Understanding Grip Strength Regulation
Grip strength autoregulation can be a useful tool in order to maximize your workouts on any given day - grip strength is a good indicator of full body readiness. If your grip strength is good, then you typically do a more challenging workout, versus a low grip strength which may be a sign to hold back or modify your workouts. Generally, grip strength testing is simple and easy to use, but should still be used intelligently in the context of your training program.
A Humble Proposal: Factoring Percentage of Reps Into Reps In Reserve Calculations
RPE (ratings of perceived exertion) and RIR (reps in reserve) can be useful training tools for some sports where the goal is to train to failure or near failure, but there is no catch-all number that works for all exercises. Generally, RPE is used for managing heavy efforts of weight or reps, and not for exercises where training to failure or near failure would inhibit the continuation of training like working on endurance for running a marathon. Instead of static numbers, RPE/RIR can function as a percentage of total effort to be applied to a wider range of workouts.