How I’ve been doing Norwegian 4×4 Intervals wrong 

 I have been persuaded that improving my cardiorespiratory fitness, measured by my VO2 Max , would be enormously beneficial, in terms of significantly improving my chances of living a long and healthy life. It’s not exactly surprising that exercise benefits your health. What has surprised me, and led to renewed enthusiasm to improve my fitness, is the absolutely enormous scale of this benefit. A 2016 scientific statement by the American Heart Association suggested that being amongst the physically fittest people, compared to the least fit, has a benefit on the same level as being a non-smoker compared to a cigarette smoker. Whilst I respect every adult’s right to make bad choices, I have always considered the decision to be a smoker to be a particularly stupid choice. It would be hypocritical of me, on finding out that being unfit is as bad for your health as smoking (or worse according to some studies), to not now make serious efforts to improve my fitness.

There are lots of ways of improving cardiorespiratory fitness. I want a way that is effective, simple and doesn’t require a large amount of free time, plus has a good evidence base behind it. The Cardiac Exercise Research Group (CERG) at the Norwegian University of Science and Technology has a solution that matches all these criteria. They advise 4×4 intervals. The idea behind these intervals is that you spend as much time as possible within the target heart rate of 85-95% of your maximum heart rate. This stresses your body (in a good way), encouraging it to make adaptations and changes that improve your fitness. Getting your heart rate at this level is hard work, which is why you intersperse the work intervals with recovery periods.

4×4 intervals start with a 10 minute warm up, where you jog at a moderate pace. This is followed by the first 4 minute work interval. During this work interval you run hard, at a consistent pace, for the full four minutes. The aim is that your heart rate should reach the target of 85-95% of your maximum heart rate in the first one or two minutes, then you maintain this level for the remainder of the interval. You then spend the next three minutes in a recovery interval. During the recovery interval you  jog at a moderate pace, or briskly walk. This active rest allows your body to recuperate for the next hard interval, whilst keeping your heart rate up (to around 60% of your max). Keeping your heart rate up is supposed to help your muscles to efficiently clear lactate, and presumably makes it easier in the work intervals to get it back up to the target heart rate quickly.You continue cycling between work and recovery intervals until you have completed four work intervals. At the end of the fourth work interval you shouldn’t feel completely exhausted (if you do you have pushed yourself too hard). Instead, you should feel like you could do a further interval. 

If you don’t have a heart rate monitor, you can still do 4×4 intervals. Instead of aiming for a heart rate, aim instead to get to an intensity where you are breathing heavily and unable to talk in long sentences, as this roughly approximates to the 85-95% of max heart rate region.

I’ve made four attempts at running these intervals now, and I’ve been impressed by the early results. Following the second week, I ran 5km at my best pace in about 8 years. This was encouraging. However the 4×4 intervals didn’t actually go to plan. I recorded my heart rate during the runs, and looking back found that I was spending a lot less time in the high target heart rate zone than CERG recommended I should be. I think this was in large part due to three mistakes I was making.

The first thing I did wrong was having a short warm up, of only 5 minutes, rather than the recommended 10. During my five minute warm ups, even jogging at the moderate recommended pace, my heart rate wasn’t getting particularly high. A ten minute warm up would have helped with that. As my heart rate was still quite low at the end of my five minute warm up, it made it much harder to reach the target heart rate during the intervals, particularly the first interval.

The second thing I did wrong, at least on my first attempt, was not running hard enough during the intervals. I still had the mindset of running a set distance and aiming for the best possible overall time. In a distance run you don’t want to push yourself too hard at the beginning, because it causes your total time to be worse, as you are too tired by the end to run at a decent pace. In intervals, there is still a limit on how hard you want to run, as you want to be able maintain the same pace for the entire four minutes. So you can’t sprint for the first minute and then be too exhausted to maintain this for the remaining three minutes of the interval. However, obviously you can push yourself much harder for those four minutes than you could  if you wanted to maintain a consistent pace for 5 kilometres. I didn’t push myself hard enough during my first interval run, which again reduced the amount of time that my heart rate was high enough to reach the target zone. This in turn reduced the amount of benefit that I got from the exercise session.

Thirdly I had my recuperation runs set at 4 minutes in length, instead of the three minutes recommended by CERG. So I was running 4 minutes of interval than having a 4 minute recuperation period of moderate jogging, then running a hard interval again. I liked the simplicity and symmetry of this approach. However, considering that this isn’t the approach CERG adopt, it’s likely my adaptation wasn’t optimal. I think one problem with my method is again the difficulty it imposes on reaching the target heart rate during the intervals. At the end of my 4 minute recuperation jogs my heart rate was lower than it would have been after just three minutes, making it harder to get back to the target heart rate during the work intervals. 

I’ve now corrected for all these mistakes. This  has helped, but it hasn’t meant that I have been able to get my heart rate into the optimal zone as much as I’d like. However I have a further card up my sleeve. I have been working on  how to optimise the settings and readouts on my Garmin watch to best help me carry out my 4×4 runs effectively. This has meant that it displays a read out showing if my heart rate is in the right zone, as well as buzzing to warn me if it drops too low. It also buzzes if my heart rate gets too high, but that is less of a problem for me at the moment. I will write about exactly how I have adjusted my Garmin in a later article.