About
Crescendo 4×4 is an iOS and watchOS interval timer and training coach built around the scientifically validated Norwegian 4×4 cardio protocol (four 4-minute intervals at 85–95% maximum heart rate with 3-minute active recoveries).
While traditional interval timers drop users immediately into full 4-minute intervals, Crescendo introduces an eight-rung progressive ladder starting with intervals as short as 30 seconds (Base Camp: 4 × 30s) to allow cardiovascular adaptations before reaching the full protocol.
Key Features:
- Progressive 8-Rung Ladder: Structured progression starting at Base Camp (4 × 30s) scaling up to the full Norwegian 4×4 (4 × 4:00).
- Screen-Locked Audio Coaching: Voice prompts guide warm-up, interval transitions, and recovery turns while ducking background music or podcasts.
- Heart Rate Zone Targeting: Automatically calculates 85–95% HRmax target zones based on age (Tanaka formula) or Apple Health metrics, with manual override support.
- VO₂max-Informed Starting Suggestion: Evaluates Apple Health cardiovascular trends to suggest an appropriate initial ladder rung without forcing user selection.
- Standalone Apple Watch Workouts: Push customized interval sessions directly to paired Apple Watch devices.
- Apple HealthKit Integration: Workouts and active calories write directly back to Apple Health.
- Privacy-First: All workout and health data remains strictly on-device; no accounts, no telemetry, and no advertising.