Switch To Another Routine
FPP states if you hit a wall for a second time switch to another routine.
As Don noted, once you stop making progress with a program, you need change it.
That because the body adapts. When the body adapts, progress stops.
Anecdotal data and research have demonstrated that...
Changes in Exercises Are More Effective Than in Loading Schemes to Improve Muscle Strength
This research looked at four method of increasing strength.
1} CICE: Constant Intensity and Constant Exercise
2) CIVE: Constant Intensity and Varied exercise
3) VICE: Varied Intensity and Constant Exercise
4) VICE: Varied Intensity and Varied Exercise
The most effective of the four (4) at increasing strength are exercise are "Changed/Varied". .
Thus, (as per Don), once when progress stops with a program, you need to start a new 4 - 8 week Periodization Training Cycle with new exercises.
Periodization Training Cycles
This is the foundation of Strength Training (Maximum Strength, Hypertrophy, Power and Speed development).
Starting over with a light load with new exercises, allow the body to recovery. Gains in strength occur during recovery.
Periodization Training ensure long term results; providing it is a well written/performed program.
Short Term Deloadsand Reloads
Decreasing the load one training session after struggling with it and then going back to that load the next training session is a short term fix.
Short term Deloads and Reloads is one the misconceptions that continues to be perpetuated.
Training Age for Periodization Cycle
This is defined as how long you have been training, not your chronological age.
Novice Lifters need to change their training exercise about every 8 week. This because Novice Lifter adapt slowly.
Advanced Lifters need to change their training exercise about every 4 weeks. That because they adapt quickly.
This can be as simple a going from a Wide Grip Bench Press to a Narrow Grip Bench Press, Incline Press or Dip,
All of these exercise work the same muscle. They are, metaphorically speaking, like Ice Cream; each a different flavor.
One is Chocolate, one is Vanilla, and one is Strawberry.
"Insanity is doing the same thing over and over and expecting different results."
Once something stop working (like Don stated), you need to change exercises.