Getting older shouldn’t mean shying away from heavy weights. In fact, Arnold Schwarzenegger actively encourages lifting heavy to build, or at least maintain, as much muscle as possible.

While lifting weights is essential for everyone as we get older, how heavy you lift matters too, particularly relative to your own strength. And Arnold’s light-and-heavy method addresses that exact problem.

Both slow-twitch and fast-twitch muscle fibres shrink as we age, but fast-twitch fibres experience a much greater reduction in both overall number and individual size – largely because people fail to properly challenge them. Writing in his latest Arnold’s Pump Club newsletter, the bodybuilding legend highlights the long-held belief that lighter weights only train your slow-twitch muscle fibres, while heavy weights are more effective at training your fast-twitch ones.

A Frontiers in Physiology study challenges that notion, though. It found that both heavy and light weights are capable of building both sets of muscle fibres when sets are taken to failure.

The issue, Arnold points out, is that people often don’t know when they’ve reached failure when using lighter weights, potentially making it harder to recruit those fast-twitch fibres.

‘The likely reason is how your body recruits muscle,’ he says. ‘It calls on slow-twitch fibres first and brings in fast-twitch as effort climbs. Light sets taken to failure eventually get there. Heavy sets may get there sooner and keep those fibres working longer.’

So, while solely performing high-rep sets with light weights can work, you’ll need to spend longer in the gym each week to achieve the same stimulus. Heavy weights can therefore be a more time-efficient way to challenge those fast-twitch fibres.

‘Everyone needs to push heavier weight, relative to their own strength, at least once or twice per week,’ Arnie adds. ‘If your training is all [resistance] bands, high-rep classes, or light dumbbells, keep it. Add a couple of heavier sets each week, too.’

If you’re not already incorporating heavy weights into your training routine, don’t feel overwhelmed or daunted. The light-and-heavy method is simple and can easily be applied to almost any training programme.

Just pick a compound movement – whether it’s a squat, deadlift, bench press or dumbbell row – at the start of your workout, and choose a weight that allows you to perform roughly five reps safely and with good form.

Complete two or three sets in your session before moving on to your preferred training style, which can then focus on higher-rep, lighter-weight exercises.

At all times, just ensure you’re working close enough to failure to make the sets challenging. This can help recruit more muscle fibres as effort increases, whether you’re focusing on heavy compounds or lighter isolation exercises.