Two women rowing at the gym

Cardio challenge: are gym cardio classes genuinely harder than going for a run?

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It doesn’t matter if you run, cycle or swim, gym cardio classes still burn like hell. So, why is gym-based cardio so hard and can we ever look forward to a day when we’re noticeably better at it? 

I’m a cardio fiend. As a runner and cyclist, I spend a lot of my week doing cardio – whether that’s getting from A to B or in order to get a body-load of endorphins. Nothing makes me feel as accomplished and happily fatigued like finishing a long run. Despite all of this, however, I find cardio classes ridiculously hard. 

Last week, I went to my first Sweat class at The Foundry. It’s a circuit session that includes light(ish) weights and cardio machines like the skier, rower and assault bike, which you work through in sections. The idea is to move for up to 40 or 50 seconds before switching to the next exercise in the section. By the time I’d finished my ‘buy in’ warm-up on the rower – a 500m distance – I thought I could taste something metallic in my throat (and I rowed at university!) and had just about managed to swallow a gulp of water before jumping straight into a set of burpees.

The burn only intensified as I carried on around the room and by the time I came out of the gym shower, I started sweating all over again. The endorphin rush was just as intense as with running but I did wonder how any casual gym goer could survive such a brutal cardio onslaught. 

The Foundry is an excellent gym but its classes aren’t extraordinary in their brutality. A few months ago, I tried the new Trax class at Fitness First – a HIIT-style cardio circuit class that also gets people to move from assault bike to rower to skier to bodyweight moves. Again, I wondered how I was actually going to make it to the end of the 30-minute session.

That all begs the question: why are cardio classes so bloody hard, even if you do plenty of cardio as part of your weekly routine? Well, it’s all to do with your VO2 max.

Cardio classes really are harder than your usual workouts

“Cardio gym classes can often feel harder as you are typically being pushed to 80-100% of your maximum heart rate (HR) when training,” explains Elouise Millard, trainer at F45 Stratford – arguably the home of tough cardio workouts. 

When we go for a run, we tend to work with around 60-80% of our maximum HR; those classes push us to work with more of our VO2 max. VO2 max is the measurement of the maximum amount of oxygen your body can utilize during exercise. The fitter you are, the more oxygen your body is able to use (so your VO2 max gets higher) – which results in being able to train harder, run faster and last longer.

You may be thinking that all cardio classes are just HIIT by a different name. Those periods of work and rest are common in HIIT sessions, which get you to work flat out for a matter of seconds before diving back in. But Millard says that this isn’t always the case with cardio, which covers the whole gamut of classes from conditioning to endurance. 

Barry’s Bootcamp, for example, is a cardio class that gets people to run for up to eight minutes on the treadmill in between periods of weight-based floor work. Spin classes don’t qualify as HIIT either, despite the fact that spinners work between longer rides, intense climbs and static pedals.

Why does cardio never seem to get any easier?

The thing that I want to know is why – like climbing stairs – cardio classes never seem to get any easier? After running every distance and lifting heavy weights, I still find gym cardio brutal.

The frustrating news is that, according to Millard, it’ll always be that way. “Cardio classes will always be challenging – and that’s coming from a trainer!” she says. That’s because you’re always pushing to that higher heart rate zone; you may get fitter week-on-week, but all that means is that your upper limit increases. 

The great thing about cardio (and strength training) is that there’s no upper limit. “You may get fitter with training but you’ll always find it difficult as you’re aiming to train at a high intensity. You’ll find that you can go a bit harder for longer, but it still won’t be easy – even with regular training.”

That’s not to say that you need to do cardio classes to be fit. You can still build and maintain a solid level of fitness even if you just do low-impact steady-state cardio (LISS) like walking, running or cycling regularly. 

“You can absolutely be fit from training with just LISS activity, alongside strength training,” Millard insists. “Essentially, as long as you are finding a way to move your body that you enjoy and that you can keep up with consistently, you’ll maintain a good fitness level.”

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Miranda Larbi

Miranda Larbi is the editor of Strong Women and Strong Women Training Club. A qualified personal trainer and vegan runner, she can usually be found training for the next marathon, seeking out vegan treats or cycling across London on a pond-green Tokyo bike.