Activity-dependent plasticity has significant implications for healthy development, learning, memory, and recovery from brain damage. However, the exact time course and the neural mechanisms behind brain plasticity are still not completely understood. In this study, longitudinal quantitative MRI protocols were used to assess training associated microstructural changes using markers sensitive to myelin and iron. We show that training improvements during a sensorimotor task performed over 4 weeks induces linear and non-linear increases in myelin and iron content in the primary motor cortex and cerebellum. This study provides new tools to assess training effects in healthy controls.