Your cells depend upon a steady flow of nutrients and oxygen in order to work effectively. This steady flow is made possible by the precise integration of many bodily processes: lungs that allow for the transfer of atmospheric oxygen to hemoglobin in the blood, the action of both heart ventricles to push the blood through the arteries and for the arterial system to deliver the precise amount of oxygen and nutrients necessary to meet the demands of the cells and for the cells to obtain and use the oxygen and nutrients and to communicate the cellular requirements to the cardiovascular control center. The body's ability to carry out this set of tasks is measured by cardio-respiratory fitness (CRF). "Clearly, CRF is directly related to the integrated function of numerous systems, and it is thus considered a reflection of total body health." (Ross, Blair, Arena, & Church, 2016)
According to the American Heart Association (AHA) there is a growing body of evidence that low levels of CRF "are associated with a high risk of cardiovascular disease (CVD), all cause mortality, and mortality rates attributable to various cancers." The AHA "scientific statement" points to epidemiological evidence that CRF is "a potentially stronger predictor" than currently established risk factors such as smoking, hypertension, high cholesterol and type 2 diabetes mellitus. If one adds CRF to these risk facts, the new list improves the reclassification of risk for adverse outcomes." (Ross et al, 2016, p. e685)
The adverse outcomes, of course, include the leading cause of death in the U.S. which is some form of CVD: heart disease, along with its cousins, coronary heart disease, heart attack, congestive heart failure and congenital heart disease.
Knowing one's CRF matters because while it is not possible to change some risk factors such as those associated with age, gender and family history, it is possible to improve one's CRF by changing one's habits: stopping smoking, losing weight, engaging in more frequent physical activity.
Unfortunately, until recently the only way to obtain a measurement of an individual's cardio-respiratory fitness was in a specially equipped laboratory. The subject was fitted with a facemask that measured the amount of air consumed and the amount and kinds of gases exhaled as the subject exercises on the treadmill, where more and more effort is required. CRF is described as the volume milliliters of O2 that an individual uses per kilogram of body mass per minute at peak activity, or VO2 max. For example, a man 50-59 years old in the top 20% of CRF will have a VO2 max greater than 42, while a woman of the same age will have a VO2 max greater than 37.
Unfortunately, the method to measure CRF which is called the gas-exchange exercise is both expensive and not practical in most health care settings. But in 2016, the American Heart Association recommended that "at a minimum, all adults should have CRF estimates each year using a non-exercise algorithm during their annual healthcare examination."
Assessing cardio-respiratory fitness (CRF), provides "the clinician with the opportunity to counsel patients regarding the importance of performing regular physical activity." (Ross et al., 2016, p. e687)
Note the phrase: "using a non-exercise algorithm," meaning that there is an alternative to the expensive gas-exchange method of obtaining a measurement of CRF. The alternative cited in the AHA recommendation is the one developed by the Cardiac Exercise Research Group (CERG) at Norway's Science and Technology University (NTNU) under the direction of Professor Ulrik Wisløf. (Nes, Vatten, Nauman, Janszky, & Wisløf, 2014)
The challenge faced by CERG was to develop an algorithm that would provide an estimate of an individual's CRF if the individual had used the exercise (gas exchange) method. Further, the CRF should also reliably predict potential adverse outcomes.
The CERG did what scientists do: they built and tested models. They identified and used variables from the research between exercise outcomes and individual variables and connected them mathematically and then tested the results against some standard.
The CERG identified the following variables: educational attainment, ethnicity, gender, age, height, weight, maximum heart rate, frequency, length and intensity of exercise, resting pulse and waistline size.
The CERG fitness algorithm was rigorously tested by measuring its predictive validity by using a data set representing the 75,032 individuals who had participated in the 1983-84 HUNT study and whose health outcomes were followed for 24 years. The individuals in the study were drawn from the "total adult population age 20 and up" from the Nord-Trøndelag County of central Norway. When they enrolled in the study, all participants had been examined by a nurse and measured for height, weight, blood pressure, and resting heart rate, as completing a questionnaire about leisure time, physical activity, smoking habits, alcohol consumption, marital status, family history of disease and educational level.
From the records, the researchers identified 37,112 participants who could be judged to have been healthy at the beginning of the study (18,764 women and 18,348 men) to include in the analysis. For each of these participants, a fitness score based on VO2 max using the CERG algorithm using the variables: age, body mass index or waist measure, physical activity, and resting heart rate.
The researchers used the Norwegian National Cause of Death Register and the 11-digit person identification number to identify mortality among the study participants and whether the cause of death was coronary vascular disease or from all other causes.
The algorithm performed its task. The estimated CRF for the 37,112 participants using the non-exercise CERG algorithm could accurately identify apparently healthy individuals who were at increased risk of prematurely dying of CVD and all-cause mortality. (Nes et al., 2014)
The CERG Fitness Calculator is freely available and has been used by more than 6,000,000 people around the world. The Fitness Calculator provides the user with a fitness age; his/her estimated VO2 normed by age compared to his/her chronological age. It does not diagnose a disease. Instead it provides a benchmark that can be used as an incentive to change because "fitness age can be altered," accordign to Ulrik Wisløf, the Director of CERG, "His advice if your fitness age exceeds your chronological years or is not as low as you would like? 'Just exercise.'" (Reynolds, 2014)
Nes, B. M., Vatten, L. J., Nauman, J., Janszky, I., & Wisløf, U. (2014). A Simple Nonexercise Model of Cardiorespiratory Fitnes Predicts Long-Term Mortality. Medicine & Science in Sports & Exercise, 46(6), 1159-1165.
Reynolds, G. (2014). What’s Your Fitness Age? New York Times.
Ross, R., Blair, S. N., Arena, R., & Church, T. S. (2016). Importance of Assessing Cardiorespiratory Fitness in Clinical Practice: A Case for Fitness and a Clinical Vital Sign: A Scientific Statement from the American Heart Association. Circulation, 2016(134), e653-e699. doi:https://doi.org/10.1161/CIR.0000000000000461
Page 2. Oxygen Consumption Relative to Exercise Intensity. Robert M. Pepper, DO, FAAFP, Associate Professor of Clinical Sciences, West Virginia School of Osteopathic Medicine.
Page 2 VO2 MAX What It Is and how can knowing it make you a better runner.
Dr. John Holton
Dr. John Holton joined the S²TEM Centers SC in July of 2013, as a research associate with an emphasis on the STEM literature including state and local STEM plans from around the nation.