Sleep Score
The Sleep Score quantifies the quality of your previous night's sleep on a 0–100 scale, based on sleep stages, total duration, awakenings, regularity, and sleep efficiency.
The science of sleep and recovery
Sleep is the single most important recovery tool available to athletes. During sleep, the body repairs muscle tissue, consolidates motor learning, regulates hormones (including growth hormone and cortisol), and restores autonomic nervous system balance.
Sleep is not uniform — it cycles through distinct stages throughout the night, each with different physiological roles:
Deep Sleep (Slow-Wave Sleep)
The most physically restorative stage. Human growth hormone is primarily released during deep sleep, driving tissue repair and immune function. Athletes who obtain more deep sleep show faster recovery and reduced muscle damage markers.
REM Sleep
Critical for cognitive function, emotional regulation, and motor learning consolidation. Athletes require adequate REM sleep to consolidate technical skills and maintain mental performance.
Core Sleep (Light Sleep)
Accounts for the majority of sleep time. While lighter, it serves as the transitional stage that enables cycling between deeper stages. Excessive light sleep at the expense of deep and REM sleep indicates fragmented or disrupted sleep.
What Flux analyses
Flux reads your sleep staging data from Apple Health — provided by your Apple Watch or a compatible third-party app — and evaluates five key dimensions:
Sleep Stages
The composition and balance between deep sleep, REM sleep, and light sleep. Flux analyses how well your sleep is distributed across all stages for optimal physical and cognitive recovery.
Total Sleep Duration
The total time spent asleep. Flux targets approximately 8–9 hours as the reference range for active athletes, with a penalty applied when duration falls significantly below the target.
Awakenings
The number of times you wake during the night. Each awakening interrupts sleep cycling and reduces overall sleep quality. Flux applies a penalty for frequent or prolonged awakenings.
Sleep Regularity
The consistency of your sleep timing and duration across nights. Regular sleep patterns optimize recovery and support healthy autonomic nervous system function.
Sleep Efficiency
The ratio of time asleep to total time in bed. Higher efficiency indicates more consolidated, uninterrupted sleep and contributes positively to the score.
Sleep Need
Beyond scoring last night's sleep, Flux also calculates your personalised Sleep Need — the number of hours you should aim for tonight. This takes into account:
- Your age and biological sex (baseline sleep requirement).
- Your Strain Score from today — harder training days require more sleep.
- Accumulated sleep debt from the past two weeks — nights of short sleep create a cumulative deficit that must be gradually repaid.
Interpreting your Sleep Score
High proportions of deep and REM sleep, few awakenings, and sufficient duration. Your body has likely recovered well overnight.
Solid sleep quality with minor compromises. Recovery has occurred but there is room for improvement.
Significant sleep disruption or insufficient duration. This will likely impact your Recovery Score and next day performance.
Tips for better sleep quality
- Keep a consistent sleep and wake time — even on weekends.
- Keep the bedroom cool (16–19°C / 61–66°F) to promote deep sleep.
- Avoid screens and bright lights for 60–90 minutes before bed.
- Limit caffeine after 2 pm; alcohol significantly reduces REM sleep.
- Avoid intense exercise within 2–3 hours of bedtime.
- Use the Sleep Need feature to guide your target bedtime each night.