Day 29 was the start of week 5, which completely switches up the workout structure. First, it goes back to the lower body starting the week. Second, this uses what Joel hilariously refers to as a "dirty MOFO" format. You only do four exercises in the entire workout, one in each block, front-loaded squats in the first block, sumo deadlifts in the second block, weighted bridges in the third block, and alternating reverse lunges in the fourth block.
The twist is that you ultimately do five sets in each block, and you increase the amount of weight you use in the first three sets and then stay with the heaviest weight for as long as you can in the other two. In each block, the first set is the traditional one-minute set, which you do with your lightest weight. Set two reduces the time to 40 seconds, but you increase the weight, and set three reduces the time to 20 seconds, but you use the heaviest weight. Then, set 4 goes back up to 40 seconds, and you try to stay with the heaviest weight. Set five is another one-minute set. Three of the four exercises are performed using a 1x3 tempo, one second up, three seconds down. The sumo deadlifts do not use a tempo.
Ultimately, this is a very challenging workout that has a huge cardio effect. There is almost no break between the sets at all, and a minimal break between each block. If anyone is old enough to have done the old Body-For-Life workouts, this format is similar in terms of going up and down in weight as you reduce the number of reps you do, but is different in that once you reach the heaviest weight, you try to stick with it instead of dropping back to a lighter weight unless you absolutely have to.