ORIGINAL RESEARCH A 5-Year Exercise Program in Pre- and Peripubertal Children Improves Bone Mass and Bone Size Without Affecting Fracture Risk Fredrik T. L. Detter • Bjo ¨rn E. Rosengren • Magnus Dencker • J.-A ˚ . Nilsson • Magnus K. Karlsson Received: 17 September 2012 / Accepted: 8 December 2012 / Published online: 22 January 2013 Ó Springer Science+Business Media New York 2013 Abstract We studied the effect in children of an exercise intervention program on fracture rates and skeletal traits. Fractures were registered for 5 years in a population-based prospective controlled exercise intervention study that included children aged 6–9 years at study start, 446 boys and 362 girls in the intervention group and 807 boys and 780 girls in the control group. Intervention subjects received 40 min/school day of physical education and controls, 60 min/week. In 73 boys and 48 girls in the intervention group and 52 boys and 48 girls in the control group, bone mineral density (BMD, g/cm 2 ) and bone area (mm 2 ) were followed annually by dual-energy X-ray absorptiometry, after which annual changes were calcu- lated. At follow-up we also assessed trabecular and cortical volumetric BMD (g/cm 3 ) and bone structure by peripheral computed tomography in the tibia and radius. There were 20.0 fractures/1,000 person-years in the intervention group and 18.5 fractures/1,000 person-years in the control group, resulting in a rate ratio of 1.08 (0.79–1.47) (mean and 95 % CI). The gain in spine BMD was higher in both girls (difference 0.01 g/cm 2 , 0.005–0.019) and boys (difference 0.01 g/cm 2 , 0.001–0.008) in the intervention group. Inter- vention girls also had higher gain in femoral neck area (difference 0.04 mm 2 , 0.005–0.083) and at follow-up lar- ger tibial bone mineral content (difference 0.18 g, 0.015–0.35), larger tibial cortical area (difference 17 mm 2 , 2.4–31.3), and larger radial cross-sectional area (difference 11.0 mm 2 , 0.63–21.40). As increased exercise improves bone mass and in girls bone size without affecting fracture risk, society ought to encourage exercise during growth. Keywords Bone mineral content Á Bone size Á Children Á Controlled Á Exercise Á Fracture Á Prospective A high level of physical activity induces anabolic skeletal effects, as does moderate activity during growth [1–10]. The most osteogenic activities include fast novel dynamic loads with high magnitude and high frequency, whereas endurance activities seem to be less effective [11, 12]. Physical activity during growth is also associated with high peak bone mass, and half of the variance in bone mass at age 70 is estimated to be predicted by peak bone mass [13]. As low bone mass in advanced age is associated with high fracture risk, exercise during growth could possibly be used as a preventive measure for osteoporosis and fragility fractures [14]. The pre- and early peripubertal years are ideal for exercise if the aim is to improve skeletal strength as mechanical load preferentially affects surfaces of the skeleton undergoing fast apposition [15]. This notion is supported by intervention studies showing that the same type of exercise mediates benefit before puberty but with no or only minor effects after puberty [1–6, 8–11]. Most such intervention studies have used bone mass as the end- point variable, included volunteers, and utilized specific training programs designed to be osteogenic; and none has so far exceeded 36 months [5, 6, 9, 11, 16]. Furthermore, The authors have stated that they have no conflict of interest. F. T. L. Detter (&) Á B. E. Rosengren Á J.-A ˚ . Nilsson Á M. K. Karlsson Clinical and Molecular Osteoporosis Research Unit, Department of Clinical Sciences and Orthopedics, Ska ˚ne University Hospital, Lund University, SE-205 02 Malmo ¨, Sweden e-mail: fredrik.detter@med.lu.se M. Dencker Department of Clinical Physiology, Ska ˚ne University Hospital, SE-205 02 Malmo ¨, Sweden 123 Calcif Tissue Int (2013) 92:385–393 DOI 10.1007/s00223-012-9691-5