Slog: Zone 2 Cardio

Slog — Zone 2 cardio you can glance at, not squint at.

Just say "Hey Siri, Start Zone 2." A workout begins. Your wrist turns green when you're in Zone 2, blue when your heart rate is too low, red when it's too high. That's the entire app. No reading numbers mid-stride.


HOW IT WORKS

1. Voice start. No tapping, no menus. Say "Hey Siri, Start Zone 2" from across the room.
2. Glance for color. Full-screen color tells you what to do — speed up, slow down, or hold steady. No squinting at a heart-rate number while running.
3. End when you're done. Workouts save to Apple Health and count toward your Fitness rings.


WHY ZONE 2

Zone 2 is sustained aerobic work at 60–70 percent of your max heart rate — what exercise physiologists call conversational pace. It's the foundation of cardiovascular fitness, supported by decades of research and recommended by the American Heart Association.

The catch: it's hard to stay in Zone 2 without a tool. Most apps bury heart rate behind charts and zones 1 through 5. Slog shows you one thing — are you in Zone 2 or not — and gets out of the way.


WHAT'S IN (THE WHOLE APP)

— Voice-activated workout via "Hey Siri, Start Zone 2"
— Full-screen color UI: green, blue, red, gray
— Heart rate displayed as a fallback number
— Elapsed time
— Auto-calculated Zone 2 from your age in Apple Health, or set manually
— Workouts saved to Apple Health and Apple Fitness rings
— Watch face complication for one-tap launch
— Haptic taps when you cross zone boundaries


ON YOUR IPHONE

Your phone is the treadmill console. During a watch workout, Slog on iPhone mirrors your heart rate live — a big number, a full-screen color, and your elapsed time, readable from feet away. Afterwards, History shows every session with time in Zone 2 and your weekly minutes against the 150-minute aerobic target. Set your range once in Zones (age-based, or Karvonen if you know your resting heart rate) and sync it to your watch with one tap.


WHAT'S NOT IN (INTENTIONALLY)

No multi-zone display. No splits, no intervals, no audio cues, no Strava bridge, no chest-strap pairing. Saying no is the product.


PRIVACY

Heart rate stays on your device. There's no account, no servers, no analytics, no tracking. Slog reads from Apple HealthKit and writes your workouts back to it. That's it.


PRICING

Free.