Sleep Trackers, Babies and Nocebos

I often get asked what I think about recovery-tracking wearables like Whoop, Oro etc…

I’m going to answer that question with a little story:

One morning when baby #1 was still very young, I got up for work at my usual time of 5am and was in my kitchen making some coffee.

I’d been doing the night feeds the previous night. At the time my wife and I had a system where we’d alternate who slept each night, so in theory there was at least one functioning adult in the house at any given time (although sometimes we had to add up 75% of an adult and 25% of an adult to make 1).

Baby #1 was at that age where she was old enough to notice if her soother fell out of her mouth and be emotionally devastated, but still too young to reliably grab it and pop it back in by herself. So being “on” for the night was always a bit of a dice roll.

You might have to get up 3 times, or 33 back then. No particular pattern.

As I was stirring my coffee, I noticed I felt pretty good that morning, and was pleased about that.

“I guess I had a decent night’s sleep despite the wake-ups”, I thought, “There must not have been that many”

But then I glanced at my smartwatch and noticed I’d already logged 839 steps between midnight and 5am...

(For context, the crib was about 9 steps away from my side of the bed, and the kitchen where we’d prepare bottles was about 40).

I’ll let you figure out the maths, but the only calculation I made was :

“Well that totally took the wind out of my sails. I’m going to stop wearing a smartwatch”

As it turns out, my intuition was backed up by leading science.

How rested we “feel” doesn't always correspond to exactly how rested we are, because humans are very strange, suggestable animals.

Sneaky researchers have shown that when you tell subjects they slept poorly and show them fancy-looking fake measurements to “prove it”, they do statistically worse on cognitive tests the next day.

It’s an example of what’s come to be known as the “nocebo effect” - the shitty version of a placebo. Instead of a sugar pill that cures your back pain, it’s an irrelevancy that makes you feel worse.

The human brain is the most complicated thing ever found in the history of the entire universe, and we just can’t accurately track and predict the tens of thousands of variables that come together to create the experience of how you feel at any given moment.

Yet these wearable devices typically measure just one (or a small handful) of variables like heart rate, or movement throughout the night and confidently declare “you are X recovered today!”...

...for real?

It’s just not very likely that 1 or 2 measurements can capture something as complicated as your recovery between sessions. Think about how many factors might go into how well you perform today:

There’s your biological state - your hormonal status, your nervous system status, how fed vs fasted you are, your blood sugar levels, your hydration status, circulating levels of amino acids, your current levels of muscle glycogen, how much sleep you’ve had etc etc

There’s your social state - are you in an environment with all your best friends? Or is it 8pm on a Tuesday and you’re the only lonely soul in the gym? Is your favourite song playing on the radio? Is there someone in the room you really want to impress?

There’s your psychological state - is that bit of stiffness in your back making you nervous about deadlifting today? Have you just had a massive fight with your significant other and can’t get your mind on your lifting? Do you have jacked up cortisol levels from worrying about how the hell you’re going to get that project finished in work? Has some stupid wristband told you you that you’re “not recovered” and shouldn’t be lifting today?

And by the way, all of these factors all interact with each other in complex non-linear ways too. It’s a twisted, knotty ball that you probably couldn’t unpick with 6 months and a team of world-class researchers.

You can’t just measure someone’s heart rate and then pretend you’ve accounted for all that.

So what do you do? Ignore the wristband, and defer to reality.

If your wristband says you’re not recovered, but you feel good and your barbell is moving fast, assume you’re fine and get lifting.

If your wristband says you’re 100% recovered, but you feel like complete poop and barely made your last warm-up set, ignore the band and go a bit lighter today.

Your subjective sense of your own recovery is likely to be more accurate than the little band - because you’re taking many more things into account at a subconscious level to arrive at that feeling.

Listen to your body, not your watch.