Accuracy of the Garmin Instinct for Heart Rate Monitoring During Forearm Exercise With and Without Blood Flow Restriction

Authors

Danilo DullasFollow
Clifford SandersFollow
Yahtziri MartinezFollow
Tevin PerezFollow
Alana TuckerFollow
Amelia WolfeFollow
Juni TimminsFollow
Catalina M. Kerwin, Southern Utah UniversityFollow
Kynlee Sperry, Southern Utah UniversityFollow
Cannon JonesFollow
Heather ZentFollow
Sam BrinkerhoffFollow
Setareh ZareiFollow
Jeff Guzman, University of Nevada, Las VegasFollow
Rodolfo I. MejiaFollow
Nathaniel Bodell, California State University - San BernardinoFollow
James W. Navalta, University of Nevada, Las VegasFollow
Merrill FunkFollow
Jeffrey Cowley, Southern Utah UniversityFollow
Marcus M. Lawrence, Southern Utah UniversityFollow

Abstract

Wearable devices are widely used to monitor heart rate (HR) during exercise, but their accuracy under blood flow restriction (BFR) remains uncertain. Because BFR is increasingly applied in rehabilitation and strength training, accurate HR monitoring is essential for both safety and prescription. The PURPOSE of this study was to evaluate the reliability of the Garmin Instinct smartwatch for measuring HR during forearm exercise with and without BFR, compared to a chest-strap criterion device. METHODS: Twenty-three healthy adults (9 females, 14 males; mean age = 24.74 ± 8.19 years) participated in a repeated-measures design. After providing consent and being fitted with the Garmin Instinct, participants completed two exercise protocols: unrestricted and BFR (with one arm randomly occluded at 50% arterial occlusion pressure, using the SmartCuffs BFR device). Each protocol included 5 minutes of rowing warm-up, followed by 1 set of 30 reps and 3 sets of 15 reps of light forearm squeezes, totaling 75 (3/10 effort), and maximal forearm contractions using a handgrip dynamometer. HR was recorded simultaneously with the two identical Garmin Instinct 2 wrist-watches and the criterion Polar H10 chest strap. Data were collected in the Exercise Physiology Laboratory at Southern Utah University (Cedar City, Utah). Validity was assessed with mean absolute percentage error (MAPE; 0.90 strong agreement). RESULTS: For non-BFR trials, the Garmin Instinct showed strong agreement with the criterion for average HR (MAPE = 2.562, Lin’s = 0.957) and maximum HR (MAPE = 3.473, Lin’s = 0.943). Under BFR, validity was maintained for average HR (MAPE = 3.939, Lin’s = 0.920) but not for maximum HR (MAPE = 12.234, Lin’s = 0.937). CONCLUSION: The Garmin Instinct provides valid estimates of average HR during forearm exercise both with and without BFR, but it is less reliable for maximal HR during restricted conditions. Chest-strap sensors remain preferable when accurate maximal HR monitoring is required. These findings have practical implications for clinicians and practitioners implementing BFR training, where precise monitoring of cardiovascular strain is desired. Future studies should evaluate validity during dynamic, whole-body BFR exercise.

Recommended Citation

Dullas, Danilo; Sanders, Clifford; Martinez, Yahtziri; Perez, Tevin; Tucker, Alana; Wolfe, Amelia; Timmins, Juni; Kerwin, Catalina M.; Sperry, Kynlee; Jones, Cannon; Zent, Heather; Brinkerhoff, Sam; Zarei, Setareh; Guzman, Jeff; Mejia, Rodolfo I.; Bodell, Nathaniel; Navalta, James W.; Funk, Merrill; Cowley, Jeffrey; and Lawrence, Marcus M. (2025) "Accuracy of the Garmin Instinct for Heart Rate Monitoring During Forearm Exercise With and Without Blood Flow Restriction," International Journal of Exercise Science: Conference Proceedings: Vol. 14: Iss. 5, Article 2.
Available at: https://digitalcommons.wku.edu/ijesab/vol14/iss5/2