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  • Writer's pictureGary Moller

When should your child specialise in a sport?

Updated: 7 days ago

(This is the updated version of an earlier article)

"It's Allometry Dear Watson" (Sherlock Holmes)

Dr Watson and Sherlock Holmes

In all but a few sports, there is a very good reason we should not, as parents or coaches, have young people overly specialise in one sport before physical maturity: The science of "allometry" or "allometric scaling". What is allometric scaling?

Allometric Scaling

The science of allometric scaling dictates that if an organism doubles in size, its power increases only by a factor of 2/3rds. To my dismay, the science of allometry, as it applies to the adolescent athlete, is poorly understood within coaching, exercise physiology and sports medicine. Allometric scaling explains why an ant can lift several times its weight, whereas an elephant cannot. The larger the organism, the less its power-to-weight ratio. This is why an ant would collapse under its own weight if it were scaled to elephant size and why an elephant can't jump. Allometry also applies to accelerating and decelerating an object: The more mass, the disproportionally more energy is required to accelerate and decelerate it. This is why a light dragster can out-speed its more powerful but heavier opponent. So a 50kg weight lifter can lift proportionately more per kg body weight than a 150kg lifter. 100m sprinters tend to be smaller than 200m sprinters because the smaller mass is more quickly accelerated, bestowing a slight advantage over a larger opponent over the shorter distance. This is why a small rugby player tends to be able out-manoever a larger opponent due to better agility and acceleration.

Size matters

Size is an advantage in sports that do not require lifting and lowering body weight. Therefore, a big rower or kayaker will have an advantage over a smaller opponent. The same applies to cycling - a big rider will have an advantage on a flat course, whereas a light rider will have it over a heavier opponent on the hills. We see this in the Tour de France, where the small riders dominate the mountain sections while the bigger riders dominate the flat sections, time trials and sprints to the line.

Running has excellent examples of allometric scaling in action. A light runner has the advantage over a heavier one in any event longer than 200m. This is because each stride raises and lowers the body weight by several centimetres. The power-to-weight ratio of the runner is more important than their total power when raising and lowering body mass with each stride. This is one of the main reasons why slightly built African runners dominate middle and distance running.

Let's do the maths:

The maths are simple when working out power to weight ratios:

A 65 kg rider with a 4-litre max O2 uptake = 61.5 ml O2/Kg

An 85 kg rider with a 5-litre max O2 uptake = 58.8 ml O2/kg

On the flat, and all other things being equal, the 85 kg rider, due to sheer total horsepower (max VO2), will have an advantage over the 65 kg rider. In contrast, on a hilly course or one that requires constant accelerating and decelerating and changing of direction, the 65 kg rider will have the edge (max VO2/Kg bodyweight per minute), other than on any long descents.

A child is their Mother, their Father, and those before them:

As a young person goes through puberty, body changes can be dramatic, and one can not defy physical laws such as allometric scaling. However, these changes can be delayed by over-exercising and under-eating. I do not recommend trying to delay the inevitable.

One can understand who that precocious adolescent athlete might become by looking at his/her parents, grandparents and close relatives. If parents do their job well with nurturing their children, they should be taller and stronger than them as adults. Please read this article:

Because of the influence of allometric scaling, a young person that demonstrates talent in one sport or physical skill should not over-specialise in these until well on the way to physical maturity, which is about 20-24 years and completed at about 28 years. A rich and varied physical upbringing allows them to switch to the activity their body best suits seamlessly, and they find out what they enjoy doing. Of course, there are always exceptions to the rules of physics, but these people are rare.

There are only two kinds of coaches in this world:

Those that have been fired and those that are about to be fired!

So, few coaches take a developmental approach with young athletes, preparing them for when they will produce their best performances from 28-34 in most sports other than gymnastics. The pressure is on the coach to produce winning performances this season, not ten years from now. As parents, you must understand this and ensure a nurturing developmental approach is taken to how your precious child is coached.

Thou shalt not injure!

Or burn out a young athlete. Bear in mind your child will not hit his or her athletic peak until about 28 years. While it varies from sport to sport, the dropout rate by 18 years, let alone 28 is horrendous: about 99%! Of those that get to 28 years and are still competitively active, few have not suffered harm, such as a knee or back injury, that takes some of the gloss off what could have been.

As parents, your job is to ensure your child is not exposed unnecessarily to risk injury, overtraining or sheer lack of enjoyment. If necessary, step in and take control if you think things are not in your child's best interests.

With my children, now still highly fit and healthy adults who love exercise and the Great Outdoors, we would change sports for a season if the coach began to demand too much. For example, when swimming was getting too serious and demanding, I suggested we switch to springboard diving next term. They said, "Yeah, let's do it!" They loved the change, learned new skills, and had lots more fun while health and exercise became an integral part of life for them, and not an imposition.

Concluding remarks

As the great detective, Sherlock Holmes, says, "It's allometry", or should we say, elementary or evident to the observer: Let your children play, have fun and to move freely from one activity to another. If they are destined for sporting greatness due to innate talent or ability, then what's the hurry?

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Grant Rawlinson
Grant Rawlinson
Jan 16, 2023

Excellent article on a point I have been thinking of recently, thanks as always for your wisdom Gary!

Gary Moller
Gary Moller
Jan 16, 2023
Replying to

I'm pleased to be of service, Grant. I'm going to do an update on the article shortly.

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