How Accurate is Smartwatch Data and When Do You Need Lab Testing?

Smartwatches have made fitness data more accessible than ever.

A device on your wrist can track your heart rate, steps, sleep, training load and estimated VO₂max throughout the day. For the everyday athlete, this can be incredibly useful for understanding habits and monitoring changes over time.

However, not every number shown by a smartwatch is directly measured.

Many metrics are estimates created using sensor readings, your personal information and algorithms developed by the device manufacturer.

This doesn’t make smartwatch data useless. It simply means you need to understand what the information can, and cannot, tell you.

Smartwatches are useful for monitoring everyday trends. Laboratory performance testing is useful when you need a controlled measurement of a specific aspect of your physiology, movement, or performance.

The question isn’t which one is better. It’s which tool gives you the information you need for the decision you’re trying to make.

What Does a Smartwatch Actually Measure and How Accurate Is Smartwatch Data?

Most modern smartwatches use a combination of sensors to collect information throughout the day.

These may include:

• Optical heart-rate sensors
• Accelerometers that detect movement
• Gyroscopes that detect position and rotation
• GPS for pace, distance and location
• Temperature or blood-oxygen sensors on selected devices

From this information, your smartwatch may provide metrics you’d probably experienced before such as:

• Heart rate
• Steps and daily activity
• Calories burned
• Sleep duration and stages
• Recovery or readiness scores
• Training load
• Estimated VO₂max
• Predicted race times

As mentioned earlier, some of these measurements are closer to what the sensor detects, while others are merely estimates using algorithms. Below are a few common smartwatch metrics and how they differ from laboratory performance testing:

Estimated VO₂max vs Laboratory VO₂max

During a laboratory VO₂max test, you’ll wear a mask connected to a metabolic analyser while exercise intensity gradually increases. The system measures the oxygen consumption and carbon dioxide produced throughout the assessment

Smartwatches, on the other hand, estimate VO₂max using information such as heart rate, running pace, age, and training history.

This means that the laboratory VO₂max test provides a more precise and controlled measurement of your aerobic capacity, while a smartwatch estimate is better suited for monitoring general trends.

Your smartwatch may tell you that your estimated VO₂max is improving, while laboratory testing can help confirm whether your measured aerobic capacity has actually changed.

Heart-Rate Zones vs Physiological Testing

Many smartwatches automatically generate heart-rate training zones using estimated maximum heart rate, your exercise history or proprietary algorithms. If you forget to log a workout or mistakenly log the wrong type that may affect what the device recommends.

These zones can be a useful starting point, but they may not fully reflect how your individual physiology responds as exercise gets harder.

Laboratory VO₂max and Lactate Threshold Testing can provide more individualised information about your response to increasing intensity.

Once your training intensities have been established, your smartwatch becomes useful again. You can use it during your everyday sessions to monitor whether you’re actually staying within those zones.

Estimated Calories vs Resting Metabolic Rate Testing

Your smartwatch estimates calorie expenditure using information such as heart rate, movement and your personal details.

A Resting Metabolic Rate Test, or RMR Test, measures something different: how much energy your body uses while at rest.

During an RMR Test, respiratory gases are analysed to establish a measured resting-energy baseline.

RMR isn’t the same as your total daily calorie expenditure, so the two numbers shouldn’t be directly compared. However, it can provide useful information for nutrition planning, particularly if your goal involves fat loss, muscle gain or body composition.

Running Metrics vs 3D Running Gait Analysis

Depending on the device, your smartwatch may provide running metrics such as:

• Pace
• Cadence
• Stride length
• Ground contact time
• Estimated running power

Advanced running watches from brands such as Apple Watch, Garmin, COROS and Polar can provide some of these metrics directly from the wrist, although the exact data available depends on the model and whether additional sensors are required.

For example, selected Apple Watch, Garmin and COROS models can provide ground contact time and running power, while Polar also offers wrist-based running power on selected watches.

These metrics can be useful for monitoring changes between sessions, but they still provide only part of the picture.

At FORGED by RF, our 3D Running Gait Analysis uses MotionMetrix technology to assess your running mechanics in greater detail.

The assessment can examine areas such as:

• Temporal and spatial stride parameters
• Ground reaction force estimates
• Joint movement and loading
• Running economy based on mechanical work and elastic energy exchange
• More than 60 running parameters across different speeds
• Comparisons against normative data from more than 50,000 runners
• Before-and-after comparisons to monitor changes over time

Our FORGED lab technicians will also review the findings with you and recommend specific drills or areas to work on based on what is observed during your assessment.

How to Use Smartwatch and Lab Data Together

Smartwatches and laboratory performance testing serve different purposes, and the most useful approach is often to use both.

Laboratory testing can establish a controlled baseline for a specific aspect of your performance. Your smartwatch can then help you monitor how your training is progressing between assessments. For example, after completing a VO₂max or Lactate Threshold Test, you can apply the training zones identified during the assessment to your regular workouts and use your smartwatch to stay within the intended intensity.

Over time, your wearable may show trends suggesting that your fitness is improving. However, these trends don’t always tell you exactly how much your underlying physiology has changed.

A rising smartwatch VO₂max estimate, for example, may suggest an improvement in aerobic fitness. Repeating your laboratory VO₂max Test can then provide a controlled comparison to determine whether your measured aerobic capacity has changed.

The same principle applies across performance testing: establish your baseline, apply the findings to your training, monitor your progress and retest when appropriate.

The laboratory gives you the benchmark. Your smartwatch helps you apply it and monitor what happens between tests.

When Should You Consider Laboratory Testing?

• Use your smartwatch for everyday monitoring: Track trends in heart rate, activity, sleep, training load and other metrics to understand how your training changes over time.
• Consider laboratory testing when you need more precise information: Tests such as VO₂max, Lactate Threshold, RMR or 3D Running Gait Analysis can provide controlled measurements when you need to establish a clearer baseline or make more informed training decisions.
• Apply your laboratory results to everyday training: Use your measured training zones or assessment findings to guide your sessions, while using your smartwatch to monitor your training between tests.
• Re-test when you want to objectively measure progress: Repeat relevant assessments after a meaningful period of training to determine whether your measured performance has changed. At FORGED by RF, we generally recommend re-testing every 8–12 weeks, depending on the assessment, training programme and goal.

Conclusion

Smartwatches are valuable because they make training data easy to access every day. They can help you monitor trends, stay consistent and see how your training is changing over time. However, not every metric on your watch is directly measured, and some aspects of performance simply cannot be assessed from the wrist.

That’s where laboratory performance testing becomes useful.

The goal isn’t to replace your smartwatch. It’s to understand where its data is useful, where its limitations are, and when a laboratory assessment can give you information that your wearable cannot.

At FORGED by RF, we make advanced performance testing accessible and practical for every athlete, helping you understand your data and turn it into meaningful next steps.

If you’re unsure whether your smartwatch is giving you enough information for your goals, speak to us and we can help you determine whether laboratory performance testing would add value.