Count reps by placing iPhone (facing up) below chest or upper abdomen during push up by using iPhone's proximity sensor.
Alternatively use touch with tip of nose during push ups.

Track your push ups !
Push up sessions and reps are saved and you can view your own push up improvements as you progresses.

Heart rate, energy burned and workout sessions are recorded via Apple's Health Kit if available and permitted.
Start push up sessions with Apple Watch workout for optimal data.

Location and workout session are also saved into records if permitted.

All your sweat are saved into iCloud and achievements integrated with Game center

Do push up daily, increase your upper body strength and health then see your progress improve.
Fitness is like a relationship. You can’t cheat and expect it to work.