Youth Sport – Does Stretching Impact Performance?

It is common practice to see stretching within every aspect of the health and fitness sector, from physiotherapy, fitness sessions, and typically before sport events, for example middle, long-distance running, and team sports – football, netball, and basketball.  Usually, stretching is grouped together within the warm up component.  Historically, the warm up has consisted of cardio-type movements (walking, slowing jogging), with the aim of increasing body and muscle temperature.  The second part of the warm up normally then moves to stretching, usually, static stretching, with the aim of elongating the muscles to improve range of motion (15, 22).  Less frequently, a third component of the warm up is performed, where dynamic activities (plyometric-type-hops, skips, and jumps) are included to prepare the participants for the transition from the warm up to the main session (possible potentiation to enhance performance) (10). 

Recently, stretching, especially static stretching has come under fire due to the reductions in strength and power (muscular) performances, with longer held stretches (>60 seconds) producing greater decrements in strength, power, and speed (11).  Stretching, however, is a mode of training and associated with improving flexibility, which is viewed as an important health-related fitness component.  Furthermore, high volumes of static stretches (5 days a week for 6+ weeks), has been shown to effectively improve range of motion (3, 7), which could be essential for daily activities (and specific sports that require higher levels of movement– dance, gymnastics, and martial arts).  The terms flexibility and mobility are frequently used interchangeably, which could lead to confusion, as they are different concepts.  Generally, mobility is described as the ‘ease’ of motion between joints or a series of joints (within a kinetic chain).  The term ‘ease’ is clearly subjective but could be thought of as the relative resistance to moving joints (rotation of a joint within an axis and joint structures sliding with minimal friction). Furthermore, as mobility is dynamic (in motion), this cannot be controlled by one factor but by a cascade of systems (muscles, joints, tendons, ligaments, and nervous system) working synergistically.  Therefore, different training modes have the potential to improve mobility, for example strength/resistance training (14), as the interplay of motor control within a range of motion might be more important that static positions. Flexibility should be viewed as one of the sub-components of mobility, with flexibility being described as, the possible extensibility of tissues (muscles, tendons, and fascia) around that joint or joints (depending on the muscle – some muscles cross one joint, others cross more than one joint).  As flexibility is one factor to overall mobility, it’s probably unlikely for individuals to be highly flexible, moreover, flexibility is potentially joint specific rather than being global.  

Relative to the term flexibility, extensibility of the tissues, especially muscles and their interaction with tendons need to be understood, as this may help to evaluate the prescription of stretching.  The interaction between muscles and tendons is extremely complex, due to being biased by the environment, task, and the individuals.  However, to make life easier, muscles and tendons are frequently compared to as springs, for example, series elastic components and parallel elastic components.  This spring/elastic analogy is due to their function i.e. from working in an optimal length-tension relationship, they can store and release elastic potential energy (energy efficiency) or transmit forces back quickly (speed). Because the muscle and tendon act as a spring, the mechanical movement or change in position (spring or elastic band) is reported back to the nervous system via receptors.  Specifically in the muscle, the receptors are known as muscle spindles.  Muscle spindles are extremely sensitive to the lengthening or elongation of the muscle, and if the muscle spindles are activated, the muscle spindles will inform the nervous that the muscle is being lengthened, which could be mechanically risky, therefore the nervous sends a message to contract that muscle – hence the term stretch reflex (the stretch reflex could be thought of as a protective mechanism, as most damage in the muscle is caused when elongated, especially as speed). Having an awareness of muscles acting like springs, activation of muscle spindles, and the stretch reflex may help to understand that physically elongating muscles is difficult and challenging to the body and highly questioned (21). 

Furthermore, as the muscle may actually resist lengthening or elongation, as this may alter the muscle length-tension relationship, thus the change in length is more likely from feedback sensation – better stretch tolerance (signals to the nervous system reduce) and/or via the tendon-complex.  Again, if we use the spring analogy, springs can be stiff or compliant.  A stiff spring means that it is more difficult to compress or elongate.  On the other hand, a compliant spring requires less effort (force) to compress or elongate.  From a mechanical perspective, stiff springs return energy quickly, where compliant springs may help in energy storage/efficiency.  Through static stretching, where a joint is moved to the muscles end range and then held, because the muscle spindles may reduce changes in muscle length, the tendon may take most of the strain leading to a more complaint tendon.  A more compliant tendon is not ‘wrong’ or ‘bad’ but for activities that require fast and reactive qualities, like in most team sports, a stiff tendon may be more appropriate.  This may explain why when static stretches are performed in isolation, the static stretches have reduced performances in power (19) and strength levels (2, 17) – clearly, the volume of the stretching training needs to be considered, with higher training volumes having more of an effect. 

Youths Tend to be More Compliant – Reducing their Strength & Speed

The term mobility, as a physical quality, is highlighted within long-term athletic development programmes and models (13).  As we discussed earlier, the terms mobility and flexibility are different.  Mobility from a youth perspective is probably more aligned or a product of other qualities, for example, motor control and muscular coordination (which is associated with strength).  Furthermore, youth’s tendon complex tends to be more compliant than adults.  This greater tendon compliance is associated with higher levels of muscular co-contraction and electromechanical delay (12).  Collectively, this reduces strength (force), rate of force development, and power.  However, as the youths mature, their tendons become more stiff.  This is aligned with maturation and greater bodyweight.  As the youths gained bodyweight and move/play, their tendon complex is exposed to greater forces (usually ground-reaction forces).  Thus, through regular activity/play, their tendon complex becomes more stiff, this reduces electromechanical delay allowing greater force development – youth seems faster, stronger, and more powerful.   An important consideration is that young girl’s tendon-complex is more complaint when compared to young boys (53%) (16).  Again, this may explain why studies report a reduction in muscular performances (jump height and sprint times) after static stretches programmes (1, 6, 9).  Therefore, as a part of a long-term athletic development programme, it is essential that youths are exposed to activities that aid in motor control and muscular coordination and static stretches are kept to a minimal, especially before team sports or training that requires fast movements.  Regular and consistent strength and plyometric training will allow the youths to explore movements, (enhancing mobility), as the systems are being trained synergistically - this explains why any neuromuscular training will help in injury reduction and long-term sport performances (8).  

What about Injury Reduction? Is there a Connection Between Stretches and Injury Reduction 

There tends to be a consensus that stretching, especially static stretching reduces power (19) and strength levels (2, 17), therefore, it is recommended that static stretching is not prescribed before powerful movements or team sports.  However, what about including stretching as a part of a complete warm up to help in reducing injures?  This is where the evidence and studies are inconsistent, as injures will always be classified as multifactorial – just too many variables to consider.  Most studies will tend to lean towards insufficient evidence to state either way (Thacker et al 2004). However, if we compare a typical warm up that contains static or dynamic stretches to the FIFA 11+ warm up (5), it is easy to see that they have removed all static-stretching, and even dynamic stretching is kept at a minimal dosage (some exaggerated hip movements).  This is an important comparison, as the FIFA 11+ programme has reported some clear reductions in injuries (4, 18) -estimated injury reduction by 35%.  – see table 1.  

Stretching, especially static stretching is a type of training that when performed with high volumes, 5 days a week for 6+ weeks, is effective in improving range of motion.  However, static stretches held for long periods (60>) seconds reduce muscle performances – power, strength, and speed.  This reduction in strength and power may be due to changes in compliance in the tendon complex.  As many team sports require powerful and movements at speed, it has been suggested that athletes and players not to perform static stretches, and potentially use dynamic stretches, as dynamic stretches have not shown reduction in muscle performances.  From an injury reduction perspective, the studies are inconsistent, suggesting that there’s not enough evidence to state if static stretches aid in an injury reduction programme.  However, reviewing the FIF 11+ programmes and their effectiveness of reducing injuries (especially lower limb injures), it seems clear that strength and plyometric training are essential for athletes to perform, especially youths.  In the context of a warm up, including activities that increase body and muscle temperature, activities that enhance the stretch-shortening cycle, and exercises that recruit muscles and develop balance leads to changes in neuromuscular function, potentially muscle coordination which is linked with injury reduction.  It is essential that coaches learn to reduce static stretches in the warm up and replace with other activities, as it seems that frequency (regular and consistent practice) are major factors in reducing sport-related injuries.  

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References 

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2. Bacurau, R.F.P., De Assis Monteiro, G., Ugrinowitsch, C., Tricoli, V., Cabral, L.F., & Aoki, M.S. (2009).  Acute effect of a ballistic and a static stretching exercise bout on flexibility and maximal strength.  Journal of Strength & Conditioning, 23(1), 304 – 308. 
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