O2 — Breath Hold Trainer

Train your breath like a professional freediver. O2 is a science-based breath-hold training app that helps you extend your breath-hold time, build CO₂ tolerance, and improve mental focus through progressive training protocols. PROVEN TRAINING METHODS • CO₂ Tables — Build carbon dioxide tolerance with decreasing rest intervals • O₂ Tables — Extend breath-hold capacity with increasing hold times • Box Breathing — The 4-4-4-4 technique for stress relief and focus • Progressive difficulty levels from beginner to advanced BUILT FOR PERFORMANCE • Designed for freedivers, spearfishers, swimmers, surfers, and athletes • Used by professionals to prepare for competition and improve underwater performance • Backed by established breath-hold training science SMART TRAINING EXPERIENCE • Haptic feedback guides you through each phase without looking at the screen • Voice cues announce hold and breathe phases • Visual timer with clear phase indicators • Track your progress with detailed statistics HEALTH INTEGRATION • Sync workouts to Apple Health • Track your training consistency • Monitor progress over time SIMPLE & FOCUSED • Clean, distraction-free interface • No subscriptions — one-time purchase unlocks everything forever • Works offline, anywhere • Family Sharing supported Whether you're training for freediving competitions, improving your surf hold-downs, or simply want to experience the mental clarity that comes with breath control — O2 gives you the tools to progress safely and effectively. Start your breath-hold journey today.