Cardiorespiratory Fitness Assessment

Cardiorespiratory fitness assessments are also referred to as exercise tolerance testing. Understanding your tolerance for cardio exercise will help you gauge both the high end and the low end of the range in which you can exercise for results.

An exercise tolerance test is a worthwhile way to assess your current level of cardiorespiratory fitness prior to progressing your current exercise program; it will help you determine the levels of intensity at which you can and should be working. An exercise tolerance test allows you to determine your VO2 max, which represents the maximal rate of aerobic metabolism you experience during exercise. Maximal heart rate is considered the greatest heart rate measured when you are exercising to volitional fatigue (i.e., stopping because you cannot exercise any longer) during a graded exercise test. VO2 max is usually measured in liters of oxygen per minute, or millimeters of oxygen per kilogram of body weight per minute. Maximal tests are by far the best way to determine the maximal ability of the cardiovascular and respiratory systems under stress. 

Unfortunately, this type of testing requires expensive facilities and specialized equipment, in addition to a maximal aerobic effort on the part of the examine. This method is often limited to hospitals and research facilities and is usually performed in the presence of a medical professional trained in advanced cardiac life support. Because maximal fitness testing can be more difficult to gain access to and then perform, submaximal testing is often used. Several equations have been developed to estimate maximal heart rate using submaximal measures.

 Thus, submaximal tests provide a reasonably accurate prediction of maximal work capacity to determine the appropriate intensity at which you should be working based on your current level of fitness. Submaximal tests are based on the linear relationship between an age-predicted heart rate and the cardiorespiratory work being performed. Submaximal heart rate testing is based on the assumption that as the heart rate increases, so does oxygen consumption. Therefore, a maximal heart rate is estimated from this linear relationship.

The prediction of maximal heart rate from the submaximal testing is determined via the following formula:

220 – ____ (Your age) = _____ (Your estimated maximal heart rate)

This formula has a margin of error as high as 15 beats for several reasons. One is the fact that the person’s resting heart rate is not considered. This is important because resting heart rate takes into account the current level of fitness regardless of age. For example, let’s compare a 40-year-old elite marathon runner with a 40-year-old who is severely deconditioned. Both have the same estimated maximal heart rate, which is absurd because they clearly do not have similar fitness levels.Therefore, if maximal heart rate is over- or under predicted (which frequently occurs when adopting a maximal heart rate number based strictly on age), so are maximal work capacity and maximal oxygen consumption. However, although there may be some error in age-predicted heart rates, submaximal testing has been proven to be accurate and reproducible. 

Keep in mind, however, that the validity of the results of submaximal fitness tests rests on several assumptions:

• A steady-state heart rate is obtained for each exercise workload.

• A linear relationship exists among heart rate, oxygen uptake, and workload.

• The maximal heart rate for a given age is predictable.

• The biomechanical efficiency of the physical activity performed (i.e., oxygen up take at a given workload) is the same for everyone.

Unfortunately, it is often quite difficult to conduct a fitness test that meets all the requirements for the four listed assumptions. For example, exercising at a given workload for only a few minutes can be insufficient for many people to achieve a true steady state. To ensure that a steady state has been achieved, the heart rate should be measured after two minutes of exercise at a given workload and again after the third minute of exercise at that workload. These two heart rates should then be compared.

 If a difference of more than five beats per minute (bpm)between the two is found, the person should continue to exercise at one-minute intervals at the same workload until two successive heart rates differ by less than five beats per minute. It is also important that the submaximal heart rates obtained be between 115 and 150 bpm, because research shows that within this heart rate range, a linear relationship tends to exist between heart rate and oxygen uptake for most healthy adults.Let’s take a look at one excellent submaximal test, the Bruce Protocol Treadmill Test. This should help you find the most appropriate heart rate training zone for your goals.