). On the other hand, central body temperature which increases proportionally to the exercise intensity, rose to approximately 38.3° C during a strenuous match (10). Plasma lactate concentration does not change or increases moderately throughout a match (2,10). During training tests, only exercises compounding more than twelve successive strokes induced an increase in plasma lactate greater than 4 mM. Such series are rare under usual conditions since in competitive singles matches on a hard surface, men play a mean of 4 strokes per rally. Blood glucose concentrations remains steady or increases during strenuous matches lasting up to 2 hours, even without carbohydrate ingestion (2,10). Possibly a longer duration may elicit hypoglycemia. Plasma free fatty 5 acid (FFA) concentration increases during matches as well as plasma urea, uric acid and creatinine (10). These data suggest that during the short bursts of intense effort energy comes principally from the phosphagen stores within the activated muscles. The duration of rallies and the low increase in plasma lactate imply only a minor participation of the anaerobic glycolytic process to the energy production. This participation may increase during an unusually long rally. The preferential utilization of the phosphagen induces an alactic oxygen debt requiring rapid repayment prior to the beginning of the next rally. Eighteen seconds of recovery constitute a sufficient time for a partial restoration of the phosphagen within the muscles via the aerobic system. This period may also favor the removal of lactate possibly formed during a rally. A more complete restoration will likely occur during the longer recovery periods provided by each change of side. A rapid recovery is probably favored by high aerobic power, short oxygen uptake transient and high myoglobin stores. On the other hand, the large increase in FFA found during the match suggests that a great part of the aerobic energy production comes from the oxidation of fat. Water loss and electrolyte changes. During the warmer seasons, heat stress adds to the metabolic heat production due to exercise and sweat production increases. Male players may lose up to 2 l.h-1 of sweat and women more than half this rate. If water intake is insufficient, dehydration occurs which may result in a compensatory increase in HR and a greater feeling of fatigue. Middle- 6 aged players appear particularly vulnerable to the consequence of dehydration (10).Thus players should regularly replace fluid loss by fluid intake. Because sweat is hypotonic compared to plasma, the electrolyte loss remains usually negligible. Thus no decrease in plasma sodium, chloride, potassium or other electrolytes had been found after a strenuous match (10). Apparently, salt supplementation is not necessary. However, alteration in the relationship of sodium, potassium, calcium and magnesium at the muscle membrane, as well as iron deficit, may favor the occurrence of fatigue and cramps. Deficiencies in these components should be detected and corrected by a daily appropriate diet. Hormonal Changes A tennis match of sufficient duration and intensity induces a rise in plasma norepinephrine concentration which may play a role in the increase of cardiac output, the control of peripheral circulatory adjustments and the FFA mobilization. No increase in plasma concentration of epinephrine (10) or cortisol (2) had been found during the matches. Possibly during a real competition, both these hormones increase as a consequence of the emotional stress. In male players plasma testosterone may rise (2). Under hot conditions, the plasma renin activity and the plasma arginine vasopressin concentrations increase during a match (10). This hormonal response tends to limit the fluid and electrolyte loss. 7 Training Success in tennis depends on numerous factors including a good racquet technique and skill, a good physical preparation, a correct psychological approach and a good on court tactic. The goal of training is to optimize all these factors according to capacity, possibility and aim of the players. Technique and Skill A good technique appears to be a good predictor of performance. Training should help players to develop a good technique, generally based on the current techniques used by champion players. The biomechanical analysis of the production of the basal strokes: forehand, backhand, serve and volley shows that a perfect achievement requires complex and co-ordinated movements of upper and lower parts of the body. These movement patterns may create individual problems and have the potential to cause injury. Consequently a good technique would be also based on the individual characteristics of the players. For beginners a relatively high amount of time will be spent on practice. In competitive players technical training will tend to maintain the strong trait, but principally to improve the individual's weaknesses Fitness Preparation Although fitness parameters cannot properly predict tennis performance, players should be able to tolerate the 8 physiological demand without failure. In competitive players, specific conditioning programs are necessary to develop basic physical qualities such as muscle strength, power and endurance, flexibility, coordination, as well as anaerobic and aerobic capacities (6, 9). Strength and power: A vital aspect of tennis is to exert muscular force at a high speed. A strengthening program serves to increase the force generated by training muscles, improve their tolerance to fatigue and ameliorate their solidity. It should be specific and concern the key muscle groups involved in the strokes. It will tend more specifically to correct muscular weaknesses. Thus a weak wrist cannot provide the strong opposition necessary to counteract the reaction of the ball and racquet and should be strengthened. Moreover, to preserve skeletal joint stability and prevent overuse injuries, the program should balance conditioning of agonist and antagonist muscles. Upper body strength should deserve particular attention for achieving optimum stroke potential. However, a proportionate amount of lower body strength exercises should be performed. The lower body should be strong enough to enable the athlete to accelerate the body over the court and strike the ball with maximum impact. In addition, strength programs should incorporate exercises which minimize the degree of structural and functional asymmetry induced by this unilateral sport. Flexibility, balance and coordination: Along with the strength training, flexibility exercises are of vital importance to keep the optimal functional range of motion 9 and thereby improve the efficiency of the strokes and prevent injuries. In addition, tennis skills require a variety of aptitudes including balance, muscle coordination, rapid target detection, low reaction time and visual-motor coordination which may be improved by specific exercises. Anaerobic and aerobic fitness: During a rally, agility and speed of lower extremities are crucial and require specific conditioning. The best result of training is generally achieved when the activity replicates the actual demands of the sport. Thus interval skill drills on court, involving work periods shorter than 15 seconds and recovery periods shorter than 30 seconds have been proposed (5). However the ideal pattern of interval training remains a debate in need of additional research. It depends upon the player's style, physical characteristics, age and sex. The most effective drills are those approaching the actions in a match. Unfortunately, it is difficult to know before a match who of the two players will impose his style. A strong base of aerobic fitness including aerobic power and endurance capacity should be developed in competitive players to facilitate a rapid restoration of phosphagen stores, delay the appearance of fatigue and prepare the cardio-vascular system to the strain imposed by the game. Specific physical programs should be developed to improve any deficient physiological qualities in individual athletes. On the other hand, programs should be adapted to players' ages, sex and level. Moreover, a periodicity of 10 training exists in elite players. The aerobic fitness is principally developed during the off and pre-season periods, maintained through the playing season, and supplemented during the latter part of the pre-season and in-season periods by interval training programs. The periodicity of the training should able to peak at the right time (6). An appropriate series of phased macrocycles, altering the activity as well as the volume , intensity and frequency of the training enable to achievement of this goal. The physical program will, of course, be fully complemented by practice and games against opponents selected to probe particular technical, tactical and physical weaknesses. Mental Capacity Motivation, concentration and self confidence are crucial determinants of tennis success. In recent years, sport psychologists have proposed a variety of behavioral strategies which are alleged to improve tennis players' performance. Unfortunately, little is known about the respective efficacy of these techniques. Injuries The incidence of injuries is low compared to popular contact sports. It varies from 2.3 to 5 injuries per player and per 1000 tennis hours (11) . The risk is lower for recreational than for competitive players. It is 11 particularly high in young elite players with an equal distribution in both sexes. Nature and Mechanisms More than 65% of the injuries have developed gradually and are considered as overuse injuries. The predominant mechanism is overuse stress to bones, ligaments, muscles, tendons, and nerves (9). The other injuries may be explained by as a single trauma and are considered as acute injuries. They are frequently caused by a strain due to incorrect placement, excessive movements in the game, stumbling due to lack of balance, slipping on the court. Less frequent acute injury mechanism is a direct contusion caused by blow or impact of ball which may reach a velocity higher than 150 km.h-1. Anatomical Location and Typical Injuries. The injuries tend to be equally distributed to the upper and the lower extremities (11) with a more frequent localization of the overuse injuries in the upper part than in the lower part. In fact, the nature and the repetitition of injury change with the level, the frequency of play and age. Thus, elite junior players sustain twice as many acute injuries than overuse injuries, with a predominance of lower body injuries. Upper extremity injuries: In the upper body wrist and hand injuries are relatively uncommon, and are usually related to repetitive direct trauma from the racquet handle. Shoulder and elbow injuries are more frequent in 12 tennis than in other racquet sports, probably related to a higher load impact with a heavier racquet. They constitute the biggest problem for championship tennis players. Tennis elbow is a pain on either side of the elbow which causes discomfort or disability when playing (7). Approximately 50% of tennis players had suffered elbow pain during their playing lifetime. It can occur at any age. However, the peak incidence is between the ages of 40 and 50 years. The mode of onset may be gradual or acute when tendons are put under strain by vigorous gripping. It may be caused by a technical error which sometimes may be determined by the location of the pain. Lateral tennis elbow, 4 times more common than medial, is frequently connected with an improperly executed backhand or serve strokes. Medial tennis elbow, generally attributed to repeated wrist flexion overload during the service or to a powerful forehand top spin, is common in elite or highly ranked recreational players. One of the factors suspected in the development of tennis elbow is the impact induced vibration of the racket-and arm-system at ball contact (7). Shoulder injuries have been reported to affect 50% of world class players sometime during their career (9). Overuse shoulder injuries are generally connected to adaptive changes to the dominant shoulder including a drooped and hypertrophied shoulder girdle with chronic over-stretch of several muscles. Overuse of the rotator cuff muscles leads to glenohumeral instability which, combined with scapular droop, may subject the cuff muscles to impingement under the acromion and the coracoacromial 13 arch especially during serving and overhead strokes. The shoulder depression could theoretically be prevented by proper training of the elevating muscles of the shoulder. Shoulder injuries may also be localized to other subacromial structures such as subacromial bursa and biceps long-head tendon. Lower extremity injuries: In the lower body, foot and ankle injuries constitute up to 50% of the injuries with a predominance of ankle sprains (11). These sprains have no specific characteristics. However, lateral ankle sprains occur more likely on hard than on clay courts which allows foot slippage. Knee injuries are also commonly seen in the competitive tennis players. Overuse knee injuries are often center around the patella and ilio-tibial band, and are associated with aggressive side-to-side and vertical jumps. A rupture of the medial head of the gastrocnemius muscle (tennis leg) may occur due to repetitive push-off from service and jumping overload to a knee-extended, ankleplantarflexed leg. Achilles tendinitis and rupture may follow a similar mechanism. This last injury is exceptionally reported in the different studies probably because it occurs principally in older recreational players. Other injuries. Back injuries, including cervical, interscapular and lumbosacral spine injuries are often associated with hyperextension mechanism during service and overhead strokes (9). Other injuries such as abdominal wall strain and eye injuries are also reported. 14 Precipitating factors Apart from previously described specific causes, various other etiological factors may play a role in the occurrence of acute injuries and in the development of overuse injuries. Improper material or equipment concerning handle size, weight, string tension, flexibility and imbalance of the racquet have been suggested to influence the occurrence of upper extremity injuries while footwear with a low shock absorption capacity or a poor side-to- side stability have been connected to lower extremity injuries. A lack of warming up, specially under cold conditions and an insufficient fluid intake under hot conditions may also be incriminated. But above all, a training error such as a sudden increase in duration or intensity or a lack of overall conditioning including aerobic fitness, flexibility, stretching and strengthening are frequently involved. These errors in training programs are favored by incomplete knowledge in physical and physiological requirements of this sport. Thus further research still is needed to help the player, coach and sports medicine specialist to improve their understanding of the game, promote maximal performance while preventing the occurrence of injuries. References 1. Buti, T., B. Elliott, and A. Morton. Physiological and anthropometric profiles of elite prepubescent tennis players. Physician Sportsmed. 12:111-116, 1984. 15 2. Bergeron, M.F., C.M. Maresh, V.J. Kraemer, A. Abraham, B. Conroy, and C. Gabaree. Tennis: a physiological profile during match play. Int. J. Sports Med. 12: 474479, 1991. 3. Chandler, T.J., W.B. Uhl T.L. Kibler, B. Wooten, A. Kiser, and E. Stone. Arm. flexibility comparisons of junior elite tennis players to other athletes. J. Sports. Med. 18:134-136, 1990. 4. Ellenbecker, T. S. A total arm strength isokinetic profile of highly skilled tennis players. Isokinetics and Exercise Science. 1:9-21, 1991. 5. Elliot, B., B. Dawson, F. Pyke. The energetics of singles tennis. J. Hum. Mov. Stud. 11:11-20, 1985. 6. Gropel, K. L. and E. P. Roetert. Applied physiology of tennis. Sports Med.. 14: 260-268, 1992. 7. Kamien, M. A rational management of tennis elbow. Sports Medicine. 9:173-191, 1990. 8. Mero, A., I. Jaakkola, and P. V. Komi. Neuromuscular, metabolic and hormonal profiles of young tennis players and untrained boys. J. Sports Sci. 2:95-100, 1989 9. Nicola T.L., Tennis, The team Physician's Handbook, M.B. Mellian W.M. Walsh and Shelton J.L., Handley and Belfus MC Philadelphia, 1990, pp 645-654. 10. Therminarias, A., P. Dansou, M. F. Chirpaz-Oddou, C. Gharib, and A. Quirion. Hormonal and metabolic changes during a strenuous match. Effect of aging. Int J. Sports Med. 12:10-16, 1991. 16 11. Winge, S., U. Jorgensen, and L. Lassen Nielsen. Epidemiology of injuries in Danish Championship Tennis. Int. J. Sports Med. 10:368-371, 1989.
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