Why You Shouldn’t Use Your Wearable to Judge Your Workout - and What It Can Tell You
If you’ve ever finished a workout, checked your Apple Watch or Oura Ring, and thought, “Only 420 calories? I need to do more!” - you’re not alone.
Wearables have become a part of daily life for many of us. They buzz when we sit too long, cheer us on when we close our rings, and flash our calorie burn like it’s a badge of honour. But here’s the truth: using that calorie-burn number as a measure of how “good” your workout was is a bad idea.
Let’s unpack why - and what these devices actually do well.
1. Chasing “calories burned” can work against you
It might sound logical that the more calories you burn, the faster you’ll reach your goals. But the body doesn’t quite work that way.
When you push to burn more and more energy, your body adapts. It often:
Reduces other activity during the day because you’re more tired (so you move less overall).
Increases hunger, driving you to eat more.
Pulls energy away from recovery, making it harder to build muscle and bounce back between workouts.
So while your watch might show a big number, your body is quietly balancing the books elsewhere. Burning more calories in the gym doesn’t always mean faster fat loss - in some cases, it can slow things down.
2. Wearables are wildly inaccurate at estimating calorie burn
This is where the science gets interesting.
Multiple studies have shown that most popular wearables - Apple Watch, Fitbit, Garmin, Polar, Oura, you name it - do a decent job of tracking heart rate, but a terrible job at tracking energy expenditure.
Research from Stanford University found that while heart-rate readings were within about 5% of true values, calorie estimates were often off by 20–75%. Other reviews show similar results, depending on activity type and intensity.
That means if your device says you burned 500 calories, it could easily be 300 - or 800.
So if you’re using that number to decide how much you can eat or whether your session “counted,” you’re basing those choices on a guess.
3. Exercise is only one part of the fat-loss puzzle
Your total daily energy expenditure (TDEE) comes mostly from:
Basal metabolic rate (BMR): the energy needed just to keep you alive (around 60–70%).
Non-exercise activity (NEAT): all the little movements throughout the day (about 15–25%).
The thermic effect of food (TEF): the energy cost of digesting and processing food (5–10%).
Exercise activity (EAT): usually the smallest slice of the pie.
So while exercise is incredibly valuable for strength, health, and longevity, it’s not the biggest driver of calorie burn. That’s why focusing purely on “burn” distracts from the real benefits of training — becoming stronger, more capable, more resilient.
4. Better questions to ask after your workout
Instead of asking “How many calories did I burn?”, try asking:
Did I lift heavier or move better than last week?
Did I finish feeling challenged but not destroyed?
Did I sleep well and recover properly?
Am I consistently showing up?
These questions lead to results. The calorie number does not.
What wearables can be great for
Before you toss your Apple Watch in frustration, let’s be clear: wearables can be incredibly useful - when you use them for the right things.
✅ Sleep tracking: Most modern devices are fairly accurate at estimating total sleep time and sleep/wake patterns. They can help you spot trends, like how stress, caffeine, or late workouts affect your rest.
✅ Heart-rate tracking: For steady-state cardio or recovery monitoring, wearables can provide valuable feedback on effort and consistency.
✅ Step counts: Not perfect, but still a good motivator to keep you moving more throughout the day.
✅ Recovery & readiness: HRV (heart-rate variability) and “readiness” scores can help you see when you’re under-recovered or stressed, prompting you to adjust intensity.
✅ Habit awareness: Even if the numbers aren’t exact, tracking movement, rest, or standing time builds awareness - and awareness drives behaviour change.
The takeaway
If your wearable motivates you to move, sleep, and take better care of yourself - fantastic. But don’t give that calorie-burn number too much power. It’s an estimate at best, and a distraction at worst.
Focus on getting stronger, moving consistently, fuelling your body well, and recovering deeply. That’s where real progress lives.
Disclaimer: This blog provides health, fitness, and nutritional information and is designed for educational purposes only. You should not rely on this information as a substitute for, nor does it replace, professional medical advice, diagnosis, or treatment. If you have any concerns or questions about your health, you should always consult with a physician or other health-care professional. Do not disregard, avoid, or delay obtaining medical or health-related advice from your health-care professional because of something you may have read on this site. The use of any information provided on this site is solely at your own risk.
