Research concerning relative, or scale-free, limb proportions has revealed interesting patterns of variability with regards to environment. However, there have been no direct attempts to correlate variability in limb proportion with unrelated stress indicators. In response, this study examined the relationship between long bone length ratios and linear enamel hypoplasia (LEH) frequency in a modern Thai population.

Distal/proximal limb bone length and relative bone length/stature ratios were calculated for 259 adults (105 female/154 male) and compared against LEH presence and frequency. Analysis using a Spearman’s correlation coefficient indicated significantly shorter relative distal limb lengths in the lower limbs of individuals with LEH presence and high LEH frequencies. This pattern was strongest in females, especially with regards to frequency. In males, the pattern between relative limb length and distal/proximal limb length ratios and LEH was not as clear, occurring only in the radius and fibula and only on the left side of the body. Examination of secular trends indicated that females from this sample were increasingly healthy – significantly longer limb lengths and reduced LEH – while males displayed the opposite response. This is may be the result of cultural changes in northern Thailand, such as reasons for donation to the collection.

Overall, these findings support the claim that distal limb growth is more strongly affected by developmental stress than proximal growth. In this study, the upper and lower limbs demonstrate different responses to environmental stress. This disparity, in addition to the strong association of limb bone length ratios and LEH frequency in females, may have significant implications for our understanding of human limb development and catch-up growth.