Flexibility, like strength or endurance, is a functional component of movement and typically refers to the range of movement (ROM) around a joint.
The development of flexibility is most commonly sought through a variety of stretching techniques. The most commonly used forms of stretching are:
-Proprioceptive neuromuscular facilitation (PNF)
For many years, stretching has been proposed as a way to increase flexibility, decrease risk of injury, prevent muscle soreness, and improve performance. All of these techniques have their own protocols and are most effectively performed at certain times.
Contrary to popular belief, pre -exercise stretching does not prevent injury, and static stretching done in the period 30-45 minutes prior to activity leads to substantial decreases (5-30%) in muscular performance. It is important for players to understand how, when and to what extent these forms of stretching should be carried out.
The static stretching exercises are the most widely used stretches in tennis. The muscle is slowly and gently stretched to the point of slight muscle discomfort and then held for 15-30 seconds. While the position is maintained, the acuity of muscle tension decreases and the athlete should increase the amplitude of the stretch.
Static stretching is effective in increasing the ROM of different joints and the flexibility of the target muscle.
Players should endeavour to perform a static stretching routine twice a day, with good times for athletes to perform static stretching being post exercise and/or in the evenings. The fact that static stretches can be performed anywhere without any form of assistance from trainers or equipment is advantageous.
Although static stretching can increase passive flexibility, there is no research to demonstrate its correlation with the dynamic flexibility required for the sport of tennis. In addition, static stretching within an hour before exercise does not reduce the risk of injury, and impairs performance in speed, power and strength activities.
The deficit in performance lasts approximately 60 minutes after the stretching routine, and may be due to changes in reflex sensitivity, muscle/tendon stiffness and/or neuromuscular activation.
Dynamic stretching involves moving parts of your body and gradually increasing reach, speed of movement, or both. Dynamic stretching is not to be confused with ballistic stretching.
Dynamic stretching consists of controlled leg and arm swings that take you (gently) to the limits of your range of motion.
Ballistic stretches involve trying to force a part of the body beyond its range of motion. In dynamic stretches, there are no bounces or "jerky" movements. An example of dynamic stretching would be slow, controlled leg swings, arm swings, or torso twists.
Dynamic stretching improves dynamic flexibility and is useful as one of the final components of a sport-specific warm-up. The primary benefits of dynamic stretching include increasing body and muscle temperature and intramuscular blood flow, as well as their application in readying the specific musculature involved in the game of tennis.
Generally, dynamic exercises are performed in sets of 8 to 12 repetitions. After reaching the maximal range of motion in a joint in any direction of movement, you should not do many more repetitions of this movement in a given workout.
Proprioceptive neuromuscular facilitation (PNF)
The techniques of Herman Kabat, the originator of PNF in the 1950’s, combine isometric, concentric and eccentric contractions with passive movements.
PNF is typically applied manually with the assistance of a trainer, however players may also perform it individually. The neurophysiological basis of facilitated exercises are summarised below:
Two types of muscle contractions are used in PNF: Isotonic and Isometric. Isotonic muscle contractions are voluntary muscle contractions that create movement. This type of contraction can be further classified as either concentric, where muscles shorten as they work, or eccentric in which muscles help control or offer resistance to movement as they elongate. Isometric contractions are voluntary contractions in which no movement is produced and the muscle length remains the same.
The muscle or myotatic stretch reflex prevents muscles from stretching too quickly or too far and thus is a protective mechanism against joint and/or muscle injury. However, as alluded to in the section on ballistic stretching, the evoking of the stretch reflex causes the stretched muscle to contract and for this reason its elicitation should be avoided when perfoming a stretch. The administration or performance of PNF stretches that are smooth and prolonged is consequently very important.
Inverse Stretch Reflex
The inverse stretch reflex is the second reflex that coaches and trainers should be mindful of when performing PNF stretches. As its name suggests, it produces the opposite effect to that of the abovementioned stretch reflex: when evoked, the stretched muscles relax. There are two ways of stimulating this reflex. First by performing a smooth and maintained isometric stretch that triggers localised muscle relaxation and an increase in range, or secondly through the use of post-isometric relaxation as follows: after an isometric contraction there is a refractory period of about 15 seconds in which it is easier (because of a decrease in muscle tone) to increase the ROM (establish a new resistance limit) of a joint or muscle.
Advantages of PNF
There have been scientific studies that have purported PNF techniques to improve flexibility more so than any other stretching technique (Moore and Hutton, 1980). The performance of isometric muscle contractions as part of the PNF technique has also been suggested to help improve muscular strength and thus be of additional benefit from an injury prevention perspective (Moore, 1979).
The role of PNF stretches in relaxing and providing improved circulation to the stretched muscle is similarly considered beneficial (Adler et al., 1993; Cherry, 1980).
Disadvantages of PNF
Players should be motivated and focused if they are to practice these techniques safely and effectively. To “get up” for stretching sessions can often be difficult for the professional player and thus the role of the trainer or coach in encouraging and motivating the player can be important here.
The need to have a coach or trainer to assist with the performance of the majority of the PNF stretches can in itself be considered disadvantageous. Likewise, that PNF stretching exercises are more complex and intense than other stretching methods may contribute to their lack of popularity among some players.
PNF uses a variety of techniques that incorporate isometric and isotonic contractions to varying degrees in order to obtain specific results. Among all the PNF techniques, ATP Trainers only use the contraction-relaxation technique (Basthold and Novotny, 2002). Contraction-relaxation is considered by the author to be the most beneficial technique for tennis performance.
This method requires that the trainer move the desired segment in a passive manner until end range is reached. At this point the player contracts the stretched musculature isometrically against a resistance provided by the trainer (5 to 10 seconds).
The player will then relax (10 to 15 seconds) before the trainer moves the segment to a “new” end range (i.e. beyond the end range reached when the trainer first passively moved the segment) where the player will again perform an isometric contraction against the resistance provided by the trainer (15 seconds).
This process is repeated three or four times with an increase in the joint’s ROM being achieved with each repetition.