Plank Timer: Core & Form Check

Turn boring plank holds into a "keep your form" game. Place your phone on your lower back (or in your pocket) and the accelerometer detects posture breaks instantly.

◆ Real-Time Sag Detection
・Calibrate once in proper plank position before starting
・Monitors tilt; instant beep, vibration, and red flash when hips drop or butt rises
・Counts only "perfect form" seconds as valid time. Cheating seconds are excluded

◆ Form Quality Summary
・Shows best time plus break count and hold rate (%)
・Review break moments via waveform to see where form failed

◆ Records, Bests & Streaks
・Update personal bests with net hold time; track daily streaks
・Screen stays on during training; zero fullscreen ads
・Adjust sensitivity from lenient to strict

Honest note: This is a placement-dependent basic check, not medical-grade. Auto-switches to stopwatch if phone can't be placed on lower back. Fully offline, on-device processing, no data sent externally (privacy-safe).