Improving an athlete's tennis-specific movement requires the coach or trainer to understand the movement patterns that occur during play, as tennis movement is highly situation specific and is performed in a reactive environment (14). This irregularity of movement and the need to continually respond to situations require the coach to spend time understanding the athlete's game style, strategy, movement strengths, and weakness, which will help aid the development of a tennis-specific movement training program. Although tennis movement has some consistent traits among all athletes, it is highly specific to the position the athletes are in on the court and what type of shot their opponent has just made. Therefore, it is vastly different than teaching a wide receiver how to break from the line of scrimmage or a track sprinter starting from the blocks. Tennis is a highly reactive sport, and movement training needs to progress from a simple closed skill environment to an open skill environment using visual stimuli. It is important for coaches and trainers to understand the role of cognition and decision making in an athlete's ability to react to a stimulus (tennis ball). This ability to react will have a direct effect on the perceived speed and agility of tennis players. As the purpose of this article is to examine the physical aspects of lateral specific movement for tennis, limited discussion will be on the important area of cognition and decision making. More in-depth discussion and review of cognition and decision making can be found in the literature (32).
TYPICAL MOVEMENT DEMANDS
In competitive tennis, the average point length is less than 10 seconds (11,12) with the recovery between points usually between 20 and 25 seconds depending on certain rules. After every 2 games (minimum of 8 points), the athlete has a 90-second break before the next point is played. Although every tennis point is vastly different, it is helpful for the coach to understand the movement requirements of competitive tennis. Tennis players make an average of 4 directional changes per point (15,27) but can range from a single movement to more than 15 directional changes on a very long point. In a competitive match, it is common for players to have more than 1,000 direction changes. At the French Open (one of the 4 major professional tournaments, also known as Grand Slam events), which is played on a clay surface, a study was undertaken on 1,540 strokes to determine the typical distances covered. Researchers found that 80% of all strokes were played with less than 2.5 m and fewer than 5% of strokes were played requiring more than 4.5 m between strokes (24). Other similar studies have found movement distances on average to be approximately 4 m per change of direction (25). Relatively short distances that a player covers on each stroke are typically less than 2.0 m, yet under higher time pressure (increased running demand), athletes can run on average about 4 m (maximum of between 8 and 12 m) (33). It is interesting to note that tennis players can cover about 0.25 to 0.50 m more on their forehand side than their backhand side (33). These are important findings, as most speed and quickness programs for other sports focus on distances that are longer where a full traditional acceleration position may be reached. In tennis, it is rare that distances are achieved where a traditional acceleration technique will be experienced by the athlete. Furthermore, the majority of tennis movements are lateral. In a study of professional players' movement, it was found that more than 70% of movements were side to side with less than 20% of movements in a forward direction and less than 8% of movements in a backward direction (33). This is a vitally important statistic for coaches and trainers because the development of lateral acceleration and deceleration in the distances described above are the major determining factors in great tennis movement. It is known that linear acceleration, linear maximum velocity, and agility are all separate and distinct biomotor skills that need to be trained separately (36), as training one will not directly impact the improvement of the other. Therefore, preferred training recommendations for tennis should be to focus training between 60 to 80% of the time on lateral movements, 10 to 30% of the time on linear forward movements, and only about 10% of the time on linear backward movement.
HOW DIFFERENT SURFACES INFLUENCE TENNIS MOVEMENT
Tennis is played on a number of different playing surfaces, even at the professional level. Although there are dozens of different surfaces around the world, for sake of discussion, there are 3 major groups of surfaces that players typically compete on-hard courts, clay courts, and grass courts. These different court surfaces result in different movement requirements due to the speed, cushioning, and friction of the court. Brody (4) has found that the horizontal frictional force greatly affects ball speed and is a determining factor in court speed. There can be as much as a 15% difference in ball speed after the bounce, depending on the court surface. Typically, a clay court is slower than a hard court. This reduction in ball speed allows athletes more time to reach the ball, therefore lengthening the duration of points played on clay courts. A computerized notational analysis of 252 professional singles matches found that rallies from women's singles matches (average 7.1 seconds) were significantly longer than rallies from men's singles matches (5.2 seconds). Rallies on clay courts at the professional level were significantly longer than any other surface (23). In a study looking at baseline points as a percentage of total points at the 4 Grand Slams found (23):
- French Open (clay court) 51%
- Australian Open (hard court) 46%
- US Open (hard court) 35%
- Wimbledon (grass) 19%
Another interesting difference between surfaces is that on hard court professional players are under increased time pressure 45% of time, whereas it is only 29% on clay courts (25). Therefore, coaches need to take these statistics into account when preparing athletes for hard court events versus clay court events.
LATERAL MOVEMENT IN TENNIS
With lateral focused agility training, the spinal reflex times of the following muscles improve (vastus medialis/lateral medialis due to anterior tibialis translation) and the cortical response time improves in the gastrocnemius medial hamstring (semimembranosus, semitendinosus) (35). This is helpful for coaches when designing training programs in the gym, as it should help to focus training on the specific muscle and movements that can help improve lateral movement performance. There are a multitude of movements that a tennis athlete performs during every match or practice (in a perfect scenario, all possible movements and distances will be trained); however, in most practical situations, a time-efficient training program needs to be implemented. To aid the coach in understanding the typical elements used during lateral movement on court, there are 3 distinct initiating movements that are usually used by players during baseline movement-jab step, pivot step, and the gravity step.
- The jab step has been defined as stepping first with the lead foot in the direction of the oncoming ball (Figure 1).
- The pivot step involves pivoting on the lead foot while turning the hip toward the ball and making the first step actually toward the ball with the opposite leg (Figure 1).
- The gravity step involves bringing the lead foot in toward the body and away from the direction of the oncoming ball and ultimately away from the direction of the intended movement (Figure 1). This small step (unweighting) actually moves the center of gravity outside the base of support.
In a study that compared the jab, pivot, and gravity steps on tennis movement, it was found that the fastest method to move laterally was by using the gravity step (2). The authors speculated that the greater speed to the ball and greater control were due to the fact that the gravity step produces an overall movement toward the ball after the initial movement of the lead leg in a direction away from the ball. Unlike the jab step (where the center of gravity remains between the base of support), the gravity step creates a “dynamic imbalance” (2). This movement of the center of gravity outside the base of support actually assists in moving the body laterally to the ball. This is a similar principle to the back step (or drop step) seen when athletes attempt to break inertia in a forward direction (17). Currently, limited data are available in the tennis literature on how best to structure lateral movement training programs using varying volumes and intensities. More research is needed to provide the coach with greater insight into volumes, intensities, and loading patterns for tennis-specific lateral movement training.
Recovery movement occurs immediately after the athletes have completed their stroke and they are attempting to return to a position that will allow for efficient movement toward the next stroke. There are 2 typical movement positions used during the recovery movement-the lateral crossover (Figure 2) or the lateral shuffle (Figure 3). The lateral crossover is more appropriate for movements that require quicker responses and greater distances (27). The lateral shuffle is more common when the athlete has a little extra time to get back in position before having to explosively move to the next shot (27). It is important to incorporate both of these when structuring tennis movement sessions.
SPLIT STEP MISCONCEPTION
Due to the evolution of tennis and the reliance on speed and power in today's game, the movement patterns of players have been adapted. Early descriptions of the split step reported both feet landing on the court simultaneously (9) and then the athlete would react left, right, forward, or backward depending on where the ball was hit. However, due to advances in the speed of the sport and the coaches' ability to analyze athletes using high-speed video, it has emerged that elite players actually react in the air during the split and land on the foot furthest from their intended target a split second ahead of their other foot. An example would be the right-handers preparing to hit a forehand, would land on their left foot first (Figure 4). Before the right foot touches the ground, the athletes subtly rotate their hip externally toward the intended movement toward the ball. In the right-handed player, this would result in the right foot landing pointing outward (Figure 4). The movement pattern described above has been a natural evolution to improve the athletes' ability to react to the incoming ball and maximize their movement to time ratio.
“ON THEIR TOES”
Many coaches profess to their tennis athletes to play on their toes (or balls) of their feet. However, this is a misconception that tennis players move this way on court. This has stemmed from the fact that tennis players typically have callous formation on the balls and toes of their feet. When analyzing foot and ankle movement mechanics of tennis players, it is clear that they use a similar heel to toe progression that is used by runners and other athletes (28). Therefore, the “on their toes” coaching cue should be eliminated from the tennis trainer's vernacular.
NEURAL ASPECTS OF MOVEMENT
Developing an athlete's maximum movement capabilities on the tennis court requires the combination of technical, physical, and neural development. This section will discuss the aspects of neural development that should be understood to aid the coach in the implementation of tennis-specific movement training. However, it must be understood that the majority of information on this area has been performed on linear movements as well as vertical jumping activities, and more information is still needed on tennis-specific agility-induced responses. Maximal intensity movements require high levels of neural activation (21). From the literature, it has been shown that measurable neurological parameters (nerve conduction velocity (NCV), maximal electromyography [EMG], motor unit recruitment, and H-reflex) alter in response to physical training (29), specifically speed training. Differences in running technique and muscle activation patterns have been reported among trained sprint athletes compared with controls or endurance athletes (29).
NERVE CONDUCTION VELOCITY
NCV is a measure of the speed an impulse can be transmitted along a motor neuron and is strongly related to muscle contraction time (1,18). A rapid NCV is a representation of a short refractory period. This decreased refractory period may allow for greater impulse frequency, which would result in an increased level of muscle activation.
MOTOR NEURON EXCITABILITY AND REFLEX ADAPTATION
An increase in motor neuron excitability leads to a more powerful muscle contraction (26). Motor neuron excitability is commonly assessed using the H-reflex. The H-reflex is often regarded as a monosynaptic reflex response analogous to the tendon reflex, although it is elicited by electrical stimulation (29). Training should have the goal of increasing this motor neuron excitability to improve the speed and force of the muscle contraction to improve movement. During the stance phase, evidence suggests that the stretch reflex makes a strong contribution to leg extensor EMG, aiding propulsive force (6). Muscle pre-activity (activity before ground contact) likely increases muscle spindle sensitivity, potentiating the stretch reflex contribution (19). The utilization of plyometric focused programs needs to be implemented with a lateral focus. Tendon compliance is the degree of compliance of the tendon, which affects the force through the muscle and the resultant feedback from the muscle spindles. It has been speculated that training for strength and power will enhance the length feedback component that originates from the muscle spindles, which may be enhanced by training, possibly improving muscle stiffness on contact (1,10,13). This is then hypothesized to improve ground reaction forces (GRFs) and translate into more powerful movements.
One other area that can have an immediate impact on how fast an athlete appears in short distances is the athlete's reaction time. Reaction time is defined as the time from a stimulus (visual awareness of the opponents stroke/ball) until the production of force (30). For over 100 years, the accepted figures for simple reaction times for college-aged individuals have been about 190 milliseconds (0.19 seconds) for light stimuli and about 160 milliseconds (0.16 seconds) for sound stimuli (3,7). However, the fastest athletes in the world consistently have reaction times less than 0.15 seconds (8,20). In identical events, women have been shown to have longer reaction times than men (22). However, reaction time does not correlate well with sprints lasting longer than a few seconds (20), yet it does correlate very well with distances typically seen in tennis play (20). Therefore, training an athlete to improve reaction time should be a component of training tennis movement, alongside technique, strength, and power. In many training drills, a visual stimulus should be used to help develop visual reaction time. An auditory stimulus (whistle, voice, and hand clap) is less tennis specific than the visual cue. The benefit of progressing from no stimulus to a single visual stimulus to multiple visual stimuli will help develop an athlete's ability to react. Improving the athletes' choice reaction time (having to respond to more than 1 stimulus (34)) may help the tennis athletes in their reactions on court and would be advisable to add this as a training stimulus during off-court training. A study looking at average reaction times (from ball machine release to initial racket movement) in skilled tennis players' volleys was 0.226 seconds for the forehand and 0.205 seconds for the backhand (5). It is important to teach movement technique before progressing to more challenging environments including visual stimulus.
After breaking inertia, the athlete's aim is to increase acceleration. Faster athletes have greater force production and horizontal velocity than the slower athletes during the last contact points on the ground (22). This means that the power output at the last stage of ground contact is higher in faster athletes, and this is an area that coaches should focus on during training sessions. Developing this increased power output at ground contact will directly increase GRFs, translating to quicker responses. Sprinting technique during an athlete's acceleration is vastly different to that of an athlete who is running at or near maximum velocity (19,31) (Figure 5). Most competitive athletes do not reach maximum velocity until 40 to 60 m (depending on training level/genetic ability). As mentioned previously, tennis athletes typically move less than 2.5 m and rarely exceed 5 m and less than 30% of movements are forward/backward (33). It is imperative that the majority of training programs are structured appropriately to train specifically for the movements experienced during tennis.
SUMMARY AND PRACTICAL APPLICATION
Coaches and trainers need to understand the patterns of movement, specificity, and reactive environment in which tennis occurs to develop training programs that progress from a simple closed skill environment to an open skill environment using visual stimuli. The demands of tennis movement are vastly different from that of other sports, and appropriate training programs should address the work to rest ratios, distance, number of directional changes, and types of movement. It is important to incorporate all these actions when structuring tennis movement sessions. Several aspects of neural development that should be understood to aid the coach in the implementation of tennis-specific movement training include the principles of improving measurable neurological parameters and reaction time. Specific speed training has been shown to improve nerve NCV, maximal EMG, and motor unit recruitment or H-reflex. A rapid NCV is a representation of a short refractory period that may allow for greater impulse frequency, resulting in an increased level of muscle activation. Training (such as plyometric programs with a lateral focus) accomplishes the goal of increasing motor neuron excitability to improve the speed and force of the muscle contraction to improve movement. Furthermore, tendon compliance has been hypothesized to improve GRFs and translate into more powerful movements.
SAMPLE EXERCISE FOR TENNIS-SPECIFIC LATERAL TRAINING
- Lateral movement with medicine ball catch: This exercise simulates the lateral movement that tennis players are required to make during points (backhand sequence for a right-handed player-Figure 6). The addition of the visual stimulus of the medicine ball (MB) being thrown to them requires the athletes to decelerate while maintaining balance to efficiently catch the MB while maintaining a strong core region and lower-body dynamic balance. An advanced progression is to hold the catch position for 2 to 4 seconds followed by an explosive release of the MB as far as the athlete can throw it. As a coach, the visual cue should be the transfer of GRF through the core and up through the upper body to generate the power into the MB throw.
- Side lateral mini hurdle runs (Figure 7 (16)): This is a lateral focused plyometric movement that focuses on the muscles of the lower body, from a stretch-shortening perspective, but also at the end of each set of 4 hurdles, the athlete needs to decelerate and come to a complete stop and hold the lower center of mass position for 2 seconds before reacceleration back into the exercise.
- Lateral resistive running: This is a more advanced exercise that should only be incorporated once an athlete has appropriate strength and stability in a lateral direction to gain benefit from added resistance without technique faltering (Figure 8). This exercises works on the muscles heavily involved in lateral movements and requires the athlete to balance the upper body, while the lower body is pushing against resistance in a lateral direction.
- Slide board: Using a slide board is a great method to develop the muscles and movements required in lateral tennis movement-especially when an athlete needs to compete on a clay surface (Figure 9). The sliding motion simulates a similar requirement during clay court tennis movement. This drill can be enhanced by using a tennis ball as an environmental cue, which the athlete would need to catch while sliding. This would increase the tennis specificity of the exercise and includes the need to react to stimulus (tennis ball) that is identical to the stimulus on court.
- T-line to S-line shuffle: This exercise has the athlete start at the T-line (the center of the court) while facing the net and proceeds to side shuffle to the S-line (singles line) and back to the T-line Figure 10). This covers a typical distance that a tennis player will have to move before changing direction during matches. Once the movement is understood, the coach can then provide visual or auditory stimulus to prompt the athlete to perform either the crossover (Figure 2) or shuffle (Figure 3) step when changing direction. This exercise can also include greater difficulty and more specificity to tennis play by adding environmental cues that would require the athlete to respond to a visual stimulus (tennis ball or player at the opposing side of the net) as the cue to start movement or change direction.
- The sample exercises provided can help the coach decide on the best exercises to incorporate into an overall periodized tennis-specific program. Table 1 provides a sample lateral-focused training session to develop an athlete's tennis-specific movement.
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