Train by feel
Autoregulation done right — when to push, when to back off, and how to do it without overthinking every set. Cited answers.
General training information, not medical advice. If you have pain, injury, or a medical condition, talk to a qualified professional.
Both — and that is the point of autoregulation. A fixed plan written weeks ago does not know that you slept badly or that last session felt unusually easy. Adjusting load or volume to your current performance and effort (often tracked with reps-in-reserve, how many reps you had left in the tank) lets you push when you are fresh and back off when you are not, without abandoning structure. The catch is that doing this well by hand requires judgment most people are still building. StrengthSync does the autoregulation for you: it adapts the next session from your logged performance plus a quick self-reported check-in — no wearable needed — and explains each change in one plain line so you are never guessing.
RIR, or reps in reserve, is how many more reps you could have done before hitting failure on a set. If you rack the bar feeling like you had two good reps left, that set was 2 RIR. It lets you gauge effort honestly without grinding every set into the ground: for most working sets, training at about 1 to 3 reps in reserve captures the large majority of the muscle and strength benefit while leaving you able to recover and repeat. One honest caveat — estimating RIR is a skill, not a fixed readout. Research shows people get more accurate with training experience and are most accurate on heavier sets close to failure; on lighter, high-rep sets many lifters believe they are nearer failure than they really are. So treat your early calls as rough and expect them to sharpen. StrengthSync uses the effort you report on your sets, session to session, to decide when to push your load or reps and when to hold — so your reps in reserve become a signal that changes your next workout, not just a number you log.
They measure the same thing from two angles, and on the modern lifting scale they convert directly. RIR (reps in reserve) counts how many reps you had left before failure. RPE (rating of perceived exertion) rates how hard the set felt on a 1-to-10 scale. In the resistance-training RPE scale introduced by Zourdos and colleagues in 2016, the two lock together: RPE 10 means 0 reps in reserve (true failure), RPE 9 is about 1 rep left, RPE 8 is about 2 reps left, and so on down. So "stop at RPE 8" and "leave 2 in the tank" are the same instruction. Which you use is preference — newer lifters often find RIR more concrete because you are counting reps, while RPE gets handy once the mapping is second nature. Either way it is an estimate that sharpens with practice, not a precise gauge. StrengthSync reads the effort you report on each set and turns it into your next prescription, so whichever scale you think in, it feeds the same adaptive decision.
For most sets, no — and the research is fairly consistent on why. Taking a set to momentary failure (zero reps left) piles on fatigue but adds only a little extra muscle growth compared with stopping a rep or two short, and reviews have not found failure training to be superior for building muscle. For pure strength, how close you stop to failure matters even less, because the heavy load is doing the work. Training close to failure does drive growth — a couple of reps in reserve on your hard sets is a solid target — but taking every set to failure mostly buys deeper fatigue, worse recovery, and sloppier reps, which is how plateaus start. A workable pattern is to keep most sets around 1 to 3 reps in reserve and save true failure for the occasional last set of an isolation exercise, where the risk is low. StrengthSync watches how your reported effort and performance trend across sessions and eases the plan when the data says accumulated fatigue is starting to cost you — so you are not the one deciding to redline every set.
StrengthSync adapts your training session to session from your own data and explains each change in one plain line. More answers · See what it does.