Your one rep max is the most weight you can move for one rep. You need to know your one rep max if your training uses percentage progressions. Plugging in your one rep max for each exercise you’ve tested is a good way to get the most out of StrengthMark. This is because there are many features geared for percentage-based strength training.
For instance, say you’re using a deadlift template with these percentages: 5 reps at 40%, 50%, 60%, then 3 reps at 70%, 80%, and 90%. If your deadlift is 400 lbs, this works out to 5 reps at 160, 200, 240 lbs and 3 reps at 280, 320, and 360 lbs. You use this template for one session, but then you increase your deadlift max for the next session. The next time you schedule this deadlift template, your workout will scale to your new deadlift max. An increase of 20 lbs would give approximately: 5 reps at 165, 210, 250 lbs and 3 reps at 295, 335, 375 lbs.
This is a good article with guidelines on how to warm up and test your one rep max for the powerlifting big three. Don’t miss the tips at the end.