No More Manual Counts: The HUNDRED Automatic Push-up Rep Counter

The Problem with Manual Rep Counting

Counting push-ups manually is like tracking your finances in your head — technically possible, but the error rate makes it pointless.

When fatigue hits at rep 15, your brain starts bargaining. That shaky half-rep becomes a full rep. You lose count at 23 and generously round up to 25. By the end of the set, the number in your head has almost no relationship to the work your muscles actually did.

Automatic rep counting solves this entirely.

How HUNDRED Counts Your Reps

Setup

Place your iPhone face-up on the floor directly beneath your chest. The app checks that the phone is laid flat using the accelerometer, then activates the front camera and waits for your face to appear in the frame.

Calibration

Before your first rep, the app calibrates by collecting 10 stable frames of your face at the "up" position. This establishes your baseline face size ratio — how large your face appears to the camera at standing push-up height. Calibration takes just a few seconds.

Tracking

As you perform push-ups, your face moves closer to the phone during the descent and farther away during the ascent. The app tracks the size of your face's bounding box in each video frame. When the face ratio exceeds a specific threshold (roughly 2x the baseline), it registers a bottom position.

A moving average of 5 frames smooths out jitter from camera noise and minor head movements, ensuring stable detection even during fast or fatigued reps.

Rep Validation

Not every movement counts as a valid rep. Each rep must take between 0.5 and 10 seconds. Movements faster than 0.5 seconds are likely camera glitches or head bobs. Movements slower than 10 seconds indicate a pause or rest, not a continuous rep.

Why Accurate Counting Matters

HUNDRED doesn't just count reps — it uses those numbers to generate your next workout. The adaptive algorithm takes your validated rep data from each session and calculates appropriate targets for your next workout.

If the data is inflated by 20% due to manual counting errors, the algorithm sets targets that are 20% too high. You fail those targets, the system interprets that as declining performance, and your training spiral becomes counterproductive.

With automated, validated counting, the feedback loop works correctly.

How HUNDRED Compares to Other Tracking Methods

• Manual counting: Free but unreliable. 20–30% error rate during intense exercise.
• Tapping the screen: Disrupts form and doesn't validate depth.
• Smartwatch detection: Can't verify depth or full range of motion.
• Camera-based body pose: Most comprehensive, but requires positioning phone at a distance.

More Than a Counter: A Full Training Ecosystem

HUNDRED isn't just a rep counter. The app provides a complete push-up training system built around accurate data. Your personalized training plan uses the "Grease the Groove" methodology — 4 working sets at tier-appropriate intensity plus an assessment set — generated fresh each day.

The app supports two equipment modes: standard (floor) and push-up board (with color-coded muscle group rotation). Additional features include workout history, performance streaks, a home screen widget, and optional cloud sync for Pro users.

Frequently Asked Questions

Does HUNDRED work on all iPhones?

HUNDRED requires iOS 17.0 or later. It works with any iPhone model that supports this iOS version and has a front-facing camera.

Does it work in the dark?

The front camera needs sufficient light to detect your face. Standard indoor lighting works fine. Very low light may reduce detection reliability.

Is the app free?

The core features — automated rep counting, personalized training plans, and one daily workout — are free. Pro ($3.99/month or $24.99/year) adds unlimited daily workouts, full statistics, cloud sync, and premium sound packs.