This is one of my favorite routines to perform (most of the time "attempt" is the correct word) when I need to diversify my push up routine or challenge myself.
This is called a pyramid due to the nature of the increase/decrease of repetitions (rep(s)).
1. Start in a push up position with your core engaged, and your glutes and thighs tight. This will protect the spine and prevent you from "sagging" at the waist.
2. Perform 1 push up rep and, while staying in a push up position, count 5 seconds.
3. Perform 2 push ups and repeat the 5 second count.
4. Continue in this manner all the way to 11 reps, and then back down to 1 rep.
5. A true test of strength and mental toughness is to resists resting in any other position other than the push up position. This means no piking, no shaking the arms out, no upward dog, no downward dog, etc.
Good Luck! I look forward to reading the comments below!!