Healthy, previously untrained, pre-pubertal boys and girls (N=335) were assigned to 16 different groups: 1) physical education, i.e. children participated only school in physical education classes (control group), 2) football (soccer) training, 3) basketball training, 4) volleyball training, 5) wrestling training, 6) martial arts training, 7) tennis training, 8) track and field training, 9) taekwondo training, 10) rhythmic gymnastics training, 11) artistic gymnastics training, 12) dance training, 13) swimming training, 14) climbing training, 15) two weight-bearing training modes, and 16) one weight-bearing and one non-weight bearing activity. Exercise training was performed three times per week for nine months and each training session had a 60-minute duration (except for the physical education classes at school in the control group). Anthropometric measurements (body height, body mass, and length and circumferences of various body segments), blood sampling, measurements of body composition (using dual X-ray energy absorptiometry or DEXA and skinfold calibers), bone measurements (bone density and bone mineral content at lumbar spine, both hips, both wrists and whole body using DEXA), and performance (cardiorespiratory fitness, muscle strength, muscle power, flexibility and motor ability) were performed at baseline and after the completion of a 9-month training intervention. Nutritional intake and habitual physical activity were measured at baseline, mid-training and post-training (using diet recalls and accelerometry, respectively). Intensity and volume of training was measured once every three months using heart rate monitoring, accelerometry, Global Positioning System (GPS) devices and jump measurement. Furthermore, two other studies were also performed as a part of this project: a) assessment of physical activity during physical education classes for primary school (using accelerometry, GPS instrumentation and jump measurement) and b) a smaller number of participants in the football, track and field, swimming and tennis training groups provided blood samples before and after a training session at baseline.