Norwegian skier Johannes Høsflot Klæbo crossing the line to win the men’s 20-kilometre pursuit race at Oberstdorf. Photo: Terje Pedersen/NTB

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

What we are seeing on our TV screens has now been confirmed by science. Johannes Høsflot Klæbo ticks all the boxes defined by researchers looking for the most important factors needed for success in mass start cross-country ski racing.

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 upcoming World Championships in Planica in Slovenia, racers are only being offered a single, traditional, interval start event. All the others will involve 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. But researchers at SINTEF and NTNU wanted to put this right. So, during a Norwegian Cup mass start race held at Gjøvik in January 2022, they fitted 57 male skiers with accurate GNSS sensors so that they could follow in detail how the race developed for each and every one of them.

“Our findings have demonstrated that many of the factors that lead to success in interval start races are also important in mass start events”, says SINTEF researcher Trine Seeberg “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”, she says.

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 fore in mass starts compared with the distance races”, Seeberg tells Gemini.

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 with his 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”, says Seeberg.

Key success factors

Neither Klæbo nor Northug have been studied by the NTNU researchers, but the study does say something in general about what happens during a mass start race, 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”, admits Seeberg.

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 his or her previous performances. If a skier starts back down the field, this significantly reduces his or her 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”, says Seeberg. “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”, she adds.

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”, says Seeberg.

Seeberg 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”, explains Seeberg. “The skiers thus became more closely bunched than normal, so there were very many accidents and accordion effects”, she says.

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”, says Seeberg. “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 are thinking today. At least, not if we base our conclusions on those that completed the 22-kilometre race at Gjøvik.

“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”, says Seeberg “Of course, there are 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.

“Moreover, if you drop back from the leading group, you will be giving up the chance of a podium place”, says Seeberg  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”, she says.

Scientific paper:

Trine M. Seeberg et al.: Race development and performance-determining factors in a mass-start cross-country skiing competition. Frontiers in Sports and Active Living, January 2023.

Facts about the project and research method

Sensors are commonly used in sports- and health-related research to measure work requirement, performance, technique and physiology within the respective domains.

In this study, called AutoActive, the researchers were looking into whether they could use the information derived from objective sensor data to modify athletes’ race behaviours with the aim of improving performance. Their aim was to investigate the importance of the work involved in racing uphill stretches, and whether sensor data can contribute towards improving performance.

The study involved a three-day intervention study carried out in Meråker in Trøndelag. For more information, visit the website In this type of study, a hypothesis is checked against a set of supposed causal factors.

The researchers also studied whether it was possible for skiers to learn in a short time how to race uphill stretches efficiently, and whether this resulted in better performance when compared with a control group who did not receive the same training.

The participants comprised 26 national-level male junior and senior ski racers. The first part of the study was for the skiers to complete a 10-kilometre test race on snow before being subdivided into an intervention group and a control group. The same test race was then repeated two days later.  

In between the test races, skiers in the intervention group were given video and sensor-based feedback of their performance in the first race. This involved a theoretical presentation followed by a practical training exercise with the aim of implementing a terrain-specific race strategy focusing on active acceleration over a particular uphill stretch that they had encountered during the test race.

The aim was to achieve greater speed over the top of the hill and thus save time as they raced down the following downhill stretch. The control group was only given the results list from the first test race, and carried out a training exercise involving a similar training load to the intervention group.

In the second race, skiers from the intervention group increased their total acceleration over the particular uphill stretch, and this did indeed save them time on the following downslope compared with skiers in the control group. However, we also noted that this performance improvement could be generalised for other sections of the course. Researchers found that even though the skiers had not trained specifically on other uphill stretches, they nevertheless produced greater acceleration on these as well, and consequently also saved time on the following downslopes compared with skiers in the control group.

The sensors with which the skiers were fitted were measuring both speed and heart rate. The skiers were also fitted with gyroscopes and accelerometers that provided the researchers with a revealing picture of the racers’ movements – in other words, their technique.

The researchers also studied the skiers’ tactical choices and compared these with the race results.

This research was part of a larger project focusing on cross-country skiing in general

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).