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How to do the measurements for determining peak height velocity (PHV)
A few weeks ago I wrote about using peak height velocity (PHV) to determine when the adolescent growth spurt is occurring in young athletes. This stage of growth marks an accelerated period for training endurance and strength. Several people have asked how these measurements are made and, most importantly, when they're made. In this article I will describe the measurements and how to make them and then suggest a schedule for taking them with young athletes.
What are the measurements?
Several measurements can be useful in analyzing growth in children and adolescents. Chief among them are height, weight, and age, the big three. In sport training it also helps to measure wingspan and sitting height. To track PHV you really only need to measure height but the other measures can give a more comprehensive look at how growth is taking place.
Using the other measures will naturally depend on how many athletes you have to track. Measurement doesn't take long and you may find the additional data useful. Although not critical the other measurements can be helpful in calculating ratios between height and wingspan, and between sitting height and standing height. Researchers sometimes measure leg length but this can be easily calculated if you already know sitting and overall height.
Measuring age is easy to do. The only thing unusual about sport biometrics is that it is calculated in months, not years like everyone is used to. Age provides a measurement of time and when combined with distance (the height measurement) you get the rate or the velocity of growth, hence peak height velocity. What we're looking for in PHV measurement is a large change in the rate of growth.
Measuring height, wingspan, and sitting height is done in centimeters (cm) to three digits with no decimal. Weight is measured in kilograms (kg) to one decimal place. The reason we don't use decimals in the height measurement is because I've found that it's usually not that accurate. Typically stadiometers are not available for this measurement and marked tapes on walls are used instead. No matter how accurate you try to be in setting up these tapes about the best accuracy is going to come at the centimeter level rather than the decimal level.
Ratios are calculated for sitting height to standing height, and wingspan to standing height. You can express these as percentages or decimals. I like using decimals.
As I noted though you really only need to measure age and height to determine PHV but you may find that the other measurements are helpful in situations where age and height is not definitive.
When should athletes be measured?
Coaches have to balance effectiveness with practicality. While it would be nice to have all that data, you don't really need it. Measuring too often though is usually not the problem, not measuring enough is.
The generally agreed on standard for measurements of this type is every three months. That's far enough apart so as not to burden coaches and often enough so that a large portion of the PHV period isn't missed by measurements spaced too far apart.
When I first started making measurements I based it on each athlete's birthdate so the measurement schedule was individualized and I was measuring each athlete every three months with their birthdate being one of the measurement days. This got to be too complicated and eventually I realized it was better to measure all athletes at the same time every three months. It might take a week to do this but everything was completed and all the data was collected at one time. This made the process much easier to deal with.
What the numbers mean
Many people confuse the terms average and rate. Rate is a measure of speed and changes throughout the growth cycle. When we're looking for PHV these changes are what we're looking for; unusual changes in the speed of growth. Large changes in height velocity signal that other changes are also taking place within the body and once we pinpoint this period we have also identified a sensitive training period that can be exploited to increase both aerobic and strength gains in training.
Notice that the chart shows a spike in growth rate around month 178 from the subjects usual 4.0 cm/year to about 8 cm/yr. Also notice that this rate continues into month 181, levels off and then spikes again through months 187 to 193 where the rate jumps to 12 cm/yr. This is obviously PHV the only question is, when did it start? Our first indication is in month 178. It may have started sooner than that but the previous measurement in month 175 showed no growth since the measurement prior to that. So we've narrowed it down to starting somewhere between months 175 and 178.
PHV typically lasts for 12 to 18 months. The chart also shows that at month 196 the rate has returned to about 4 cm/yr and has leveled off in the measurement periods that follow. This athlete's PHV period has lasted about 15 months.
Bill Price (firstname.lastname@example.org) is the owner and Chief Data Scientist at Sportkid Metrics.