Physical ExertionShort-Wave TherapyExerciseCross-Over StudiesOccupational DiseasesExercise TestConfidence IntervalsRisk FactorsMyocardial InfarctionPhysical FitnessMotor ActivityPhysical EndurancePhysical Therapy ModalitiesHeart RatePhysical Education and TrainingPerceptionOxygen ConsumptionBicyclingSportsDyspneaErgometry