You’ve probably seen the viral Norwegian 4×4 workout doing the rounds – pushed by running influencers and coaches alike. It’s popular for a reason. But most people still get it wrong.

Not because of the intervals themselves, but because of how they approach the recovery.

By trying to run each effort as fast as possible, it’s easy to stretch the rest periods to maintain pace. That might improve the quality of individual reps, but it reduces the time spent working near VO₂ max – one of the key drivers of aerobic fitness.

‘The mistake isn’t the intervals, it’s the rest between them,’ says Dr Fraser Thurlow, PhD in Human Performance. ‘Longer rest increases the speed of each interval, but if your goal is to maximise the physiological stimulus, shorter recovery can be more effective.’

He explains that shorter recoveries – around 1-2 minutes:

• Maintain VO₂ elevation
• Increase time spent near VO₂ max
• Raise lactate levels, creating greater metabolic stress

In simple terms: longer rest improves rep quality, while shorter rest increases overall training stimulus.

The Norwegian 4×4 protocol that Thurlow refers to is typically structured as follows:

• Warm-up: 10 minutes of low-intensity work – a light jog and dynamic stretches
• Intervals: 4 minutes at 85-95% of your max heart rate. This can be running, cycling, rowing, swimming or even high-intensity bodyweight work. For runners, think roughly 5k-10k pace
• Active recovery: 3 minutes of low-intensity movement, such as walking or easy jogging, bringing your heart rate down to 60-70%
• Repeat: Complete 4 total intervals
• Cool-down: Gradually lower your heart rate, then stretch

As part of his research, Thurlow tested whether the original three-minute recovery – used in the 2007 Norwegian protocol – is actually optimal, analysing six endurance studies from the past two decades.

‘When you rest longer, you can run faster – as you’d expect,’ he explains, noting that speeds peak with around four minutes of recovery. ‘But here’s what’s interesting: you spend less time at VO₂ max.’

Shorten the rest, and the picture changes.

‘Your speed drops slightly, but your body is working much harder,’ he says. One-minute recoveries produce ‘by far the most time above 90% of VO₂ max’ – a key driver of aerobic adaptation.

Blood lactate levels are also highest under these conditions, ‘meaning greater glycolytic stress’ and a stronger anaerobic stimulus.

Put simply: long rest equals faster running, while short rest equals greater physiological demand.

A recovery window of 2-3 minutes may offer a practical middle ground. But Thurlow emphasises that the real lever is progression – ‘how you change rest from week to week’ to drive improvements in VO₂ max.

Kate is a fitness writer for Men’s Health UK where she contributes regular workouts, training tips and nutrition guides. She has a post graduate diploma in Sports Performance Nutrition and before joining Men’s Health she was a nutritionist, fitness writer and personal trainer with over 5k hours coaching on the gym floor. Kate has a keen interest in volunteering for animal shelters and when she isn’t lifting weights in her garden, she can be found walking her rescue dog.