Norwegian skier Johannes Høsflot Klæbo crossing the line to win the men’s 20-kilometre pursuit race at Oberstdorf.

Researchers confirm that Johannes Klæbo is the perfect skier for mass start races

What we have seen on our TV screens has now been confirmed by science.

It has now been some time since elite cross-country ski racing involved competitors starting at fixed intervals and ploughing their way all alone along tracks laid out deep in the forests.

During the World Championships in Planica in Slovenia, racers were only offered a single, traditional, interval start event. All the others involved mass starts of some form or another.

Up until recently, however, no research had been carried out into mass start events. All previous focus had been on interval starts.

Researchers at SINTEF and NTNU wanted to put this right.

Monitored male skiers

During a Norwegian Cup mass start race held at Gjøvik in January 2022, the researchers fitted 57 male skiers with accurate GNSS sensors so that they could follow how the race developed for each and every one of them in detail.

“Our findings have demonstrated that many of the factors that lead to success in interval start races are also important in mass start events,” SINTEF researcher Trine Seeberg says. “For example, the best athletes are those that gain most time on the uphill stretches and then succeed in maintaining higher speeds throughout the race."

Seeberg is a PhD student at the NTNU Centre for Elite Sports Research.

“But there are also other success factors that come more to the forefront in mass starts compared with the distance races,” Seeberg says.

Most elite races today are organised as mass starts, and competitors have little to offer unless they can put some distance between themselves and Norwegian superstar Johannes Høsflot Klæbo before the sprint finish. It was just the same for fellow countryman Petter Northug before him.

“Our study has shown that many of the characteristics exhibited by Northug and Klæbo are important factors when it comes to success in mass start events,” Seeberg says.

Key success factors

Neither Klæbo nor Northug have been studied by the NTNU researchers, but the study does say something about what happens during a mass start race in general, and which factors are most important for success.

The 57 skiers who took part in the study were only just a little below world elite level.

“These are things that we’ve always believed but had not proved for a fact. This is hardly rocket science,” Seeberg says.

The very first scientific study of the most important success factors in mass start races has in fact confirmed what TV viewers who follow cross country races can see for themselves on screen.

Researchers believe that the following five factors are the most important:

  • A good start position
  • An ability to avoid accidents and problems caused by the so-called ‘accordion effect’
  • A resilience to major variations in race intensity
  • An ability to maintain a steady speed throughout the race, especially on the uphill stretches
  • A talent for sprinting

A racer’s start position usually depends on their previous performances. If a skier starts back down the field, this significantly reduces their chances of finishing among the very best. This became evident when the researchers fitted the skiers with sensors that measured what really happens during a race.

“Those who started some way down the field lost almost 20 seconds in the first few hundred metres after crossing the start line. It’s difficult to regain the time you lose here, especially when you have many skiers to overtake during the rest of the race,” she says. “This is important and useful information that can be taken into account during a skier’s training."

The accordion effect

The accordion effect occurs when a bunched-up field starts to climb an uphill stretch. Skiers in the leading group will of course slow down a little. In the worst case, those towards the back of the field will have to brake even before they reach the foot of the slope.

“The accordion effect is very well demonstrated in our data, although at present we are unable to quantify how much extra energy is expended by those towards the back of the field, and how much time they lose, especially when the effect arises repeatedly during a race,” Seeberg says.

She adds that during the Norwegian Cup event at Gjøvik, skiers at the back of the field encountered many more accidents and problems than those at the front. A lack of snow only made conditions worse for those further down the field.

“The course was narrow and there was too little snow. This meant that the race organisers were forced to construct a shorter lap than they would have liked. The skiers thus became more closely bunched than normal, so there were very many accidents and accordion effects,” Seeberg says.

Hang back and save energy

One of the issues that Seeberg is looking into is whether it might be beneficial for a skier to hang back a little and create a small group of competitors racing just behind the leaders. This might reduce problems caused due to bunching, as well as save energy.

The energy saved in this way could be used to gain time towards the end of the race.

“It might be interesting to study the accordion effect in more detail. We might find out more about how much this really costs a skier and whether it might be advantageous to race in a group a little further behind the leaders,” she says.

However, this is not how cross-country skiers think today.

“Most of those taking part in our study raced with a strategy that had them hanging on to the leaders for as long as they could, even though the speeds were higher than they were able to maintain all the way to the finish,” says Seeberg.

A difficult balance

The study demonstrated that all the skiers maintained a high speed from the start of the race, but those that finished in the top ten also succeeded in delivering consistent lap times from lap two all the way to the finish after the sixth lap.

All those who finished outside the top ten exhibited lower speeds and slower lap times once they lost contact with the leading group.

“Other studies have shown that skiers who start their races too hard perform less well overall than those who spread their energy expenditure more evenly during the race. There are of course also major benefits to be had from racing in a group where the air resistance is lower, and where there is less friction on your skis because the tracks are warmed up,” she says.

Seeberg adds that if you drop back from the leading group, you will be giving up the chance of a podium place.

"So, there is always a difficult decision to be made between hanging on to the leading group when the speed gets too high, or dropping back a little,” she says.

It also emerged from the study that it is performance on the uphill stretches that serves to separate the best ten racers from the next thirty, for whom 60 per cent of the time they lost was when tackling the uphill sections.

Racing in spurts

It goes without saying that if the best sprinters succeed in keeping up with the leaders for an entire race, they will have a great advantage at the finish. But in order to do this, they have to be prepared to race in fits and starts.

Major variations in race intensity occur when skiers who are not sprint specialists try to break away from the field.

“This is something that Petter Northug was very good at,” says Seeberg. “Rumour has it that he actually practised racing in spurts when he was training."


Seeberg et al. Race development and performance-determining factors in a mass-start cross-country skiing competition, Frontiers in Sports and Active Living, vol. 4, 2023. DOI: 10.3389/fspor.2022.1094254

About the project

Name of the project: AutoActive

Duration: 2019–2022

Funding: Research Council of Norway

Partners: SINTEF, NTNU, Olympiatoppen (the Norwegian Elite Sports Centre), Meråker Upper Secondary School, Nord University, the University of Oslo and Oslo University Hospital.

The objective of the project is to develop tools, methods and models with the aim of extracting useful and reliable information linked to human performance and activity from a variety of sensor-derived data.

The data acquired will serve as a tool that can be used to develop models that in turn will give us an overall understanding of performance, physiological responses and movement techniques in the field of outdoor cross-country skiing competition and training, as well as the monitoring of people suffering from MS.

The AutoActive project is being funded by the Research Council of Norway as part of its IKT-Pluss programme (project no. 270791).

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