One Physician’s Approach to Quantified Self: My Key Performance Indicators and How I Track Them

Paul SufkaFitness, Hobbies, Med Tech


”What gets measured, gets managed.” – Peter Drucker

Despite being considered one of the techie people in the physician/rheumatology community and a self-proclaimed Apple fanboy, it might be surprising to know that I don’t own (or want) an Apple Watch.

Part of my reasoning comes from the importance of avoiding interruptions.

But the main reason I don’t own any type of smartwatch is that I don’t see anything useful that they allow me to track.

When I look for things to track, I look for key performance indicators (KPIs): things that I consider modifiable activities, that when tracked or measured, correlate with improvement in specific goals.

With this in mind, I’ll start with a few of the more common activities that I don’t track (and why):

  • Steps per day. Although the recommendation to walk 10,000 steps per day is an arbitrary number, I do find that it is an excellent suggested baseline level of activity for most people. However, since I’m a fairly active person that exercises most days of the week (and even uses a standing desk at work and at home), I don’t find that this has any correlation with my fitness level.
  • Bodyweight. I’m fortunate enough that my bodyweight has varied little throughout my life. I credit this mostly to exercise (primarily strength training since my teenage years), along with generally watching my diet. Certainly, if my bodyweight would increase (especially in the form of adipose tissue), this would quickly become one of my KPIs.
  • Calories. In recent years, increased importance on the type of foods that we eat has been recognized. While the total energy that we consume certainly matters, the effects of different types of food also clearly play an important role. In other words, you would expect your body to react differently to 2,000 calories of pure sugar versus 2,000 calories of grass-fed steak.

Activities that I track (and how):

Heart Rate Variability (HRV). HRV is a measure of how much beat-by-beat variation occurs in your heart rate, which is governed by the balance of sympathetic and parasympathetic nerve activity. More simplistically speaking, HRV can give a sense of how much stress the body feels at a given time. (PDF of a review here). In a fully rested/low stress state, you should have a high HRV, and under conditions of high stress, you would expect your HRV to decrease. Increasingly, high level athletes are using measure of HRV to titrate their level of training for the day.

I use an app called HRV4Training (App Store) to track my HRV most mornings, which uses the iPhone camera and flash to measure your heart rate via plethysmography with surprisingly good accuracy (especially if used in a dark room). After this, your HRV can be viewed in the form of rMSSD (the unit by which HRV is calculated, called the Root Mean Square of the Successive Differences).


In my case, whenever my HRV rMSSD is above 80, I’m fairly well rested (which means I’ll probably do deadlifts that day).

I’ve found that my HRV seems to most strongly increase with the amount of perceived rest that I get, with frequent moderate-high level exercise, and with meditation. My HRV seems to decrease the most when I’m sleep deprived, when I’m sick (or feeling like I might be getting sick), or after overly intense exercise (especially too many deadlifts).

Exercise. I track exercise using a website called beyond the whiteboard, which is popular in the CrossFit community, and fits very well with the style of workout that I often perform. The site allows you to analyze your overall fitness level in comparison to other athletes who use the site, and also helps you identify strengths and weaknesses in your overall fitness.


Sleep. I have a Sleep Number bed that has built in sleep tracking, although I don’t find that it always correlates with my perceived level of rest. Sometimes, this is because I’ll fall asleep in my son’s room while putting him to bed, so the data is wrong (such as on Sunday of the picture below).


Meditation. Over time, I’ve come to find a great deal of benefit from meditation (and I’ll give Dr. Ronan Kavanagh credit for initially turning my onto the idea of it.) I currently try to meditate 10–20 minutes each morning using the Headspace app (Web | App Store), and have felt increased ability to focus and generally calmer.


Other: Mobility & Diet. I use an app called Way of Life (App Store) to get a big picture view of a few things I’m tracking, such as meditation and exercise, and other things I’m trying to watch, such as doing some mobility work (especially hips, ankles, and shoulders) most days. The app essentially allows you to check yes or no for each day, and encourages you to go on a streak of 3+ days.