Our Methodology
TestMi uses peer-reviewed methods to assess maturity, predict adult height, and flag injury risk in young athletes. Here's how each one works and what it means for coaches.
Maturity Assessment — The Mirwald Method
The Mirwald maturity offset equation estimates how far an athlete is from their peak height velocity (PHV) — the point during adolescence when they are growing fastest. This gives coaches a “maturity offset” in years: a negative value means the athlete has not yet reached PHV, and a positive value means they have passed it.
The equation uses standing height, seated (sitting) height, weight, and chronological age. Separate equations are used for males and females.
What it tells a coach
Whether an athlete is early, on-time, or late in their physical development relative to their age. This helps with bio-banding (grouping by maturity rather than chronological age), understanding performance differences, and adjusting training loads during growth spurts.
Limitations
The Mirwald equation is a prediction — not a direct measurement of PHV. It works best for athletes aged approximately 10–16 and is less accurate at the extremes of the age range. Accuracy depends on correct measurement of sitting height, which requires a trained measurer.
Reference: Mirwald, R.L., Baxter-Jones, A.D.G., Bailey, D.A., & Beunen, G.P. (2002). An assessment of maturity from anthropometric measurements. Medicine & Science in Sports & Exercise, 34(4), 689–694.
Adult Height Prediction — Khamis-Roche
The Khamis-Roche method predicts an athlete's adult (final) height using their current height, current weight, and the heights of both parents. It is one of the most widely used non-invasive methods for height prediction in paediatric sports science.
TestMi asks coaches whether parent heights were clinically measured or self-reported. Self-reported heights are adjusted using Epstein et al. correction factors before being used in the prediction, as self-report tends to overestimate height.
What it tells a coach
An estimate of how tall the athlete will be as an adult, along with a 90% confidence interval. Combined with current height, this gives the athlete's percentage of adult height — a useful indicator of how much growth remains.
Limitations
Accuracy depends on accurate parent height data. The method was validated on a North American population sample and may be less accurate for athletes from other genetic backgrounds. It works best for athletes aged 4–17.5.
Reference: Khamis, H.J. & Roche, A.F. (1994). Predicting adult stature without using skeletal age: the Khamis-Roche method. Pediatrics, 94(4), 504–507.
Correction factors: Epstein, L.H., et al. (1995). Estimation of stature from self-report. American Journal of Epidemiology, 142(8).
Growth Velocity & Injury Risk
TestMi calculates height velocity (cm/year) from repeated height measurements across testing sessions. Rapid growth is associated with increased injury risk in young athletes — particularly for apophyseal injuries (e.g. Osgood-Schlatter, Sever's disease) and muscle-tendon overuse injuries.
The Growth Tracker view shows each athlete's current growth velocity and flags those in a rapid growth phase. Risk levels (Low, Medium, High) are based on the combination of growth velocity and proximity to PHV.
What it tells a coach
Which athletes are currently in a growth spurt and may need modified training volumes, reduced plyometric loading, or closer monitoring for overuse complaints. This is not a diagnostic tool — it is an early warning system that supports informed coaching decisions.
Limitations
Growth velocity requires at least two height measurements taken at different times. Accuracy improves with more frequent measurements (ideally every 6–10 weeks). A single anomalous measurement (e.g. incorrect technique) can produce misleading velocity values — TestMi flags suspected measurement errors automatically.
Measurement Quality
All of the methods above depend on accurate measurement data. TestMi includes automatic anomaly detection that scans an athlete's measurement history and warns coaches about potential data entry errors — such as height decreasing between sessions, implausible growth rates, or sitting height exceeding standing height.
These checks run automatically when session data is saved and when viewing an athlete's profile. They are non-blocking — coaches can choose to correct the data or proceed if the values are correct.
Validation in Practice
TestMi's implementation of these methods was developed and validated in partnership with Move4Sport, a specialist youth S&C coaching provider. Their coaches — with backgrounds in Olympic sport, professional football, and international tennis — tested the platform across multiple sports and age groups.
The calculation logic is covered by automated tests verified against published reference values. If you have questions about the methodology or would like to discuss the implementation, please get in touch.