Dr. Hanif warmly Welcomes you! Thanks for consulting at my virtual clinic. I have carefully worked through your case, and I can realize your health worries. Being your physician, I assure you not to worry as I will take care all of your medical concerns.   It seems more like a muscular pain as it is typically related to specific posture and isn t related to physical activity like running and/or walking. I want to assure you that its not a matter of much medical concern, but , to be on the safe side, consult your physician to rule out any kind of possibility of cardiac involvement in this pain. He will do an EKG and will do some exercise tolerance test. You also need a fasting lipid profile and comolete blood count. Being lean and active doesn t merely rule out the cardiac disease. Cardiac diseases have a lot of factors to be kept in mind and they matter a lot varying from patient to patient. Hope it helps. If you need further, detailed and quick assistance related to any health issues in future, feel free to ask me a question directly from my profile. Have a wonderful time ahead.   Best Regards! DR. MUHAMMAD M. HANIF USA