As we become stronger the human body adapts to a tension that is greater than what has been previously experienced.. in a gradual manner of course. This gradual increase in workload is referred to as Progressive Overload, which is a gradual increase in volume (sets × reps × weight), frequency or time under tension. It can also be created through a decrease in rest time between sets or changing the resistance angle in some cases.
As a person gains muscle and strength, the body requires fewer muscle fibers to lift the same load for the same volume. Strength training results in muscular and neural adaptations, which in turn, enable muscles to produce more force. Therefore, it is important to increase the training load/ mechanical stress to recruit the majority of a muscle’s fibers.
In other words, as we get stronger, if you were squatting 20lbs for 12 reps for three sets (90 seconds rest between sets), continuously doing so will become suboptimal for muscle fiber recruitment.
To achieve progressive overload in this case, one can do the following:
Solution 1: Squat 20lbs for 12 reps for three sets (60 seconds rest between sets)
Solution 2: Squat 20lbs for 14 reps for three sets (90 seconds rest between sets)
Solution 3: Squat 25lbs for 12 reps for three sets (90 seconds rest between sets)
Solution 4: Squat 20lbs for 12 reps for four sets (90 seconds rest between sets)