JMIR Publications

ABSTRACT

Background:

Photoplethysmography (PPG)–based smartwatches are increasingly used for continuous heart‑rate (HR) monitoring. Their accuracy has been demonstrated at rest or during low‑intensity activity, but data are scarce for maximal‑intensity exercise, when motion artefacts and rapid hemodynamic changes can degrade the PPG signal. Validating these devices under such demanding conditions is essential before they are applied to clinical exercise testing, athletic training, or remote health monitoring.

Objective:

The primary aim of this study was to evaluate the validity of the Samsung Galaxy Watch 6 (GW6) in estimating HR throughout a graded, maximal ramp cardiopulmonary exercise test (CPET) performed on a treadmill. A secondary aim was to explore whether measurement error varies across five predefined intensity zones (50–60 %, 60–70 %, 70–80 %, 80–90 %, and 90–100 % of the maximum HR determined individually for each participant).

Methods:

Fifty‑five healthy adults (30 men, 25 women; mean ± SD age = 30.3 ± 8.2 years) completed a symptom‑limited incremental treadmill protocol to volitional exhaustion. Simultaneous HR recordings were obtained from the GW6 (left arm) and a Polar H10 chest‑strap monitor, which served as the reference standards. For each intensity zone, the following agreement indices were computed: intraclass correlation coefficient (ICC), typical error of measurement expressed as a percentage of the mean (TEM %), and mean absolute percentage error (MAPE %). Bland–Altman analysis was performed to quantify the mean bias and 95% limits of agreement (LoA) between the GW 6 and the Polar H10. Statistical significance was set at p < 0.05.

Results:

Across the five intensity zones, GW6 HR values were consistently lower than the criterion Polar H10 values (Table 2). The ICC ranged from 0.49 (80–90 % HRmax, 95 % CI 0.26–0.67) to 0.70 (50–60 % HRmax, 95 % CI 0.54–0.81), indicating poor to moderate relative agreement. TEM increased with workload, from 2.97 bpm (95 % CI 2.50–3.66) at 50–60 % HRmax to 6.25 bpm (95 % CI 5.26–7.70) at 80–90 % HRmax; TEM % values were consistently low across all intensity zones (2.9 %–4.2 %). MAPE values were modest throughout, decreasing from 3.7 % ± 3.9 % at the lowest intensity zone to 1.9 % ± 3.7 % at 90–100 % HRmax. Bland–Altman analysis showed that the GW6 consistently underestimated HR compared with the Polar H10, with an overall mean bias of −2.67 bpm and wide limits of agreement (−16.90 to 11.57 bpm). This negative bias was present across all heart rate zones, with no proportional bias detected. Agreement was adequate for group-level comparisons but displayed substantial individual variability.

Conclusions:

The Samsung GW6 provides a good degree of validity for HR monitoring during maximal treadmill CPET in healthy young adults. Although measurement error increases modestly at near‑maximal workloads, absolute errors remain well within clinically acceptable thresholds. These findings support the potential use of GW6 as a convenient, non‑invasive alternative for HR tracking in laboratory‑based exercise testing.