Heterotrophic ossification (HO) is a well-described phenomenon in patients with spinal cord injury, head injury, burns, hip replacement, and general trauma. However, it has also been described through a relative paucity of case reports that repeated microtrauma from the use of weight-bearing leg prostheses is an additional possible cause of HO. In our case, we examine a patient who developed an extreme case of HO after he began an exercise regimen with assistance from a running limb. This abnormal formation was actually advantageous because it created a more snug fit of the prosthetic device and improved the patient's ability to run.