Definitions, Guidelines

How Fit Should You Be ?

Most of us would say being fit is a good thing – but exactly how fit do we need to be ? The answer – like most things in life – tends to be ‘it depends’. If your goal is to improve your athletic performance then definitely more is better (well trained world class athletes tend to have 2-3x higher fitness than the average untrained person).

However if you’re someone like me who does not want to compete in the Olympics (!) but does want to stay healthy, then is there a fitness level you could target? What is a healthy fitness level … lets see if science can give us an answer.

Fitness = Maximum Oxygen Uptake

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As I had defined in an earlier post, fitness or more precisely cardio-respiratory fitness is the ability of the body to supply oxygen to muscles during times of increased physical activity. Fitness is typically expressed as VO2Max, i.e. the maximum oxygen your body can uptake during structured exercise. And usually estimated by measuring oxygen uptake while progressively increasing running or biking speed until the person reaches maximum oxygen uptake (commonly called a “stress test” or maximal test). Athletes typically have higher VO2Max numbers (Norwegian cyclist & junior world champion Oskar Svendson has one of the highest reported fitness numbers / VO2Max of 97.5 ml/kg/min). VO2Max is typically expressed in units of ml/kg/min which basically translates to the maximum ml of oxygen per kg of body weight the body can utilize in a minute. Of course higher VO2Max by itself doesn’t guarantee a better race outcome – motivation, training status, efficiency and a host of other factors matter. But having lower fitness certainly makes it more important to work on the rest.

11 METs = Healthy Fitness Level 

METs-chart-(intensity)_03

From a health perspective, fitness is usually expressed as METs (Metabolic Equivalents) – a more clinically meaningful metric – both to understand how healthy the person is as well as to determine how much exercise intensity the person can cope with.  Essentially 1 MET =~3.5 VO2 units, which basically is the amount of oxygen you need to sit & watch TV! METs also provide an easy way to compare the relative intensity of different activities (the chart on the left is adapted from lists created by the CDC & ACSM).  The intensities are directly comparable – so sex is therefore almost 5 times as intense as watching TV. And your fitness needs to be at least 6 METs for you to be able to have sex, safely!

This gets even more relevant when you look at people with different fitness levels and their health outcomes. One of the seminal studies that looked at the relationship between fitness, cardio-vascular health & all-cause mortality was conducted by a group led by Saturo Kodama. They combined data from 33 different studies that covered 100,000+ subjects and segmented people into different levels of fitness.

METs-chart-(fitness)_03

In categorical analyses, individuals with low CRF (<7.9 METs in MAC) had a substantially higher risk of all-cause mortality and CHD/CVD compared with those with intermediate and high CRF (7.9-10.8 and ≥10.9 METs in MAC, respectively) … These analyses suggest that a minimal CRF of 7.9 METs may be important for significant prevention of all-cause mortality and CHD/CVD

Those with fitness of less than 7.9 METs had a 40% higher risk of mortality than those with intermediate fitness (7.9 – 10.8 METs) and 70% higher risk than those with high fitness (10.9+ METs).  And every 1 MET increase in fitness tends to result in ~15% improvement in cardiovascular health. Based on the Kodama findings & other studies, I would categorize fitness into five zones (chart on the right). So increasing fitness beyond 7.9 METs yields dramatic improvement in health outcomes. And a fitness level of 11 METs or higher would be considered healthy.


Disclaimer: The content on this blog (and linked websites) is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this blog or linked websites. Reliance on any information provided on this blog is solely at your own risk.

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Definitions

What is Fitness ?

I was inspired to create this blog by a recent Show & Tell I did at Quantified Self Boston – sharing data on how I normalized my blood pressure by measuring & improving my fitness. And it seems pretty clear to me that while most people talk about wanting to be fit, very few have actually measured their fitness (or even realize that this is measurable!).

So I decided to pull together some of the resources I was familiar with into one place so that others interested in understanding, measuring, tracking and improving their fitness would find it easier.

We often use fitness in the context of “looking fit” (and I’m guilty of this as much as anyone else). However fitness is not about how much you weight – in fact you can be both fat & fit (though of course if you’ve been sedentary for a while you’re likely to put on weight & lose fitness).

Fitness is also not about how active you are – being active can of course help you stay fit or even improve your fitness but this is by no means a given. The impact on your fitness varies considerably by the type of activity / training you engage in and we will touch upon this in later posts.

Fitness often also tends to imply or suggest muscle strength & endurance. Undoubtedly this important and is often described as “functional fitness”. However for the purposes of this blog and in the interests of creating a common understanding of the term I’m going to separate fitness from muscle strength.

So What is Fitness?

In scientific terms, fitness is shorthand for “cardio-respiratory fitness” – i.e. the ability of the body to supply oxygen to muscles when they become active. (See Wikipedia for a more detailed definition). Another word for this is aerobic capacity. As your fitness improves your arteries & capillaries expand so that your heart can pump more blood (each time it beats) and supply that to the muscles to fuel activity. So in simple terms, the fitter you are – the faster you could run or cycle (though there are other factors that influence your performance including motivation, efficiency etc.).

But the really interesting evidence about fitness relates to its effect on overall health & wellbeing – according to a recent policy statement published by the American Heart Association (Kaminsky et al, The Importance of Cardio-Respiratory Fitness, 2013), fitness:

… appears to be one of the most important correlates of overall health status and a potent predictor of an individual’s future risk of CVD. Besides being perhaps the strongest predictor for CVD and total mortality, CRF (i.e. cardio-respiratory fitness) is also strongly associated with other important health and functional outcomes, including depression and dementia, and their related mortality risks, as well as mortality rates attributable to various cancers, especially of the breast and colon/digestive tract.

In simple terms – you want to stay healthy the one metric you should measure & look to improve would be your fitness.

Over the next few posts I hope to add more information on various ways in which you could measure fitness, various hacks to improve fitness and what science is telling us about the effects of fitness on different health conditions. Alongside I hope to share my own personal data / experience (including from the Show & Tell as well as other information) and I would welcome others who are interested in doing the same.


Disclaimer: The content on this blog (and linked websites) is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this blog or linked websites. Reliance on any information provided on this blog is solely at your own risk.