It’s not the weight that works the muscles, it’s the muscles that work the weights. This is an important part of biofeedback and internal cues that is a departure from a focus on how much is on the bar lifted for how many reps. The emphasis switches to internal aspects of performance like perceived exertion and affect; angle of contraction, muscle shortening, muscle activation potential etc.. It is an emphasis on how much stress a muscle is under; not how much weight is being lifted. This is the beginning of training maturity not measured in numbers, but felt in experience. The focus then becomes not how much a trainee can lift, but rather how much a trainee "should" lift for the desired effects.
Increasing workload capacity is one of the most important aspects of improving development.
David Behm’s research article “Neuromuscular Implications and Applications of Resistance Training” came to the following sound conclusion so important to those of you interested in developing a better physique: “Maximum strength training methods with their high intensity resistance but low volume of work do NOT elicit substantial muscle hypertrophy.” Therefore a higher volume of work, (greater than 6 reps, with multiple sets) is needed to ensure a concentration of intracellular amino acids to stimulate protein synthesis