With post-fatigue you are starting with the compound movement and then perform the isolation movement. This allows you to fully stimulate the target muscle, but doesn’t affect the amount of weight you use on the bigger exercise.
You perform 2 exercises for a single muscle group back to back; first a compound lift, and secondly an isolation lift with limited rest in between sets. The aim is to wear down a large muscle group with heavy weights, and finish while it is fatigued with an isolation lift.
A post-exhaustion superset is a serious workout for intermediate and advanced trainers, it should not be attempted by someone who has been training less than a year. The reason is you are causing muscle damage using compound movements with supersets, using an isolated movement working in the 5-7 rep range to target the larger fast twitch fibres.
This post exhaustion superset training should be used by people who have already increased their lean body mass from weight training by at least 20 pounds. Also someone who is capable of correct form and knows how to eat correctly.
Below is what a good post-exhaustion superset workout would look like. You should use compound movements to first reach the point of exhaustion before moving onto an isolated movement to completely exhaust the targeted muscle.
The recommended tempo 2-1-2 means that the weight is lifted or pulled concentrically for 2 seconds followed by contracting for 1 second at full contraction and then lowering the weight eccentrically for 2 seconds.
Chest post-exhaustion; Bench press followed by D/B flyes.
Back post-exhaustion; Barbell rows followed by (straight arm) lat-pulldowns.
Shoulder post-exhaustion; Military press followed by side D/B lateral raises.
Quads post-exhaustion; Squats followed with leg extensions.
Hamstring post-exhaustion; Romanian deadlifts followed with leg curls.
Biceps post-exhaustion; Palm up chin ups followed with cable curl.
Triceps post-exhaustion; Close-grip bench-press followed with triceps pushdowns.
Calves post-exhaustion; Standing calf raise followed with seated calf raise.