Physical Activity/Fitness Level: Can Your Wearable Monitor Track and Improve This Vital Sign?

This is an update of a post first written in 2016. As we approach New Years Day 2021 undoubtedly many of you will be resolving to begin or expand your exercise program. Herein I touch on methods that physicians and patients can use to assess current fitness level, begin a fitness program, and gauge performance using wearable activity monitors relative to activity guidelines

The skeptical cardiologist routinely probes his patients’ activity and exercise levels and encourages them to engage in 150 minutes of moderate exercise weekly.

Initially, I was skeptical of the benefit of treating such assessments as a vital sign (like blood pressure or heart rate)  as a 2016 AHA scientific statement suggested but I now think it makes sense. I was concerned about seeing still another item on a chart checklist that would have to be recorded in the EHR but fitness is such an important parameter it truly is worth putting in with heart rate, blood pressure, and weight.

The 2016 AHA statement suggested that ideally, physicians should be measuring their patients’ fitness by obtaining maximal oxygen consumption (VO2 max) by utilizing an expensive and rarely utilized cardiopulmonary exercise test. Failing that, the AHA statement recommended doing a treadmill stress test. Despite this recommendation, made in 2016, I have seen little evidence that clinicians are routinely performing treadmill exercise tests on their patients to estimate their cardiorespiratory fitness (CRF.)

In the absence of stress test information, rather than utilizing my simple question to patients: “How active have you been?”,  the 2016 AHA statement recommended doctors utilize a formal questionnaire to estimate their patients’ CRF such as the one provided at World Fitness Level.

Estimating Your CardioRespiratory Fitness Without a Stress Test

World Fitness Level was developed by Norwegian exercise physiologist Ulrik Wisloff the leader of the Cardiac Exercise Research Group (CERG) whose laudable goal is “to uncover how to treat and prevent major societal health problems, such as obesity and cardiovascular disease.”
You can read more about their methods on CERG’s excellently referenced NTNU website The Fitness Calculator estimates your fitness age measured as maximum oxygen uptake (VO2max). On the NTNU website you will learn that  VO2max is the most precise measure of overall cardiovascular fitness and can find your own risk of dying early from cardiovascular disease along with ideas on how you can reduce the risk.

In 2016 I went online to take this CRF estimator (which is based on this paper)
I was asked for the following information:

  • Country and City
  • Ethnicity
  • Highest Level of Education
  • Gender/Age/Height/Weight
  • Resting and Maximal Pulse
  • How often do you exercise?
  • How long is your workout each time? (over/under 30 minutes)
  • How hard do you train? (I had to choose between “I go all out”or “Little hard breathing and sweating”)

The info on location, level of education and ethnicity is only utilized for CERG research whereas gender/age/heigh/weight are relevant factors for the CRF estimator.


When you have finished answering the questions you are given an estimate of your fitness age. When I did this online in 2016 and answered truthfully I got the result to the right: I had the fitness of a 41 year old with an estimated VO2 max of 49 !

(interestingly this estimate corresponds exactly with VO2 max derived from a recent stress test I had completed.)
I used the app (which appears no longer to be available) and changed a few parameters:

  • I increased my resting heart rate or pulse  from 60 to 68 beats per minute (BPM)
  • I switched from exercising 2-3 times per week  and longer than 30 minutes  at “all out” level to the lowest level for all 3 questions.

The change was dramatic and depressing: I went from 39 years old to 67 years old in the bat of an eyelid! Thus, the key to youth is obviously exercising at intense levels a lot which among many other things results in a low resting HR.

A Simplified Assessment of Physical Activity

Interestingly, a 2018 AHA statement on “Routine Assessment and Promotion of Physical Activity in Healthcare Settings” came up with a totally different approach to assessing CRF, one quite similar to mine.

Make PA assessment a priority in all visits, in particular when the focus is CVD (cardiovascular disease) or preventive care, using one of two simple, standardized tools:

Physical Activity Vital Sign (PAVS):

– “On average, how many days per week do you engage in moderate or greater intensity physical activity (like a brisk walk)?”

– “On average, how many minutes do you engage in this physical activity on those days?”

●If the product of those responses (MVPA in minutes per week) indicates a lack of compliance with the aerobic component of the US PA guideline recommendation of 150 min/wk, individuals should be advised of the health benefits of regular PA and encouraged to gradually increase either their frequency or duration of activity.

An equally effective approach is contained in a single sentence question:

In the past week/past month, on how many days have you done a total of 30 minutes or more of physical activity, which was enough to raise your breathing rate? This may include sport, exercise, and brisk walking or cycling for recreation or to get to and from places, but should not include housework or physical activity that may be part of your job.”

Starting Exercise To Increase Your Fitness Level and Lower Your Fitness Age

Whatever approach we use to assess our patient’s fitness level/physical activity whether it is a stress test, the world fitness level calculator, or the single question method it is important to have an equally valid method for boosting the patient’s fitness level/physical activity level.

The 2016 AHA statement includes this complicated table with PA dosage recommendations which comes from the American College of Sports Medicine:

The types of exercise which improve CRF are ones which “involve major muscle groups” and are continuous and rhythmic such as brisk walking, jogging, and dancing. I have typically called this aerobic exercise.

Strengthening exercises, although important for many reasons, do not improve CRF.

The intensity should be enough to get heart rate to >50% of the heart rate reserve.

For some patients, just pointing out that they need to increase the duration and intensity of their walks, bike rides or other aerobic activities is effective.

Many patients, however, despite acknowledging that they are out of shape and recognizing the benefit of ramping up their exercise, fail to begin or sustain regular exercise programs.

Others consider their very slow walks with their dogs as satisfying criteria for moderate exertion and thus fail to reach the recommended PA dosage.

On CERG’s website, you can get information on a 7-week program to increase your fitness level. This is a very good start for sedentary individuals looking for a science-based approach to getting more fit. The PDF is available here.

The CERG program emphasizes high-intensity interval training (HIT or HIIT.) The equally acceptable more mainstream approach is exemplified by the CDC guidance on getting started with physical activity (see CDC Move Your Way PDF.)

A key determinant of the dose of PA is intensity: remember that every minute of “vigorous” counts double the minutes of “moderate” exercise toward achieving the desired 150 MVPA minutes.

The CDC offers a simple, low-tech method for gauging whether one is engaged in moderate versus vigorous exercise:

Variations on the “talk test” have actually been validated as measures of exercise intensity, but I would prefer a more objective measure.

Are WAMS the Solution For Measuring and Motivating Physical Activity?

Lately, I’ve become obsessed with the methods by which various wearable monitors might more precisely measure the dose of physical activity.  My recommendations for exercise suggest 150 minutes per week of moderate activity or 75 minutes of vigorous activity and they include the following suggestions on what constitutes moderate or vigorous activity:

Examples of Different Aerobic Physical Activities and Intensities

Moderate Intensity

  • Walking briskly (3 miles per hour or faster, but not race-walking)
  • Water aerobics
  • Bicycling slower than 10 miles per hour
  • Tennis (doubles)
  • Ballroom dancing
  • General gardening

Vigorous Intensity

  • Racewalking, jogging, or running
  • Swimming laps
  • Tennis (singles)
  • Aerobic dancing
  • Bicycling 10 miles per hour or faster
  • Jumping rope
  • Heavy gardening (continuous digging or hoeing, with heart rate increases)
  • Hiking uphill or with a heavy backpack

But is there a better way of determining whether you are doing moderate or vigorous exercise and reaching PA goals beyond the individual’s recollection of the type and duration of activity?

Can wearable activity monitors (WAMs) like FitBit, Apple Watch and Garmin Vivofit provide a more reliable assessment of PA thereby guiding and motivating patients to achieve the magical level of 150 minutes weekly of MVPA?

The 2018 AHA statement goes into great detail on WAMS and even has a chart rating them according to 5 criteria: validity, how readily the device classifies MVPA minutes versus just counting steps, feasibility (which assesses battery life and cost), health care data integration, and incorporation of elements of behavioral change

They concluded:

Despite the growing use of WAMs, an ongoing challenge is that few of them collect and report PA data in a manner that enables assessment of compliance with the PA guidelines. Most WAMs and mobile apps focus on daily step counting, with the somewhat arbitrary goal of 10 000 steps a day, rather than reporting the World Health Organization, Centers for Disease Control and Prevention, and AHA guideline metric of MVPA minutes per week, largely because step counting is easier technically, with studies showing good accuracy. Estimating PA intensity has been more challenging, with suboptimal results when devices are studied systematically.Many WAMs and smartphone apps report active minutes and calories burned as indicators of PA intensity, but little information has been available on the specific algorithms used and how these measures correspond to the guideline-based MVPA minutes.

You can view a tabular summary of their report by downloading this PDF:

The problem with assessing WAMs is that they are a moving target, continuously upgrading and modifying the algorithms they use. Thus, the ratings in the 2018 AHA document are mostly irrelevant for current devices.

It is my sense, however, that currently available WAMs are trying to incorporate many of the features the 2018 AHA statement mentions.

Specifically, WAMS manufacturers are attempting to provide an assessment of the wearer’s MVPA minutes and then provide feedback that encourages the wearer to achieve the 150 minutes MVPA per week goal.

Personal Activity Intelligence

Professor Wisloff, of CERG fame, has developed a free smartphone app that takes heart rate data from any wearable and generates an assessment of MVPA minutes.

This MVPA assessment method is called Personal Activity Intelligence (PAI) and it has a solid scientific background and a laudable goal:

The PAI algorithm was derived from one of the world’s largest health studies involving 45,000 people over 25 years, and it has been further validated across broader populations of over 730,000 people, with over a million person-years of data. 

The objective was to develop a single, easy-to-understand personalized activity tracking metric that could help everyday people manage their health. The PAI algorithm was the result of this research. 

Published studies have demonstrated evidence associating a PAI Score of 100 and above, with reduced risk of mortality across many cohorts and sets of data

What I particularly like about PAI is the link provided to a complete listing (with the complete papers) of the research supporting the program. For example, this seminal paper:

I’m in the process of evaluating the PAI app and comparing it to WAMs like Apple Watch, Garmin VivoSmart, and the Amazon Halo. I’ll post that analysis along with a discussion on heart rate reserve and methods for calculating MVPA minutes in the near future.

In the meantime, I hope all my non-exercising patients will get off the couch and start accumulating those MVPA minutes and raising their World Fitness Level.

Dynamically Yours,


h/t Mark Goldstein for suggesting I evaluate PAI


23 thoughts on “Physical Activity/Fitness Level: Can Your Wearable Monitor Track and Improve This Vital Sign?”

  1. Dr Pearson, would your exercise advice for someone on a high CAC percentile change at all? I’ve seen studies where only the very highest levels of exercise (basically intense and every day) get the full benefit once CAC is >400 (which presumably most people on a high percentile will reach in time). I believe the study I saw showed their 12 year risk of MACE to be 5% as opposed to 25%(!) for the completely sedentary. But even moderate exercise was still 10-15%, so intense and regular does seem markedly more beneficial in that instance.

  2. I discovered your blog just before Christmas, and have read it ‘cover to cover’. I am 56, and was too inactive in my desk job and somewhat overweight. I took your advice, bought an apple watch, a chest strap and am working on cardio to keep my PAI above 100. I have started losing weight, and am hoping to get off of my daily 4mg of Coversyl. After 8 weeks of exercise, I feel better than I have in a long time. Thanks for the inspiration!
    I do have one question: I am finding that keeping my PAI above 100 is a lot of work. It seems like their target is more like the ACSM 300 minutes of moderate or 150 vigorous, versus the lower effort 150 minutes of moderate or 75 minutes of vigorous. I suspect I know the answer to this, but is the extra effort worth it? Put another way, how much extra benefit does one get by 300 minutes of moderate versus 150 minutes?
    Thanks, and thanks again for getting me off the couch!

  3. 68 year old female runner. My Garmin estimates a V02 max of 43-44 depending on workout. The fitness test gave me a 42. BTW my max Hr which was hit this morning is 185. I wear a chest strap when running and am not using the wrist based HR. My resting HR is 51. The guidelines for max heart rates have me puzzled.

    • The guidance for heart rate ranges are based on a formula. There are a whole slew out there…..every one purporting to be more accurate than the rest. And they might be……for some. Problem is they’re all derived from an average figure for a given demographic and even with a highly selective group, there’ll be a random scatter of measured maximum heart rates.

      I used the Fox et. al. formula of 220-age when I first started using an HRM nearly 20 years ago and didn’t know better and based training zones (for cycling) off that. Added a few more bpm to those figures for running. Was quite surprised at my first VO2Max test to hit 184 bpm. That’s when I realised the topic was a bit more complicated than my understanding.

      As performance measuring devices have become more sophisticated, age predicted max heart rate has fallen out of favour as a stand alone figure for determining training zones.


  4. As always, your postings are very interesting and valuable – thank you. One problem with understanding how this information relates to me is that I have been taking a beta blocker twice a day for most of my life (I’m 71) – which is very effective at keeping my heart rate artificially low. My resting heart rate is 55 – 60, and even with vigorous exercise it is difficult to get it above 100. I do an hour daily on the treadmill at 3.7 mph with an 8% grade, and can’t get my heart rate above 84. How do you properly exercise your heart muscle when you take a beta blocker? Happy New Year to everyone – hope 2021 is an improvement for all! Rick

    • Not Dr. P here Rick but I have something of a take here. Along with personal experience of beta blocker usage, I’m a dentist by training, husband’s a physician (hepatologist) and daughter a veterinary cardiologist (arrhymias are her bread and butter) On top of that, prior to moving to the foothills of the Rockies here in Colorado, I was also a fitness instructor….primarily SPINNING….for a dozen or so years. I mention this because SPINNING was the first fitness programme to be introduced that used HRM training as a tool… I’ve stumbled across all the ways that heart rate monitors DON’T work in the way folk imagine.

      Let me tell you… are a PERFORMANCE MACHINE. Whatever heart rate feedback you’re getting, you probably have a stroke volume to rival Secretariat’s!! 3.7 mph is a decent clip even on the flat, but at 8% incline you are a LOT of work and being able to maintain that for an hour is the measure of a superior fitness level.

      Just for the heck of it, I squeezed in a 5 minute interlude on my treadmill run this morning. Set the incline to 8% but I had misread your comment and set the belt speed to 3.4 mph. I would not be able to do this at 3.7 mph. Raised my heart rate to around 140 or so. “Comfortably uncomfortable “/RPE 6-7 on a scale of 1-10 (to use my coaching cues). I would not be able to maintain this for even 30-40 minutes!

      Sorry to hog the thread but this was a common issue for me in my classes and I occasionally had class members get so focused on getting their heart rate up, they even suggested they might not take their pills that day.


      • Thanks for your comments Vivienne. I know I am in very good overall physical condition for a 71 year old – but my concern is that I am not adequately exercising my heart muscle if I can’t get my heart rate up. I don’t know if obtaining a relative exercise heart rate increase of 40% over resting heart rate does the trick, or if I also need to somehow get to an absolute HR of 135 bpm to adequately exercise the heart machine? Perhaps with a medically helped resting heart rate at 60, the exercise heart rate getting up to 85 is sufficient exercise for the heart since it is never called upon to go higher?

        • Rick,
          I have similar questions and to some extent my last post is starting down the path to answer that. I and others are on beta blockers which slow the maximal heart rate ( and confuse activity trackers) and I’ll be writing about this soon.
          My gestalt is that you having nothing to be concerned about. You are doing a great job of achieving MVPA minutes irrespective of what heart rates you achieve but I’d like to provide more definitive evidence.
          Dr P

        • Well, Rick, one of the training workshops I attended in the early days of my fitness career was on HRM training. The title was “Heart rate monitored training……it’s more than a number”. Pretty much everything I thought I knew about the topic……and stuff I’ve seen since…..was debunked!

          Certainly, for someone like yourself who’s very beta blocked (don’t know if that’s actual a clinical term) using an HRM is almost contraindicated. A heart doesn’t have to beat fast to be working hard. Indeed, with improving fitness most folk can expect to see a diminished response to a given sub max workload.

          I know this ultra low rate is artificial but your heart’s still working up a storm. In the early days of my afib when I was also relatively unfit from the effects of altitude on my fitness and I relied almost totally on RPE. If I overexerted myself (very easy in my mountainous nabe) the “Shaking hands with Mr. Pukey” feeling kicked in at a modest 125-130 bpm. FWIW…….my experiment this morning had a much higher HR response than that so I think you should imagine what your effort might produce without the beta blockers. Don’t let your HRM mess with your head.


            • Here’s another morsel for Rick. I added another 5 min interlude to my treadmill run this morning…..this time at a belt speed of 3.7mph this time and the 8% incline. I did it early on in the run 15-20min mark so I was well warmed up but before cardiac drift had a chance to kick in. I struggled to hold the effort for even 4 minutes, hit the highest heart rate for the whole run and had to back off quite a bit to recover.

              To be able to hold this for an extended period is a spectacular effort. The cardiac output necessary for this workload is obviously being met so, if it’s not coming from heart rate, it must be stroke volume…..which I’m thinking might arguably be an even better way to condition the heart since. I manifestly wasn’t joking about Secretariat.

              I’m actually going to introduce this into my training regimen on days when my legs feel too spanked to run as a way to condition my cardiovascular system without overloading the musculoskeletal.

              There’s a paper here for someone….mark my words 😉


  5. Very interesting article…thank you.

    Took the survey and, at age 68, received a fitness age of 40 and VO2 Max of 38…..a figure that concurs with the estimate that my Garmin kicks out. May or may not be accurate but my measured VO2 Max just before my 60th birthday was a hair over 45, so it MIGHT be correct. However, in the interim, I’ve relocated from sea level on the East coast to an altitude of over 6000ft (and suffered mightily for a while), develop Afib and dealt with beta blockers interfering with my training and messing with my head (me…..on beta blockers????) . No episodes for the last 2 years and a slow taper off the Sotalol has allowed me a steady return to fitness so I’ll pretend that I’m as fit as a 40 year old.

    I will mention, though, that the recommendation of starting a new fitness regimen at such high intensity looks to me to be a bit daunting. A 4 minute interval at such a high heart rate range is pretty darn hard to sustain.

    Happy New Year!


    • I added a hyperlink to the second time I mention world fitness level that should take you directly to that site.

  6. Thank you for the update. Could provide the link on how to take the fitness test?
    I looped thru your article and went to the Norwegian website and could not find it.

    A Happy New Year to all.

    • Brian,
      Thanks for those comments. I do note the PAI website is clearly trying to attract employers. Having been subjected to employee wellness programs I know very well how intrusive they can be. I’ll see what Al Lewis has to say about PAI in that respect.
      Dr P

  7. I have been using Fitbit – on my third one now- for over 4 years. Seeing the steps add up has been very motivational. I’ve logged over 5800 miles walking and put in 45 or more minutes per day almost every day. I also lost 30 pounds after my heart failure and fib diagnosis over 5 years ago, gave up most ultra processed foods, and cut way back on sodium. I’m 78 and still going fairly strong without ‘vigorous exercise.’ Walking is one of the safest exercises (still have my own knees), and I love the outdoors which is fine for such activity most of the year here in northern California. We don’t have many pesky flying insects either.

    • It’s great to hear this success story for a WAM. I see many patients who are able to walk regularly and achieve the 150 MVPA minutes on a consistent basis. Weather, however, becomes an issue for those of us not able to live in California or other milder winter climates. Walking outside becomes more difficult and with the pandemic, the mall walks or Walmart walks are no longer encouraged. In addition, going to gyms right now seems like high risk behaviour.
      For those unable to walk outside them home consistently a home treadmill may make sense.
      Dr P

      Dr. P

  8. Thank you for this article, Dr. Pearson. I look forward to the follow-up article re HRR, because I am particular interested to read any comments from your readers who may be using the MAF formula.

  9. Unless you’re doing an actual (and absolute) VO2 max test at an exercise physiology lab, then your VO2 max score is bogus. As an aside, the worst thing about estimated (and relative) VO2 max scores is that you can increase the score just by losing weight. In fact, you can DRAMATICALLY increase your score from being slightly overweight BMI to slightly underweight BMI. I’ve known people who went from being relatively normal VO2 max scores (40’s) on the Cooper test to becoming very good VO2 max scores (60’s) by losing 30+ lbs.


Please leave your comments. The skeptical cardiologist loves feedback. He reads all and replies to all that warrant a reply.