This 40-minute treadmill workout cut my 5km running time by 8 minutes - here's how to do it

I love running, but I'm not a fast runner by any means, and I have no desire to be. I do want to be an efficient runner, though, and the two often go hand in hand. Having taken three months away from my running shoes, I was also keen to boost my cardiovascular fitness again before the new year.

But, as it's winter, I wanted to turn my outdoor runs into treadmill workouts at the gym. It was here that I discovered the Norwegian 4x4 workout, after speaking to a running specialist and personal trainer. Created by the Cardiac Exercise Research Group at the Norwegian University of Science and Technology (NTNU), it's a high-intensity interval training (HIIT) session.

I did the Norwegian 4x4 workout once a week for two months throughout September and October. This is how it went, and why it was so effective in boosting my cardiovascular fitness.

How to do the Norwegian 4x4 workout

This workout consists of four-minute bursts of exercise, done at 85 to 95% of your maximum heart rate. Afterwards, you get three minutes of active rest. It looks like this:

• Warm-up: 5 to 10 minutes of light activity, such as brisk walking, cycling, or jogging.
• Intervals: For 4 minutes, run at 85 to 95% of your maximum heart rate. It should feel difficult and tough to speak in full sentences by the end of the first minute.
• Active Recovery: For 3 minutes, work on bringing your heart rate down to 60 - 70% of your maximum heart rate by turning your run into a slow jog or a walk.
• Repeat: Repeat the above intervals and active recovery instructions for 4 rounds in total.
• Cool down: 5 to 10 minutes of slow walking, followed by some light stretches.

How to work out your maximum heart rate

Calculate 220 minus your age to find your maximum heart rate. Then, use a heart rate monitor or one of the best fitness trackers to keep an eye on this number during your running workout. Your heart rate should reach this number during the four-minute intervals.

If you'd rather avoid the electronics, you'll know you're in the right place when the effort feels intense, you're breathing hard, and you'd be unable to speak in full sentences.

Benefits of the Norwegian 4x4 workout

1. Improves cardiovascular fitness

If you do the Norwegian 4x4 workout, the first thing you'll notice after a couple of weeks is how much your fitness improves. From experience, I can tell you this translates to more than being able to run faster. I've found brisk walks to the train station, climbing stairs in the office, and my strength workouts have all felt much easier.

A review published in the Journal of Cardiovascular Development and Disease shows that interval training, which includes this workout, is one of the quickest and most effective ways to boost heart health by lowering blood pressure, cholesterol, and body fat levels, and increasing heart rate variability.

2. Versatile

Many people hear the word 'high intensity' and immediately think it's going to be tiring, sweaty, and put us out of action for a few days, but that's not the case with the Norwegian 4x4 (well, apart from the sweating part).

It's a versatile workout, says Steph Davis, Olympian and running coach with Runna, one of woman&home's favourite running apps. "Four minutes is a sweet spot where you can maintain a strong pace, tap into your aerobic power, but not build up too much lactate, which will help you recover quicker," she says.

3. Helps runners improve speed

As mentioned, by the end of my two months, I experienced some serious running benefits. I became more efficient, so I could run for longer distances and faster without struggling too much or feeling exhausted after the workout. As part of this, I became naturally faster, shaving off 7 minutes and 51 seconds from my very best 5km time, which I set three years ago.

Whether you're looking to boost your cardiovascular health or you've got big running goals next year, this workout is designed to help those who enjoy running improve their fitness. "It is a well-rounded workout for all race distances. 5k or half marathon, you can adapt the effort you put into the reps," she explains.

"If you are training for a 5k race, then you’d aim to push the pace closer to your 5k effort, whereas if you are training for a half-marathon, then you can slow the pace down. A great way to practice dialling into the correct pace."

4. Builds resilience

Regular exercise teaches us that our bodies are capable of a challenge and helps build resiliency, which translates to everyday life. This workout has this benefit as well.

"Four-minute reps are long enough to feel long when you are working hard," says Steph. "This will improve your mindset when things feel tough! It will improve your ability to stay focused and keep pushing when it gets tough - a very valuable skill."

Studies also show it can help boost mental wellbeing, reducing symptoms of anxiety and depression.

5. Suitable for other cardio activities too

Can't or don't want to run, but still want the heart health benefits? Try this workout formula in an activity you do enjoy, such as swimming or cycling workouts. The most important thing is that you stick to the heart rate thresholds and active recovery intervals.

"Its scalability makes it appealing to a wide range of fitness levels," says Andy. "Ultimately, the Norwegian 4x4 is a simple yet powerful method to transform your fitness, backed by real science and results. For those ready to step up their cardio game, it’s time to go Nordic."

Is the Norwegian 4x4 workout suitable for beginners?

If you are running as a beginner, it's important to work your way up to this treadmill workout. It's not suitable for those who've never run before, Steph warns. "The 4×4 is a high-intensity, fast-paced running session that is too demanding for someone with not much running experience," she says.

"Before taking on harder workouts, beginners should focus on being able to run for longer periods at a lower intensity. This is to allow their body to adapt to the impact, build leg strength and improve their aerobic capacity," she says.

This could mean doing a bit of slow running for a few weeks or following the run-walk method known as Jeffing, which found new popularity this year.

"Once you hit this milestone, then you can layer on the intensity. The top rule in running training: don’t build volume and intensity at the same time," says the coach.