Post #27: Which Wearable Parameters Are Really Worth Tracking and What Are They Telling Us About Our Health?

Today’s post (#27) is about deciphering the data our wearables are putting out every minute of every day, in a way that one can do something actionable with. People either find the data from wearables too overwhelming or they reach incorrect conclusions; I hope that by the end of this post you will have a better sense for which parameters from the wearables to focus on, how to interpret them correctly and what specific things you can do to improve them.

Many individuals use wearables like the Apple Watch, Garmin, Fitbit, Oura Ring, Whoop Band or any of their various cousins. While most of them provide the same or similar outputs, their accuracy levels and definitions of metrics sometimes vary. The most common metric tracked is the number of steps with 10,000 steps being the magic number (or closing the circle on an Apple Watch) that folks try to achieve. However, there are many more metrics that I personally use as a leading indicator of the health of my physical and blood markers. The following is a list of the primary metrics I use, what value I try to achieve (quantitatively and qualitatively) and what actions I take based on each metric, if it is out of whack. 

Resting Heart Rate (RHR): It is the lowest heart rate you drop to and it should typically happen sometime in the early to middle part of your night time sleep. If it happens during the middle of the day when you are active, that is a bad sign. A lower RHR is usually a sign that you are pretty healthy but in a few cases a lower RHR can happen because you are exhausted, stressed or are experiencing some side effect of certain medications. So while your heart rate should fluctuate significantly during periods of exercise, it should drop during periods of sleep. If your RHR is between 60 beats per minute (bpm) and 70 bpm, you are at the population average; anything in the 50s is considered really good and if you are in the 40s or lower, you are either very fit or there is something really wrong with your health. Most doctors will put you on a Zio monitor (or some equivalent) for a 1-2 week period if they are concerned about your heart rate. 

I found my average RHR dropped by about 6% over the last 3 years as I increased my strength training, eating a lighter dinner and keeping a 3 hour gap between dinner time and bedtime.

Heart Rate Variability (HRV): HRV is the variation in time between each heartbeat. E.g. If someone has a heart rate of 60 bpm, you would imagine their heart beats exactly once every one second. However, in reality, the first beat may happen 0.993 seconds after the previous beat and the next one may happen 1.04 seconds later. This deviation is a reflection of the body's ability to adapt to stress, indicating autonomic nervous system function and cardiovascular health. Non-intuitively, the higher the HRV value, the better. 

It is important to keep a few things in mind about this metric. The days you exercise a lot or experience mental or emotional stress, you will see a low HRV value the following night (which is when most wearables measure the HRV, but not the Apple Watch). That is perfectly fine and suggests that the body needs to recover. However, it is critical to both push your body through exercise on certain days as well as allow it to recover on other days, so you will see significant variations in your HRV values over time. One should never compare HRV values across people but rather look out for variations in this metric for a given individual over time; this is because there is a strong genetic component to HRV but the variation for a given person over time does provide valuable insight.

I observed a 13% increase in my HRV values over the last year, primarily by picking the days I did my exercise viz. I avoid doing strength training on the days my HRV is below my 25th percentile because on those days I found that my ability to push my body was lower given the higher stress it was under. On the other hand, the days my HRV is above my 75th percentile, I try to push my maximum weights or reps. In addition, the interventions I described above to lower my RHR also help with increasing my HRV.

Total Sleep Time: The range for this metric varies widely by age, genetics and other factors. Typically 6 to 8 hours of sleep is considered normal but there are people who need less or more. The key is to ensure that if you aren’t getting enough sleep, it isn’t because of issues like stress, sleep apnea, etc. and if you are getting too much sleep, it isn’t because of sleep disorders, mental health issues or an effect of medication. Track your overall sleep time and if it is outside the 6 to 8 hour window (for adults), investigate the root cause with your doctor, a sleep clinic or a lifestyle intervention program.

In my case, I require less sleep than the average, which prompted me to go to the Sleep Clinic at Stanford to eliminate causes like sleep apnea, etc. I didn’t have any issues they could see but, having said that, I would say that a few interventions have improved my total sleep time by 15% over the last 3 years, such as sleeping in a room that is at about 65 degrees F (18 degrees C) as per research done by Professor Matthew Walker (this deserves a whole post in itself), trying to stick to the same one hour window every day to go to bed (I am successful about 60% of the time but that’s better than had I not tried), avoiding drinking water for at least 2 hours before bedtime, practicing 5 minutes of deep breathing just before going to bed as well as in the middle of the night if I wake up and can’t go back to sleep. In fact, recent studies have shown that maintaining a consistent schedule around bedtime and wake up time plays a more crucial role in health metrics and energy levels than the total amount of sleep.

REM Sleep and Deep Sleep: REM sleep is crucial for cognitive functions like memory consolidation, emotional regulation, and learning while deep sleep is vital for physical restoration, immune function, and overall recovery. Both stages are essential for overall health and well-being. Recommended values for REM sleep are typically 15-25% of total sleep, while deep sleep should constitute about 15-20%. 

I have found that my level of energy is determined more by these two metrics than my total sleep time and so I have really tried to figure out what most impacts them. While I used to drink one glass of wine or a Bloody Mary once every 2-3 weeks, I found that it dramatically reduced my REM sleep percentage. Although alcohol helps make one sleepy initially, it disrupts the quality of sleep over the night. This has caused me to pretty much bring alcohol down to one glass, once every 6 months or so. Another aspect that impacted my REM sleep was taking antihistamines (typically found in allergy medication). I have switched my allergy medication as well as the timing of it. Keeping that 2-3 hour gap after dinner as well as having a lighter dinner both positively impacted my deep sleep and REM sleep.

Fat Burn Minutes and Cardio Minutes: Zone 2 exercise enhances aerobic efficiency, burning fat for fuel (hence the term fat burn), and improves endurance with moderate intensity. Regular cardio boosts cardiovascular health, burns calories, and strengthens the heart. Both are vital for overall fitness. Walking at a brisk pace where you can just about continue a conversation without losing your breath would be considered Zone 2, while anything more would be considered cardio; anything less than Zone 2 (Zone 1) would be considered movement, which is still valuable to do through the day, but will not help with either fat burn or cardio fitness. While most wearables don’t explicitly report these metrics, you can decipher the fat burn minutes vs. the cardio minutes by looking how many of your exercise minutes (or zone minutes or whatever name your wearable may call this metric) are in Zone 2 vs Zones 3, 4 and 5. During the week, one needs a healthy balance between the two with about 80% to 90% being in fat burn and the remaining in the cardio zone. If you are training for an intense event, these ratios will be different but for most of us, this is a reasonable goal to shoot for.

I have been able to maintain a daily ratio of about 90 fat burn minutes to 20 cardio minutes, with the former happening daily during my work calls, where I pace up and down the room, while the latter mostly happens during soccer on the weekends for about 150 minutes but averages out to 20 minutes per day over the week. It is worth mentioning that even a cardio activity like Tennis, Soccer or Basketball doesn’t keep your heart rate in Zones 3, 4 and 5 throughout the activity because there are periods of walking during which our heart rate drops to Zone 2 or maybe even Zone 1. So it is important to break up all your exercise into the appropriate zones. Note that for most folks, strength training keeps the heart rate below Zone 2 and so although it is exercise, it will not usually show up in these two metrics.

The Rest of the Metrics from Wearables: There are many other metrics reported by wearables, such as the Calories Burned, Light Sleep, Steps, Breathing Rate, Skin Temperature, Oxygen Saturation, VO2 max, etc. While I do look at them from time to time to see if there are any clear trends, I don’t spend too much time on them because they aren’t either very actionable (skin temperature, etc.), aren’t very meaningful (walking 10,000 steps doesn’t have any real scientific evidence to back it), or they aren’t very accurate (e.g. I would rather go do a VO2 max test at a proper facility than rely on what my wearable provides).

Some Non-Wearable Metrics: Although the non-wearable metrics that I consider important deserve a longer post, I will list the important ones here for one to consider tracking. These include: CGM data, Body Fat %, Muscle Mass %, Total Calories Consumed, Carb %, Fat %, Protein %, Fiber %, Time between Last Meal and Bed Time, Intermittent Fasting Time, etc. 

I personally track all my metrics by connecting my wearables (Oura Ring, Fitbit and CGM) and non-wearables (Renpho Health and iHealth BP Monitor) to Apple Health and then feeding those into my GeneClinicX app (a free app on the App Store and Google Play) . I also track my non-wearable metrics directly into the GeneClinicX app that you can use if you want to track your metrics and their trends all in one place. I have found that just tracking these metrics makes one more aware of how our bodies are behaving and responding to our lifestyle. However, it is equally important to not get too obsessed with them where your mental or emotional state of mind for the day gets impacted by the daily numbers. This is a long term play to ensure we keep our bodies and minds healthy as we age, so we truly experience a great health span for whatever lifespan we end up with. 

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