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Following on from my last blog post which spoke about relative age in a chronological fashion, in this blog I will be talking about biological age and how that can play a large role in the training of a swimmer and the progression rates at an early age. Besides the obvious factors of those who physically develop earlier being generally taller and stronger at a younger chronological age, there are also some considerations to be taken into account for them physiologically, which will mean that their training needs to be different to those at a younger biological age. This will often lead to various accusations of favoritism when “swimmers who are fastest” get preferential treatment or “get pushed more”, but hopefully in this blog post I will be able to explain the various different reasons that training variation is a positive and also for those developing later, can be a benefit if treated correctly.

Peak Height Velocity and Biological Development

Peak Height Velocity is a fancy term to say the point at which a child reaches their fastest rate of growth since being a newborn baby (also referred to as a growth spurt). Girls will tend to reach their PHV at a younger age, boys will generally reach it later, but boys will grow even faster during it. Most of the time PHV coincides with the onset of adolescence, where hormones increase in the body and cause various different changes. These two areas are important for an athlete in their physical development and provide different opportunities to develop than pre PHV and adolescence. Those who start adolescence earlier are referred to as having an older biological age than those who start the process later.

How does biological age impact on training and development within swimming?

Once reaching PHV athletes are growing at an accelerated rate, this is not just on the outside, but is also happening internally. This means that the development of the aerobic system is also accelerated during this period of time. By developing capillaries, increasing the output from the heart and increasing the density of mitochondria within the muscle, swimmers will train their aerobic capabilities on a regular basis. This will give swimmers an increased amount of efficiency in delivering oxygen to the muscles and allow the body to perform at a higher level for longer, but it will also give swimmers the tools to remove and recycle byproducts of anaerobic energy production such as lactate. Without an effective and efficient aerobic system, the more intense training that swimmers do as they progress will be less impactful and in some instances stall and plateau their development.

So initially, biological age has an impact on when a swimmer should increase the amount of aerobic training that they do. Secondly, due to adolescence flooding the body with various different hormones, it also gives a handle to coaches on when to start more anaerobic training. Pre-adolescence, young swimmers do not have the same hormone production, which means that their anaerobic system is not as active as it will become and therefore not as productive to train this system within the body.

Therefore, those swimmers who do have a biological age that is more advanced, will more than likely be exposed to certain types of training earlier (so long as the technical foundations are in place to allow for it) they will also need to look at doing more training (volume) at an earlier chronological age (again, so long as the technical and skill-based foundations are in place).

What does this mean for the swimmers with a younger biological age?

In my last blog, I mentioned the roadblocks that swimmers need to face and how the mental side of the sport can lend itself to swimmers who have to struggle in the early stages of their swimming career. Swimmers who are later physical developers can also see some benefits from the situation they find themselves in. Firstly, all swimmers will eventually go through puberty and reach their full physical development – the positive note for developing later, is that those swimmers will have more time in the earlier stages of their development to improve their technical abilities and their general training ability. This means that when they reach the stages of their development where their body develops (PHV) they could be in a really strong place to take advantage of these stages of development. If a swimmer is not technically efficient, or their general training abilities are not at a strong level, they will not be able to fully take advantage of any physical changes in their body at that point.


All swimmers develop at different rates and have their own journey within swimming. Comparisons do not help a swimmer’s own development and mindset, so take the advantages that you will get (there are two sides to every coin) and recognise that you will get the same opportunities as everybody else, it will just depend on how hard you work to take those opportunities!


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