We investigated brain plasticity in a long jumper top athlete with an artificial lower limb prosthesis (R.M.) in order to examine the mechanisms of dexterous control the artificial leg. In the study, three participant groups were recruited and compared: 1) RM, 2) healthy long jumper athletes and 3) non-athletes with artificial lower limb prosthesis. We recorded the brain activity of participants using fMRI during rhythmic muscle contraction involved in lower limb joints (ankle, knee and hip) in both right and left sides. In RM’s brain activity during contraction of intact knee muscles with artificial leg side, we observed prominent large and bilateral activations in motor-related areas compared to other participants. The observed bilateral activations in the cortical motor area during knee muscle contraction of the affected side likely resulted from long-term training of the long jump, and are probably related to the improved ability to fine tune the artificial limb.