I've written before about why you don't need to take every set to failure to build muscle, and the latest research suggests that stopping a few reps before failure can lead to just as much growth as training to failure.

But there's a tacit assumption baked into the above: That you have a pretty good idea of how hard you're already training.

For example, let's say you finish a set thinking you could have done two more reps, but in reality, you had four more reps left; you can see how this might impact your progress: how hard you think you're training isn't really how hard you're actually training.

This is worth discussing if you lift weights and you aren't seeing as much progress as you'd have hoped.

To start, let's look at what we mean by 'hard enough'.

How hard is 'hard enough'?

While training intensity can have a few different definitions, for the purposes of this article, we'll define it as how close you're taking each set to failure.

Generally, we quantify this as reps in reserve, or RIR (some people call it rate of perceived exertion or RPE, but I find RIR more intuitive).

To illustrate, if you performed ten reps and could have performed twelve reps, then you were at a 2RIR — that is, if you took the set to complete failure, you would have managed to eke out two more reps.

This matters because research suggests muscle growth increases when you take sets close to failure.

So the solution sounds pretty simple, right? Just take each set to failure and save yourself the stress of judging RIR. That can be one solution, but I'd generally advise against it for a few reasons.

Firstly, taking every set to failure makes it harder to sustain your performance.

If you take the first set to complete failure (and I do mean genuinely failing the set, not stopping when it burns a little), you’ll likely get fewer reps on the second and third sets, or need to drop the weight to stay in your rep range.

Obviously, that isn't the end of the world. But it can make it harder to maintain your performance throughout a workout.

Second, training to failure seems to increase fatigue without a real benefit for muscle growth compared to stopping a few reps short of failure.

In an eight-week study, 18 trained men and women trained one leg to failure and stopped one or two reps short with the other. Average quadriceps growth was similar, while the leg trained to failure showed larger drops in repetitions and lifting speed across sets.

Moreover, constantly training to failure can extend recovery time, and you might feel worse outside the gym. In one study, participants who trained to failure reported greater muscle soreness and perceived discomfort and generally felt worse overall than participants who trained with 3 reps in reserve.

Quick aside: I often see people online claiming the whole fatigue thing from training to failure isn't a big deal. Naturally, most people making these claims have lives that revolve around training, and they have all the time to rest and recover. But fatigue doesn't exist in a vacuum. If you have a demanding job, kids, and other life stressors, then training fatigue is absolutely a consideration.

With that in mind, I think most people, most of the time, will be better off familiarising themselves with reps in reserve and using it in their training. And that leads nicely to the next bit.

RIR is a skill

When you first start using RIR, you probably won't be very accurate, and that's ok. RIR is a skill, and the more you use it, the better you'll get at estimating how close you are to failure.

In a six-week study, 26 participants new to RIR completed six supervised training sessions. Each session included three sets of bench press and three sets of leg press.

During each set, they called out when they thought they had four reps left (4RIR), then again when they thought they had two reps left (2RIR). After that, they kept repping out until they actually hit failure.

Over the six sessions, their RIR estimates became more accurate on average in both exercises. For example, when judging two RIR on the bench press, average error fell from 1.6 to 0.8 reps in the younger group, and from 1.2 to 0.8 reps in the older group.

So, even if your ability to estimate RIR right now isn't that great, the good news is you can improve it with practice.

How to judge RIR

Imagine you’re doing a set of bicep curls. There you are, you handsome fuck, curling away. Then, at some point, you realise this shit’s getting hard. My god, you think, this is getting really hard.

Your biceps are shouting at you, that burning sensation is kicking in, and you’re about to ready to drop the weight. But despite how sucky you might be feeling, you could probably do a few more reps.

No, this isn't just another way of me saying "fuck your feelings" – it's actually true.

The burn you experience during lifting is caused by a combination of chemicals your muscles release during intense exercise. This causes the pain sensors in your muscles to light up, which sends a signal to your brain that your muscles are on fire...well, proverbially speaking.

But here's the kicker: Just because your arm feels like you deepfisted Sauron doesn't mean your muscles were incapable of performing more reps.

Case in point: In this study, researchers took a group of trained lifters and had them perform sets of knee extensions to their "self-determined repetition maximum" (i.e. the point where they believed that if they attempted one more rep, they would fail).

Then the researchers probably laughed at them because, when those same lifters did separate sets to true muscle failure, they averaged two additional reps beyond what they'd previously thought was their absolute limit.

The point is, your brain dials up discomfort way before your actual muscles stop producing mechanical force.

Now, you might be wondering what any of this has to do with judging RIR. Well, quite a lot, actually.

If you're confusing the discomfort of a set with actual muscular failure, you're going to think you're much closer to failure than you really are.

Learning to distinguish between "this feels terrible" and "I physically can't complete another rep" is an important first step to judging RIR more accurately. Gettit? Cool. Now we can get to more of the practical stuff.

1. Occasionally train to failure

If I told you to complete a set with 2 reps in reserve and explained how to do it, you’d struggle to gauge what that actually means if you don’t know what true failure feels like (unless you're the child of immigrants, in which case we all know what true failure feels like).

On the other hand, if I made you do a set to complete failure and then asked you to stop 2 reps before reaching that point, you'd probably be more accurate because you now have a reference point.

Interestingly, research suggests that people generally get better at estimating how many reps they have left as they get closer to failure.

As such, occasionally take a relatively safe exercise to muscular failure. As you perform the set, note when you think you've hit your target RIR, and then keep going until you physically can't complete another rep with good form.

If you thought you had two reps left but then managed another six, congrats! Your RIR prediction sucks, but at least now you can work on improving it.

Doing this periodically can help you get a better feel for what different levels of effort actually feel like. You don't need to take every set to failure, but occasionally testing your limits can help you calibrate your estimates.

As for when to do your failure set, I recommend saving it for your last set of the exercise. There's nothing inherently wrong with doing it earlier, but the whole point is to see how accurate your RIR estimates are. By saving it for the last set, you can compare how many reps you thought you had left in your earlier sets with how many you actually managed when you pushed to failure.

2. Pay attention to rep speed

One of the more useful signs that you're approaching muscular failure is how quickly you can lift the weight.

For example, the first several reps of an exercise will move relatively quickly. But at some point, rep speed slows, and each rep takes considerably more effort. It's this involuntary slowing you want to pay attention to because it indicates you're getting close to failure.

Conversely, if you're breezing through every rep with little effort or no noticeable drop in rep speed, you're not training anywhere near hard enough for the set to be productive. So you should probably sort that out.

3. Be mindful of testing RIR with higher reps

​Research suggests people generally find it easier to estimate how many reps they have left during lower-rep sets compared to higher-rep sets.

If you look at the image below, you can see that people were generally pretty good at estimating how many reps they had left when performing sets of up to around 12 reps. However, once sets went beyond 12 reps, their estimates became increasingly inaccurate.

One possible reason is the discomfort of high-rep sets. If you've ever lost your mind and done 20-rep squats or leg extensions, you know exactly what I mean.

But as I explained above, that feeling isn't necessarily an accurate reflection of how close you are to failure.

The problem, however, is that knowing this information doesn't make the set suck any less. So now you're trying to judge how many reps you have left while contending with your terrible life choices.

So I recommend starting with lower rep sets to gauge RIR (e.g., 6-10 reps). As your accuracy improves, you can then apply that to higher-rep sets.

Putting RIR into practice

So, how does all of this translate into your actual workouts?

Let's say your program calls for three sets of bicep curls for 8–12 reps while aiming to leave two reps in reserve.

You complete your first ten reps and realise you probably could have managed another five. In this case, the weight was too light.

So, for your next set, you increase the weight slightly. This time, you finish ten reps and reckon you could have squeezed out another two. Perfect, you've found a more appropriate weight.

By the end of your third set, you manage only eight reps and believe you couldn't do another, so you've reached 0RIR.

Now, while you've gone a little closer to failure than intended, you've still managed to hit the bottom end of your rep range. We also have to consider that some fatigue has built up over the three sets.

As such, rather than increasing the weight again, you could start with this same weight next week and aim to improve your performance while staying closer to your target RIR.

The example above also highlights another benefit of using RIR: it's more informative for weight adjustments.

For example, if you finish a set with five reps in reserve, you have a lot more room to increase the weight than if you finish with just one rep left. So instead of going back and forth with incremental weight increases, you could opt for a slightly bigger jump.

One last thing: I generally recommend using an RIR range rather than aiming for one specific RIR target. So, instead of 2RIR, you would aim for anywhere between 1-3RIR. This gives you more flexibility, accounts for normal fluctuations in your performance from one session to the next, and stops you from making unnecessary weight adjustments.

Finally, just to round things off. I appreciate that all this RIR talk might be overwhelming for some. So despite writing ~1,700 words on the topic, I'll still tell you what I tell my clients most of the time: don't stress it.

The point of RIR isn't to obsess over getting the perfect estimate every time you train. Rather, it's a tool to help you gauge how hard you're actually training. But if you think you've stopped at 1RIR when you actually had three reps left, it's not the end of the world.

Ultimately, RIR is a skill, and the more you use it, the better you'll get at predicting how close you are to failure. And I think it's worthwhile to use it every now and then to see how accurate your RIR predictions actually are.

TL;DR

• You don't need to take every set to failure to build muscle. Stopping a few reps short can be just as effective, without the additional fatigue.
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• But there's a catch: To stop a few reps short of failure, you need a reasonably good idea of what failure actually feels like. Just because a set burns doesn't mean you couldn't do a few more reps.
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• This is where reps in reserve (RIR) comes in. RIR quantifies proximity to failure. For example, if you performed ten reps but could have managed another two, that would be 2RIR (or 2 reps in reserve)
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• RIR is a skill. When you first start using it, you probably won't be very accurate, and that's ok. The more you practise, the better you'll get at estimating how close you are to failure.
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• To improve your RIR accuracy, occasionally take a relatively safe exercise to failure to test how accurate your RIR predictions are.

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–Aa

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