Self Help Guides
The Process of Stretching
Our muscles have an in-built safety mechanism which prevents us from over-stretching and injuring ourselves. If effective, stretching is to be achieved this needs to be understood.
The Stretch Reflex
Wrapping around some of the muscle fibres are specialist nerve endings called muscle spindles.
These are sensitive to the degree and rate of stretch applied to the fibres. If there is a sudden dramatic lengthening, they are sensitised and send "help" messages to the central nervous system (CNS). This generates a nervous impulse back to the muscle telling it to contract. This prevents the tearing which may otherwise have occurred due to the rapid lengthening. This is a reflex action which is a bit like how a seat belt in a car functions, ie. pull on it too quickly and it stops.
This teaches us one of the first things about stretching. We should achieve a stretch by lengthening a muscle SLOWLY.
Muscle tissue (myofibrils) are themselves very elastic and will stretch very readily. However the connective tissue (epi, peri and endomysium) are only pliable when the temperature of the muscle is raised about 6oc (104of).
This teaches us that muscle must be WARM before stretching them.
Due to connective tissue wrappings of the muscle the stretch needs to be held in one position a minimum of 5-10 seconds to allow the connective tissue to give and 'creep'.
This teaches us that a MAINTENENCE stretch should be held for 6-10 seconds.
The Inverse Stretch Reflex
When a muscle is stretched and held at a high degree of tension further physiological changes can occur.
Within the muscle tendon junction are Golgi tendon organs (GTOs) which are sensitive to the tension being applied to the tendon. They have a higher threshold than the spindles. When considerable tension is generated these can be sensitised or 'fired'. They send a nervous impulse to the CNS saying 'there is a lot of stretch here - we need the tension taking off us!" hence, the CNS returns a message to the muscle saying 'relax'. This is the Inverse Stretch Reflex and is felt by the giving or yielding sensation within the muscle. This causes the muscle to relax even further and so it can be stretched further.
When the muscle is then stretched further and a greater ROM achieved, this is referred to as a development stretch. This process can be repeated 3 or 4 times, each time allowing the muscle to relax and then going a little further each time. Research shows that this is the most effective method of making flexibility gains.
This teaches us that to actually improve our flexibility DEVELOPMENT STRETCHING needs to be performed.
The Sliding Filament Theory (How Muscles Contract)
When a muscle receives a nervous impulse from the nervous system, telling it to contract, the cross bridge between all the pieces of actin and myosin, then length of the myofibril, are disconnected., The myosin slides closer towards the actin and then more cross bridges are made, AT this point there will be some overlap of the actin and myosin, When the muscle is told to relax the cross bridges disconnect again, the myosin slides back to is original position and some of the bridges are reconnected. The more the muscle contracts the more overlap there is between the actin and myosin and shorter the muscle becomes. The explanation of how the muscle contracts is referred to as 'The sliding filament theory'.
When a muscle is stretched the actin and myosin are eased apart and the muscle is lengthened. Providing some of the cross bridges remain intact the muscle is not damaged. If the actin and myosin are pulled apart in a violent way the cross bridges may be broken. This may lead to minor muscle tearing associated with muscle soreness.
Understanding ATP
ATP (Adenosine Triphossphate) is a very special molecule being the 'energy currency of the body'. This is because of its chemical structure, which enables it to supply immediate energy to drive all energy requiring chemical reactions in the body including those required to MAKE MUSCLES CONTRACT.
ATP consists of a molecule of adenosine, on to which are linked three phosphate groups. ATPs special energy-donating ability lies in its phosphate bonds, specifically, the bond between the second and third phosphate groups. This bond contains chemical energy, which can easily be unlocked when the bond is broken and importantly, readily stored again when the bond is reformed.
When the high-energy bond is broken to release energy to do work, the Adenosine triphosphate breaks down into adenosine disphosphate (ADP) and a free phosphate group is released. When (ADP) is resynthesised, free phosphate is bonded back onto ADP during which energy is once more locked up into the bond.
Ultimately, all the energy required to synthesise high energy ATP from ADP and phosphate comes from high-energy electrons from chemical bonds in the food we eat. These electons pass through metabolic system (known as oxidative phosphorylation and electron-transport chain), which harvest their energy by converting ADP back to high-energy ATP. Once their energy has been harvested, these electrons are passed on to oxygen. It is a bit like a waterfall, turning an ATP-producing mill.
Under normal aerobic conditions, ATP can be regenerated rapidly enough from ADP and high-energy electrons flowing down the chain, to meet energy demands. When energy demands are very high and can't be met aerobically, ATP can be temporarily generated from other pathways.
What happens when there's no more oxygen?
At higher exercise intensities, the aerobic production of ATP simply can't keep up demand. For example, if your muscle had to rely solely on aerobically production ATP, stores would be almost entirely depleted of ATP within just one-to-two seconds of maximum exercise. During intense or very intense muscular contractions, the body has to use back-up systems to generate the extra ATP required. These are the glysolysis and the phosphor-creatine systems.
Glycolysis is a way of partially extracting the energy from the electrons in the chemical bonds of food (stored as muscle glycogen), without the presence of oxygen, and can help to regenerate ATP from ADP and phosphatequite rapidly. However, this pathway produces fatigue-inducing lactic acid as a by-product and takes a few seconds to become fully active.
The phospho-creatine system, on the other hand, can produce very large amounts of ATP almost instantly by donating the high-energy phosphate bond present in creatine phosphate on to ADP, which regenerates ATP. The phospho-creatine system therefore forms an 'ATP buffer', keeping the concentration of ATP next to the contracting myosin fibres high and allowing around 10 seconds of maximal work to be produced before fatigue sets in.
Although we said that ATP is shuttled over from the mitochondria to the contracting myosin fibres, this is not strictly true - much of this high-energy phosphate shuttling is done by creatine phosphate, whose second major role is to act as a spatial buffer.
The concentration of creatine in muscle tissue is around five times higher than ATP. This actually makes creatine better at shuttling energy in the form of high energy creatine phosphate across the cytosol from the mitochondria where ATP is being produced to the myofilaments where the contractions are occurring.