NorthShore Blog

Drafting – How big a deal for marathon inline skating?

This article is part of our SkateIA Skill Building Series, a partnership between NorthShore Inline Marathon and Skate IA to achieve our shared goal of getting more people on skates and increasing their skills. This skill-focused article series leads up to CONNECT-CAMPskateIA on August 14/15/16 2020. This camp will offer classes via video/zoom by a variety of instructors around the world, rotating activities and training sessions for Race/Marathon/Distance skaters, dance (jam and artistic), Slalom and Basic through Intermediate skills. CAMP will offer 20 minute classes, time to practice and film yourself as well as an opportunity to have the instructors review your video and give you direct feedback. The following article will also be reviewed and discussed at CONNECT-CAMPskateIA by the author. The entire CAMP will be recorded and available for attendees to view on our platform (attendees will get free access, non-attendees will need to pay to view). CONNECT-CAMPskateIA – August 14, 15, 16, Virtually at 9am PDT and Noon EDT. Visit skateia.org/camp for more info.

Skate Instructors Association is an organization that serves both skaters and skate instructors. While we started out as an instructor organization, we are clear that we have something to offer everyone who straps on wheeled skates.

Drafting – How big a deal for marathon inline skating?

by Jacques Thibault MSc

As the marathon season is approaching it is time to discuss drafting during racing events. Most skaters know that drafting can make a difference and help save energy during races. However, understanding how to take the best advantage of drafting can make the difference between winning and losing or having the best vs the worst race of your life!

There are many elements of physics and tactical aspects responsible for optimal drafting during races and taking advantage of them when and where possible is key to become a successful competitor.

The first concept to understand is that drag forces or forces created by going forward through the air are proportional to the square of the speed a skater is traveling. In other word the faster you go, drag (wind resistance) will increase exponentially and demand the production of more and more power to keep a constant speed. This is why cars consume so much more gas when going faster:

Example of auto consumption efficiency (from fueleconomy.gov):

  • 3% less efficient at 100 km/h
  • 8% less efficient at 105 km/h
  • 17% less efficient at 112 km/h
  • 23% less efficient at 120 km/h
  • 28% less efficient at 128 km/h

The shape, the material and the size of a car or a skater and the air density also affect drag forces. The bigger the surface area in the wind the more power will be required to maintain a constant speed. This is why skaters bend their upper body forward, wear thigh fitting clothes, and love the speed performing faster at high altitude races.

Most of the above concepts are generally well understood by inline skaters, however the concept of Wind-Speed is often not recognized in the same way, especially when racing outdoors. Wind is a critical consideration of marathon racing. A strong head wind is not a simple linear force added during a race but it is also subject to the same drag equation as for the car example above. Drag forces including the head wind will be proportional to the square of the Wind-Speed encountered by the skater. Maintaining ground speed for example of 30 km/h in a head wind (traveling at 10 km/h for example) will have an exponential effect on power output proportional to 40 km/h required to maintain the same speed.

In inline racing, the drag forces must include skater speed as well as wind speed (and direction) to calculate the true drag forces. Strategies such as drafting and lower frontal area exposed to the wind become more or less important depending on the wind.

Consider the following:

  • At 16km/h wind-speed, drag forces are negligible. This could be the result from a skater skating in still air or skating at 40 km/h with a tail wind of 24 km/h
  • At 30km/h wind-speed, drag forces account for about 80% of all power expended to maintain speed. In this example, traveling at 30 km/h is a combination of wind and speed created by the skater
  • At 40 km/h wind-speed (this is world record marathon average speed) around 95% of your power is used against combined drag forces.

Aerodynamic positions are constantly changing during a race depending on the wind direction and the relative Wind-Speed of each skater. Race positioning, favoring limiting power output to what is absolutely necessary, and recovery where possible through drafting and lower wind profile must be constantly analyzed and strategically considered during the race by a competitor to attain better performances.

A second concept for discussion is that drafting is caused by a skater in front disturbing the air, thus leaving a trail of turbulent (low pressure) air that is easier to go through than undisturbed air. Drafting subsequently reduces the amount of power needed to maintain a constant speed. Further, research in wind tunnels has confirmed that drafting not only helps the person that is drafting but also helps slightly the person that is in front. The distance behind the skater in front is very important for optimal drag reduction.

For example:

  • Drag can be reduced by 38% if skating inches behind someone
  • Drag is reduced by a lesser degree to approximately 27% if skating 1 meter behind
  • And Drag reduction is very low if skating 3 meters behind

Therefore, following closely the skater directly in front (by inches) while matching strides in order to be very close (and used all air turbulence vortexes) will be the best option to reduce drag when Wind-Speed frictional forces are high.

Research has also shown that the place you occupy in a line of skater in not very different for the first 4-7 skaters when looking at drafting advantages (as long as you stay directly in line with wind direction). However, who you choose to be behind could make a big difference. Drafting behind a large skater is an advantage as this skater creates a more turbulent (low pressure) air flow as they skate.

Finally, it has been shown that staying further back down a line of skater is a clear racing mistake as the benefits of a slightly lower drag are offset by the gaps that often appear between skaters, creating conditions that require increase power production.

The last important concept to understand in drafting is the effect of crosswinds. Crosswinds have been the subject of much research in a variety of sports and are still controversial in their effects. Research has shown that in a crosswind situation, drag is reduced by only 5% when following behind at a slight side offset. However, it is possible to reduce drag by up to 35% if moving to the side of the leading skater slightly overlapping just behind them. This is a successful strategy when experiencing crosswind conditions during a lengthy event.

Conclusion

The key concepts presented above are essential to outdoor inline racing and in-line marathon events. By adopting different strategies, it is possible to reduce drag and subsequently reduce power necessary to maintain a specific speed. Changing the lead often is an effective way to balance everyone’s effort but sooner or later the physical power output the skater can create will be the critical factor in racing results. Efficient use of power will result in the fastest overall time to cover the course of the event.

A.G. Edwards, W.C. Byrnes Aerodynamic characteristics as determinants of the drafting effect in cycling

Medicine and Science in Sports and Exercise, 39 (2007), pp. 170-176

Jacques Thibault participated in long track speed skating at the 1980 and 1984 Olympics and was a World Championship silver medalist! After obtaining his Master’s degree in Science – motor control and learning Jacques worked with some of the top athletes in the world in his role as National coach and Program/General Manager of the Olympic Oval in Calgary from 1990 to 2003.

Jacques is recognized as world-class sports expert, and original contributor of Canada’s Own the Podium program for the 2010 Olympic Games in Vancouver where Canada won a record 13 gold medals and Own the Podium Russia prior to the 2014 Olympics in Sochi and is now working on a similar program for China’s 2022 Winter Olympics. He is the author of two books on training design (short track and speed skating) and a complete high performance guide to short track including KPIs. He just published his third book on skills acquisition for individuals with an Intellectual Disability.

He is an National Coaching Certification Program (NCCP Canada) level 5 coach (the highest) and was directly involved with more than 50 Olympic medalists in speed skating, short track, hockey and cycling. Jacques collaborated for many years with in-line skating programs including Skate IA camp, Alien In-line and in-line training for speed skaters.