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Why does cardiorespiratory fitness matter?

Updated: Feb 21


We tend to use traditional markers like weight, blood pressure, cholesterol, and BMI to quantify our health. While these do offer useful insights, most people are not even aware that there's a far better metric for assessing your risk of early death: cardiorespiratory fitness.



The latest research shows that cardiorespiratory fitness (CRF) is a stronger predictor of mortality than previously established risk factors like smoking, high blood pressure, high cholesterol, and type 2 diabetes.


Low levels of cardiorespiratory fitness are associated with a high risk of cardiovascular disease, all-cause mortality, and mortality rates attributable to various cancers.



In fact, those with low CRF have a 56% higher risk for cardiovascular mortality and a 70% higher risk for all-cause mortality.


Scary? Yes.


But the opposite, optimistically, is true too: the higher your cardiovascular fitness, the lower your incidence of mortality.


Wait, what actually *is* CRF, you ask?


CRF is directly related to the combined function of numerous systems in our body. It reflects the integrated ability to transport oxygen from the atmosphere to our cells to perform physical work, and we can use it as a measure to quantify the functional capacity of an individual. CRF is an indicator of total body health. Think of it as assessing weight, blood pressure, cell’s ability, heart function, transportation in blood, meeting oxygen requirements and metabolic demands, the function and communication of the control centres all-in-one. No wonder it’s such a powerful predictor of health!


Genetics accounts for only about 45-50% of CRF and the rest is determined by your lifestyle. The good news is that this means that what you do can significantly reduce your odds of dying young.


The most stunning conclusion from the data is that the largest and most maximal benefits occur when an individual progresses from the least fit to the next least fit level; more than 1/2 the reduction in all-cause mortality. Exceptionally high CRF levels are not necessary to provide significant health benefits. In fact, you get the most bang for your buck in terms of health benefits when you improve from the low end of the CRF continuum.


So if you’re a sedentary or low-fit person, you have the most to gain by engaging in even modest activity levels! An increase of even 1 MET (the unit of energy cost for humans) is associated with a 10-20% decrease in mortality rates.


Comparatively, if you’re moderately fit, you have a 50% lower mortality than those with a low CRF. And if you’re already fit you’re reaping the benefits and have 4 times a decreased risk of all-cause mortality compared to least fit individuals.


Want more reasons to start moving and know your CRF? The data is insane!


CRF is not only the strongest predictor of cardiovascular and all-cause mortality, but it’s linked with cardiovascular and non-cardiovascular surgical complications, postoperative complications, and short and long-term surgical outcomes. Even when adjusting for potential confounding variables; including cigarette smoking, alcohol consumption, overweight/obesity, hypertension (high blood pressure), type 2 diabetes, and a family history of CVD, the inverse association between CRF and stroke mortality remained.


CRF strongly predicts outcomes across a wide spectrum of CVD outcomes, including those related to stroke, heart failure, and surgery. Optimizing CRF prior to surgical interventions (termed “prehabilitation”) improves outcomes including surgical risk, mortality, and function in post-surgical period.


Higher levels of CRF is linked to reduced risk of developing both dementia and Alzheimer disease, lower measures of anxiety and symptoms of depression, and risk of developing prediabetes, metabolic syndrome, and type 2 diabetes, and a lower risk of developing certain cancers (20% lower risk of all-cause cancer mortality in moderately fit people and 45% lower risk of all-cause cancer mortality in highly fit people) compared to those in the low CRF group -- irrespective of adiposity (fat mass).



Sooooo, how do you actually improve your CRF? Good question.


The answer to increasing your CRF is increasing your cardiac output; cardiac output = heart rate x stroke volume (the volume of blood pumped per heart beat). Since heart rate is something that changes based on exertion and is beyond your control, increasing your maximal stroke volume and your arteriovenous O2 difference is the way to improve.


There are 3 key adaptations to increase your stroke volume; increase in total blood volume, improvement in left ventricular distensibility, and improvement in diastolic function. The way to increase O2 extraction (aka arteriovenous O2 difference) is to make changes in skeletal muscle by increasing muscle capillary density (most important) and increase the size and number of skeletal muscle mitochondria and oxidative enzymes after training.


These are all training responses that are influenced by the duration and intensity of training.


Specifically, what is the most effective way to increase your CRF?


The greater the activity amount of intensity, the greater the increase in CRF. CRF is impacted by an increase in intensity (aka the effort with which you are active) more than an increase in session duration (how long you’re active) or frequency (how often you are active).  Both high-intensity training (think intervals or sprints) and moderate-intensity continuous training (think slow and steady on a cardio machine or running at the same pace for 30 minutes) can be effective for increasing CRF, but if the same total amount of energy expended is the same then high-intensity training results in greater increases in CRF over moderate-intensity continuous training.


The most powerful predictor of your mortality is within your control and now you can not only know it, but change it.

CRF can be measured directly, and is expressed, as maximal oxygen consumption -- what you might know as VO2 max.


VO2 max is the “gold standard” for assessing exercise capacity. VO2 max values vary widely; from <10 mL O2/kg/min in patients with advanced chronic disease such as end-stage heart failure to >80 mL O2/kg/min in young elite endurance athletes, and it's influenced by age, sex, genetics, lifestyle/exercise training habits, and varied disease states.



CRF is now recognized as an important marker of health and mortality, but it’s the only major risk factor not routinely assessed in clinical practice. The regular assessment of CRF will improve clinical care and reduce healthcare expenditures, but there are typically many barriers to knowing your VO2 max; such as costs associated with equipment, professionals with advanced training, and the administering and interpretation of that data.


We want to change that.


The VO2 max test is one of the advanced health and fitness assessments that Body Insight offers.


Because CRF has been established as the most powerful predictor of mortality, this assessment can not only give you control over the risk of early death, but can change your health and life.



Have you ever measured your CRF with a VO2 max test?

What else would you like to know about CRF and your VO2 max?


Comment below with your thoughts and if you want to find out your CRF, book your VO2 max test today!


And if you found this as fascinating and powerful as us, please forward to a friend or share on social media!


P.S. Not only can you know your CRF from our VO2 max test, but you can also measure what 1 MET is for you with our metabolism test!


References:


Ross, R., (2016). Importance of Assessing Cardiorespiratory Fitness in Clinical Practice: A Case for Fitness as a Clinical Vital Sign: A Scientific Statement From the American Heart Association. Circulation, 134(24): e653-e699. doi:10.1161/CIR.0000000000000461.