Sleep quality (not just duration) significantly affects training adaptation, body composition, mood, and immune function. Tracking with wearable (Apple Watch, Garmin, Oura, Whoop) reveals patterns most users don't notice.
What to track
Total sleep duration. Deep sleep percentage. REM sleep. Wake-ups during night. Sleep latency (time to fall asleep). Trends over weeks.
Most users discover their sleep is worse than they thought. Adjustments — earlier bedtime, cooler bedroom, no screens — produce measurable improvements.