Use a smartwatch by all means, but take its data with a large pinch of salt

The best triathlon watches are great at many things: recording all manner of activities; guiding you with turn-by-turn directions; letting you perform contactless payments and stream music to name a few. 

Remarkably the manufacturers of these wrist-worn devices costing several hundred dollars also claim they can perform the function of medical devices costing multiple times more. 

That sounds too good to be true and probably is. Academic studies comparing the measurements of smartwatches to bespoke scientific tech have generally found their accuracy wanting.

I’ve tested and reviewed multisport watches, and still use the Suunto Race to record runs, rides, hikes and strength training. But when I’m not tracking an activity, it stays on the shelf, not on my wrist. 

Here’s why I think you should consider doing the same. 

Health and wellness data issues 

Many smartwatch users wear their device overnight to track their sleep duration and quality despite research casting doubt on their data.

A 2023 study into the accuracy of consumer sleep trackers, including the Fitbit Sense 2 and Google Pixel Watch, concluded that wearables generally overestimate sleep duration although they are better at registering deep sleep stages. And they did seem to be a superior solution to ‘nearables’ or motion-sensor sleep trackers.

To track your sleep more accurately, consider an Oura Ring, which the academics found detected sleep stages more reliably. This is potentially because it tracks body temperature and circadian not just body motion, which can cause the device to mistake periods of motionless wakefulness for sleep. We’ve reviewed a close competitor to the Oura, the Ultrahuman Ring Air. 

The saying that ‘what’s measured can be improved’ usually holds. When it comes to sleep, some experts are concerned that it can lead to orthosomnia, where the desire for perfect sleep produces anxiety surrounding it. 

In light of this, why not just manually record an estimate of how well and long you’ve slept in your physical or digital training log, or simply postpone demanding workouts if you haven’t been sleeping well. 

As part of their ‘24/7 health and wellness tracking’, smartwatches are claimed to measure much more than sleep. It sounds implausible that they can perform functions you’d usually visit a laboratory or doctor’s surgery for. 

Academic research backs up my scepticism with regards to blood pressure and pulse oximetry. So a smartwatch doesn’t seem to be a replacement for medical-grade equipment or regular doctor’s check-ups. 

Fitness estimates versus proper testing 

Another thing many multisport watch owners like to use their devices for and probably shouldn’t is fitness measurement. 

Principally you see this with Functional Threshold Power estimation. In fairness to brands whose watches incorporate this feature, they call it an estimate and include pre-loaded protocols so you can test it properly.

However, I’ve known several cyclists who take this estimate as gospel. Granted, they tend to be sort who only brag about their FTP instead of using it to set training zones for structured training. But since FTP is itself an approximation of lactate threshold and varies day to day, you’re on shaky physiological ground if you base anything on a watch’s educated guess. 

In my experience, smartwatches and bike computers’ estimation of my FTP and VO2 max always indicates I’m a far better athlete than I am. So forget the ego and do a well controlled field test or stump up for a lab test. 

Interestingly though, smartwatches displayed higher accuracy when estimating running race times, so they could help you devise a pacing plan for your triathlon run leg. Obviously bear in mind you’ll have swum and biked beforehand. 

No substitute for a dedicated sensor 

Quite often smartwatches purport to be able to fulfil the role of an expensive sensor developed to track a complex metric.

Running power is among the most egregious of these. Widely regarded as the best in its class although not perfect, the Stryd Running Power Meter estimates running power from the laces of your running shoes to give a better indication of your effort than speed and heart rate. 

Crucially Stryd claims its device takes wind into account, so in theory it knows if you’re holding a steady power into a headwind but moving slowly. 

Smartwatches’ running power measurement can’t record wind speed though and rely on local weather data, which should reduce the accuracy of their data. 

The way in which smartwatches estimate hydration status is similarly flawed. How much you’ve sweated in a session is simple to estimate by weighing yourself before and after. You also have to take in account fluid intake and potential urination loss. 

If knowing more detail about your sweat and electrolyte loss is important you can take a sweat test (Precision Fuel and Hydration do them) or buy a hydration sensor from Flowbio, for example.

In short, as with my other points, don’t think a non-specialist device can replace one made for the job. It sounds too convenient to be true and probably is.