Stretching

Geschatte leestijd: 12 minuten The exact effect of stretching on muscles is unknown or disputed by many. Stretching, according to some, may lead to fewer injuries, while according to others, it may lead to more injuries. Some athletes stretch for better athletic performance, while others believe stretching has a negative effect. There is also debate about when you should stretch—before or after training. Opinions also differ on how and how long you should stretch. This provides a great opportunity to attempt to bring order to the chaos and provide clarity on the effects of stretching. To truly understand the usefulness and functioning of different stretching methods, we need to return to the functioning of the muscle and its attachment. Hence, I will start with relevant anatomy and the theories behind stretching before delving into practice. Of course, you can also scroll directly to the practical explanation. However, knowing the underlying processes often allows you to better assess how to use them for your personal goals in practice and can help you avoid common mistakes.

Muscle Elasticity and Attachment

The flexibility of joints is largely determined by the length and elasticity of the muscles that run over them and the attachments that connect them to the bone (1). How “flexible” or agile you are depends on this combination that forms the engine of joint movements, much like a rope pulling on a lever. The article on the functioning of muscles describes how the muscle cell itself is made up of chains of units that contract and relax. The muscle attachment is elastic but cannot contract actively. Therefore, when it comes to stretching, its usefulness and efficiency can be viewed separately. However, it is the interaction between the muscle and its attachment that determines practical functioning, so ultimately, they should be seen as one unit. The point at which the muscle attaches to the bone is called the attachment. A distinction is made between:

• The origin: the fixed point from which the muscle contracts (or pulls the bone toward it).
• The insertion: the movable point to which the muscle is attached (the muscle pulls the insertion towards the origin).

Both points can move independently of each other and can be on opposite sides of the joint. The muscles and their attachments are usually set up in such a way that they can pull the bones from all sides to create various movements. To function properly, both the muscle and its attachment must be healthy and flexible. Throughout the day, the muscle and its attachment are constantly lengthening and shortening in response to external factors such as gravitational forces, the position of the joint, and the amount of tension exerted on the muscle. This ensures that the muscle remains functional and does not become stiffer or shorter over time. However, when the muscle is not used optimally, such as when it is subjected to repetitive movements, or when it is placed under constant tension for a prolonged period, it can become shortened and lose its elasticity. This can lead to stiffness and reduced range of motion in the affected joint, making movement more difficult and increasing the risk of injury. Stretching is one way to counteract these effects by elongating the muscle and its attachment, restoring or improving flexibility, and increasing range of motion in the joint. By regularly stretching the muscles around a joint, you can help maintain or improve their elasticity and prevent stiffness and loss of mobility over time. However, the effectiveness of stretching depends on various factors, including the type and intensity of the stretch, the duration and frequency of stretching, and individual differences in anatomy and physiology. Not all stretching techniques are equally effective or suitable for everyone, and it may take some trial and error to find the methods that work best for you.

Muscle Viscosity and Attachment

In addition to elasticity, another important property of muscles and their attachments is viscosity. Viscosity refers to the resistance of a substance to flow, or in the case of muscles, the resistance to lengthening or shortening. A more viscous muscle will be stiffer and less flexible, while a less viscous muscle will be more pliable and easier to stretch. The viscosity of a muscle is influenced by various factors, including its composition, hydration level, temperature, and degree of activation. For example, a well-hydrated muscle with adequate blood flow will be less viscous and more elastic than a dehydrated muscle with poor circulation. Similarly, a muscle that is actively contracting or has recently been exercised will be more viscous than a muscle that is at rest. Stretching can help reduce the viscosity of muscles and their attachments by increasing blood flow to the area, promoting hydration of the muscle fibers, and stimulating the release of tension and metabolic waste products. This can make the muscle more pliable and easier to elongate, allowing for greater range of motion and flexibility in the joint. However, it’s important to note that stretching alone may not be sufficient to significantly alter the viscosity of a muscle, especially if it is already highly viscous due to factors such as age, injury, or chronic tension. In such cases, additional interventions such as massage, heat therapy, or manual therapy may be necessary to help soften and mobilize the tissues before stretching.

Stiff or “Flexible” Muscles and Attachments, Range of Motion

The terms “stiff” and “flexible” are often used to describe the relative mobility or rigidity of muscles and their attachments. A stiff muscle or attachment is one that is resistant to elongation and has limited range of motion, while a flexible muscle or attachment is one that is pliable and can be stretched easily. However, it’s important to understand that stiffness and flexibility are not binary traits but exist along a continuum, with most muscles and attachments exhibiting a combination of both qualities depending on factors such as age, conditioning, and activity level. Stiffness and flexibility are also highly context-dependent and can vary from one individual to another and even within the same individual from one moment to the next. For example, a muscle that feels stiff and inflexible during a period of inactivity may become more pliable and elastic after a warm-up or stretching routine. Similarly, a muscle that feels flexible and easy to stretch when relaxed may become stiff and resistant to elongation when actively contracting or under load. This is why stretching techniques that target both passive and active components of muscle stiffness are often recommended for improving overall flexibility and range of motion.

Stretch Shortening Cycle

The stretch-shortening cycle (SSC) is a physiological phenomenon that occurs when a muscle is rapidly stretched before it contracts, such as during a plyometric or “bounce” movement. When a muscle is stretched, it stores elastic energy, which is then released as kinetic energy during the subsequent contraction, resulting in a more powerful and efficient movement. The SSC is thought to enhance athletic performance by allowing muscles to produce more force and generate greater power output in a shorter amount of time. However, it also increases the risk of injury, especially if the muscle is not adequately prepared or conditioned to handle the forces involved. Proper warm-up and stretching can help reduce the risk of injury during plyometric activities by improving muscle elasticity and preparing the tissues for rapid lengthening and contraction. However, it’s important to note that excessive stretching or stretching performed too close to the activity may impair muscle function and decrease performance.

Inverse Stretch Reflex

The inverse stretch reflex (or autogenic inhibition) is a protective mechanism that prevents muscles from being stretched too far or too quickly, which could lead to injury. When a muscle is stretched beyond a certain threshold, specialized sensory receptors called muscle spindles are activated, sending signals to the spinal cord to initiate a reflex contraction of the muscle. This reflex helps maintain joint stability and prevent overstretching by automatically contracting the muscle in response to excessive tension or elongation. However, it can also limit flexibility and range of motion if the muscle spindles are overly sensitive or if the reflex is chronically activated due to factors such as poor posture or repetitive movements. Stretching techniques that target the inverse stretch reflex, such as proprioceptive neuromuscular facilitation (PNF) and static stretching, work by gradually increasing the length of the muscle while bypassing the reflex contraction. By holding the stretch for an extended period or engaging the muscle in a resisted contraction before stretching, these techniques help override the protective mechanism and promote greater elongation and flexibility.

Conclusion

Overall, the flexibility and range of motion of muscles and their attachments are influenced by a complex interplay of factors, including elasticity, viscosity, stiffness, and reflex mechanisms. Stretching is an effective way to improve flexibility and maintain joint mobility by elongating the muscles and reducing tension and resistance to movement. However, stretching techniques should be chosen and performed carefully to avoid injury and achieve the desired outcomes. It’s important to consider individual differences in anatomy and physiology, as well as the specific goals and needs of the individual when designing a stretching program. By incorporating a variety of stretching techniques and modalities, you can help optimize flexibility, enhance athletic performance, and reduce the risk of injury over time. “` This passage delves into the anatomical and physiological aspects of muscle elasticity, viscosity, and attachment points. It also discusses the role of stretching in maintaining or improving flexibility and range of motion while highlighting the factors influencing these properties. Furthermore, it addresses the stretch-shortening cycle and the inverse stretch reflex, both of which are relevant in understanding muscle function and flexibility. If you need further clarification or additional details on any specific aspect, feel free to ask! Een ander voorbeeld is wanneer je je romp opeens opzij laat vallen waardoor er (aan de andere zijde) een grote rek komt op de zijwaartse buikspieren (obliques abdominus). Om te voorkomen dat je in een foute houding zou verder lopen, corrigeert het lichaam dit (deels) zelf al door de gerekte kant aan te spannen.

Praktijk: Diverse stretchtechnieken. Statisch, ballistisch, DROM en PNF

Er zijn verschillende methoden om te stretchen. Sommigen zijn ontwikkeld met specifieke doelstellingen in gedachten, andere zijn een resultaat van nieuwe inzichten in de werking van spieren en aanhechtingen. Je kan veel van de verschillende stretch-methoden indelen in twee klassen: Actieve stretches en passieve stretches.

Passief stretchen

Bij passief stretchen gebruik je andere spieren of hulpmiddelen om een specifieke spier en aanhechting te rekken. Denk bijvoorbeeld weer aan het voorover bukken met gestrekte benen om de hamstrings te rekken. Dit is een passieve stretch waarbij gebruik gemaakt wordt van het gewicht van het bovenlichaam om de hamstrings gestrekt te houden. Een ander voorbeeld is wanneer je de ene arm gestrekt voor je borst houdt (door de rechterarm naar links te laten wijzen of andersom) en de andere arm gebruikt om deze tegen de borst aan te houden. Bij deze passieve stretch voor de schouder (en triceps wanneer de arm gebogen wordt) gebruik je de spieren van de andere arm om de rek vast te houden.

Actief stretchen

Bij actief stretchen gebruik je de spier zelf of de antagonist om deze te rekken. De agonist is de spier die aanspant voor een bepaalde beweging. De antagonist is de spier met de tegenovergestelde werking van de agonist (zoals biceps en triceps, quadriceps en hamstrings). Denk weer aan het rekken van de hamstrings. Bij het voorbeeld van de passieve stretch bogen we voorover met het hoofd richting knieën en voeten. In de actieve stretch brengen we juist het been omhoog met behulp van de quadriceps om zo de hamstrings te rekken. Naast deze algemene verdeling tussen passief en actief heb je specifieke stretch-methoden zoals:

Statisch stretchen

Statisch stretchen houdt in dat je de stretch voor een spier en de aanhechting voor een bepaalde duur vasthoudt en de spier zo op een vaste lengte houdt. In het voorbeeld van voorover bukken, is dit statisch wanneer je bijvoorbeeld zo voorover gebogen 15 seconden blijft staan (straks meer over de ideale duur van een stretch). Dit is de traditionele, meest gebruikte vorm van stretchen. Statisch stretchen is de veiligste manier van stretchen (14,15), maar niet de snelste manier om de range of motion te verbeteren. Er zijn heel veel voorbeelden te geven.

Dynamic range of motion (DROM)

Dynamic Range Of Motion (DROM), of dynamisch stretchen, is een methode waarbij de stretch herhaaldelijk uitgevoerd wordt in een gecontroleerde beweging. Denk bijvoorbeeld aan het uitvoeren van dynamische squats om de heupen op te warmen voor zware squat-oefeningen.

Ballistisch stretchen

Ballistisch stretchen is een controversiële vorm van stretchen waarbij je een veerkrachtige, stuiterende beweging gebruikt om de spier op lengte te brengen. Dit kan bijvoorbeeld zijn door herhaaldelijk te springen tijdens het rekken van de hamstrings. Hoewel sommige atleten deze methode gebruiken, wordt het over het algemeen niet aangeraden vanwege het verhoogde risico op blessures.

PNF stretchen

PNF staat voor Proprioceptive Neuromuscular Facilitation. Het is een geavanceerde vorm van stretchen waarbij je gebruikmaakt van spiercontracties en ontspanningen in combinatie met stretchen. Een veelvoorkomende PNF-stretch is de contract-relax-methode, waarbij je de spier eerst isometrisch aanspant (ongeveer 5-10 seconden), dan ontspant en vervolgens verder strekt. Deze techniek wordt vaak gebruikt bij revalidatie en kan zeer effectief zijn voor het verbeteren van de flexibiliteit.

Ideale duur van een stretch

Over het algemeen wordt aanbevolen om statische stretches tussen de 10-30 seconden vast te houden, maar sommige bronnen suggereren dat stretches tot 60 seconden of langer voordelig kunnen zijn, vooral bij PNF-stretches (16,17). Het belangrijkste is om binnen je comfortzone te blijven en niet te veren buiten je normale bereik van beweging. Bij dynamische stretches wordt meestal aanbevolen om 5-10 herhalingen uit te voeren, waarbij elke herhaling de spier iets verder rekt. Het is belangrijk om te onthouden dat stretchen slechts een onderdeel is van een complete trainingsroutine en dat het niet noodzakelijk is om vóór elke trainingssessie uitgebreid te stretchen. Dynamische stretches kunnen echter nuttig zijn als onderdeel van een warming-up om de spieren voor te bereiden op activiteit, terwijl statische stretches effectiever zijn aan het einde van een trainingssessie om de spieren te helpen ontspannen en flexibiliteit te verbeteren. Shrier mentions several reasons why stretching before a workout or competition may have no or even a negative effect on injuries (27). First, he points out that most injuries occur during the eccentric phase of a movement. For example, consider bending the knees (where standing up again is the concentric/positive phase). In this example, most injuries will occur on the way down and not when you have already reached there. By stretching, you increase the previously mentioned range of motion, allowing you to bend your knees even further, thus shifting the endpoint of the movement. However, since the endpoint is not where most injuries occur, shifting it adds little to injury prevention. Of course, this is different if you are doing ballet or gymnastics and need to be able to do splits. Then it makes sense to increase the range of motion, but even in those cases, it’s not just one stretching session before training that makes this possible. Additionally, Shrier points out the danger of the so-called analgesic effect of stretching. This is the pain-relieving/numbing effect of stretching (40,41,15). By stretching the muscles before a workout, you reduce the signaling effect of pain. Then, by not noticing or noticing later that there is a problem (which the pain signal wants to inform you about), complaints may arise that you could have otherwise prevented. Finally, he refers to a study showing the possibility that even light stretching can lead to muscle damage at the cellular level (27,42). In the study he refers to, “light stretching” was lengthening the muscle at rest by 20%.

It does not seem prudent to decrease one’s tolerance to pain, possibly create some damage at the cytoskeletal level, and then exercise this damaged anesthetized muscle. Of note, no basic science evidence suggests that stretching would decrease injuries. Finally, some basic science data suggest that a warmup may help to prevent injuries I. Shrier, SMBD-Jewish General Hospital

Practice: How Long to Stretch?

When you stretch statically, how long should you hold the stretch? If you stretch dynamically or use PNF, how often should you repeat this? This has also been extensively studied in various research studies. Static Stretching: How Long? The aforementioned researchers from the University of Central Arkansas looked at hamstring flexibility after stretching in another study (43). In 1994, they only looked at the duration of stretching. They had their subjects (men and women aged 21-37) stretch for 15, 30, and 60 seconds to measure the difference in the effect on flexibility (range of motion). They stretched five days a week for six weeks. Ultimately, the researchers found that stretching for 30 and 60 seconds resulted in a greater increase in flexibility than 15 seconds. There was no significant difference between 30 and 60 seconds, leading them to conclude that 30 seconds is sufficient for optimal results.

The results of this study suggest that a duration of 30 seconds is an effective time of stretching for enhancing the flexibility of the hamstring muscles. Given the information that no increase in flexibility of the hamstring muscles occurred by increasing the duration of stretching from 30 to 60 seconds, the use of the longer duration of stretching for an acute effect must be questioned. W.D. Bandy, University of Central Arkansas

Three years later, the same researchers again compared the difference between 30 and 60 seconds, as well as the frequency of stretching (44). They divided their subjects (aged 21-39) into different groups: those who did not stretch, those who stretched for 30 or 60 seconds, and those who stretched 1 or 3 times a day. They found that all groups that stretched had more flexible hamstrings than the group that did not stretch. Among the groups that stretched, they found no difference. Their conclusion was that stretching once a day for 30 seconds is enough to increase flexibility. Longer or more frequent stretching did not have a greater effect. The authors even suggest that a shorter stretching duration (15 seconds) might be sufficient for the acute effect. There are more and more indications that stretching just before training may not be effective or may even be harmful. For example, Weldon et al. found in a study in 2003 that stretching significantly reduced the sprint and jump performance of the subjects, probably due to the fact that the muscles were less stiff and therefore performed less efficiently (13). A study in 2005 by Behm and Chaouachi came to the same conclusion, among other things because the jumping height decreased after stretching (14). On the other hand, the indications that stretching after training would be beneficial are increasing. There are studies that indicate that stretching after training can lead to fewer injuries. However, it remains difficult to make any conclusions about this because there are also studies that show the opposite.

Practice: Dynamic Stretching and PNF

Given the above arguments against static stretching before training, it seems that dynamic stretching (see section “Dynamic Stretching”) and PNF (see section “PNF Stretching”) may be better choices. The only possible argument against PNF stretching is that this type of stretching is intense and fatiguing. The arguments against dynamic stretching are the same as for PNF, but it is more difficult to overload the muscles to the same extent. The combination of dynamic stretching and PNF stretching with passive stretching (stretching the muscle while relaxed) is probably the most effective (45).

Therapy: Heat

Heat (see section “Heat and Ice”) can be a good tool to prepare the muscles for stretching or to increase relaxation. However, you should not use it immediately after training or in case of swelling. In these cases, cold is the better choice.