Beat: Fitness First's answer to interval training might be my favourite ever workout class

When it comes to workout classes, I'm pretty fickle. I'm just as likely to pick Street Dance as Circuit Training, depending almost entirely on what time they're happening.

But I might have discovered a class I would go out of my way to attend on a regular basis. Introducing Beat, heartrate-based training that incorporates high intensity traning with resistance and strength work.

On arrival I'm given a heart monitor to wear, which is linked up to the computer system that records your workout for you (this will be emailed over after the session). On screens around the room my heart rate is displayed, along with everyone else's so you can see how much work you're putting in compared to everyone else.

Then a trainer takes the group through some warm up exercises both on the machines and floor (warning: burpees have a prominent place in this class). After warm up the class continues using weights, sandbells, medicine balls and the bikes, rowing machines and runners around the room. And all of this is with one eye on your heart rate as a measure of how much more or less effort you need to put in.

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Initially you just need to keep your heart rate above 70 per cent so as long as you're doing that you can pull back a little if you start to get too exhausted. Your trainer will tell you when it's time to put in more welly.

About halfway through the class we're told to really give it our all for two minutes. My heartrate soars to 98 per cent and my competitiveness kicks in (I wanted to have the highest heart rate), though I do vaguely wonder what happens if you get above 100 per cent - will my heart explode?

After the two minutes we rest for one and then head to a different machine to go all out for another two minutes.

It sounds awful. I loved it.

The machines are slightly different versions to the ones I'm used to using at the gym. The running machine is concave and starts under your weight, so it takes more effort to get going and you have to pay attention while you're on it.

The rowing machine uses your force to create its resistance so the more you put in the more you'll get out. And there's a new machine I've never seen before which we use to push our heart rates into the orange zone (above 80 per cent). It's essentially a ladder with moving hand and leg holds so you feel like you're constantly climbing, balancing the pressure on all your limbs. It's pretty hard work (see below).

There is some interaction with other members of the class but nothing too scary. I'm paired with another girl, to whom I have to throw a sandbell, and catch her throws. It's soon clear neither of us would make the netball team, but no one seems to care.

A few stretches to end and I leave the class on quite a high. I feel like I've done a full-on workout in just 45 minutes, that ticks both the aerobic and resistance exercise boxes so I can head off home feeling great.

I ache quite signifianctly for the next few days, which I believe is the sign of a good new workout. When my legs stop hurting, I will be back.

Beat is available at Fitness First: Charing Cross. Keep an eye out as it spreads across the country.