Fig. 2. Midshaft periosteal modeling rate (left y-axis, circles), and Haversian remodeling rate (right y-axis, squares) versus R, the distance from the midshaft to the hip joint (x-axis) in juveniles (A), subadults (B) and young adults (C). Runners, filled symbols; controls, unfilled symbols. Values are means ±1 S.E.M. The energetic cost of added mass is approximately proportional to the square of R. Modeling rates are higher in proximal than distal bones, and decrease with age, whereas remodeling rates are higher in distal than proximal bones, and increase with age. The effects of exercise are greatest in juveniles, and non-significant in all adults. See Tables 1 and 2 for tests of significance.