Reps In Reserve (RIR) is a method used to measure how close you are to failure you are while performing a movement. It involves assessing the number of repetitions you could have performed before you could no longer complete another repetition with good form.
RIR is expressed as a numerical value, with a higher number indicating that you had more repetitions left in the tank before reaching failure.
A note on failure
Failure is the point at which optimal technique is no longer able to be maintained.
You may be able to muscle through a few more repetitions but if you need to compromise technique you have gone too far.
Breakdown
0 RIR: You have reached complete technical failure and could not perform another rep with proper technique.
1 RIR: You could perform only one more repetition before failure.
2 RIR: You could perform two more repetitions.
3 RIR: You could perform three more repetitions.
4 RIR: You could perform four more repetitions.
5+ RIR: You could perform five or more repetitions.
Why RIR is optimal
And I do mean optimal.
Training with RIR is a much more useful and intentional way to train than adhering to specific weights because it allows for more flexibility and individualization in your training. Instead of being tied to a specific weight, RIR allows you to adjust your intensity level based on how you're feeling that day and how your body is responding to your training. Every session, therefore, is adequately challenging for how you’re feeling in that moment.
One of the main advantages of using RIR is that it takes into account the fact that people's ability to perform exercises can vary from day to day. Your ability to lift a specific weight may be affected by factors such as recovery, stress, sleep, nutrition, and other lifestyle factors. With RIR, you can adjust your training intensity based on how you're feeling on that particular day.
For example, if you're feeling well-rested and energized, you may be able to perform more reps at a higher weight than you would on a day when you're feeling tired or stressed. By using RIR, you can adjust your intensity level based on how you're feeling, which can help you avoid overtraining and injuries, while still challenging yourself and making progress toward your goals.