How hard do you have to work to build muscle?

Irish Times

02-06-2025

You're sweaty and sore, and just hoisting your gym bag on to your shoulder makes you groan. The
workout
was exhausting, but was it effective?
Many trainers and athletes have long believed that lifting to failure – the moment when you can't complete another repetition of an exercise – is the best way to build muscle. But
recent research
has challenged that idea, suggesting that training at a slightly lower intensity can produce similar results.
'The question I ask people is: 'Are we getting better or are we getting tired?'' said David Frost, an associate professor in the kinesiology department at the University of Toronto.
If you're new to lifting, it can be tough to know how hard your workout should feel. Learning what failure feels like – and understanding when you should push that far – can help you build a sustainable strength-training routine and allow you to safely progress as you get stronger.
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Training to failure?
There are two types of failure in strength training.
'Technical failure' is when you can't do another repetition with proper form and control, so you may have to rely on other muscles and joints to lift the weight.
'Muscular failure' happens when your muscles are so fatigued that you can't lift the weight at all.
Although you can build muscle mass by training to failure, some experts say the risks may outweigh the benefits. 'If you push yourself to failure and damage your muscles to a very extreme degree in a single workout, that's going to impair what you can do the next day and the next day,' Frost said. Pushing yourself to lift with poor form can also increase your risk of injury.
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What matters more is that you're working hard each time you step into the gym. Challenging your muscles creates microdamage in the tissue, which is what makes them change. When you rest, that tissue repairs, grows and gets stronger.
'You don't need to necessarily be pushing to failure, but a high level of effort is required over time,' said Brad Schoenfeld, a professor in the exercise science programme at Lehman College in New York who studies how different methods of resistance training affect muscle growth.
How much to lift?
When you're starting out with strength training, perform new exercises with just your body weight first so you can learn proper form, said Elizabeth Davies, a strength coach in Kent, in England, who works primarily with women who are relatively new to lifting.
Once you're ready to add weight, start by picking up a weight that feels light to you. Focus on moving with good form rather than trying to do as many repetitions as possible.
You can use what's known as the reps-in-reserve, or RIR, scale to find out how much weight you can handle for a full set. When you perform an exercise, estimate how many more times you could lift the weight – your RIR – before feeling maxed out. You want to choose a weight where at the end of your set, you feel like you have a few repetitions left in the tank.
The RIR method lets you adjust your workouts for how you feel – which can vary based on everything from sleep and diet to hormonal changes and stress – rather than sticking to a set amount of weight.
Working to build muscle
As a new lifter, your muscle tissue will generally adapt quickly to training, so you can stop when you feel like you have five or six RIR and still see progress, Davies said.
As you get stronger,
research suggests
that stopping two or three repetitions before failure can be ideal for maximising muscle growth. Once you're able to complete the same number of repetitions in a given set for two or three weeks in a row, add a bit more weight and see how that changes your sense of effort, Frost suggested.
When you're familiar with an exercise and can practice it consistently with good form, it can be worthwhile to occasionally train to failure to refine your sense of how hard you need to work. After all, 'if you don't train to failure, you don't know how far away from failure you are', Dr Schoenfeld said. When your body is pushed beyond its limits, it will also try to adapt to meet that challenge more easily next time, he said.
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If you really enjoy the feeling of hitting your maximum effort, failure can have an occasional place in your workouts. Davies gives her clients that opportunity on single-joint moves such as bicep curls that won't leave them too exhausted and hinder their progress, she said.
The key to getting the most out of strength training is stacking up hard work over time, Frost said. On most days, that means aiming to push yourself a little bit more than you did the day before.
– This article originally appeared in
The New York Times