What We Learnt from 750 Fitness Tests!


Weight is a very poor proxy for fitness (even though culturally we think fitness = “being in shape”). Increasing activity improves fitness but does not lead to lower weight. Fitness declines with age, but this is not a given. Improving recovery is an ‘easy’ win for everyone.


Revvo is the first exercise bike to measure an individual’s fitness profile : Aerobic Fitness/VO2Max, Recovery and Endurance/Threshold. And right from the earliest test, we’ve captured information on the individual’s demographics and current weight, activity levels (mainly because it was required pre-screening information).

1. Test Fitness

While we’re definitely not the first to aim to understand how these different variables correlate, the fact that we are measuring a wider range of variables on the same individuals with a pretty high degree of accuracy and consistency should hopefully provide some additional insight. Details on the test methodology can be found here: Revvo: Science.

1. We tested people across a wide range of fitness levels

While our sample is not a fully representative one (we do not have many at the lowest and highest ends of the fitness spectrum), it does represent a broad spectrum of fitness levels – both in terms of VO2Max and Recovery.


Interestingly, Recovery is skewed lower than the VO2Max results and this is something that we’ve anecdotally observed in quite a few “fit” individuals. Recovery is partly an indicator of lifestyle – stress, lack of sleep will show up here. So if you’re looking to enhance performance or general wellness, check your heart rate recovery status — sleeping better and reducing stress might give you immediate results.

2. If you’re already fit, focus on recovery

In fact this opportunity to improve Recovery becomes more obvious when you cross-analyze VO2Max and Recovery data. In general, there is a positive correlation between the two i.e. higher the VO2Max, higher the expected Recovery. However this is a weak correlation as you’ll see from the plot.

Vo2Max Vs. Recovery.png

I’ve often seen people with relatively poor VO2Max scores who’re doing fine from a health perspective since their heart rate recovery is good and also fit people with poor recovery that indicates underlying health issues (perhaps genetics the culprit here rather than lifestyle). Fit people also often have poor recovery due to excessive training loads i.e. if you ran an ultra-marathon over the weekend, it will take a few days for recovery to return to normal levels.

3. You could be fat & fit or thin & unfit

We often conflate weight and fitness – but these are two semi-independent variables. We’re seeing lots of people who are relatively heavy but score pretty well on VO2Max (despite the fact that weight is the denominator in VO2Max calculations). And on the other hand many who have perfect BMI but with suffer from aerobic fitness.

VO2Max Vs. Weight.png

Above 250lbs however, its rare to find someone who’s really fit. But below 200lbs there’s a huge variation in fitness levels – if we only analyzed that population there would be very little correlation between fitness and body weight. So just because some looks thin doesn’t mean they are fit and vice versa.

Recovery versus body weight shows the exact same pattern.

Recovery Vs. Weight

4. Being active improves fitness, but doesn’t impact body weight

We’ve now seen a ton of data confirming that activity, on its own, doesn’t seem to make much difference to body weight. And our analysis supports that conclusion.

There’s practically zero correlation between how active people say they are and how much they weigh and a slight negative correlation when you contrast BMI vs. Activity. Yet we keep telling people that they should exercise more to lose weight, setting them up for failure!

Body Weight Vs. Activity

BMI Vs. Activity Level

Why does increasing activity levels not help with weight loss? Vox did a fantastic summary of the available evidence in this video and article.

The real benefit of activity is an improvement in fitness – and this is what our analysis reveals as well. Higher activity levels correlate pretty well with higher levels of fitness.

And aerobic fitness (VO2Max), as I’ve explained before, is not just an indicator of athletic potential but also the single best overall indicator of health. The primary purpose of exercise is to improve the functioning of your heart and muscle. Weight loss, if it happens, is a spin-off benefit.

Therefore if you want to assess if exercise is yielding results, track your fitness level, not your body weight.

VO2Max Vs. Activity

This is not of course not a perfect correlation as different types of activities have different effects: walking for an hour will not improve VO2Max as much as 10 minutes of high intensity interval training. And genetics also effects how well activity translates into an improvement. Which is why, even for people at the same level of activity, there is such a wide variation in fitness levels.

The correlation between Recovery and Activity is not as strong – and this makes sense. Lifestyle factors (sleep, stress etc.) often have a bigger effect on improving Recovery than increasing activity per se. And of course being too active can negatively impact Recovery. Recovery is intrinsically a more complex variable.

Recovery Vs. Activity

5. Fitness can – but need not – decline with age

At a general population level, VO2Max is reckoned to decline ~1% per year as we age and our analyses confirms the broad trend. However within that trend, there is huge variation: we’ve seen so many young people who are less fit than their grandparents and so many older individuals who’s fitness level has been an inspiration to me personally.

So your fitness is in your hands (or legs!).

VO2Max Vs. Age

Recovery seems to be even less correlated with declining age.

Recovery Vs. Age


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


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 


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.


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.


How to Measure Your Age!

How long you’ve lived is clearly one way to measure age — but if aging is about the gradual decline of body function and eventual mortality then perhaps there is another contender for the best way to measure age – your  fitness. And unlike your calendar age, you can actually change your fitness. In my last two posts I talked about my personal experience reducing blood pressure by improving fitness and the massive published data validating the link between fitness and aging induced blood pressure.

Now a group of Norwegian researchers from HUNT University have published a study looking at ~38K men & women who they followed-up for a mean duration of 24 years to demonstrate that fitness was a very good predictor of mortality at all age levels and perhaps the best predictor for those less than 60 years of age. Every 1 MET increase in fitness resulted in 15% lower risk of all-cause mortality amongst men and 8% lower risk amongst women.  In this particular example fitness was estimated using demographic + activity data (which gives a rough indicator but is not that accurate).  The accompanying NYT article has more detail on the study and related research.

The group also created a really cool online calculator — you can plug in your data and get an estimate of your fitness, compare it to age cohorts. Worth trying out!

From the study, here’s what your fitness should look like on average, if you’re aging well:


Fitness & Blood Pressure

How I Normalized my Blood Pressure via Anaerobic Interval Training

Reproducing the talk that I gave at the Quantified Show & Tell in Boston on how I was able to eventually improve my fitness and blood pressure when I shifted to anaerobic interval training.


Siva Raj was interested in lowering his blood pressure. With a family history of cardiovascular disease and heart attacks he was worried about slightly elevated blood pressure (pre-hypertension). As someone engaged with understanding and building fitness applications he thought he would be able to lower his blood pressure by staying on track with a regular exercise program that focused on cycling. Interestingly his blood pressure measurement didn’t respond to his constant exercise or weight loss. After reading more research literature about the link between fitness and cardiovascular health Siva decided to change his training to improve his fitness. He decided to incorporate a increased intensity into his routine. After a short period of time he had increases in this fitness and was able to observe the reduction in blood pressure he was looking for. In the video below, filmed at the Boston QS meetup group, Siva explains his methods and talks about how he was able to track his body’s response to different fitness routines.

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.


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.