Physical ExertionShort-Wave TherapyExerciseCross-Over StudiesOccupational DiseasesExercise TestConfidence IntervalsRisk FactorsMyocardial InfarctionPhysical FitnessMotor ActivityPhysical EndurancePhysical Therapy ModalitiesPhysical Education and TrainingHeart RatePerceptionOxygen ConsumptionBicyclingSportsDyspneaErgometry