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



Accuracy of Revvo in Measuring VO2Max Without Oxygen Masks

Ever since I started working on Revvo a few years ago one of the key questions for me has always been how accurate is the data compared to gold standard measurement of VO2Max using oxygen masks in a lab. And now we have an answer — and it looks like we are getting really close !



In our previous methods we were close for most — but for some we did see an over-estimation. The new method is overall slightly more accurate but also consistently accurate across everyone tested.


19 people tested on Revvo (following our standard process) and also tested in a lab using gold standard Parvomedics metabolic measurement cart that measures their respiratory gases (oxygen, carbon dioxide etc.) to firstly estimate their VO2Max and also estimate their ventilatory thresholds (which corresponds to their lactate threshold).

The sample consisted of men and women, 30-50 years old, with VO2Max levels ranging from <20 to >70 (which is a pretty wide range). This validation sample also included some of the highest (70) and the lowest (18) VO2Max scores from amongst the 600+ tests we’ve done so far which gives us confidence that our methods have the potential to span a very wide range of humans. Our goal is to continue to enlarge the sample and look for diverse populations to test.

Interval Training

The Science Behind Interval Training

This video is a very scientifically grounded yet easily understood review of how short bouts of interval training can achieve dramatic improvements in your fitness level (VO2Max). Great effort by the Australian Broadcasting Corp!

In brief, high intensity interval training increases the mitochondrial density of your muscle cells. These are the energy producing elements of your muscle — more you have, the more oxygen your muscles can uptake to burn glucose as fuel.

Low mitochondrial density not only makes you less fit but also exposes you to a range of health risks.


How to Measure Your Fitness Level

Last week I attended the first ever Quantified Self Expo in San Francisco – which had a ton of interesting products and sessions on various topics covering areas of self-measurement. I was there demoing Revvo and also gave a talk titled “How to Measure Your Fitness Level”, which I thought would be useful for a wider group to review. Below are my slides :


Fit at 50 !

I was inspired to write this post by a slew of recent studies showing that midlife fitness (midlife roughly defined as 40-65) makes a big difference to health outcomes and cognitive function for the rest of your life. I’ve certainly experienced this personally – increasing my fitness at 40 helped normalize my blood pressure levels. And I’m probably fitter today than I was in my 20s (talk about wasted youth!).

Here’s a short list of recent studies showing the connection between fitness, age and health issues / benefits. (Fitness, as I’ve explained earlier, is the ability of your body to supply fuel to muscle when you are active):

1/ Fitness measured for 45-62 year olds predicts chances of 10-year survival. (John Hopkins Study)

2/ Higher fitness delays age-associated increase in blood pressure. (USC Study) (Henry Ford Study)

3/ Fit older adults (55-82) did as well as younger adults on cognitive function. Unfit older adults did poorly. (Boston University Medical Center Study)

4/ Higher midlife fitness prevents the brain from shrinking (Boston University School of Medicine Study)

5/ Higher midlife fitness associated with lower risk of certain cancers in men (University of Vermont Study)

The interesting thing about these studies is that you don’t have to be a super-athlete at 50 to stay healthy – the level of fitness expected – 12-13 METs is well within the reach of the average 50-year old male as you’ll see from the charts below.


(Many of these studies have been conducted amongst male cohorts so difficult to be as precise for women — I’m hoping to see more studies on female fitness & health impact in the future).

The other interesting question that it raises – if you can stay as fit as the average 30-year old (which is an achievable goal for most 50-year olds) can you entirely avoid aging related health issues ?

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 I Ignored Conventional Wisdom To Achieve My Fitness Goals

Yes its the time of the year when a remarkably large number of people resolve to do something they will predictably give up within a few weeks of starting i.e. trying to get fit. And until recently I was part of this pattern — resolving countless times to get fit yet giving up within a few weeks of starting an exercise program. Something however changed the year before & for the last ~2 years I’ve actually managed to stay at it for long enough to now genuinely claim that I am indeed fit.

The biggest challenge with getting fit – as we all know – is to actually stick with it through thick & thin – rain, snow and heat – long days & sleepless nights (thanks to my 2-year old!). And to achieve this I had to completely ignore conventional wisdom on the subject (as reflected in countless articles – for example, see here & here).

1/ Find Something You Like Doing

Conventional wisdom suggests you should find an activity you like doing and do just that if you want to get fit. I LOVE cycling along the Erie Canal (which is a few minutes walk from where I live) — I can cycle for hours. Yet I managed to do this just twice in the whole of last year!

It’s not difficult to explain why — I need to dedicate a significant chunk of time for the activity, the weather needs to be decent and my kids cannot ask to join me (which they inevitably do & I find difficult to refuse and in which case all we end up doing is a short & gentle trip where my heart rate goes up only because my 8-yr old keeps trying his best to jump into the canal).

Also the reason why I like the long canal biking trips so much is their rarity .. if I was doing this daily (say this was my commute), I’m pretty sure I’m not going to like it quite that much.

So forget trying to do the thing you like … instead focus on finding something that you can actually do on a daily basis.

2/  Find a Friend 

When I was 27 (that feels like a looong time ago!), I had a friend living in the apartment below who would wake me up at 5.30 so both of us could go for a run. And on days that he was being lazy I would pay him back! Even after nights of partying until 2 am I still managed to get out for a run early the next morning, thanks to him.

Things change when you have kids — your friends don’t control your schedule, your kids do. And that’s true for your friends too. Its still possible occasionally to co-ordinate our schedules so we can all get together for activity. However its incredibly rare to be able to do this on a daily basis.

So ignore conventional wisdom & find an activity you are happy to do on your own. Think of this as your time, free of work, kids, family & social commitments.

3/ Set a Weight Loss Goal

This is the conventional wisdom that in my opinion is the most dangerous & counter-productive. Yet how could you argue against setting a weight loss goal ? The reason – weight loss does not really happen via exercise alone. Many studies have shown that the average person loses very little weight solely through exercise. And some of course even gain weight (because we want to reward ourselves for that long ‘hard’ run we just finished!).

And so if you do set a weight loss goal, you’ll probably end up giving up on exercise because you won’t see results.

The real reason why you should exercise is so that you can stay fit. Fitness, as I pointed out in an earlier post, is not about your weight. Its about how effective your body is in providing & utilizing oxygen to fuel your physical activity. And is perhaps the single best indicator of your overall health.

Ideally you should measure and track your fitness (which until now has required a visit to an exercise science lab). Or track a proxy – such as your average heart rate for the same activity level, or your average pace / finish time for a fixed distance you run or bike. And particularly if you’ve been sedentary for a while, you’ll see improvement within a few days / weeks of starting an exercise program.

So what are my personal suggestions to help you meet your fitness goals?

1/ Set a Fitness Goal

2/ Find a Short Workout Effective at Improving Fitness

3/ Integrate that into your Daily Life

My workout is indoor cycling (at home), at high intensity, for 10 minutes daily — I can do this rain or shine, sleepy or otherwise. It may not be quite as much fun as cycling on the canal but it does not require that I change my lifestyle, plus I can watch music on youtube as I bike. I track changes in my fitness each time I workout so I know how much meaningful progress I’m making. I am change the intensity as I make progress so I don’t plateau. (Full Disclosure : I’m building a smart exercise bike called Revvo that does all this).

I do this pretty much the same time everyday — its now literally like brushing my teeth or taking a shower so it doesn’t require an enormous amount of willpower to get me going. It’s just a habit and that’s how it should be.

Happy 2015!

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

Interval Training

Could 10 Minutes of Exercise Make You Fit ?

Study after study shows that we are in denial about a number of things – our weight and our calorie intake both of which we generally tend to under-estimate. But nothing comes close to the amount by which we over-estimate how active we are.

In a 2011 study published in the American Journal of Preventative Medicine, US adults self-reported close to 60 minutes of daily activity everyday (this includes exercise and also other casual activity such as gardening, household chores or walking to the pantry to pick up a chocolate!). However when activity levels were actually measured using an accelerometer turns out we are active for an average of just 9 minutes daily!

Guidelines provided by the American Council of Sports Medicine and endorsed by other leading health organizations suggest 150 minutes / week of moderate intensity activity (i.e. brisk walking or jogging) – which only 9% of US adults actually achieved. This level of activity is considered necessary to maintain / improve fitness.

So how do we resolve this problem ? A team of exercise physiologists from McMaster University, led by Gillen JB looked to see if we could improve our fitness by exercising for just 10 minutes, 3 times a week (Martin Gibala, a co-author to the study is a pioneer in interval training). After completing a 2-minute warm-up, study participants cycled all out for 20 seconds, followed by 2 minutes of recovery where they cycled at a gentle place. This was repeated 2 more times during that session and then finished off with a 3 minute cool down for a total time commitment of 10 minutes per session.

The results were astonishing – within 6 weeks both men & women saw a significant increase in their cardio-respiratory fitness by ~12%.


Gillen JB, Percival ME, Skelly LE, Martin BJ, Tan RB, et al. (2014) Three Minutes of All-Out Intermittent Exercise per Week Increases Skeletal Muscle Oxidative Capacity and Improves Cardiometabolic Health. PLoS ONE 9(11): e111489. doi:10.1371/journal.pone.0111489

In addition, they also saw important health benefits – mean arterial pressure (which correlates with blood pressure) decreased by 7%. Insulin sensitivity (important for those with pre-diabetes & diabetes) also improved amongst both groups. 24-hour glucose levels however only dropped amongst men (& not amongst women, which warrants further study).


This is not the first study to show significant benefits for interval training over continuous exercise – a meta-analysis published in the British Journal of Sports Medicine by Weston et al showed 2x improvement in fitness through interval training compared to moderate intensity continuous exercise. Another review by W Kent in the same publication indicated a 15% increase in fitness within 6 weeks of interval training.

What’s unique in this study is the relatively low time commitment required to achieve this remarkable improvement in fitness and health – a level of commitment that almost everyone should be able to make (with of course brief moments of intense effort). In other words there are no more excuses for not getting fit!

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