Hypermobility is surprisingly common and can be a real problem for many patients. I have talked a great deal about hypermobility and stretching in previous blogs. Here are some links to a post about hypermobility and also the problems hypermobility leads to.
Some science stuff:
Around all your muscles and the muscle fibres in those muscles is connective tissue. As it says on the tin, this is the stuff that holds you together. It is composed of a base substance and two different kinds of protein-based fibre which gives you two types main of connective tissue:
1. Collagenous connective tissue. This connective tissue consists mostly of collagen (hence its name) and provides tensile strength.
2. Elastic connective tissue. Elastic connective tissue consists mostly of elastin and (as you might also guess from its name) provides elasticity.
The base substance is a mucopolysaccharide. This acts as both a lubricant (allowing your muscle fibres to easily slide over one another) and as a glue (holding the fibres of the tissue together into bundles).
There are two broad groups of muscle fibres: intrafusal muscle fibres and extrafusal muscle fibres. Extrafusil fibres are the ones we usually mean when we talk about muscle fibres. Intrafusal fibres are also called muscle spindles and lie parallel to these extrafusal fibres. These will become important a bit later.
It seems that the ratio between the two types of connective tissue is where this problem originates. If you have a higher level than normal of the elastic connective tissue then you will be more bendy than normal. This is why there is a range of hypermobility and why it’s not a Y/N condition. And this is the underlying cause of problems with stretching and hypermobility.
What happens when you stretch
The stretching of a muscle begins in the basic unit of contraction in the muscle fibre, the sarcomere. At a microscopic level, there is an area of overlap between some thick and thin myofilaments, called actin and myosin, in the sarcomere. These myofilaments can slide across each other causing the sarcomere to contract. When billions of these sarcomeres contract you get a contraction of the wider muscle and movement. In reverse, as they stretch, the area of overlap decreases, allowing the muscle fibre to lengthen.
When all of your sarcomeres are fully stretched your muscle fibre is at its maximum resting length. Any additional stretch then places force on the surrounding connective tissue. As the tension increases, these collagen fibres (the tensile strength ones) in your connective tissue align themselves along the same line of force as the tension. So, stretching is where the muscle fibre is pulled out to its full-length, sarcomere by sarcomere.
During stretching, some of the contracted fibres lengthen, but other fibres may just remain at rest. The length of the entire muscle depends upon the number of stretched fibres. So, just as the total strength of a contracting muscle is a result of the number of fibres contracting, the total length of a stretched muscle is a result of the number of fibres stretched. The more fibres stretched, the more length developed by the muscle for a given stretch. Which is why we hold the stretch for as long as we do.
The nerve endings that relay all the information about the musculoskeletal system to the central nervous system are called proprioceptors or mechanoreceptors. Proprioceptors are the source of all proprioception which is the perception of one’s own body position and movement. These detect any changes in physical displacement (movement or position) and any changes in tension, or force, within the body. They are found in all nerve endings of the joints, muscles, and tendons. They are the structures that allow you to touch your nose in the dark and not stick a finger in your eye.
The proprioceptors related to stretching are located in the tendons and in the muscle fibres. There are three key structures that deal with stretch:
1. As mentioned, intrafusal fibres are also known as muscle spindles, or stretch receptors, are the primary proprioceptors in the muscle.
2. There is another proprioceptor that’s important during stretching – the golgi tendon organ. This is in the tendon near the end of the muscle fibre. When muscles contract it places tension on the tendons where the golgi tendon organ is located. The golgi tendon organ is sensitive to the change in tension and the rate of change of the tension.
3. A third type of proprioceptor, called a pacinian corpuscle, is located close to the golgi tendon organ and is responsible for detecting changes in movement and.
When the extrafusal fibres (the real muscle fibres) of a muscle lengthen during a stretch, so do the intrafusal fibres (muscle spindles) alongside them. The muscle spindle contains two different types of fibres (or stretch receptors) which are sensitive to the change in muscle length and the rate of change in muscle length.
The problem with stretching and hypermobility
So, this is the crux of the issue. If you have a genetic allocation of a more than average ratio of elastic connective tissue to collagenous connective tissue then you will be more flexible than average. The more you have, the more flexible you will be, and at some (unspecific-ish) point you will be hypermobile. Also, the more elastic connective tissue there is around a joint, the greater the range of motion in that joint. This will cause you problems with stretching and hypermobility.
You will feel the need to stretch your muscles because they have been working hard holding you together. You will try the normal stretch, but this will end up in stretching your elastic connective tissue, and not your muscle fibres. Beacuse your intrafusal fibres will not get stretched, you will not feel the stretch, and you’ll get no relief. You will then attempt to stretch the muscle even further and start to injure joins. Because these joints are unprotected by collagenous connective tissue which means you can move them beyond their normal range of motion. This can lead to joint injury.
The solution is that you must not try to pull your muscles apart, but push them apart. This is best done using massage balls, foam rollers and deep tissue massage.