15 second assessment of hand and foot motor skill using a smartphone

Motor skills are essential for daily functioning and serve as key indicators of healthy development and aging. However, existing assessments of motor skill are inaccessible to the public and do not directly measure the quality of the movement. Here, we developed a convenient and robust measure of motor skill that uses a smartphone app to provide on-the-spot assessment in just 15 seconds. To validate our method, we asked 1675 participants between the ages of three to eighty-eight years old to trace circles at a fixed rhythm with a smartphone, which was either held in the hand or strapped to the ankle. Motor skill was quantified by the smartphone app using an algorithm that calculated the variability in the accelerations trajectory. Our assessment revealed significant changes in the skill of the hands and feet with age and practice. The variability of the hands and feet linearly decreased and matured in the mid-teens, but it regressed gradually thereafter. Laterality, or the difference in the motor skill between the left and right limbs, increased with age as the non-dominant hand and foot regressed faster in the elderly. Motor practice affected both skill and laterality as left-handers who were forced to write with their right-hand during childhood had a tell-tale sign of stronger right-handedness and, surprisingly, right-footedness. Our assessment aims to democratize motor skill assessment, making it accessible for professionals and users of all ages.