Size does matter! Conductive toe skin cooling in matched male and female volunteers

Differences were found in the rate of toe skin cooling between unmatched males and females, with a moderate correlation suggesting a relationship to foot volume (Lunt et al 2014). To remove the confounding factor of foot dimension, the present study recruited pairs of males and females matched for foot volume. It was hypothesised that the rate of toe skin cooling is related to the dimensions of the foot and not the sex of the person.

Nine males and nine females matched for foot volume (mean [SD] volume 847 [198] cm³ and 837 [198] cm³, respectively) gave their informed consent to participate in the ethically approved study. All volunteers cycled at 50W for 12 min and then in a seated posture exposed the soles of their feet to a gradually cooling metal plate (which cooled from 35 °C to 15 °C at a mean (SD) rate of -1.7(0.2) °C.min^-1. Great toe skin temperatures and laser Doppler skin blood flow were measured on the Great toe and 5th(little) toe throughout. Toe skin cooling rates for male and female volunteers matched for foot volume do not differ (Great Toe t=0.714, p=0.486; little toe t=0.861, p=0.402). Foot volume correlated with Great toe and little toe skin cooling (r=0.88, r²= 0.78; r=0.64, r²= 0.411 respectively). Overall foot volume was positively correlated to the rate of Great toe skin cooling (r=0.93, r2=0.87) and moderately so with little toe skin cooling(r=0.55, r²=0.29).

Pairs of male and female volunteers matched for foot dimensions showed that the rate of toe skin cooling in response to the same cooling stimulus is associated with foot volume. Thus, the hypothesis can be accepted, foot morphology is the main determinant for cooling, not sex.