As a trainer, I usually work with one of two types of clients.
On one hand, we have the client who is always chasing heavier weights and pushing their boundaries. On the other, we have the client who is always playing it safe and rarely wants to step outside their comfort zone.
Just yesterday, I explained to a client — who definitely belongs to the first group — why pushing yourself to the limit day in and day out usually works against you.
Be patient. We'll get there.
Let's back up for a minute.
As trainers, we want to keep a close eye on the load or intensity at which our clients are training. The obvious reason is to steer adaptations — for example, higher repetitions and lower loads for muscular endurance, and higher loads and lower repetitions for strength. Load and intensity are just two of the variables to consider when
designing a workout programme for a client.
Recent research has suggested that different training loads actually share many adaptations previously believed to be exclusive to either high-load, low-repetition training or low-load, high-repetition training. In particular, hypertrophy can occur across a fairly wide range of loads, while heavier loads generally produce greater improvements in maximal strength (Lopez et al., 2021).
But that's a topic for another article.
Another reason to monitor intensity is the amount of fatigue and technical breakdown that can occur when training very close to failure.
So, how hard should your clients really train?
Two terms that have gained a lot of attention within resistance training research over the last couple of years are
RIR and RPE.
What they have in common is that they are subjective measures of internal intensity.
Put simply: How hard are you pushing yourself?
Within endurance training, subjective measures of intensity have been commonplace for many years, most famously through the Borg RPE scale developed by Swedish researcher Gunnar Borg (Borg, 1970).
Repetitions in Reserve (RIR) asks the client to estimate how many additional repetitions they could have performed after completing a set.
For example, a client performs 10 repetitions with 70 kg.
We ask:
"How many more repetitions do you think you could have performed if you pushed yourself to the limit?"
The client answers:
"Probably two more."
That would put the set at 2 RIR.
A set taken to complete failure is therefore 0 RIR, while an easy set with plenty left in the tank might sit around 5–6 RIR.
Similarly, Rating of Perceived Exertion (RPE), as it is commonly used within strength training, also allows the client to rate how close they were to their maximum effort.
The main difference is the direction of the scale.
A set taken to complete failure would be approximately RPE 10, meaning that the client pushed themselves to their absolute maximum. An easy warm-up set might land somewhere around RPE 4–5.
As a quick summary, when referring to training very close to failure, we are generally talking about:
The closer you get to 10 RPE, the closer you are to 0 RIR.
How close a client should train to failure should partly depend on their experience.
Here, both their overall training experience and their proficiency in the specific exercise matter.
Put simply, if a client is inexperienced with training in general — or with a particular exercise — there is usually little reason to push them very close to failure.
This is also one of the reasons why the first sessions with a new client should be used to learn how they move, communicate and respond to training. We cover this in more detail in our guide to
the first Personal Training session.
With that said, it is still important to challenge your clients.
Most clients want to be pushed, but preferably without feeling completely out of control.
This is where you should be smart about which exercises you choose to push them in.
Exercises that require relatively little skill and are easy to control — machine exercises, for example — can generally be taken closer to failure than technically demanding exercises.
This is a topic that has been heavily debated within the scientific literature.
Current evidence suggests that training to complete failure is not necessary to achieve gains in strength or hypertrophy in most situations (Grgic et al., 2022).
When it comes to hypertrophy, the important point seems to be that the set is sufficiently challenging, rather than that every set has to end in complete failure.
On social media and fitness forums, this is of course also heavily debated.
One common argument is that most people are poor at accurately estimating their proximity to failure, and therefore should simply aim to train to failure.
This is an important point. Research does show that RIR estimates are generally more accurate when sets are performed closer to failure and at higher relative loads (Russo et al., 2026).
But it does not necessarily prove that training to failure is better. Rather, it highlights the need for proper instruction when using subjective measures such as RPE and RIR.
More on that later.
No.
When deciding how close to failure a client should train, you should also consider the type of exercise being performed.
For technically demanding multi-joint exercises, it often makes sense to keep more repetitions in reserve — particularly when the client is inexperienced.
Exercises where technique, speed or coordination are essential should also generally not be pushed until technique starts falling apart.
On the other hand, isolation exercises and machine exercises that require relatively little skill can usually be taken closer to failure.
Implementing RIR does not really require much more than common sense.
When it may make sense to train further from failure:
- Early in a training period
- When a client is learning a new exercise
- In technically demanding multi-joint exercises
- When training volume is high
- When fatigue could negatively affect technique
When it may make sense to train closer to failure:
- Later in a training period
- Later in a training session
- When the client is very familiar with the exercise
- In single-joint or machine exercises that require relatively little skill
These are not strict rules, but they provide a useful starting point.
What's really nice about RIR and RPE is that they are individual ratings.
Two people performing the same workout may train at the same relative intensity while using completely different absolute loads.
It also means that you do not need to spend hours performing rigid strength testing just to find an appropriate starting weight.
Of course, as previously mentioned, it does require some teaching before it can be used effectively.
A client should gradually become familiar with what an easy set feels like and what a true 0 RIR / RPE 10 set feels like. Research on RIR accuracy supports this point: estimating repetitions in reserve is a skill, and accuracy tends to improve when people are closer to actual muscular failure (Russo et al., 2026).
As the trainer, you should also pay close attention to body language and movement speed.
During a set taken very close to failure, movement speed will usually slow significantly towards the end of the set and the client should show clear signs that they are struggling — facial expressions changing, breathing increasing and technique beginning to deteriorate slightly, without completely falling apart.
Here's an example.
Let's assume we have programmed 3 sets of 10 repetitions at 3 RIR, and this is the first time performing the exercise with the client.
Trainer: Today we're performing the seated dumbbell shoulder press. It's a great exercise for building strength in your shoulders. Have you performed this exercise before?
Client: No, but I've seen other people doing it.
Trainer: Not a problem. Here's how to do it!
Trainer demonstrates the exercise.
Trainer: Now I want you to pick a weight that you think you could lift about 13 times, but you're going to stop at 10. In other words, you should feel like you could have performed a few more repetitions.
The client performs 10 repetitions without much strain and the movement speed stays relatively constant throughout the set.
Trainer: How did that set feel?
Client: It felt good. Not too heavy and not too light. I did feel my shoulders working!
Trainer: Great, then we're on the right track. I do think we could increase the weight slightly. It looked like you could probably have performed another 5–6 repetitions. Would you agree?
Client: Yes. If I really pushed myself, I think I could have completed about five more.
Trainer: Would you be comfortable increasing the weight slightly for the next set? Perhaps another 1 kg in each hand?
Client: That sounds like a good idea!
And this is basically the process for most exercises.
If the client already has experience with the exercise, even better. You may be able to find the appropriate load much faster.
One obvious mistake is
not monitoring effort at all.
Perhaps the trainer comes from a "no pain, no gain" culture and believes that training should always be extremely hard.
A second mistake is putting too much trust in the client's rating without questioning it.
Make sure you actually teach the scale and dare to challenge their estimate:
"Was that really 5 RIR?"
If the bar or weight was moving easily and the client showed almost no signs of effort, their estimate may not be accurate.
The final mistake is not fully understanding how RIR can be used.
RIR can be used to prescribe and monitor training intensity, as described throughout this article. But it can also help you identify progression.
For example, a client performs 10 repetitions at a certain weight and rates the set as 2 RIR.
The following week, they perform the same 10 repetitions with the same weight but now rate it as 3 RIR.
Nothing changed on paper — but the exercise became easier.
The client has progressed.
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