Two reps in reserve means you estimate that about two more good repetitions were possible. It is not a rating of sweat, discomfort or how dramatic the last repetition looked.

Use the intended movement and range. If extra swinging or a much shorter movement makes another repetition possible, you have changed the task. Also record when balance, pain or grip made you stop.

Here is a fictional example: ten repetitions with three remaining, ten with two remaining, then nine with two remaining. The final set is not automatically a failure. You have recorded repetitions and effort together.

Studies have found useful gains without taking every set to failure. Some results depend on the programme and muscle measured. Avoid turning one experiment into a rule that failure is always necessary or always pointless.

RIR is a judgement, especially on unfamiliar movements. Learn with appropriate guidance and a suitable setup. Do not force an unsafe failed repetition just to prove that you can estimate the number precisely.

Keep load, rest and technique clear enough to compare. Watch the pattern over time. The full article includes a simple log and explains why stopping for pain is different from reaching muscular failure.