The growth calculation estimates the moment at which a child grows fastest: the peak of the growth spurt. It is an estimate, not an exact prediction. If you know how accurate the estimate is and where the margins lie, you can put the outcome to good use in training.
Why an estimate?
The peak of the growth spurt can only be determined with certainty once it has passed. To do that, you would have to measure a child regularly for years and look back to see when growth was fastest. For coaches that is too late: they want to know in advance what is coming.
That is why the growth calculation uses the Mirwald method, which the Athletic Skills Model also builds on. Based on a single measurement of height, sitting height, weight, age and sex, the formula estimates how far a child is from the peak. This is called the distance to the peak, expressed in years before or after the peak.
How accurate is the estimate?
Research shows that the estimate is accurate on average, but has a margin of about half a year either way for each child. For some children the difference can be as much as a year. This means that if the calculation says the peak will come in a year, the actual peak will probably fall somewhere between six months and eighteen months from now.
For assigning growth periods, that is usually accurate enough. Phases P1, P2 and P3 each span several years. Only around the transition from one phase to the next is caution needed.
When is the estimate less reliable?
The formula works best for children who are close to the peak. The further a child is from it, the greater the uncertainty. Pay particular attention to these situations:
- Young children, well before the peak. The formula tends to place their peak too early.
- Children who are well past the peak. Here too the estimate becomes less precise.
- Children who mature much earlier or later than average. The formula pulls the outcome slightly towards the average. For an early maturer the peak may therefore come even earlier than calculated, and for a late maturer even later.
- Inaccurate measurements. An error of a few centimetres in sitting height can shift the outcome by months.
How to make the calculation more reliable
Several measurements show whether the estimated peak stays stable.
Measure more often. One measurement gives a first impression. With each new measurement, the growth calculation recalculates the peak. If the outcome stays roughly the same over several measurements, the estimate is more reliable. If it keeps shifting, you know to be careful.
Look at the growth rate. If growth per month is increasing, the peak is approaching. If it is decreasing, the peak has passed. That is a good check on the calculation.
- Measure every three to four months, at a fixed time of day.
- Always measure the same way, with the same stool, measuring rod and scales.
- Preferably have the same person do the measuring.
- Re-measure doubtful cases. The measurement form shows the previous measurement; a large, unexpected jump is often a measuring error.
How do you use the outcome in practice?
Treat the calculated peak as a reference point with a range. If, according to the calculation, a child is six months before the start of the growth spurt, assume that they may already be in it. Combine the outcome with what you see: if a child is visibly growing fast, is temporarily clumsier or more often has knee or heel complaints, those are signals that confirm the calculation.
Use the growth phase mainly to adjust training, not to select or assess children. The margin is too large for that, and a child’s development is too varied.
In short
- The calculation is an estimate with a margin of about half a year, sometimes more.
- It is most accurate around the peak and less accurate well before or after it.
- Several careful measurements make the estimate more reliable.
- Always combine the outcome with your own observations.
The calculation is a tool and does not replace medical advice. In case of persistent complaints, consult a (sports) doctor or physiotherapist.
- Mirwald, R.L. e.a. (2002). An assessment of maturity from anthropometric measurements. Medicine & Science in Sports & Exercise, 34(4), 689–694. doi.org/10.1097/00005768-200204000-00020
- Malina, R.M. & Kozieł, S.M. (2014). Validation of maturity offset in a longitudinal sample of Polish boys. Journal of Sports Sciences, 32(5), 424–437. Voor de marges en de afwijking bij vroeg- en laatrijpe kinderen.
- Moore, S.A. e.a. (2015). Enhancing a somatic maturity prediction model. Medicine & Science in Sports & Exercise, 47(8), 1755–1764.
- Kozieł, S.M. & Malina, R.M. (2018). Modified maturity offset prediction equations. Sports Medicine, 48(1), 221–236.
