I have tenderness only when i touch my sternum. no chest pain or cough or any other problem only when i touch it is this dangerous ?

Probably not: It is not feasible to provide a meaningful opinion without taking additional history, physical examination and may be some tests. It would be prudent to see your doctor at your convenience. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex, if you have sex. Get HPV vaccine

Costochondritis: If your heart and lungs have been'ruled out' as sources of your chest pain( and this is of paramount importance) than inflammation of the ribs as they attach on the sternum or the rib 'lining' itself can become 'inflamed' occasionally w/ exercise. This is generally treated w/ NSAIDs ( ibuprofen, etc.)A diagnosis can sometimes be made by an examination prior to and after ecersise or bone scan . GL!