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Shaking All Over – Conquering Vibration for Better Marathon Skating Performances

Mike Ward
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Training

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.

Shaking All Over – Conquering Vibration for Better Marathon Skating Performances

by Mark Greenwald, MSc.

When first asked to contribute an article on improving performance in marathon skating, a great deal of flashbacks rolled through my head. Visions of blurred air rising off sweltering pavement in the summer heat, crazy courses and terrains, silver dollar size blisters, race strategies and tactics; these are the fond memories I have from such events. However, it is my desire in writing on in-line skating, to break fresh ground and explore a novel topic to which most in-line skaters can relate. Every skater has spent time on a patch of rough road wishing it would come to an end sooner rather than later; this is of course part of the sport of in-line skating. But how does vibration resulting from a skating surface really impact an athlete, and can anything be done about it?

This article explains the effects of vibration when in-line skating, and examines in more detail the results when experienced by the human body. Armed with this knowledge, we’ll make recommendations for solutions that result in improved performances, better skating experiences, and more smiles at the finish line. In considering your marathon skating approach, there is little doubt that the right choice of equipment can make your marathon effort a literal “skate in the park”, or an endless slog that leaves you searching desperately for sight of the finish line! Making the right choice about what’s under your feet therefore becomes very important.

The fatiguing effects of vibration-

Think back to road-tripping as a youth in your friend’s VW or Gremlin, vs the same trip via a Cadillac or Lincoln (think land yacht)? Did the latter trip not seem quicker and more relaxing?  Not to jar anyone’s vivid memories of youthful adventures, but there are real physical reasons some complete the journey more rested than others. And some of this resulting fatigue, can be attributed to the underlying effect of vibration and the human body’s response.

In-line skating is generally considered more friendly to the body when compared with the pounding absorbed in a sport such as marathon running. However, at the wheel-surface interface there is a great deal going on that may not be readily visible. Some of this involuntary “action” transfers to the body resulting in muscular fatigue and ultimately has a significant effect on movement efficiency.1 On in-line skates this fatigue factor takes a toll on a participant’s, muscles, joints, and nervous system. A small amount of vibration, such as experienced driving over a cattle gate or rumble strips in a car may be annoying but is easily tolerated, but imagine driving over that surface for an hour or more!

An in-line skater encounters millions of minute vibrations that impact the body over the course of a marathon event. Muscle activation is necessary to attenuate this additional load and energy expenditure.1 This means your muscles are working overtime like little shock absorbers to absorb these almost imperceivable impacts. While you may not always sense it, this vibration has a cumulative effect on your body!

A 2002 study found that vibration from in-line skating resulted in a 10% decrease in maximum voluntary contraction of plantar flexor force and a decrease in ankle proprioception after skating.2 In elite level sports, 1 or 2% performance increments are often the difference between 1st and 25th place! Consider this load on top of the mechanical work the muscle is already expected to perform in order to maintain velocity over the course of a race, and it becomes significant.1 As further demonstrated in this study, fatigue resulting from vibration has the potential to inhibit auxiliary and stabilizer muscles. Such small muscle groups would normally assist in maintaining technical efficiency required to maintain higher race velocites.2 This is why from a physiological perspective, wheel choice is one important variable that can have a great deal of effect both on efficiency in terms of total time to skate the event, and how one feels at the finish line.

Understanding a little more about the potential of this fatigue effect on the body, we can now look at how to make improved choices regarding the best equipment to overcome such a detractor. Vibration can be characterized as the “action” or deviation occurring at the interface of a wheel and surface. As skaters know, on a smooth surface this deviation remains small, however on a rough surface it becomes larger and can often be physically sensed. To better understand each deviation (impact) in a visual form, one might compare it to a radio wave where many cycles of waves would be characterized as frequency, and the size of the waves amplitude (picture FM and AM radio waves). Therefore, if we experienced many small impacts, we would see an increase in frequency, and larger surface impacts would show an increase in amplitude. How a given set of wheels either “rolls over” or “absorbs” surface imperfections encountered, either reduces or contributes to vibration. Whatever action is not reduced at the wheel/surface interface, will determine how much additional work the body must do to neutralize such effects.

Wheel variables and performance considerations-

A great deal of very good quality information has been written about wheel choice, ranging from diameter (does size really matter?) to durometer, using 3, 4 or 5 wheels, bearing considerations, wheel profile, rocker/radius and arrangement (e.g. mixing various sizes and durometers). A quick internet search provides many such articles; here are some links to a few of the better ones:

In-Line Skate Wheels 101 – https://www.liveabout.com/inline-skate-wheels-4122926

Hardness of In-Line Skate Wheels – https://bladeville.com/blog/hardness-of-inline-skate-wheels/

Physics of the In-Line Skate Wheel – http://www.online-skating.com/articles-2661-physics-of-the-inline-skate-wheel.html

All of the variables noted in these thorough articles can be considered important in choosing the right setup for a marathon skate event. However, such considerations also tend to be very individual.

The mechanics of wheel performance for in-line skates – Pt. 1 –

For purposes of analysis and explanation pertaining to vibration, we will focus on two classic aspects of in-line skate wheels: diameter (size) and durometer (hardness). By breaking things down even further, we can look deeper into the performance characteristics of these factors.

The first is the principle of leverage and pertains more to the size of the wheel. Larger wheels, with the same sized axle, will have more leverage between the wheel edge as it encounters the surface, and will have fewer rotations to cover the same distance. Therefore, the resistance at the axle will be lower and subsequently the wheel more efficient.  One could characterize the wheel as being faster, as it requires less energy to overcome axle friction. Larger wheels will also generally roll over ground imperfections more easily, and therefore take less energy to overcome rougher surfaces. Ultimately, larger wheels overcome resistance to the condition of the ground surface and reduce the energy necessary to maintain velocity.3

Big Wheels – the trade off-

Of course, as with many good things in life, larger wheels come with a trade-off.  While rolling resistance and vibration is reduced with a larger wheel, one of the consequences that a marathon skater must deal with is a raising of their Center of Gravity.  Center of Gravity can be defined as the point where all the forces of gravity at work are said to be concentrated. Gravity will always want to pull something it is acting upon to the ground.

As a proficient skater, we are generally pretty good at overcoming this, using our balance to remain upright on our skates.  When we elevate our Center of Gravity however, the effort to use our muscles in order to position us to balance and remain upright becomes just a little more difficult. For a short distance this may not be significant, but when needing to maintain control and technical skating efficiency over a sustained period, this can become an issue.  When we combine this with the tendency of vibration to fatigue our muscles, elevating our Center of Gravity can become an undesirable tradeoff for reduced effects of vibration by using larger wheels.  Any skater who has ever finished a race with wobbly ankles, wondering if they will continue to place their skates down in a balanced position and stay upright to the finish line will be familiar with this dilemma. It can feel like pushing a rubber-band. By the time one realizes they are to this point of fatigue, they have long past the point of performing their most efficient skating. They are now fighting just to stay on their feet and forceful pushes, efficient transfer of weight, and speed, are in the rear view mirror.

The mechanics of wheel performance for in-line skates – Pt. 2 –

The second major wheel factor to consider pertains to the material the wheel is made of, referred to as the “durometer”. With regard to wheel durometer, or the hardness of the wheel, this factor can be adjusted to provide relief from the fatiguing characteristics of vibration.  Essentially, a harder wheel will roll over a given surface with less deformation upon encountering a surface imperfection. However, the lesser ability of the harder wheel to absorb the shock of a rougher surface, will result in the tendency for the force encountered to transfer up the chain to a place it can be absorbed. This can include the frame, boot, or even muscle and bone of the skater.  A softer wheel will tend to absorb the imperfection, much like a shock absorber, dampening these undesirable effects of vibration and subsequent muscle fatigue.

Wheel Hardness -the trade off-

The trade off with use a lower durometer wheel (softer) is a potentially slower rolling wheel due to more frictional force encountered at the rolling surface. The mechanics of absorbing surface imperfections requires energy and tends to slow the rotation of the wheel. Also, much like a car tire with low pressure, a softer wheel has a larger surface contact patch, and consequently requires more energy to keep turning. A lower durometer will dampen the effects of vibration transferred on to the body, and also tend to lower associated fatigue. However, a wheel that is too soft requires more physical energy by the muscles to turn over and to keep turning in order to maintain a desired velocity.  Consideration and balance should be given to what is gained and given up by the choice of a harder/softer wheel.

As one can see, wheel choice for a marathon skating competitor becomes quite important. Likely the best approach is through trial and error, as each individual will not only be affected by these variables differently (due to weight differences, strength, endurance, etc.), but will likely have a personal preference depending on which factors they feel affect them the most.  Trying different variations at shorter distances may be a way to “test” combinations of equipment in order to find the best, most efficient setup for each individual.

Changing up wheel size and durometer in order to find the “right” combination for an individual skater is a most effective way to deal with the negative but often overlooked effects of vibration on a marathon skater. Conquer vibration and you will make marathon skating a lot more enjoyable, as well as faster to the finish!

Examples-

Example 1: Marathon athlete A finds themselves continually fatigued in the second half of their marathon effort and unable to maintain their speed.  They have a solid skating technique. They try moving to from a 90mm wheel to a 110mm wheel to reduce surface resistance and try a boot with a stiff Kevlar upper or buckle system to reduce the instability as a result of raising their center of gravity.

Example 2:  Marathon athlete B finds that they have trouble with balance and maintaining efficient speed generating technique toward the end of their marathon event. The have purchased expensive boots recently that are very comfortable, with good support, and they do not want to make another investment as finding a good fit can be tricky for them. This skater decides to try maintaining their 100mm wheels but moves from 84a to 82a durometer (or even some combination of the two durometers on the same frame), in order to reduce the effects of vibrational fatigue. This allows them to maintain a lower Centre of Gravity, while reducing vibration, maintaining balance and muscular fatigue, and overall technical skating efficiency needed to cover the marathon course faster.

References

  1. Jordan, M. (2020, June 16). Interview with Dr. Matt Jordan [Effects of vibration on muscle at the cellular level].
  2. Thompson, Cynthia & Belanger, Marc. (2002). The effects of vibration in inline skating on the Hoffmann reflex, force and proprioception. Medicine and science in sports and exercise. 30 November, 34(12):2037-2044.
  3. Meden, J. (2016, June, 1). Why do bigger wheels roll faster? What is the physics behind this?, Quora. June 5th, 2020 {https://www.quora.com/Why-do-bigger-wheels-roll-faster-What-is-the-physics-behind-this}

Mark Greenwald – Mark is one of the founding members of Alien In-Line Skate School, based in Calgary, Alberta, Canada. Hailing from Chicago/Park Ridge, he represented the USA in Long Track Speedskating, competing in the 1988 & 1992 Olympic Games achieving a top ten finish. He competed successfully on wheels for Team Speed Specific (team members of the US National Speed Skating Team (ice)) as well as Rollerblade Canada and K2 Pro Teams through 1994. Mark possesses an undergraduate degree in Kinesiology and an MSc. in Kinesiology (motor learning). He has served as both Director of Sport and Director of the Calgary Olympic Oval, contributing as an architect of programs helping Oval athletes win over 20 Olympic Medals for Canada. Mark also served US Speedskating in the role of CEO/Executive Director and was Co-Chair of USS’s Sport Science Commission from 2014 through 2018. Mark became certified as a Level I and II instructor and eventual Instructor Examiner Canada for the IISA/ICP in the mid 90’s and early 2000’s. Mark maintains a current Level I and II with Skate IA and is a co-founder of Skate PE. He presently leads the company he helped found, Alien In-Line, as Managing Director.