There is something about the easy memorability of motivational quotes such as “no pain no gain” that makes them feel instinctively right. This could be partly because, as at least one psychological study suggests, we believe things more readily when they rhyme. It also makes a sort of intuitive sense to those of us who, even if we do exercise, are not as fast, muscular or lean as we’d like. There must be something we’re getting wrong; is it our unwillingness to endure pain, or the discomfort of extreme effort? But how true is the adage, and is it possible to make gains without feeling the burn?

“In fitness, the answer is always: ‘It depends,’” says Zack Cahill, a senior trainer at Evolve Fitness in London. “What is the goal? What are you trying to achieve in the workout?” For aerobic exercise such as longer runs, the slower and longer you go, the better. So, if you’re planning on tackling your first 5k – or even a marathon – it’s fine to take your training sessions at a modest pace at which you could still hold a (slightly out-of-breath) conversation. “Most training for endurance events should be done to build a strong aerobic engine, which means easy runs,” says strength and endurance coach Beatrice Schaer.

Steve Magness, an elite running coach and author of Do Hard Things, says: “The way I like to think of it is that, for most fitness goals, you just need to slightly embarrass your body. In running, that means the consistent mild stress on your heart, lungs and so on that occurs with easy running.”

If all we did was easy workouts, though, we would eventually plateau, so if we want to keep progressing, says Magness: “We have to make things tougher occasionally – but where people get it wrong is that we want to introduce ourselves to more stressful workouts gradually. Take elite runners: even on their hard workouts, for the vast majority of them they are hard but under control. They aren’t the go-till-you-puke workouts you see on Instagram.”

The good news is that the long, slow efforts can make harder sessions feel less uncomfortable, too. A key distinction to understand is the difference between “aerobic” workouts, which are the long slow ones where your body can use its stores of fat in conjunction with the oxygen you breathe, for fuel – and “anaerobic” ones, where you simply can’t take enough oxygen on board to fuel your faster efforts so your body needs to burn glycogen, which it gets from consuming carbohydrates. According to the research, the more efficient your aerobic system, the higher its contribution to the total energy expended throughout higher-intensity anaerobic sessions, which reduces fatigue overall.

Personal trainer Rose Mac is training for the Liverpool half-marathon, which takes place later this month, and says: “I’m working with a heart-rate-based plan using a smartwatch, where it actually tells me when to speed up and slow down to make sure I’m training my aerobic and anaerobic capacity.” She says she has been surprised to find that, rather than struggle with the fast bits, it took the most discipline to slow down when prompted, “but my anaerobic threshold has definitely improved from slowing down”.

So that’s cardio. But surely in the gym, you need to push for the burn? Well, not necessarily. For a start, it depends whether your goal is to put on muscle, or simply to be able to move more weight, which is subtly different. Being able to lift more is about teaching muscle fibres to fire together, which doesn’t necessarily mean bigger muscles. “If your goal is pure strength, you’re probably going to be doing fewer repetitions in each set, five or fewer, because you’ll be lifting heavier weights,” says Cahill. “At that rep range, the limiting factor isn’t pain. You stop the sets when you hit the number of reps you’re going for, you don’t grind out difficult reps. Pain doesn’t really come into it.”

In fact, if you’re aiming for pure strength in specific movements, you should probably stop your sets a bit before you hit “failure” – the point where you literally can’t make your body perform one more curl, press or squat. A meta-analysis of the research on training to failure published in 2021 found that it had almost no benefit for increasing muscle strength or size compared with simply lifting for a prescribed number of reps in each set. And if you’re training for pure strength (as opposed to bulk), it makes sense to stop at the point when the speed of each individual rep is slowing – given the importance of teaching muscle fibres to fire together, by messing up the movement pattern, you might be making your training less effective. Some trainers talk about “greasing the groove”, or simply doing lots of very easy sets of, say, press-ups throughout the day – making your body more efficient at the movements, without ever hurting.

What about putting on muscle? Is this where the adage holds most true? “Yes, at some point you’ll need to include sets that induce a bit of discomfort,” says Cahill. “Muscle grows by a few different mechanisms, but one of those is metabolic stress, which is what gym-goers often call ‘the burn’. We used to think this was down to lactic acid, but now believe it’s due to a combination of factors. Anyway, it seems to be a factor in muscle growth, and so we should include some higher rep – think 12-15 rep – sets that bring the burn if we want to build muscle.”

In layperson’s terms, this means that to put on muscle, you need to take your sets to the point where you want to stop, then push a little further – but, remember, not quite to failure. “This is pain with a purpose, or ‘good pain’, as I sometimes tell my clients,” says Cahill. “It should be done sparingly and for a specific reason. This also reframes the pain, and tends to make it more bearable. Even then, though, there are ways to minimise how much it hurts – for instance, by doing more reps in an allotted time, known as escalating density training.”

So if you can run further, lift heavier and even put on muscle without your workouts being horrible, the obvious question is: why does anyone do the really unpleasant stuff at all? Sometimes, it comes down to expectations: if you are a personal trainer, and your workouts aren’t making people exhausted, sweaty or sore, then some clients simply won’t believe they are getting their money’s worth.

And it does work: just maybe not as efficiently as advertised. To use the example of high-intensity interval training (known as Hiit) popularised by Joe Wicks, the key is in the first two words: you really do need to keep the intensity high to see results. If you are doing endless sets of lacklustre star jumps with very little rest in between, you might be working up a sweat without your workout being very effective. And even working under the desired intensity level, this type of workout can be pretty demanding on your nervous system, meaning that most people shouldn’t do it more than once or twice a week at most, or risk becoming more vulnerable to illness or “overtraining” – where you are fatigued, can’t concentrate and don’t sleep well.

It might work better to spend the time on lower-intensity stuff instead. “As a trainer, it’s my responsibility to prescribe the minimum effective dose,” says Aaron Jahn, a Muay Thai coach. “The aim is to have my students feeling stronger and more energised each and every time they leave the gym. Each session is treated as a practice of skill. I know that if my students focus on movement quality, they’ll feel and look better as a result.”

The overall lesson, then, is that it is possible to make huge gains in the gym or on the road without really suffering. By keeping sessions manageable but consistent, you will make your body more efficient at the movements you repeatedly do. In fact, if there is any reason to do the teeth-gritting, lung-burning stuff, it might not be to do with your body at all. “​​I think, ultimately, it’s about balance,” says Mac.

“I believe the right amount of discomfort, sometimes, allows us to evolve and grow.

“Psychologically, it can give you a boost to think: ‘I pushed further and now realise I am more capable than I thought.’ I see it when people run a sub-25-minute 5k for the first time – all of a sudden there’s this extra belief, and I think that these small wins definitely help with everyday life.”

No strain, but still in pain? We answer those burning questions

I did an easy workout, but my muscles really hurt. Why?
This is Doms, or delayed onset muscle soreness. It is caused by a combination of factors, including microtrauma to muscle fibres and connective tissues, and inflammation. It typically comes from either doing exercises your body is not used to, doing more volume (the total number of reps in a workout) than you are used to, or doing a lot of “eccentrics” – basically, the lowering bit of, say, a squat or a press-up.

OK, I don’t like this. How can I stop it from happening?
One way is to limit the amount of eccentrics you do: moves such as the kettlebell swing don’t really have a downward bit, as you are letting the kettlebell fall under gravity’s control, rather than using your muscles.

It’s getting worse. Is it safe to work out like this?
Yes. Doms typically peaks two days after the training session, and the good news is that doing some light exercises with the affected muscles can ease the pain – you will get blood to them, aiding recovery.

It just means I’ve had a good workout, right?
Not necessarily. It’s possible to have a really effective workout, as in one that makes you stronger, faster or otherwise fitter, without being sore afterwards.

Is this always going to happen?
Honestly, it does get easier. The worst Doms happens when you do something radically different from what you are used to, so it will never be as bad as when you first start exercising.