= S. Yaemsiri
{c}
\b[<S. Yaemsiri>] is first author of a 2010 study measuring human <nail (anatomy)> growth with <N. Hou>, <M. M. Slining> and <K. He>. Twenty-two young adults marked their nails and recorded mark position and elapsed time. The reported mean rates were 3.47 millimetres per month for fingernails and 1.62 for toenails.<Growth rate of human fingernails and toenails in healthy American young adults by S. Yaemsiri and others>[Primary byline; Abstract, Methods and Results]{ref} The study links an accessible physical measurement with interpretation of a slowly growing biological sample.
An original example illustrates the measured quantity. A mark that moves from 1.0 to 7.0 millimetres from the reference fold over 60 days has average <growth rate>
$$
v=\frac{7.0-1.0}{60}=0.100\,\mathrm{mm\,day^{-1}}.
$$
Expressing that result as 3.00 millimetres per month additionally chooses a 30-day month. Reporting the elapsed days avoids silently mixing calendar and fixed-duration units.
The measured displacement describes advance of a nail mark over an interval; it is not an instantaneous measurement of every cell's production rate. In a <longitudinal study>, consistent landmarks and repeated measurements help define what changed. Extrapolating from a group mean to the exact age of an individual clipping would require assumptions about that individual's growth history.
For a purely illustrative constant-rate comparison, a 10-millimetre travel distance takes $10/3.47\approx2.88$ months at the reported fingernail mean and $10/1.62\approx6.17$ months at the toenail mean. These calculated times are not individual predictions. The work's value is to make the time axis of biological sampling measurable rather than implicit.
Back to article page
