Flexibility and stretching: preventing sports injuries

Two sports physiotherapists show why flexibility is so important, and explain the science behind it

Achieving a certain degree of flexibility is absolutely critical for anyone involved in sports; otherwise there will be at some stage a breakdown in body tissues leading to an injury.

Don't kid yourself if you never stretch: it is only a matter of when you get injured, not if. In addition, if you are too tight in certain parts of your body, you are functioning below your real potential - remember that performance enhancement is the second very important reason to stretch: flexible muscles perform a lot better than tight muscles.

From chess players through to Olympic gymnasts to Sumo wrestlers, we all must invest time in gaining and maintaining the flexibility that is specific to the requirements of our particular sport. It is the one side of the coin (the other being muscle strength and control) so often ignored by athletes, at their peril.

If you get soreness with stretching or have an injury that won't heal by itself, always consult a physio who specialises in sport. Stretching can make an existing injury worse.

In order to improve flexibility, it's important to first understand some of the science underpinning the principles of stretching. This is also critical in order to avoid direct injury from trying new stretches that you are unfamiliar with. The following article by my fellow sports physiotherapist Chris Mallac does just that. Ulrik Larsen

What is the science behind flexibility?
Most coaches, athletes and sports medicine personnel use stretching methods as part of the training routine for athletes. Many would agree that it forms an integral part of training and preparation. However, most of the theoretical and practical factors in stretching are often incorrectly applied. The purpose of this article is primarily to provide an overview on the theoretical basis of stretching routines.

What is flexibility? De Vries defines it as the range of motion available in a joint, such as the hip, or series of joints such as the spine. This encompassing definition takes into account a number of important aspects about flexibility. That is, it deals with a joint or series of joints used to produce a particular movement, and it considers that flexibility is both static and dynamic in nature.

It is important to highlight some points regarding flexibility. First, flexibility is joint specific. That is, you cannot say someone is flexible just because they can touch their toes. The same person may not even be able to reach around and scratch the small of his/her back because their shoulder has poor flexibility. Second, flexibility is sport specific. You would not expect a front row rugby forward to have the same flexibility as an Olympic gymnast, because it is not required for his sport. In fact, in a contact sport like rugby, being that flexible would be detrimental to his body.

Components of flexibility
Flexibility has two important components: static and dynamic flexibility. 1. Static flexibility describes range of motion without a consideration for speed of movement. This is the maximum range a muscle can achieve with an external force such as gravity or manual assistance. For example, holding a hamstring stretch at an end-of-range position.

2. Dynamic flexibility describes the use of the desired range of motion at a desired velocity (usually quickly). Dynamic flexibility is the range athletes can produce themselves. For example, a javelin thrower or baseball pitcher needs a lot of shoulder rotational flexibility, but they also need to be able to produce it at rapid speeds of movement.

Here are some useful points:

a) Good static flexibility is a necessary prerequisite for good dynamic flexibility; however, having good static flexibility does not in itself ensure good dynamic flexibility.
b) Dynamic flexibility is vitally important in those high velocity movement sports such as sprinting, kicking and gymnastics.
c) Dynamic flexibility is limited by the ability of the tissues to lengthen quickly, and the inhibition of what is called the 'stretch reflex', which if present would act to limit the range of motion (more about this later).

Stretching also forms an integral part of rehabilitation programmes following injury. For example, it is accepted that a muscle tear will heal with scar tissue. This scar tissue tends to be functionally shorter and have more resistance to stretch than normal healthy muscle tissue. Therefore stretching is used at an appropriate time in the healing process to assist in lengthening this contracted scar tissue.

Good flexibility improves posture and ergonomics. Our bodies have a tendency to allow certain muscles to tighten up which will affect our posture. Vladimir Janda, a Czech rehabilitation specialist, describes a group of muscles in the body that universally show a tendency towards tightness and also being overactive in movements. Some of these include the hamstrings, rectus femoris, TFL, piriformis, adductors, gastrocnemius and quadratus lumborum. These muscles are often implicated in postural syndromes causing musculoskeletal pain.

Flexibility, because it allows good range of motion, may improve motor performance and skill execution. Think of a sprinter who needs flexibility in the hip flexors to allow good hip extension at toe off, and good hip extensor flexibility to allow necessary knee drive in the leg recovery phase of sprinting. Skill execution and reduced risk of injury will be greatly enhanced if the body has the flexibility necessary for that particular sport.

There is also an argument that stretching may reduce post exercise muscle soreness, or DOMS, by reducing muscle spasm associated with exercise.

Relative flexibility
Shirley Sahrmann, an American physiotherapist, uses the term 'relative flexibility' to describe how the body achieves a particular movement using the relative flexibility available at a series of joints. She believes that in order for the body to achieve a particular range of motion, it will move through the point of least resistance, or area of greatest relative flexibility.

A good example is to think of a rower at the bottom of the catch position. In this position the rower must have his hands (and the oar) past his feet in order to generate the drive necessary to transfer force from his body to the oar. If for some reason the rower has excessively tight hips and can't bend up (or flex) the hips (usually due to gluteal tightness), his body will find somewhere else to move to compensate for that lack of hip flexibility. More often than not, this rower will flex the lumbar and thoracic spines to make up for the lack of hip flexion. That is, the back has more 'relative flexibility', and therefore contributes to the overall range of motion. In this case however, the back will exhibit movement that is more than ideal, possibly leading to lumbar and thoracic dysfunction and pain.

The concept of relative flexibility is vital when understanding movement dysfunction in athletes. It is imperative that joint movements are not looked at in isolation, for other more distant joints will influence that movement. Try this simple test to highlight this point. Sit on a chair with your upper backed slumped (that is, assume a poor posture). Now, maintaining this position, try to elevate both arms above your head. Now straighten yourself up (assume a good posture) and try it again. Unless you have gross shoulder dysfunction, you will be able to elevate more with a straight back than a curved one. By assuming a slumped position, you prevent the upper back (thoracic spine) from extending. This extension of the upper back is necessary for full range elevation. Without extension, it is difficult for the shoulder to fully elevate. If you do this for long enough (months to years) eventually the lack of movement will attempt to be taken up elsewhere (such as the lower back, or the shoulder itself). This may eventually lead to breakdown of these joints due to the excessive movement they may eventually demonstrate.

What factors limit flexibility?
Flexibility can be limited by what are called 'active' or 'contractile' and 'passive' or 'non-contractile' restraints. Muscle contraction is one of these 'active/contractile' restraints. Flexibility can be limited by the voluntary and reflex control that a muscle exhibits while undergoing a stretch, in particular a rapid stretch that activates the 'stretch reflex'. As a muscle is rapidly stretched, a receptor known as a 'spindle' causes the muscle to reflexively contract to prevent any further stretch. If left unchecked, the stretch reflex would work to prevent elongation while the muscle was being stretched. A benefit of ballistic or fast stretching is that the nervous system learns to accommodate by delaying the stretch reflex until closer to end of range of movement (more on this later).

Furthermore, a resting muscle does not always mean that it is 'resting'. Muscles usually exist with a certain degree of muscle 'tone'. An increase in tone will increase the inherent stiffness in muscles. If you are scientifically minded, this describes the way actin and myosin remain bound and thus resist passive stretching of the muscle. The actin and myosin stay bound because of a constant low-level discharge in the nerves supplying that muscle. With actin and myosin unbound, a muscle should in theory be able to stretch to 150 per cent of its original length (in theory of course).

'Passive/non-contractile' restraints in the form of connective tissues will also limit flexibility. The passive restraints include the connective tissues within and around muscle tissue (epimysium, perimysium and endomysium), tendons and fascial sheaths (deep and superficial fascia). The important microscopic structure to consider in passive tissues is collagen. The way collagen behaves with stretching will be discussed shortly.

Other passive restraints include the alignment of joint surfaces. An example of this is the olecranon of the elbow in the olecranon fossa that will limit full extension (straightening) of the elbow. Other joint constraints include capsules and ligaments. The joint capsule/ligament complex of the hip joint is important in limiting rotation of the hip.

The nerves passing through the limbs can also limit flexibility. As a limb is taken through a full movement, the ropey nerve tracts also become elongated and become compressed. The nerve endings and receptors in the nerves trigger a reflex response that causes the muscle to increase its resistance to stretch.

Chris Mallac