Microvascular Sex and Age-related Day-to-day Variability in Healthy Subjects

The goal of this observational study is to learn more about the microcirculation in the skin by examining sex and age-related day-to-day variability in healthy subjects. The main questions the trial aims to answer are: * What is the day-to-day variability of the optical measurement techniques in the microcirculation, and does age and gender affect this? * Does the day-to-day variability differ in the foot compared to the arm? Participants will rest whilst skin measurement by optical measurement techniques are performed. Baseline measurements and post-occlusive reactive hyperemia will be studied on the forearm and foot. This measurement procedure is repeated within one week, in order to study variability.