Adenosine Triphosphate – ATP
ATP is made up of some protein, a chemical called adenosine and three molecules of phosphate shown below. These are joined together by energy to form ATP molecules. ATP is the only substance that can provide energy for our muscles to move, or contract. All the other chemicals that provide energy are used to rebuild ATP when it has broken down to release it’s own energy.
When the muscles require energy, they ‘call’ upon the ATP molecule to split from one of it’s phosphate molecules, releasing energy in the process. This leaves a molecule called Adenosine diphosphate (ADP), adenosine and the two remaining phosphate molecules.
To rebuild the ATP, and therefore, allow it to release energy once more, a phosphate molecule must be found as well as a form of energy. ATP can not move to muscles which are working from other parts of the body, therefore, when a molecule loses its energy (and some phosphate), other sources of energy must be found within the same fibre in order to avoid becoming severely fatigued – which all must be done almost immediately.
ATP does not just have to rely on finding another phosphate molecule, there are substitutes that can be used. This also applies to the energy source it acquires. For the purposes of this article, I will focus on one of the four chemicals: creatine phosphate.
This chemical provides the quickest source of energy and replacement phosphate to rebuild the ATP. It contains both creatine and one molecule of phosphate, with energy binding the two. These both combine with the ADP to allow the reformation of an ATP molecule and thus, energy for use in muscular contraction.
Although the rebuild process can be completed extremely fast, the drawback is that is can only be used for approximately 4-5 secs of max effort (di Prampero 1971) and therefore, a maximum rate of muscular contraction can only last for 4 to 6 secs.
A very small amount of CP is available afterward as phosphate and energy will be utilised in replacing ATP. Although, after a period of recovery and once all the ATP have been reformed, the left over phosphate will recombine with the creatine, formed with energy.
ATP-CP System in Training
Experts have, I feel, overstated the importance of training this system. Although it is observed that increasing the storages of ATP and CP results in athletes maintaing maximum speed for longer, the benefits are minor and would only likely be seen in 25 and 50m races.
Even in those shorter distances, it is hard to identify any reason why it would be important to develop this system. The normal rate of ATP-CP metabolism can provide energy for almost all of the maximum speed during a race, with the exception perhaps for the legs during the start or turns. The latter, however, is accommodated anyway as training alone will increase ATP and CP supplies as a by-product.
For even the improvements training the ATP-CP system would produce – likely less than 0.20 sec in a 25 or 50 event – time would be better spent developing other areas. Apart from technical training, a swimmer can significantly improve their maximum speed by increasing the size and strength of their muscle fibres (in particular groups) to improve power, and by recruiting fibres at a faster rate in an improved pattern. These can be both improved through land training and also in-water sprinting, the latter of which should be prioritised in order to allow muscle-fibre recruitment to occur in patterns which are in the correct sequence.
In short, the improvements seen in the ATP-CP system during training is sufficient enough not to require specific development. Training for maximum speed is better spent on technique and improving muscular strength as well as recruitment patterns.
Yours in Swimming,