A device, such as an implantable cardiac device, and methods for determining exercise diagnostic parameters of a patient are disclosed. Specifically, a maximum observed heart rate of a patient during exercise can be identified when an activity level and a heart rate measurement of the patient exceed predetermined thresholds. Included are methods for filtering out premature heartbeats or noise from the maximum heart rate determination. Methods of determining other exercise parameters, such as workload are also disclosed. The device includes hardware and/or software for performing the described methods.