Should You Trust Your Smartwatch?

Four commonly available smartwatches were compared against gold-standard measuring devices to determine their accuracy during both endurance and resistance exercise. Heart rate measurements were generally comparable to electrocardiography (ECG) across devices, though accuracy varied by brand during resistance training. Energy expenditure estimates, however, were poor across the board. So, should you trust your smartwatch data? Let's see what this article tells us.

Overview

• What did they test? Sixty-two healthy men completed standardized endurance and resistance exercise while wearing four different smartwatches (Apple, Galaxy, Fitbit, and Garmin). Gold-standard measures of heart rate (ECG) and energy expenditure (indirect calorimetry) were also recorded for comparison.
• What did they find? During endurance exercise, they found that heart rate measurements from all smartwatches were comparable with ECG. During resistance exercise, although accuracy was high, only Apple Watch showed no significant difference from ECG. For energy expenditure, there was limited accuracy across all four devices during endurance exercise, and they performed even more poorly during resistance training.
• What does it mean for you? Smartwatches are useful for monitoring heart rate, whether tracking intensity on a run or watching how it responds between sets in the gym. But you shouldn’t trust their calorie calculations. If you're using their energy expenditure numbers to inform nutrition or fat loss decisions, treat them as rough trends at best, not figures to plan your calorie intake around.

What’s the Problem?

Wearable technologies were identified as the leading global fitness trend in 2025 1. One such device that is commonly used is the smartwatch. They use built-in technology to track, or estimate, a range of health and fitness-related metrics, such as heart rate, sleep, energy expenditure, steps, and more. Given their widespread use, including use as a tool in the management of chronic diseases 2, it is important to understand the accuracy of these tools.

Purpose

This study aimed to evaluate the validity of smartwatch-derived heart rate and energy expenditure measures when compared with gold-standard reference measures during standardized endurance and resistance exercise.

Hypothesis

No specific hypothesis was stated by the authors.

What Did They Test and How?

Participants

Sixty-two healthy men completed the study. They were aged 26.55 ± 4.21 years, 175.08 ± 5.22 cm tall, and weighed 73.29 ± 7.81 kg, with a body fat mass of 13.49 ± 4.14 kg. Eligibility criteria for the study included having a body mass index (BMI) ≤ 25 kg/m², and having no concerns that may impact participation in exercise, such as musculoskeletal or cardiovascular conditions.

Study Procedures