Cross-Country Ski Injuries

Janus D. Butcher

BACKGROUND

Cross-country skiing is one of the three Nordic skiing disciplines along with ski jumping and Nordic combined (skiing and jumping). Most historic references to Nordic skiing discuss its military use. Indeed, the sport of biathlon (skiing and shooting) has its origin in this historic relationship.
Cross-country skiing is generally associated with a low injury rate, and it is considered to be one of the highest aerobic demand activities. Although generally confined to the northern tier and mountain states, its popularity in the United States continues to grow.
Cross-country skiing had remained relatively unchanged from its remote beginnings until dramatic innovations in equipment and technique were introduced over the past 30 years. Currently, two very distinct techniques are used, the diagonal stride (classic) and ski-skating (freestyle).

COMPETITION

Elite-Level Competition

The International Ski Federation (FIS) governs international competition. The FIS establishes race rules, schedules, doping control systems, athlete injury surveillance, and most other aspects of World Cup and World Championship racing.
The specific events held at elite competitions are varied in both distance and technique. Formats include sprint (1 km), sprint relay, middle distance (5, 10, and 15 km), team relay (4 × 5 km, 4 × 10 km), long distance (30 and 50 km), classic/skate pursuit, and others.
One unique aspect of elite cross-country skiing is that the athletes frequently compete as both sprinters (1 km) as well as marathon skiers (30 or 50 km) within the same race schedule. Historically, most competitors trained and raced in both the classical and skating techniques. More recently, there has been some athlete specialization in terms of event distance and technique.

Nonelite Competition

Marathon distance races are held in nearly all of the countries of Northern, Central, and Eastern Europe as well as Japan, North America, and Australia.
In the United States, a full calendar of local, regional, and national marathon races are scheduled throughout the winter months. The largest of these, the American Birkebeiner is 52 km long with over 7,000 participants.
High school and college cross-country ski teams are common in the Northeast, upper Midwest, and Western states. These competitions include races 5-15 km in length with both classic stride and skating formats.

BIOMECHANICS

Technique

Diagonal (Classic) Technique

The diagonal stride technique has been used for centuries and remains a popular style for ski touring and back-country skiing.
In the diagonal stride, forward propulsion is accomplished through alternating kick and glide actions of the skis. This requires a full stop of the kick ski to propel the skier forward. Backward slip of the planted ski is limited by the application of high-friction kick wax on the cambered portion of the ski surface. The requirement to plant the ski to generate thrust limits the maximum speeds obtainable (19).
In the diagonal stride, the poles are used primarily for balance but can contribute up to 30% of forward thrust in higher level skiers (19). Double poling (planting both poles simultaneously) is used to maintain forward momentum as increasing tempo limits the effectiveness of the kick and glide action.

Skating Technique

Developed in the late 1970s, this new technique has rapidly evolved and become the method of choice for most nonelite competitors. Skating is the only technique used in both biathlon and Nordic combined competitions.
The skating technique generates forward momentum by driving the skis at an angle to the direction of travel in a motion analogous to speed skating. There is no kick phase and thus no stopping of the ski during the cycle. Several different strides (V1 skate, V2 skate, marathon skate) are used depending on terrain and skier tempo.
Double poling is used in most skating strides to transfer upper body energy to the skiing surface and can provide up to 60% of the forward propulsive force (24).

Biomechanical Comparison of the Techniques

Skating is much more energy efficient than the diagonal stride technique (11). In addition, with skating there is no need for a high-friction kick wax; so low-friction glide waxes can be used along the entire surface of the ski.
These factors, combined with the use of extremely light-weight composite construction materials as well as improvements in skiing surface preparation, have resulted in a 10%-30% increase in average speed since the 1950s (11,25).

INJURY EPIDEMIOLOGY AND PATHOPHYSIOLOGY

Overall Incidence

Historically, the injury rates in cross-country skiing are reported to be between 0.1 and 5.63 injuries per 1,000 skiers (3,23). The true incidence is difficult to determine because skiing is not generally limited to a confined venue.
In the limited data available from more controlled circumstances, such as endurance races, the incidence was found to be substantially higher at 10-35 per 1,000 skiers (4,19). The majority of these injuries were fatigue related.
Studies evaluating injury patterns in elite-level skiers report higher injury rates. One study reported a rate of 11% in World Cup competitors (9). In another 12-month study, the annual rate of injury in a group of elite Finnish skiers was 62%. However, the majority of the injuries occurred in nonskiing training activities (20).

Changing Injury Patterns

As the technique and equipment have changed, several equipment-injury relationships have been suggested (2,7,13,14,22), although data supporting these associations have been scant at best.
- Increased pole length with the skating technique accentuates demands on the shoulder and elbow.
- Stiffer bindings and rigid boot construction with heel-ski fixation devices in skating equipment may increase the risk of ankle and knee injuries.
The biomechanics of the new technique are also suggested in the changing injury patterns.
- The skating stride places significantly greater demands on the hip adductors and external rotators (19).
- A greater emphasis on upper body strength in the double poling action has been implicated in increasing upper extremity overuse injuries (7).
- Ski recovery at the end of the skate cycle places greater demand on the lateral and anterior compartment of the lower extremity, resulting in an exertional compartment syndrome.

Comparison of Techniques

Initial reports suggested greater incidence of injury in the skating technique; however, this remains unsubstantiated (2,4,7).
In one report of injuries occurring during a long-distance event where the skating technique was the dominant style used, the injury rate was found to be higher than reported for similar races in the years prior to the adaptation of the skating technique (4).

INJURY DISTRIBUTION

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