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Stretching is a form of physical exercise in which a specific muscle or tendon (or muscle group) is deliberately flexed or stretched in order to improve the muscle's felt elasticity and achieve comfortable muscle tone. The result is a feeling of increased muscle control, flexibility, and range of motion. Stretching is also used therapeutically to alleviate cramps.
In its most basic form, stretching is a natural and instinctive activity; it is performed by humans and many other animals. It can be accompanied by yawning. Stretching often occurs instinctively after waking from sleep, after long periods of inactivity, or after exiting confined spaces and areas.
Increasing flexibility through stretching is one of the basic tenets of physical fitness. It is common for athletes to stretch before (for warming up) and after exercise in an attempt to reduce risk of injury and increase performance.:42
Stretching can be dangerous when performed incorrectly. There are many techniques for stretching in general, but depending on which muscle group is being stretched, some techniques may be ineffective or detrimental, even to the point of causing hypermobility, instability, or permanent damage to the tendons, ligaments, and muscle fiber. The physiological nature of stretching and theories about the effect of various techniques are therefore subject to heavy inquiry.
Although static stretching (see image on the right for an example) is part of some warm-up routines, a study in 2013 indicated that it weakens muscles. For this reason, an active dynamic warm-up (movement of the muscle groups with lights weights for example) is recommended before exercise in place of static stretching.
Studies have shed light on the function, in stretching, of a large protein within the myofibrils of skeletal muscles named titin. A study performed by Magid and Law demonstrated that the origin of passive muscle tension (which occurs during stretching) is actually within the myofibrils, not extracellularly as had previously been supposed. Due to neurological safeguards against injury, it is normally impossible for adults to stretch most muscle groups to their fullest length without training due to the activation of muscle antagonists as the muscle reaches the limit of its normal range of motion.
Types of stretches
There are three kinds of stretching: static, dynamic (bouncing), and Proprioceptive neuromuscular facilitation (PNF), where the muscle is passively stretched, then the muscle is contracted, then stretched further.:42 However, static and dynamic stretching are the two most common forms seen. Dynamic stretching is a movement based stretch aimed on increasing blood flow throughout the body while also loosing up the muscle fibers. An example of this could be high knees or lunges. Whereas static stretching is a more stationary stretch, where one will hold a stretch for a certain duration of time without moving. This will give the muscles a more intense and deeper stretch when compared to dynamic.
Stretching does not appear to reduce the risk of injury during exercise, except perhaps for runners. There is some evidence that pre-exercise stretching may increase athletes' range of movement.
There are different positives and negatives for the two main types of stretching, dynamic and static. Static stretching is better at creating a more intense stretch because it is able to isolate a muscle group better. But, this intense of a stretch may hinder one's athletic performance because the muscle is being over stretched while in this position hold, and once the tension is released the muscle will tend to tighten up and may actually become weaker than it was previously. Also, the longer the duration of static stretching, the more exhausted the muscle becomes. This type of stretching has been shown to have negative results on athletic performance within the categories of power and speed. Dynamic stretching, because it is movement-based, may not isolate the muscle group as well or have an intense of a stretch, but it is better at increasing the circulation of blood flow throughout the body which in turn increases the amount of oxygen able to be used for an athletic performance. This type of stretching has shown better results on athletic performances of power and speed when compared to static stretching. However, both of these types of stretching have been shown to have a positive impact on flexibility over time by increasing muscle and joint elasticity increasing the depth and range of motion an athlete is able to reach. This is evident in the experiment "acute effects of duration on sprint performance of adolescent football players." In this experiment football players were put through different stretching durations of static and dynamic stretching to test their effects. They were tested on max sprinting ability and overall change in flexibility. Both static and dynamic stretching had a positive impact on flexibility. But, whereas dynamic stretching had no impact on sprint times. Static stretching actually had a negative result on the outcome, worsening the time the participants were able to sprint the distance in. And whereas the duration of stretching for dynamic had no impact on the overall results, the longer the stretch was held for static, the worse the times results got. Showing that the longer the duration of stretching held, the weaker the muscle became.
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