Rules
1 grace day per month
Fail if you miss 2 days consecutively (grace doesn’t count as a miss for failing).
Hold substitute: If you can’t do reps, swap to a hold (plank / wall sit / hollow hold).
1 rep = 5 seconds of holding.
50 reps = 4:10 total hold · 100 reps = 8:20 total hold.
Break it into as many sets as needed and rest as long as required between sets.