Slow, easy runs may be getting all the praise right now, but there are times when going for a jaunt around the block after work just doesn’t cut it. Whether you want to beat your neighbour at Parkrun or earn some vital bragging rights for your next pub trip, chasing down a new PB can be incredibly satisfying.

Doing all the work behind the scenes? That’s slightly less enjoyable. The rapid improvement you make as a beginner aside, we all know that running faster or longer takes a lot of hard work, especially when you have to push the pace during interval sessions. But according to a new study, pushing yourself to the max for 1km periods might not always be the key to performing at your best.

The research, from the University of Copenhagen, found that runners who used the 10-20-30 intervals technique to train over the course of six weeks saw more improvement in their final pace when they ran their fastest interval at 80% of their maximum effort, compared to going all-out. But what does that mean in practice? 

To understand the results of this study, you’ll need to be acquainted with the 10-20-30 interval technique, which has long been held up as a way to improve both health and performance. In 2012, a study of 18 “moderately trained” runners found the method could improve VO2 max and decrease blood pressure.

How to do 10-20-30:

• Run 30 seconds slow
• Run 20 seconds at a medium pace (around 60% effort)
• Run 10 seconds very fast
• Repeat 3-4 times

There are numerous ways to structure a 10-20-30 session, but all sessions involve three different running paces: slow, medium and fast. The slow pace is adopted for 30 seconds, followed by a 20-second medium-pace block and a final 10-second sprint. The amount of times this is repeated tends to vary, but after a certain number of rounds you’ll typically have a recovery block followed by another block of 10-20-30 rotations.

The good thing about 10-20-30 training is how personalised it is to each individual – what feels fast to you might not feel fast for someone else, and vice versa. It’s all about running to feel, rather than running to a clock.  

We know the 10-20-30 interval technique works to improve performance, but the most fascinating finding from the new research is that those final 10 seconds don’t need to be as intense as you might think.

To reach this conclusion, the researchers recruited 19 runners and asked them to replace their normal training with 10-20-30 sessions. Each of these sessions involve three to four 5-minute blocks with recovery periods in-between; the participants took part in three of these sessions every week over the course of six weeks.

However, there were some differences between what these runners were asked to do. While half of the group stuck to the usual 10-20-30 approach – running at 100% intensity for those final 10 seconds – the second half were asked to hold themselves back a bit on the final section, only using 80% of their maximum effort.  

The researchers recorded the 5k times of the runners both before and after the six weeks of training and found that those in the 80% group achieved an average improvement of 42 seconds, compared to a 24-second improvement recorded in the 100% group. Both groups saw an average VO2 max improvement of 7%.

So, why is this? According to Professor Jens Bangsbo, who headed the study, it’s all to do with the impact of interval training on heart rate. “The result of the study really came as a surprise,” he explained.

“We think that it is related to the fact that training at 80% of one’s maximum still gets the heart rate up significantly higher than a runner’s typical training. A higher heart rate leads to improvements in heart function and circulation, as evidenced in their times and fitness levels.”

It’s worth noting that the sample size of this study is too small to be truly representative, so more research is needed to confirm that this approach to interval training is genuinely beneficial.  

While interval training can play an important role in training for longer distances, the researchers found that decreasing the effort of that final sprint may not be beneficial the longer you’re aiming to run.

After analysing the muscular impact of the training on the runners involved in the study, they found that only the 100% group formed more mitochondria – aka, the tiny powerhouses found in our cells. Because mitochondria are particularly important for muscular endurance, it’s a good idea to continue sprinting at 100% effort in the fastest blocks of your interval sessions if you’re training for a half or full marathon compared to a 5k.    

Images: Getty