The law says that the mobility increases from proximal to distal parts of the body. In this paper the authors looked at the foot TPD (Two Point Discrimination)
values of the diabetic patients and say that the law donot hold good in diabetic patients, but in normal patients it works well. In normal subjects, the TPD values in the foot goes higher at the ankle to lower at the toe gradually. In diabetic patients, this is not so, TPD values varies haphazardly.
THis is the quote from the paper as it is:
"Research on cutaneous sensibility was undertaken in the nineteenth century by Vierodt [6] and Weber [7]. Weber introduced the point localization test and the accompanying measures, two-point discrimination (TPD) and localization error, as measures of cutaneous sensibility. Density of mechanoreceptors in an area determines the TPD. A dense population leads to finer TPD and the receptors have smaller receptive fields. Mapping of the whole body revealed large differences in the sensibility between different parts of the body. Vierodt generalized this observation into the 'law of mobility', which states that the TPD improves with the mobility of the body part. TPD correlates with the Degree of Freedom (DOF) of the body part. It is to be noted that no exception to this law has been found yet. After the work of Weber and Vierodt, little attention was given to this field until the 1950s [8] and 1960s [9]. Weinstein observed significant effects of body locus. Lowest TPD was found for the fingertips (2.5 mm). TPD for the trunk was approximately 40 mm. Sensitivity decreased from distal to proximal regions, and thresholds correlated with the relative size of cortical areas subserving a body part. Another important observation was that good TPD did not necessarily mean good sensitivity to pressure, that is, a low detection threshold."
Intra-observer reproducibility of the feet soles two-point discrimination test in asymptomatic elderly and young individuals.
Franco PG, Bohrer RC, Rodacki AL. Rev Bras Fisioter. 2012 Nov 27.
Comparison of reliability and efficiency of two modified two-point discrimination tests and two-point estimation tactile acuity test.
Zimney K et al Physiother Theory Pract. 2020 Jan 29:1-10