Gelatinous transformation (GT) of the bone marrow is rare and associated with a variety of clinical diseases from malignancy to chronic infection in combination with malnutrition or wasting. A new clinical picture of GT has emerged with excessive physical activity in combination with a voluntary insufficient calorie intake in the young adult male. Overtraining syndrome and systemic inflammation may play a role in the pathogenesis of GT in these patients, but further studies on GT and the effect of training and overtraining on the bone marrow are needed.