Exercise testing

Exercise testing is done to assess cardiac dynamics and aerobic capacity. The primary way people are exercise tested in the U.S. is on a treadmill using the Bruce protocol. Generally, cardiac compromised patients do not possess the ability to run for very long or at all for many reasons. Therefore, Dr. Bruce decided to use a walking speed for the protocol.  For this reason, he was forced to use an excessive hill to create the workload. The initial grade is ten percent and goes to sixteen. When engineering roads I have been told on several occasions the maximum grade is seven percent. I am not sure if that is true, but this grade, lack of musculature, and dorsi flexion of the foot contribute to excessive lactic acid accumulation making the protocol very difficult. Heart rate and blood pressure are elevated many times by orthopedic pain or stress as well as fear of falling rather than cardiac demand. We could most likely scare someone badly enough for them to reach maximum levels of heart rate, but do not think this would be a way to measure cardiac demand. Did anyone try to get a blood pressure on a patient on a motor-driven treadmill?  It is sometimes difficult. The MET jumps are quite large using the Bruce protocol at about three per stage. The speed chosen for the fourth stage of the Bruce protocol is 4.2 m.p.h. which is awkward because for the average person it is between a walk and a run while at a sixteen percent grade. Many patients cannot be tested on the treadmill for a variety of conditions such as orthopedic injuries, neuropathy, arthritis, tendonitis, bursitis, peripheral vascular disease, and COPD. It might sound that I am bashing Dr. Bruce, but I never mean to because he started exercise testing. He realized that by exercise testing, we could precipitate cardiac abnormalities one cannot see at rest. This may seem simple now, but at the time with the EKG just being invented this was great accomplishments. The Bruce protocol is difficult, but the alternative is worse. The alternative is the chemical agents  persantine, dobutamine, or adenosine. Most physicians will agree that this is not the most desirable way to stress test someone. 

 
 

Exercise testing on cycles or leg ergometers are generally not used in the U.S. because problems reaching maximum heart rates and lower VO2 values on the standard cycle than using the treadmill. The problems associated with cycle ergometry are protocols that hold RPMs constant while changing resistances and lack of musculature. The lack of musculature stems from only using the lower body muscles primarily the quadricep. Workload on a cycle is determined by the product of, Revolutions per minute, flywheel travel, and kilograms of resistance. This gives you kilogram meters which is a unit of force. Here is where things get interesting. Kilogram meters are speed dependent. Six-kilogram meters equals one watt. Watts are a unit of resistance that is not speed dependent. Using watts only and providing the ability to pedal at any speed comfortable or varying speed makes exercise testing on a cycle much better. The next step was to add arm handles so the patient or client can use any combination of arms or legs at any speed making this the best cardiovascular machine for evaluation or conditioning. Blood pressure measurements are much easier on the cycle. The cycle is safer, more comfortable, and effective. 

 
 

 
 

Exercise testing is valuable to a patient or client to determine aerobic capacity in relation to heart rate. An exercise physiologist can use this to determine the vo2 and target heart rate zone. From this information, appropriate speed and grade on a treadmill or resistance of a cycle can be accurately established to reach a heart rate that will burn fat for the client. Anyone with documented heart disease should have an exercise test once per year Submaximal or maximal exercise tests may use a variety of equipment, but the treadmill is generally used in the United States. A test is considered maximal if the individual reaches ninety percent of age predicted maximum heart rate or greater and a Respiratory Expiratory Ratio or Respiratory exchange Ratio (RER)of 1.1 or greater. RER is the expiratory ratio of carbon dioxide to oxygen which definitively expresses exercise intensity and metabolism. Maximal exercise testing is often referred as the cardiac stress test and should not be completed by anyone over the age of thirty=five without a physician present. The purpose being to analyze cardiac dynamics and establish max aerobic capacity. 

 

In some research settings, exercise tests may use a metabolic cart to collect and analyze the expired gases to assess oxygen consumption and metabolism. Submaximal exercise tests take the person up to eighty-five percent of age predicted max while monitoring exercise intensity or oxygen consumption for the exercise bout. The results accumulated may be used to plot heart rate on the y axis and VO2 or resistance on the x axis. The line of best fit can pe interpolated to present a quite accurate VO2 analysis. 

 

To reach a Maximal exercise test, the person must reach ninety percent or greater of age predicted maximum heart rate and RER of `1.1 or greater. RER represents the carbon dioxide to oxygen ratio for expired gases. At a ratio of .7, the subject is burning fatty acids and carbohydrates. Protein and carbohydrates are being used for energy at a RER of .8. Carbohydrates sre being used exclusively at a .9 RER or greater. A RER of 1.1 or greater qualifies as a maximal value.