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Using maturity offsets to determine age at peak height velocity
I came late to the game with biometrics and have only recently been studying and using them to help determine growth stages in young athletes. Most biometric measurements are used in clinical and research situations but some are useful for sport coaches because they can inform training decisions for young athletes. Sport governing bodies can use them to generate statistics about athlete cohorts and estimates for athlete growth.
One of the calculations, the maturity offset, is used to determine how far away a youngster is from peak height velocity (PHV), the early teen 'growth spurt'. This article will explain how to calculate the maturity offset and how to determine the age at peak height velocity (APHV), an important training milestone.
Biometric measurements used in determining the maturity offset include height, age, weight, sitting height, and leg length. There are two equations that can be used to calculate the maturity offset, Moore and Mirwald. You can get a complete discussion of the equations here.
Female offset = -7.709133 + (0.0042232 x (age x height))
Male offset = -8.128741 + (0.0070346 x (age x sitting height))
In the equations below leg length is derived by subtracting sitting height from height; the weight:height ratio is simply weight (kg) divided by height (cm).
Female offset = −9.376 + (0.0001882 x (leg length x sitting height)) + (0.0022 x (age x leg length)) + (0.005841 x (age x sitting height)) + (-0.002658 x (age x weight)) + (0.07693 x ((weight/height) x 100)
Male offset = −9.236 + ((0.0002708 x (leg length x sitting height)) + (−0.001663 x (age x leg length)) + (0.007216 x (age x sitting height)) + (0.02292 x ((weight/height) x 100)
The Science for Sport website has a spreadsheet tool that uses the Mirwald equations to calculate offsets. It is much easier to use than plugging everything into the equations above. Click here for instructions on how to do the measurements.
Update 6 October 2018 - Note that the Mirwald male equation does not use the age/weight interaction. This is not an error.
Update 19 June 2019 - The female Mirwald equation has been corrected. The age/weight interaction should be added rather than subtracted as we had it in the original article. The formula above has been corrected.
These are predictive equations that rely on accurate measurements and proximity in time to actual APHV. They should be done periodically, for example every four months, as a young athlete ages. Theoretically the result is more accurate the closer the measurements are made to the APHV.
What do the results mean?
The maturity offset represents the number of years the athlete is away from PHV. If the offset is negative it means that the athlete has not yet reached PHV. A positive offset indicates that PHV has already occurred. If so, and if the offset is less than 1.5, then it's possible that the athlete is still inside the PHV period.
To determine APHV simply subtract the offset from the athlete's age at the time the current measurements were made. This is the age at which the equations predict the athlete will reach PHV.
Age at Peak Height Velocity (APHV) = Age at measurement - maturity offset
Why is this important?
PHV represents a period of intense growth. It is typically called the teenage growth spurt but it sometimes occurs prior to the teenage years. It lasts from 12 to 18 months with variation so the period of time an athlete spends in PHV offers a unique training window that does not reoccur.
Knowing when PHV is likely to occur allows coaches to design training programs that can lead up to this important growth point and then take advantage of training effects available during and immediately after PHV, especially in the cardiovascular and strength areas.
Bill Price (firstname.lastname@example.org) is the owner and Chief Data Scientist at Sportkid Metrics.