Impact exercise increases bone mineral density and improves bone geometry in weight-bearing bones. However, long-term effects of impact exercise on bone turnover as well as dose-dependency are not known. To study the effects of high-impact exercise on bone turnover and calciotropic hormones, we performed a 12-month population-based, randomized, controlled exercise trial in 120 women (age 35–40 years). Subjects were randomly assigned to an exercise group (EG; n=60) or a control group (CG; n=60). The exercise regimen consisted of supervised high-impact exercises three times per week. Daily impact loading was assessed by using an accelerometer (Newtest Ltd., Finland). Bone turnover markers, calciotropic hormones and turnover balance (Uncoupling Index, UI=Z(PINP)–Z(TRACP5b)) were analyzed at 0, 6 and 12 months. Thirty-seven women in the EG and 39 women in the CG completed the study. The Uncoupling Index increased in the EG and decreased in the CG (0.32 vs. -0.28; p=0.03). PTH decreased significantly more in the EG than in the CG (-11.2 vs. -2.2 pg/mL; p=0.03). The most active subjects with the highest number of impacts exceeding accelerations of 2.5g had higher increases in the UI compared to the least active subjects (0.86 vs. -0.48; p<=0.001). The number of these impacts separating the most and the least active subgroups was 400 impacts per day equivalent to half an hour of impact exercise like jogging, running or jumping. In conclusion, regular impact exercise alters bone turnover balance in favour of bone formation in a dose-dependent manner. Effective dose is reached during normal exercise training indicating potential to affect bone strength with impact exercise. The Uncoupling Index seems to have potential to reflect the effect of exercise on bone turnover.