Abstract Summary/Description
Wearable fitness devices use photoplethysmography (PM) which emits and receives light to determine blood volume changes. Evidence shows that blood flow can be altered with sustained muscular contractions, such as resistance training, which could affect the validity of the devices. PURPOSE: To determine the HR validity of a PM device during sustained high force contractions of the wrist and finger flexors. METHODS: Fourteen subjects (10 male, 4 female) completed five protocols of either sub-maximal (15%, 35% or 55% MVC) muscular contractions of the forearm or blood pressure cuff inflation (50 mmHg or 150 mmHg) on the upper arm while cycling at 60 RPM. For each protocol subjects cycled for 1 minute (U1), then simultaneously had increased resistance (maintaining cadence) and performed the muscular contraction or cuff inflation for 30 seconds (R+G). Subjects then maintained cadence for an additional 1 minute with resistance (R) and 1 minute without resistance (U2). Subjects wore 5 devices, two on the experimental wrist/arm, two on the control wrist/arm, and an electrode chest strap (criterion). Raw data was extracted and temporally aligned with criterion for analysis. RESULTS: Mean Absolute Percent Error (MAPE) was calculated for each protocol and the specific stages within each protocol. MAPE at the wrist location was highest during the R+G and R phases, 13% and 19%, respectively. CONCLUSION: HR validity of PM devices is negatively affected at the wrist location during the sustained high force contractions and for up to 1 minute after cessation of the contraction.
