VO2 Flow: Norwegian 4x4 Timer

VO2 Flow is built for the Norwegian 4x4 protocol, the research-backed interval method athletes use to raise VO2max. Four 4-minute intervals at 90 to 95% max heart rate, with 3-minute recoveries. Studies show a 10% VO2max increase in 8 weeks. Run Norwegian 4x4 or build your own protocol. Tabata. 10x1. 8x2. Any work and rest combination, any number of rounds. Free in the app: - Norwegian 4x4 protocol built-in and ready to start - Workout history, every completed session logged and grouped by month - One custom interval profile - Apple Music integration, album art and controls during your session - Audio cues and haptic feedback on every phase transition - Keep screen awake during workouts - Landscape and portrait support Pro upgrade, $4.99 one-time: - Remove all ads forever - Unlimited custom interval profiles - Achievement badges, 7 milestones you can share - Every future Pro feature, no subscription This is a timer, not a fitness platform. No social feed. No subscription. No complexity. Launch, pick a profile, start.