The Crux of Human Movement Variability.

Despite intense training, even a seasoned baseball pitcher has difficulty throwing a ball to the same location repeatedly. I describe my research team's finding that such movement variability comes from muscles that activate at imprecise times and introduce a new method that uses a smartphone to robustly quantify movement variability, which is tightly related to the arm muscles' timing precision. This useful method reveals how movement variability, a measure of dexterity, changes with growth and age, and it quantifies the degree of handedness and footedness. [ABSTRACT FROM AUTHOR]