Fitness, VO2 max, Peak METs and Longevity

We intuitively know that “fitness” is good for us, but “fitness” is a vague definition. In this post I will discuss how we can measure fitness quantitatively and what fitness levels confer healthspan and mortality benefits. 

In an article published in JAMA, (Journal of the American Medical Association) the Cleveland Clinic analyzed 23 years of patient data from 1991-2014 (122,007 patients) and evaluated the association of all-cause mortality (death for any reason) and cardiorespiratory fitness. They also evaluated age, gender, race/ ethnicity, and co-morbidities such as diabetes, hypertension, smoking and coronary artery disease (CAD).

The findings were remarkable. Their findings on typical risk factors were consistent with what we often see. Having diabetes, coronary artery disease (CAD), smoking, or hypertension conferred approximately a 1.2-1.4X mortality risk or an approximately 20-40% increase risk of death from any cause, but here is the remarkable aspect, being out of shape or having low fitness conferred a 5x mortality risk, in other words a 400% increase risk of death from any cause over any time period. In other words being out of shape was 3 to 4 times worse than smoking, having diabetes or having CAD.  ​

Photo cred:​https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2707428

Other groups have published similar findings.  In a circulation article published in 2014, Blair et al found that for every 1-MET (Metabolic equivalent) increase in exercise capacity, mortality risk was 12% lower. A study performed by the National Cancer institute evaluated 654,827 individuals and found up to a 4.5 year gain of lifespan with increasing activity. 

There are a few ways to quantitatively measure fitness.  In the Cleveland Clinic study mentioned above they used METs as they had Exercise Treadmill Tests that evaluated peak METs. For those who have never heard of METs or peak METs. A MET is the amount of energy used during any activity. One MET is defined as the amount of oxygen consumed while sitting at rest and is equal to 3.5 ml oxygen per kg body weight x minutes of activity. For reference,  walking (3.5–4 mph) is generally around 5 METs. Singles tennis is approximately 8 METs and running a 10 minute mile is approximately 10 METs. As the intensity increases the number of METs increases. Testing a person’s peak METs is one way to establish fitness. Below is a chart of activity and expect METs.

Photo cred: ​https://oss.adm.ntu.edu.sg/xloh002/activity-range/

Another way to evaluate fitness is the measure the volume of oxygen the body can use, measured in milliliters per kilogram per minute. This measurement is called VO2 max and it is the gold standard for measuring aerobic fitness. Vo2max depends on cardiac output (the pumping ability of the heart stroke volume x heart rate), air exchange in the lungs, blood flow to the muscles and atmospheric oxygen available (due to elevation). Vo2 max is measured by an exercise physiologist as the patient or athlete runs or bikes at progressively harder levels while wearing a mask connected to a machine that evaluates exhaled oxygen and carbon dioxide. Using VO2max we can evaluate relative endurance. 

To me the data on fitness argues that fitness testing, ideally a VO2max test should be a part of every person's preventative health plan. We need to understand where we are in order to implement a targeted plan to achieve our health goals.

References:
​
Ruegsegger GN, Booth FW. Health Benefits of Exercise. Cold Spring Harb Perspect Med. 2018 Jul 2;8(7):a029694. doi: 10.1101/cshperspect.a029694. PMID: 28507196; PMCID: PMC6027933.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6027933/ 

​Mandsager K, Harb S, Cremer P, Phelan D, Nissen SE, Jaber W. Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Netw Open. 2018;1(6):e183605. doi:10.1001/jamanetworkopen.2018.3605
https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2707428

​Blair SN, Kohl HW, Paffenbarger RS, Clark DG, Cooper KH, Gibbons LW. Physical Fitness and All-Cause Mortality: A Prospective Study of Healthy Men and Women. JAMA. 1989;262(17):2395–2401. doi:10.1001/jama.1989.03430170057028
https://jamanetwork.com/journals/jama/article-abstract/379243

​Meyers J, Prakash M, Froelicher V et al. Exercise Capacity and Mortality among Men Referred for Exercise Testing. N Engl J Med 2002; 346:793-801. DOI: 10.1056/NEJMoa011858 https://www.nejm.org/doi/full/10.1056/NEJMoa011858

Blair S et al. Age-Specific Exercise Capacity Threshold for Mortality Risk Assessment in Male Veterans. Circulation 2014;130:653–658. 
https://www.ahajournals.org/doi/full/10.1161/circulationaha.114.009666

https://med.virginia.edu/exercise-physiology-core-laboratory/fitness-assessment-for-community-members/vo2-max-testing/
​
Moore S et al. Leisure Time Physical Activity of Moderate to Vigorous Intensity and Mortality: A Large Pooled Cohort Analysis. PLOS Medicine. November 6, 2012 https://doi.org/10.1371/journal.pmed.1001335
https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1001335