Are you an athlete? Do you do those long marathons? Are you a triathlete? Are you an ironman or an ironwoman?
In these modern times there is no reason why an athlete should not be able to monitor his vital signals. A pulse oximeter is an excellent choice to monitor your pulse and oxygen levels.
Being an athlete not withstanding, simply if you pulmonary handicapped a pulse oximeter can keep you informed as to the state of your oxygenation. Computerization and miniaturization has made great products possible.