I've had this conversation at least 500 times:
"CJ, my watch says I burned 800 calories today, but I'm still not losing weight. What's going on?"
Here's what I tell them:
Your watch is lying to you.
Not intentionally. Not maliciously. But those numbers you're obsessing over? They're estimates. And sometimes, they're way off.
I'm not anti-technology. I wear a fitness tracker. My clients wear them. They're useful tools. But if you're making decisions based on those numbers without understanding what they actually mean, you're setting yourself up for frustration.
So let's break down what your fitness tracker is actually telling you—and what it's getting wrong.
Calories Burned: The Biggest Lie
Let's start with the big one: calories burned.
Your watch says you burned 600 calories during your workout. Feels good, right? Now you can eat an extra meal, right?
Wrong.
Here's the problem: Your fitness tracker estimates calories burned using a formula based on:
- Your heart rate
- Your age, weight, height, and sex
- Movement data from accelerometers
But here's what it DOESN'T account for:
- Your actual fitness level – A trained athlete burns fewer calories doing the same workout as a beginner because their body is more efficient
- Muscle mass – More muscle = higher metabolism, but most trackers don't know your body composition
- Exercise type – Lifting weights spikes your heart rate but burns calories differently than running
- Your unique metabolism – Some people burn more, some burn less. Your tracker doesn't know which one you are
The research backs this up: Studies show fitness trackers can overestimate calorie burn by 20-40%. Some trackers are worse—off by 50% or more.
That "600 calories burned" might actually be 350. Or 450. Or 750. You don't know.
What This Means for You
If you're "eating back" the calories your tracker says you burned, you might be eating way more than you think. And that's why you're not losing weight.
Here's what I tell my clients:
Use the calorie number as a trend, not an absolute truth. If your tracker says you burned 600 calories today and 300 yesterday, you probably did more activity today. But don't treat that 600 as gospel.
Heart Rate: More Accurate, But Still Flawed
Heart rate tracking is one of the better features on fitness trackers. Most wrist-based trackers are 90-95% accurate compared to chest strap monitors.
But here's where people mess up:
They think higher heart rate = better workout.
Not true.
Your heart rate tells you intensity, not effectiveness. Just because your heart rate is 170 bpm doesn't mean you're getting a better workout than someone at 140 bpm.
Context matters:
- Lifting heavy weights – Your heart rate might spike, but you're resting between sets. Total calorie burn is lower than cardio, but you're building muscle (which increases metabolism long-term)
- Steady-state cardio – Your heart rate stays elevated, burning more calories during the session, but less muscle-building benefit
- HIIT – Heart rate spikes and drops repeatedly. Great for conditioning and calorie burn, but hard to recover from
The point: Don't chase a heart rate number. Chase progress in your lifts, endurance, or body composition.
Resting Heart Rate: This One's Actually Useful
One metric that IS worth tracking: resting heart rate (RHR).
Your resting heart rate is how many times your heart beats per minute when you're completely at rest (like first thing in the morning).
A lower RHR generally means better cardiovascular fitness. As you get fitter, your heart gets stronger and doesn't have to work as hard to pump blood.
What's normal:
- Average adult: 60-100 bpm
- Active/fit adult: 50-70 bpm
- Elite athlete: 40-60 bpm
If your RHR is trending down over weeks/months, you're getting fitter. If it's trending up, you might be overtraining, stressed, or getting sick.
This is one of the most reliable metrics your tracker gives you. Use it.
Steps: Better Than Nothing, But Not the Full Picture
10,000 steps a day. Everyone's obsessed with it.
Here's the truth: 10,000 steps is arbitrary. It was a marketing number from a Japanese pedometer company in the 1960s. Not based on science. Just a catchy goal.
That said, tracking steps is useful. Not because the number is magic, but because it gives you a baseline for daily movement.
What I care about more than step count:
- Are you more active today than you were last month?
- Are you moving consistently throughout the day?
- Are you hitting your step goal most days without stressing about it?
If you're getting 8,000 steps a day and feeling great, that's better than forcing 10,000 and hating it.
Also: Not all steps are equal. Walking 10,000 steps at a leisurely pace burns fewer calories than walking 7,000 steps uphill or at a brisk pace. Your tracker counts them the same.
Sleep Tracking: Helpful, But Take It With a Grain of Salt
Most fitness trackers now track sleep. They tell you how much deep sleep, REM sleep, and light sleep you got.
Here's the problem: They're not that accurate.
Fitness trackers estimate sleep stages based on movement and heart rate. But the gold standard for measuring sleep is a polysomnography (PSG) test—the thing they do in sleep labs with electrodes on your head.
Your watch can't do that. It's guessing.
Studies show fitness trackers are decent at telling you how long you slept, but they're not great at telling you what kind of sleep you got.
What I tell clients:
Use sleep tracking to spot trends, not absolute truth. If your tracker says you got 4 hours of sleep and you feel like garbage, you probably didn't sleep well. If it says you got 8 hours and you still feel tired, maybe the quality wasn't great—or maybe you're overtraining, stressed, or need more recovery.
Don't obsess over the exact breakdown of deep vs. light sleep. Focus on: Are you consistently getting 7-9 hours? Do you feel rested?
Stress and Recovery Scores: Interesting, But Not Magic
A lot of trackers now give you a "readiness score" or "stress level" based on heart rate variability (HRV), sleep, and activity.
HRV is actually legit. It measures the variation in time between heartbeats. Higher HRV generally means your body is recovered and ready to train hard. Lower HRV means you're stressed, fatigued, or need rest.
But here's the catch: HRV is highly individual. My "good" HRV might be your "bad" HRV. You can't compare your numbers to anyone else's.
And fitness trackers measure HRV differently, so even comparing your Apple Watch score to your friend's Whoop score is pointless.
How to use it:
Track YOUR baseline over time. If your HRV is consistently lower than normal, consider taking a rest day or doing lighter training. If it's higher, you're probably recovered and can push hard.
But don't let your watch tell you NOT to train if you feel great. And don't force yourself to train hard if the watch says "go" but your body says "no."
You know your body better than your watch does.
So What Should You Actually Do With All This Data?
Here's my advice after 13 years of watching clients obsess over their trackers:
1. Use Your Tracker for Trends, Not Absolutes
Don't obsess over individual workouts or single days. Look at patterns over weeks and months.
- Are your steps trending up over time?
- Is your resting heart rate going down as you get fitter?
- Are you sleeping more consistently?
That's what matters. Not whether you hit exactly 10,000 steps today.
2. Don't Eat Back Your "Calories Burned"
If weight loss is your goal, do not eat back the calories your tracker says you burned. It's probably overestimating.
Instead, set your calorie target based on your total daily energy expenditure (TDEE) and stick to it—regardless of what your watch says.
3. Listen to Your Body First, Your Watch Second
If your tracker says you're recovered but you feel exhausted, take a rest day. If your tracker says you need rest but you feel great, train.
Technology is a tool. It's not your coach. You are.
4. Focus on What Actually Matters
At the end of the day, these are the metrics that actually drive results:
- Are you lifting heavier weights over time?
- Are you getting stronger and more conditioned?
- Are you sleeping 7-9 hours most nights?
- Are you hitting your protein target?
- Are you consistent with training?
Those are the things that matter. Not whether your watch says you burned 587 calories or 612.
The Bottom Line
Fitness trackers are useful. I'm not telling you to throw yours away.
But treat the data for what it is: estimates and trends, not absolute truth.
Your watch doesn't know your metabolism, your muscle mass, your stress levels, or how you actually feel. It's guessing based on formulas that work for the average person—and you might not be average.
Use your tracker as one data point. But don't let it control your decisions.
Track progress through:
- Strength gains in the gym
- How your clothes fit
- Energy levels throughout the day
- Consistency with training and nutrition
Those are the metrics that actually matter.
Your tracker is a tool. Not a guru.
— CJ Critney
Owner, FYTS Fitness | Westlake Village, CA
"Technology should support your training, not control it. Trust your body first."