Using literature to estimate biological age
This article will explain the specifics of calculating biological age, to understand why Biological age is important for sports scientists please read Understanding Growth and Maturation
The literature underpinning the maths
The review features four studies that look into the growth and maturation of children in Europe and North America, one of the major caveats here is they're all caucasian.
The paper presents the average age at PHV for males and females, which is 13.37 and 11.29 respectively.
| Study | Male - Avg (SD) | Female - Avg (SD) |
| Thissen (Cal Berkley) | 13.06 (1.08) | 11.01 (0.83) |
| Thissen (Denver Child) | 13.31 (1.08) | 11.01 (0.91) |
| Thissen (Fels Research) | 12.99 (0.93) | 10.96 (0.8) |
| Thissen (Harvard) | 12.9 (0.94) | 11.13 (0.87) |
| Berkey | 13.57 (1.11) | 11.49 (1.17) |
| Tanner & Whitehouse | 13.91 (0.84) | 11.89 (0.9) |
| Mirwald | 13.82 (1.01) | 11.58 (0.92) |
| Avg | 13.37 (1.00) | 11.29 (0.91) |
| Range | 12.37 -13.37 - 14.37 | 10.38 - 11.29 - 12.2 |
The average age and average standard deviations from these studies has been carried forward as the 'expected age at PHV'.
Early - On-Time - Late
By minusing the SD from the expected age at PHV we have the lowerbound estimate and by adding SD to the expected age at PHV we have the upperbound estimate.
After collecting the required measurements to achieve a prediction of how far away an athlete is from PHV we can compare their actual PHV vs expected. e.g. Jimmy is 11.0 years old and his assessed PHV is -1.2, therefore his age at PHV is 12.2 (11 - -1.2) this is lower than the 12.37 lowerbound estimate calculated from the studies above. Jimmy is an early developer.
If an athlete falls between the lower and upperbound, they are considered On-Time.
If an athlete's predicted PHV is higher than the upperbound, they are considered a Late developer.
Calculating Biological Age
Now we have an athletes age, their PHV and the average age males and females reach their PHV we can assume the following.
Jimmy is 11.0
His PHV is -1.2
The average age of PHV is 13.37
Therefore his expected PHV to be on-time is -2.37 (11 years old - 13.37)
The difference beetween his expected PHV and actual PHV is 1.17 (-2.37 - -1.2)
Jimmy is 1.17 years older than expected at this current time, so we can say he is currently 12.17 years old biologically.
For a late developer it would look like this
Clarissa is 14
Her PHV is 1.5
The average at at PHV is 11.29
Her expected PHV is 2.71
The difference between the two is -1.21
Therefore she is biologically 12.79
We have created two age group categories in our system 'Real Age' and 'Biological Age' - athletes will receive an MVP Score where they're compared against their real age peers and their biologically matched peers. This will help to unveil three key scenarios
1. A late developer scores poorly against his age matched peers, but versus biologically matched people they score quite well. Give them time to grow, they will shine soon.
2. The opposite may be true for an early developer who is appearing very good against biologically younger people in their year group but score poorly versus bio matched peers. Others will catch up with them.
3. A male 12 year old is an early developer and has a good MVP Score in both assessments. He is clearly good vs other year 7s at school because he is biologically year 9, but also scores well vs year 9 aged kids. Then you know you have a good athlete on your hands.
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