Have you ever felt that something was not right with your body during your training or racing? It could be chest pain, breathlessness, an unexpected drop in your heart rate for a given workload, dizziness or something else. It is concerning enough that you go see your doctor, but she examines you and maybe does an ECG or a chest x-ray and tells you that she can’t find anything that is wrong. While that is certainly good news to hear, there is still a concern in the back of your brain that something is going on – you just don’t feel that an assessment at rest accurately reflects what is occurring in your body near maximum exertion. You want an assessment while exercising, and you can have it.
What is Cardiopulmonary Exercise Testing (CPET)?
Cardiopulmonary exercise testing (CPET) allows for evaluation of your cardiac and pulmonary systems under stress. It consists of exercise supervised by medical experts that obtain valuable data about your heart and lungs and how they work synergistically during exercise. If someone is having problems during exercise, it is imperative to evaluate what actually happens during those moments.
What does CPET measure?
The cardiovascular portion of CPET evaluates heart rate and rhythm with progressive exercise. It is valuable in picking up any arrhythmias or abnormal increases of heart rate with progressive workload. Blood pressure measurements with exercise can be of added value, but can sometimes be challenging to obtain when running at high speeds. The pulmonary measurements involve using a metabolic cart to analyze gas exchange. Respiration at the cellular level is coupled with external ventilation, so by measuring gas exchange we are looking through a window to the cellular level. The metabolic cart measures 4 pieces of information: how much air is exchanged with each breath, how many breaths per minute, the amount of oxygen being consumed and the amount of carbon dioxide that is expired.
Without getting too bogged down with exercise physiology, as we increase our workload, we begin to shift the source of energy generation to more anaerobic systems (non-oxygen dependent systems), and consequently we generate more carbon dioxide (in reality we generate energy from many different energy pathways, it is the percentage of energy derived from each pathway that shifts with the amount of energy required for the given task). Measurement of oxygen saturation can help determine if the blood continues transporting sufficient oxygen throughout exercise.
How hard should clients exercise in the lab?
A CPET is different from a typical “cardiac stress test” performed in many cardiologist’s offices, which primarily evaluates heart function. A cardiac stress test usually involves walking and then perhaps jogging/running, following the Bruce protocol, which starts at a very low workload and progresses in intervals to some pre-defined workload or heart rate. Too often the patient is stopped before maximum workload without fully stressing the heart and lungs. Sometimes patients are stopped when they reach a predetermined workload or heart rate of 85% of age predicted maximum heart rate.
The formula for age predicted maximum heart rate (220 minus age) is not an ideal indicator of exercise effort, as there is a large population standard deviation (±12 bpm) which introduces a significant error in over and under-training intensities. Consequently, if you stop at what that formula tells you is maximum for that age, it might not be the maximum for the individual patient. Triathletes are different from most people, and they usually require a significantly higher workload to max them out than your average person. Ideally, the operator of the test will know triathletes and understand how to coach the client to their max.
How do you know you have truly performed a maximum test?
We use several parameters to ensure our patients perform a true maximum test. We use their heart rate, but we also evaluate the respiratory ratio (RER). RER is the ratio of carbon dioxide expired per unit of oxygen consumed. If it exceeds 1.0, we know our subjects are nearing maximum workload. Probably the most important data point we use is the rating of perceived exertion or RPE. We use a scale created by Swedish exercise physiologist professor Borg in the 1970s. The scale is numbered 6-20, and if they exceed 17 it is further evidence they have performed a maximum test.
How long should clients exercise in an CPET?
The treadmill always wins. We can always find a speed and incline grade where the client will fatigue, and we want that to occur at around 8-12 minutes. That time frame allows appropriate warm up and progression with time to equilibrate at each progressive workload. It is also brief enough to allow subjects to reach a maximum workload before becoming too fatigued.
Is walking/running the only mode of exercise used for CPET?
Clients can bike or even erg, as long as they are able to perform maximum workload on the chosen modality. Most Americans are more comfortable on the treadmill. However, Europeans tend to use the bike for CPET. The ECG is cleaner on the bike and the wattage correlates more closely to a given energy expenditure than the treadmill. Logically, the bike tends to yield lower oxygen consumption values due to less muscle mass recruitment. However, deciding which modality is right for the patient comes down to safety, comfort and symptom provocation. The tester needs to determine which modality is right from information obtained during the history portion of the exam.
Is it safe to perform a CPET?
It is extremely safe. When considering all subjects, including individuals 6 weeks post myocardial infarction, the risk of death is 1 in 10,000 tests and any concerning event 1 in 2500 tests. I have personally performed over 1000 tests, mostly in a wellness center, but also clinically in my sports medicine practice, and no adverse events have occurred.
What is VO2max?
One of the pieces of data obtained during testing that can be valuable to triathletes is VO2 max. It is the best measure of one’s fitness and is the maximum amount of oxygen utilized per kilogram per minute. It is somewhat modifiable with training, but more modifiable with weight reduction for individuals who are overweight. If you are biking in a group over a progressively steep hill, chances are those with a higher VO2max will be the ones pulling off the top.
What is Onset of Blood Lactate Accumulation?
Onset of blood lactate accumulation is somewhat interchangeable with lactate threshold – it describes when the body begins to accumulate more carbon dioxide than it can successfully buffer. It clinically manifests as beginning to breath very fast. The run speed, workload or wattage at lactate accumulation correlates more closely with race time than VO2max. This value, unlike VO2max, is modifiable with training.
With progressive training, the body increases the number of capillaries in the muscle where gas exchange occurs, as well as increases the quantity of enzymes that help with energy utilization (and of course many other adaptations to exercise). In other words, it is not the person who climbs the best, but the one who can maintain a sub-maximum level for longer. This metabolic level is the point where you can sustain the workload for an hour.
Two questions we ask of everybody upon completion of the test.
The first question we ask our clients is why they stopped the test. I always want to hear that it is because their legs burned. We interpret leg pain as consistent with an appropriately working heart and lungs. The limit was not chest pain or breathing difficulty, but a physiologic limit to deliver oxygen to the working muscle and consequent leg burn. The second question we ask is if we reproduced the symptoms. We want to see what happens when the client is symptomatic, so if we can’t make that happen, the test is less valuable.
What are some other clinical and non-clinical utilities for CPET?
There are many reasons to have a cardiorespiratory test: some clinical and some to obtain data for training and racing. As a sports medicine physician who specialized in shortness of breath in the athlete, the range of clinical problems we use CPET and exercise for in our office includes chest pain, palpitations, breathlessness, asthma testing, vascular problems, upper airway assessment called continuous laryngoscopy with exercise (www.cayugamed.org/sob). We see many patients who have been incorrectly diagnosed with asthma but in reality, have an upper airway problem called exercise-induced laryngeal obstruction (read more here).
Other problems that benefit from CPET include evaluation for poor performance, basic metabolic rate for those not responding to nutrition manipulation for weight loss, fuel substrate utilization, training zone determination, running mechanics assessment, and bike fit by measuring workload at certain wattage in different bike positions.
In conclusion, we strongly advise triathletes to ensure that their exercise related problems involve observed exercise with data acquisition as part of their work up. The workload must be a sufficient load for the individual instead of a one size fits all.
Andrew Getzin, MD is the head team physician for USA triathlon. He is a previous USAT level 1 coach, many year USAT age-group All-American and has qualified and competed in Kona. He is a fellow of the American College of Sports Medicine. Dr. Getzin is the medical director of Cayuga Medical Center Sports Medicine and Athletic Performance in Ithaca, NY, www.cayugamed.org/sportsmedicine and the director of their shortness of breath in the athlete clinic, www.cayugamed.org/sob.
Matthew Kampert, MS DO is a Sport and Exercise Medicine Fellow at the Cleveland Clinic. He is actively conducting Obesity research at the Cleveland Clinic through Intensive Behavioral Therapy for Obesity, focusing on both Nutritional and Exercise prescription based off of CPET. Recently accepted as Doctoral Candidate and planning to pursue his Ph.D. while working as a Sports Medicine Physician following completion of his current Sport and Exercise Medicine Fellowship.
Anthony Spinelli, ATC, CCEP is an Athletic Trainer and Clinical Exercise Physiologist at Cayuga Medical Center Sports Medicine and Athletic Performance in Ithaca, NY. He run CMC Endurance Performance Center with services that include, cardiopulmonary exercise testing, buffalo treadmill protocol concussion testing, Bike Fit, run/gait analysis, continuous and therapeutic laryngoscopy with exercise, exercise-induced asthma provocation testing, ankle/brachial index testing pre and post exercise, run/cycle speed at-lactate threshold, heart rate zone interpretation, skinfold and In-Body bioelectrical impedance body composition measurements.