44 yrs old fit and well. Known asthma, been cycling for the last 12 months. Just recently been experiencing sharp inspiratory left sided chest pain below sternoclavicular joint. Only occurs when high intensity exercise and disappears within a couple of seconds, but reproducible. Chest tender sometimes and if I do a deep breath in can sometimes reproduce the discomfort at rest. No family history of heart disease, non smoker, height 173cm, weight 68kg, PEFR 620... Wondering is this costochondritis???