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The purpose of the study was to validate optical segment tracking, a new method for in vivo human tibia deformation measurements and to assess bending in a three-point bending test. The approach relies upon optical motion capturing of reflecting marker clusters affixed to the bone via screws inserted three millimeters into the corticalis in local anesthesia. The method was tested in five healthy subjects. Screws were left in place for six to eight hours and a variety of exercises performed. A pain questionnaire was used to assess pain levels. PQCT-images were taken to locate screw holes in the bone. A three-point bending test was performed and repeatability evaluated. The new method shows good feasibility though this was previously considered impossible by many experts. Local anesthesia works for screw implantation and explantation. Results show linearity with an average of 0.25 degrees per 10 kg of weight applied with good repeatability (average variation coefficient 8%). Optical segment tracking is feasible for human in vivo bone deformation measurements. There is a variety of possible clinical and experimental applications including stability testing of osteosyntheses and joints, monitoring of bone healing, evaluation of exercises in physiotherapy, and assessment of bone deformation patterns in bone disease.