Day 51 runs Day 31's session in reverse order, and the reversal is the point. Four 15-second intervals - elbow strike and knee strike on the right, knee strikes on the right, then the same pair on the left - three to seven sets, one minute of rest.
Three weeks ago you built the knee strike first and added the elbow afterwards. Today the combination comes first, while you are fresh, and the isolated knee strikes follow it. That means the fifteen seconds of continuous knees now arrive on a hip flexor that has already been driving through a combination, which is a considerably steeper ask than the same interval was on Day 31. Same two strikes, same two sides, and a harder order of operations.
Elbow across the body at head height, then the knee driving up from the same side while your hands pull down to meet it. On the isolated interval, keep the knees quick and high and rise onto the ball of the standing foot with each one. Guard resets between every rep, both intervals.
The same two strikes you met on Day 31 - stacked in the order that costs you more.
Make it Harder: Alternate sides within the combination interval so the elbow comes from one side and the knee from the other.
Make it Easier: Take the isolated knee strike interval at half pace and put your full effort into the combination.
