Reps in Reserve (RIR) is a way to measure how many more repetitions you could still perform at the end of a set before reaching failure. Using RIR helps track long-term fatigue by providing insight into how hard your body is working and how much recovery it needs. When you leave some reps in reserve instead of pushing to failure every time, you reduce excessive fatigue buildup, which can impair recovery and performance over time.
By monitoring RIR, you can adjust training intensity to match your current capacity. For example, if you usually leave 2-3 reps in reserve but find yourself only able to leave 1 or none, it signals accumulated fatigue or reduced readiness. This feedback allows you to modify training loads or volume to avoid overtraining and injury. Over weeks and months, tracking RIR helps you balance effort and recovery, ensuring consistent progress without burnout.
RIR is often used alongside the Rate of Perceived Exertion (RPE) scale, where an RPE of 9 corresponds to about 1 rep left in reserve. This system helps lifters avoid training to failure too often, which can cause central nervous system fatigue and increase injury risk. Instead, leaving 1-3 reps in reserve on main lifts manages fatigue better and supports long-term strength gains. It also helps maintain technique quality by preventing form breakdown from excessive fatigue.
In practice, athletes can log their RIR each session to see trends. If RIR values decrease over time without planned increases in intensity, it may indicate accumulating fatigue. Coaches and lifters can then adjust training variables such as volume, intensity, or rest days to promote recovery. This approach leads to smarter programming that respects the body’s limits and promotes sustainable progress.
Sources
https://rippedbody.com/rpe/
https://www.mensjournal.com/health-fitness/what-is-escalating-density-training
https://trainkilo.com/blogs/inside-the-system/the-numbers-that-guide-the-process-why-tracking-metrics-matters-in-strength-training
https://www.jefit.com/wp/general-fitness/break-through-strength-plateaus-jefit-guide/
https://www.minimumviablepump.com/guides/rir
