Reps in Reserve (RIR) is a way to measure how many more repetitions you could perform before reaching failure in a set. When training with a slow tempo, which means performing each repetition more slowly than usual, RIR can be a useful tool to manage effort and intensity effectively.
Slow tempo training increases the time your muscles spend under tension, which is a key factor for muscle growth and strength development. Because slow reps make each repetition more challenging, you often reach fatigue faster even with lighter weights. Using RIR helps you avoid pushing too close to failure every set, which can lead to excessive fatigue or poor form. Instead, you can stop a few reps short of failure, preserving quality and control while still benefiting from the increased time under tension.
Additionally, slow tempo training exposes weak points in your movement by forcing you to control the weight throughout the entire range of motion. Monitoring RIR during these slow reps allows you to adjust effort based on how your muscles feel, helping to target specific weaknesses without overtraining.
However, very slow tempos reduce the total number of reps you can perform, so relying solely on RIR without considering tempo might underestimate the training stress. It is important to combine RIR with an understanding of how tempo affects fatigue and muscle activation. For example, a set with slow eccentric phases (lowering the weight slowly) and pauses can feel much harder than a faster set, even if the RIR is the same.
In summary, RIR is quite useful in slow tempo training because it helps regulate intensity, manage fatigue, and maintain good technique during longer time-under-tension sets. It allows for effective training without pushing to failure every time, which is especially important when reps are deliberately slowed to maximize muscle engagement and control.
Sources
https://www.shifttostrength.com/post/rest-pause-drop-sets-and-tempo-work-breaking-through-plateaus
https://fitnessrec.com/articles/exercise-tempo-for-muscle-growth-master-time-under-tension-and-strength-gains
https://pathtowellnessnow.com/the-power-of-tempo-in-strength-training-how-speed-affects-your-results/
