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SPACE GUIDE TO WINTER SPORTS – CROSS COUNTRY SKI

SPACE GUIDE TO WINTER SPORTS – CROSS COUNTRY SKI

Education

We start the new year with a look at Cross country skiing..

Cross-country or Nordic skiing is the oldest form of skiing and is generally practised over flatter ground or rolling terrain, in either the classic or skating style.

Cross-country skiing is something that anyone can take up and can be a fantastic way to see the area surrounding a resort or even away from ski centres with enough snow cover. Cross-country trails can take you far away from the hustle and bustle of the main ski pistes and lift lines, giving you a different perspective on the mountains. It’s also fantastic for your fitness, and at the competitive level is one of the most cardiovascular-intense sports in the world. Several British athletes, most of whom developed their skills in Scotland, represent GB at World Cup level and in the Winter Olympics. It is a relatively easy sport to learn and the basic equipment is cheap, though descending takes a certain amount of skill and top end equipment can rival alpine ski kit in price.

Equipment

Cross-country skis differ from alpine skis in that they’re lightweight, very thin and designed specifically for self-propelled travel over a wide variety of terrain, not just downhills. Even if you’ve skied before, it is very different to regular skiing and the skinny skis can take some getting used to. The boots used are also lightweight and attach to the skis at the toes only, with the bindings enabling your heels to lift off the ski, allowing a striding motion. Waxless cross-country skis are far easier to use and preferred by many over their waxed equivalents. They achieve grip by means of a scaled texture set into the ‘kick zone’ (the area of the ski base under your toes), allowing you to propel yourself forward. Waxable skis require different types of wax for different snow conditions.

If you’re trying cross-country skiing for the first time it’s a good idea to investigate the difficulty of your chosen route before you set out. Because the skis are thin and often without metal edges, and the boots light and flexible, even a gentle downhill gradient can be a lot more difficult than it would be with downhill equipment! Stick to the already established cross-country tracks, where two parallel grooves in the snow are set to make controlled descents easier. Many areas will have trails rated according to difficulty.

There are also wider ‘touring’ cross country skis which are designed to be used in deeper snow where there are no trails, these often have metal edges to help with turning and control on descents.

Technique

There are two main techniques in cross-country skiing; classic, and skate (free) skiing. The classic style is where skiers stick to the parallel tracks cut into the snow, moving forward with a striding motion and use of poles. Cross-country skis have a camber which means the textured ‘kick-zone’ underfoot is not in contact with the snow when weight is evenly distributed between both skis for gliding. On downhill sections, a snowplough can be used to control speed.

Skate skiing involves movement similar to ice-skating, transferring weight from one ski to another, with skis moving outwards in a diagonal direction to propel you forward. To skate effectively, you need a specifically designed skate ski, or a ‘combi’ ski which allows both classic and skate skiing.

Our first look at Cross Country skiing comes in the form of a study of the biomechanics of low back pain in young cross country skiers..

 

Biomechanics and LBP in Young Skiers

Although the injury rate among skiers is low, there is an increasing number of low back pain (LBP) among adolescent skiers. Studies including younger skiers have shown a high frequency of LBP, compared to age-matched control groups. The type of technique used in skiing has been suspected to play a major role in the development of back pain in skiers, and most of those with a history of LBP reported diagonal skiing to be the most provocative. During diagonal skiing, hip extension is an important force producer; therefore, the ability to extend the hips becomes highly relevant. Furthermore, increased cycle rate along with a large peak leg force is key factor in achieving a rapid diagonal stride.

The repeated hyperextension of the lumbar spine seen in every hip extension was the potential cause of the pain noted in classical skiers. Prolonged static contractions of the erector spinae muscle could be the cause of pain with the diagonal technique.  Increased tension in the hip flexor muscles and increased soreness of the erector spinae muscles were common among skiers with LBP. The increase in muscle tone of both these muscle groups could be the cause of increased lordosis of the lumbar spine. The one-sided poling in diagonal skiing also necessitates rotation of the torso, which is mostly done in the thoracic spine.  Repetitive torsional trauma may cause instability in the low back and that repeated rotation with the diagonal technique may result in LBP.

In double poling, a strategy to achieve a more effective double poling technique, skiers exhibit a higher hip angle velocity along with a smaller minimum hip angle. This repeated flexion and extension in the poling phase is also considered as being another potential cause of pain.

The relation between back pain and altered biomechanics shows decreased mobility of the hips, reduced thoracic mobility and particularly, decreased thoracic extension in young females who suffered from LBP. Also, an increased lordosis among those females with back pain. Studies have shown an increase in the relation between thoracic kyphosis and lumbar lordosis among young elite cross-country skiers over a 5-yr period. The skiers suffering from LBP at follow-up had a significantly increased thoracic-lumbar relation, compared to skiers without LBP.

Reference:

Article:
Spinal alignment, mobility of the hip and thoracic spine and prevalence of low back pain in young elite cross-country skiers
2016 Feb;12 :21-28.
Publication Date (Web): 2016 February 23 (Original Article)
doi:https://doi.org/10.12965/jer.150255

Photo:

Front. Physiol., 24 July 2018 | https://doi.org/10.3389/fphys.2018.00976
Developments in the Biomechanics and Equipment of Olympic Cross-Country Skiers

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