Why Your Apple Watch Sleep Score Might Be Telling a Very Different Story Than Garmin
Garmin approaches human sleep from the perspective of an uncompromising endurance coach. In the flagship Garmin Cirqa, sleep tracking does not exist in an isolated silo. It serves as one input inside an aggressive training readiness score designed to dictate power outputs and interval paces.
Garmin calculates nightly sleep scores by synthesizing sleep architecture, total duration, awake interruptions, and restless moments. But the decisive factor remains the nocturnal HRV baseline. Rather than taking intermittent snapshots, Garmin records heart rate variability continuously from the moment you drift off until you step out of bed. It tracks the root mean square of successive differences (RMSSD) between heartbeats millisecond by millisecond.
Garmin then layers your sleep score on top of acute-to-chronic workload ratios, recovery time countdowns, and daytime stress tracking derived from Firstbeat analytics. If you log seven hours of sleep with decent sleep staging, but your HRV drops four milliseconds below your baseline, Garmin slashes your training readiness score. To Garmin, an elevated resting heart rate combined with depressed parasympathetic tone means muscle tissue and glycogen reserves have not fully restored.
