Skating techniques

Sámi with plate stick and hunting gear on skis of unequal length

One-sided skate strides during changes of direction and two-sided ones in the final sprint have always been part of a racer's technique in cross-country skiing.[4] In the early 1970s, the first signs of the increased use of the skate stride could be observed. Strictly speaking, the origins of this form of movement lie even earlier: the single pole catapult technique in medieval Scandinavia used two skis of different lengths. The longer one, the glider, was used for gliding and the shorter one, the andor, was used mainly for pushing off and was covered with skins. The locomotion, in which a shearing of the skis was advantageous, bears a marked resemblance to the asymmetrical form of movement used in skating today.[5]

Before the advent of skating, steady improvements in training methods and equipment, as well as machine-tracking of trails, had led to an increase in running speed and greater use of the double pole thrust in the 20th century, with greater emphasis on upper arm strength. Some races were won on skis prepared exclusively for gliding, with no leg push in the track. New forms of movement developed out of the drive for even higher running speeds.[6]

From 1978, especially the stronger popular skiers increasingly used the half-skate step in icy and fast conditions, where one ski stays in the track and the other is sheared out to the side. The imitators called this Finnstep or Siitonenstep, after Pauli Siitonen, one of the first to use this technique. This also led to an innovation in the preparation of cross-country ski trails - half-tracked, half-rolled. Later, other forms of movement outside the track developed. In the World Cup, the US skier Bill Koch was the first to recognize the advantages of this technique. He won the Engadin Marathon with it in 1981 and the overall ranking of the FIS Cross-Country World Cup in 1982.[4]

In the period that followed, there were heated discussions about regulations, and calls for a ban on the skating technique came from amateur sports as well. The diagonal stride, the main form of movement in the classic style, threatened to disappear completely from competitive sports, and this would have weakened the possibility of identification of the popular athlete with the top sport.[4] At the 1985 World Championships in Seefeld, an excessively difficult cross-country ski trail was deliberately chosen, where no other mastering than in the classic technique seemed possible - the overwhelming majority of skiers nevertheless used the new technique and thus ensured the final breakthrough.[7]

For the 1985/86 season, the FIS introduced parallel competitions in classic and free technique, with half of the World Cup competitions being held in one of the two techniques. The 1987 World Championships in Oberstdorf and the 1988 Winter Olympics in Calgary were the first major events with the coexistence of classical and skating competitions. In the biathlon and Nordic combined, it was agreed that all competitions would be held in the free technique.[8]

As before, most of the top skiers in the cross-country skiing disciplines train in both techniques. The FIS also counteracted specialization by not awarding separate trophies for each technique in the cross-country skiing World Cup, but by holding the same number of races in the classic and free techniques in all competitions. In 1988, pursuit races were introduced, which are run first in the classic technique, then in the free technique. In this case, the skating race is included in the so-called chase start, which means that the start is made according to the time intervals of the first race.[6] Since 2003, this discipline has existed as double pursuit or ski duathlon. Here, the competitions are no longer held on two consecutive days, but directly one after the other, and the change of equipment is also part of the competition.[9]

Athletes in the biathlon and Nordic combined disciplines train almost exclusively in the skating technique, occasionally using the classic technique to train endurance rather than technique per se. In contrast, many recreational skiers continue to use mainly the classic technique, some practice both techniques, and few specialize in the skating technique. There are still fewer prepared trails for the skating technique than for the classic technique. The fears of stress damage to the joints expressed by some sports medicine during the advent of the skating technique have not come true.[10]

Body center of gravity and horizontal leg push-off force during skate stride

The leg movement in skating corresponds to the basic form of the skating stride. The impression takes place alternately from the ski gliding obliquely to the direction of movement, which in the final phase of the impression - still gliding - is increasingly clearly tilted up. The body's center of gravity performs a rhythmic pendulum movement at right angles to the direction of movement, with the push-off and gliding phases merging into one another. The angle of the skis depends on the terrain, the speed and the particular form of movement. In the various movement techniques of skating, the use of the pole results in certain variations of the skating stride, especially as far as symmetry is concerned.[10][11]

During the support phase of a ski, two distinctive force peaks occur, with a force minimum in between just before half of the ground contact time. This minimum divides the support phase into two parts of approximately equal length, to which different functional meanings can be assigned. The first force peak coincides with the end of the leg push-off of the opposite side, which ends the short-lived double support phase, i.e. the period during which both skis are in the snow. Towards the end of this phase, the new gliding ski has absorbed the weight-shifting movement from the opposite side. The significantly higher maximum force in the second, somewhat longer section of the support phase reflects the leg push-off. For optimum leg push-off, it is important to feel the maximum possible pressure on the ski edge, even under constantly changing snow and terrain conditions. It is also crucial that the body is neither in forward nor backward position during the main phase of the leg push-off, so that the impact force is transmitted evenly over the entire ski.[11]

In principle, the double pole push corresponds to that of the classic style and is divided into three phases: It begins with a pull phase after the arms swing forward, when the poles enter the snow at a slightly acute angle. The upper body is then brought forward including the hips. Using body weight, the skier now pulls himself towards the poles, bending the elbows to varying degrees depending on speed. Just before the hands pass the knees, the pushing phase begins. The upper body is then in its lowest position. While upper arm, shoulder and back muscles can be used in the pull phase, only the arms work in the push phase. To prolong the pushing phase, the hands can be opened towards the end, still guiding the pole with the thumb and index finger. When the poles leave the snow, the swing phase begins, which lasts until the poles are used again.[12]

In particular, the swing phase varies considerably when using the double stick thrust in the different movement forms of skating. The most similar to the pure double stick thrust of the classic style is the stick use in the arm swing technique, but even here lower maximum forces occur because there is a relief through the leg work. Due to the high frequency of stick use, the average stick force per cycle is higher in the single-stroke than in any other form of movement and therefore requires strong upper body muscles.[13] In the leading arm technique, the peculiarity occurs that the force impact is not the same on both sides, which in other cases corresponds to optimal execution, but is about 20 percent greater on the leading arm side than on the other side.[14] The average stick force per cycle is higher than in any other form of movement.

Model representation of technique selection depending on terrain slope and speed

Diagonal skating is a pure uphill technique used for steep climbs. It is a symmetrical technique and the only main form of movement in which the poles are not used simultaneously, but individually. When setting off, it starts as a pace movement - pole use with simultaneous leg push-off on the same side - but turns into a diagonal movement, then, as in the diagonal step of the classic technique, one arm comes forward at the same time as the opposite ski. The skis are presented on the shortest path, so there is no leg lock. The upper body turns on the gliding ski, but does not go with the pole. If a gliding phase is no longer possible on a greater incline, this form of movement corresponds to the burr step of the classic technique.[19]

Diagonal skating is very rarely seen in competition. Even by recreational skaters it is used only occasionally, usually only when a glide phase is no longer possible. The reason for this is that it is not trained enough compared to the other forms of movement and is therefore poorly executed.[19]

For climbs and in difficult terrain, the lead arm technique is suitable. This is the most asymmetrical of the main movement forms, only every second leg push-off is a double pole push. The leg movement is an asymmetrical skate step with main push-off leg and main sliding leg. The stick work does not correspond to the classic double stick push, the arm on the side of the main gliding leg is the guide arm. The stick of the guide arm is placed relatively vertically close to the ski, the other much lower obliquely in front of the body. Both poles and the ski of the main gliding leg get contact with snow at the same time. The body makes a relatively strong pendulum motion transverse to the direction of movement, with the position somewhat erect on the side of the main push-off leg, but quite low on the other side; one drops, so to speak, onto the main gliding leg. The arm and body movement appears to be motion related to stand-up paddling.[19][20]

Due to its versatility, this technique is the most important in skating, especially in recreational sports. This form of movement is also suitable for transversely inclined sections of the trail, with the guide arm on the uphill side. Regardless of the terrain, it is advantageous to change sides from time to time, as the type and intensity of muscle strain on both sides differs significantly. For a side change, two skate steps can be performed in succession without the use of a pole. Alternatively, a short, indicated stick use can initiate the change, which is immediately followed at the next step by the next stick use with the guide arm changed.[20]

No form of movement in skating shows so many individual variations.[19] For example, the poles are often not set at the same time, but the pole of the guide arm side follows a little later. In addition, there is also the jumped form, which requires high strength endurance and is therefore practically only used in competition. Here, the main push-off leg is bent more strongly and the already short gliding phase on this side is deliberately interrupted. From the leg flexion, a space-grasping jump is executed in the direction of the main gliding leg, and the stick use begins during the flight phase.[10]

The fully symmetrical single-beat is a very powerful form of movement that also requires great coordination skills. With each step, there is also a supportive double pole thrust. This technique is used primarily on easy climbs, for acceleration and as a sprint form in the finish area of competition courses. Slightly before the leg push-off, the pole insertion takes place, the poles are used roughly parallel to the still gliding ski, the upper body is bent in the direction of the gliding ski. The pole work is performed before the leg push-off is completed with the leg extended. After lifting off the push-off ski, the upper body straightens up, the entire weight is shifted to the sliding ski on the opposite side until the body's center of gravity is above the sliding ski. Since the double pole thrust must be executed at a high frequency, it is not possible to swing the arms forward as actively as in the arm swing technique.[11]

This technique requires not only high strength endurance, but also a very secure sense of balance when gliding on a ski, which is especially difficult when the track is poor. That is why this form of movement is seen somewhat less often in recreational sports. However, it is also the most dispensable main form of movement, since there are only a few sections of cross-country skiing where guide arm or arm swing techniques are not a perfectly suitable alternative. On the other hand, this technique is also said to have the greatest movement aesthetics.

The arm swing technique is one of the symmetrical forms of movement, although it is obviously not completely symmetrical, since the double stick thrust only occurs at every second step, i.e. only on one side as in the lead arm technique. Nevertheless, the arm swing technique exhibits considerably greater symmetry than the lead arm technique, especially in terms of footwork and tracking. The arm swing technique is mainly used on slightly sloping terrain or to maintain a high speed on the flat. The movement sequence is similar to the single stroke, as with this the double pole push occurs in the direction of the sliding ski. The leg push-off begins after the pole insertion, this is a significant difference from the guide arm technique and allows to maintain an accelerating force for a longer period of time. Only in good trail conditions or sufficient skill is it possible to almost complete the double pole thrust on the gliding ski before the leg push-off begins. The weight transfer takes place completely on the other ski. In contrast to the single stroke, the body's center of gravity is not only lowered during the double pole thrust when the arms are swung through, but also in a mirror image during the forward swing of the arms, which is initiated slightly before the leg push-off on the opposite side. This active forward swing of the arms also contributes to propulsion.[21]

Since this technique is also not completely symmetrical, it is advantageous to change sides from time to time. As with the guide arm technique, this change is possible by two successive steps without the use of a pole or by double pole thrusts directly following one another. With the latter variant, several double pole strokes can also follow directly one after the other - thus the side change takes place in connection with a brief change to the single pole. In cross-country skiing sections, it is advantageous to execute the double pole thrust on the ski on the valley side, but the side selection adapted to the terrain is not as decisive as with the guide arm technique.[21]

The largest gear of the five-speed model is sometimes abbreviated and somewhat misleadingly referred to simply as the skate step. This form of movement is used when, due to excessive speed, it is no longer economically possible to accelerate with a double stick push. The sticks can be clamped under the arms or pressed horizontally against the body. The opening angle is very small, the gliding phases are as long as possible. To reduce drag, a low stance can be adopted. At even higher speeds, there is no more leg push-off and the body position corresponds to the downhill squat.[19]

With this form of movement, even somewhat steeper downhill sections can still be supported in an accelerating manner. The pure skating stride is also used for target sprints or for acceleration at the start. In particular, the arms are then actively swung along with the poles drawn up to the forearm, as in long-track speed skating. However, this requires a lot of free space in order not to endanger other track users or competitors. Also, the skating stride without the use of poles can already be used at lower speeds to recover the arm muscles. This is practiced this way in biathlon before shooting, for example.[19]

More for historical reasons, there is the Siitonen step as another technique of skating, as it played an essential role in the transition from classic to skating style. It is a half-skate step in which one ski glides in the track of the track while the other is sheared out sideways. The push off of the sheared out and edged ski is assisted by a double pole push. Since the preparation of separate trails for the two styles, the Siitonen step is still practiced mainly by skiers who want to switch from the classic to the free technique as a learning aid.[8]

The downhill and braking techniques did not differ from those of the classic technique. Compared to the latter, the more stable fixation by boot and binding is advantageous and facilitates the execution, for example, when snowplough turn.[22]

A distinction is made between the passive and active curve treading techniques. Passive stepping on the bow, also known as stepping around, is executed in the same way as the classic style: the ski on the outside of the bow is only loaded briefly in order to be able to lift the unloaded inner ski at the front and turn it inwards. Afterwards, the unloaded outer ski is pulled in and tracked. While passive bowing is performed without the use of a pole, active bowing is supported by a dynamic double pole thrust on the inner ski of the bow. A strong push-off is required from the outer ski. Compared to the passive variant, the active bow kicking is used at lower speeds or larger curve radii and enables the speed to be maintained or even increased in curves.[10]

Different models of skis for skating

Unlike skis for the classic technique, skating skis are designed entirely for gliding, so there is no adhesion zone in the center of the ski. Another important aspect of skating skis is the lateral stability and torsion, which ensures the most even distribution of the push-off force to the base. Like classic skis, skating skis have camber and preload. This is even stronger, even when a ski is loaded with the entire body weight, the center of the skating ski should not be completely pushed through. The aim of this design is to distribute the pressure as evenly as possible over the entire ski surface, as this ensures the best gliding properties. The pretension and elastic deformation of the ski also allow some of the energy invested during push-off to be subsequently converted into propulsion energy.[24]

As in alpine skiing, the ski width is not the same for the entire ski. The intention is not to increase the turning ability of the ski, but to support an even footprint over the entire ski and to achieve good gliding properties.[23] After significant waists were common in the past, manufacturers have returned to a more uniform width. Skis tend to be narrower in the front than in the back. On average, the ski width is about 43 millimeters, although it usually varies by less than four millimeters.[25] Weight plays a more important role in skating skiing than in the classic technique, since the ski is lifted off the snow for a not inconsiderable part of the time. Since weight reduction cannot be achieved at the expense of stability, techniques and experience from aircraft construction have been used to optimize the weight of the ski.[23] There are skis weighing less than one kilogram.[25]

For the selection of a suitable ski there are models with different length and hardness (stiffness). In determining these individual parameters, the main role is played in particular by the body weight and the intended intensity of the practice of the sport, and only then the height. Compared to the classic technique, shorter skis are used, the maximum ski length is only slightly above 1.90 meters. Longer skis would have better gliding properties, but would be a hindrance in narrow passages and especially on climbs, also because the ends of the skis would cross over too far at a large shearing angle.[23]

There are also combination models that can be used for the classic and skating technique. When used in the classic technique, a climbing wax is applied in the center of the ski, while in skating the ski is prepared throughout for gliding. However, such so-called all-round skis are less common.[23]

Shoe and binding

In terms of bindings, there are two systems that practically share the world market: NNN (New Nordic Norm) by Rottefella and SNS (Salomon Nordic System). These are not compatible, the type of binding must be matched to the boot, but not to the ski.[26] In both systems there are special skating bindings, where the connection with the ski is more stable compared to the classic technique. The boot is attached under the ball of the foot and not just at the toe of the boot, as is usually the case with the classic style. A rubber pin or spring makes it easier to pull the ski towards the sole of the foot and prevents the ski from falling off the front. There are bindings where this spring force is adjustable, making them suitable for both techniques, since a stronger force is advantageous in skating.[23]

A skating boot is cut higher compared to a model for the classic technique. The sole is relatively hard and therefore torsionally stiff. The axis of motion supports the activity of the upper ankle joint to match the motion sequence when skating. There are also more shoe models that are suitable for both styles. This also applies to competitive sports, as since 2003 in the double pursuit both techniques are skated directly behind each other in one competition.[23]

Poles suitable for skating

The construction of the ski pole corresponds to the classical technique, it is a hollow tube with a handle and loop at the top and a tip and a stick plate at the bottom. The optimal stick should be as light as possible and resistant to breakage, which are opposing requirements in terms of manufacturing technology, especially for very long sticks. The tube material used is usually carbon or aluminum. There are also cross-country ski poles with adjustable length.[23]

As a rule, slightly longer poles are used for skating than for the classic style; according to the rule of thumb, the optimum length is between 85 and 90 percent of the body height. Longer poles can be advantageous at higher levels of performance. Shorter poles are more beneficial for sprinting distances or steep climbs.[27]

With the emergence of the skating technique at the end of the 1980s, extremely long poles were preferred, the length of which sometimes even exceeded the body height, so that pole support was possible even at high speeds.[8] Studies carried out in 1993 showed that the optimal pole length is very individual and depends on technical and physical conditions. Most of the runners studied could be recommended to use shorter poles than before.[28]

The rise of the skating technique was associated with the confidence that the preparation of the skis would become easier, since "only" the gliding ability would have to be optimized. In the field of competitive sports, this hope has not been fulfilled, since good gliding ability is of even more decisive importance in skating than in the classic technique, and optimization efforts in this area have therefore taken on unexpected dimensions.[29]

Grinding of a brand new ski

Three main factors are distinguished when optimizing glide: the grind, the structure and the waxing. Grinding and structure primarily determine how the melt water created by the pressure of gliding under the ski is displaced and guided along under the ski. In particular, it is important to avoid suction effects. The structure represents a refinement of the grind. A commercially purchased ski already has a grind, usually a universally oriented one, but there are also skis already specially prepared for cold or warmer conditions. The grind is cut into the ski with a special grindstone and diamond and can only be removed by regrinding. The structure is pressed into the ground base. A linear, coarse structure is suitable for wet snow, while fine cross structures are more suitable for dry conditions with crystalline snow. There are handy devices for applying the structure, but their use is almost exclusively limited to racing. Like the wax, the structure disappears after repeated use.[30]

Waxing is considered to be about as important as grinding and structure. When waxing, a distinction is made between liquid and hot waxes. Liquid waxes are the easiest to use; they are simply applied and polished, which can also be done on the trail. Hot waxes are applied with the help of a precisely temperature-controlled clothes iron. The main hot wax used in recreational sports is paraffin wax, which is available for different temperature ranges. Somewhat higher-quality fluorinated wax is used in the same way as kerosene wax. In the field of competitive sports, there are other processes, some of which are combined, such as pure fluorine wax, wax based on nanotechnology, and special powders or sprays.[30]