HOUDIJK, H., J. J. DE KONING, G. DE GROOT, M. F. BOBBERT, and G. J. VAN INGEN SCHENAU. Push-off mechanics in speed skating with conventional skates and klapskates. Med. Sci. Sports Exerc., Vol. 32, No. 3, pp. 635–641, 2000.
Purpose: Personal and world records in speed skating improved tremendously after the introduction of the klapskate, which allows the foot to plantar flex at the end of the push-off while the full blade continues to glide on the ice. The purpose of this study was to gain insight into the differences in skating technique with conventional versus klapskates and to unveil the source of power enhancement using klapskates.
Methods: Ten elite speed skaters skated four 400-m laps at maximal effort with both conventional and klapskates. On the straight high-speed film, push-off force and EMG data were collected. An inverse dynamics analysis was performed in the moving reference plane through hip, knee, and ankle.
Results: Skating velocity increased 5% as a result of an increase in mean power output of 25 W when klapskates were used instead of conventional skates. The increase in mean power output was achieved through an 11-J increase in work per stroke and an increase in stroke frequency from 1.30 to 1.36 strokes·s−1. The difference in work per stroke occurs during the final 50 ms of the push-off. This is the result of the ineffective way in which push-off forces are generated with conventional skates when the foot rotates about the long front end of the blade. No differences in muscle coordination were observed from EMG.
Conclusion: A hinge under the ball of the foot enhances the effectiveness of plantar flexion during the final 50 ms of the push off with klapskates and increases work per stroke and mean power output.
Anew era in speed skating has started after the recent introduction of theklapskate in the international arena. This new type of skate is equipped with a hinge between shoe and blade under the ball of the foot. This hinge allows plantar flexion of the foot at the end of the push-off while the full blade remains in contact with the ice (8). The introduction of the klapskate was accompanied by a remarkable improvement of personal records and all world records were shattered during the season of 1997–98. Skaters who switched to klapskates were able to increase their skating speed by as much as 4%. This is equivalent to an increase in mean power output of about 10%.
The idea that speed skating performance might be improved using a skate that allows plantar flexion of the foot while the blade continues to glide over the ice was described in literature as early as 1987 (6). It was based on biomechanical research into the specific characteristics of the gliding push-off technique in speed skating and the push-off mechanics of vertical jumping.
Despite the high velocity that can be achieved in speed skating with the gilding push-off technique (6), this push off is a very constrained movement. Speed skaters must keep their trunk horizontal to limit the influence of air friction, which is considerable at high velocity (4). At the same time the speed skater, skating with conventional skates, has to suppress plantar flexion of the foot in order to perform a gliding push-off and to prevent the tip of the blade from scratching through the ice (7). Thus, with conventional skates, only rotation of upper and lower legs can contribute to the acceleration of the skater’s body center of mass (BCM). Furthermore, it has been noticed that the absence of a powerful plantar flexion not only limits the contribution of the ankle plantar flexors but is also accompanied by an incomplete knee extension at the end of the push off (7). This is attributed to the way that rotational velocity of the leg segments is transferred into translational velocity of the BCM. As can be derived mathematically this transfer is constrained by the geometry of the system, causing the velocity at which the hip moves away from the ankle to decrease before the knee is fully extended (5). For speed skaters, this decrease in push off velocity occurs at a knee angle of about 150° (7). After this time, the inertial force of the relatively heavy trunk and contralateral leg will pull the push-off leg from the ice. The remaining range of knee extension is performed while the leg is in the air and, hence, cannot contribute to push-off energy.
It should be noticed that only a small percentage of skaters on conventional skates succeed in suppressing plantar flexion entirely (13). However, this plantar flexion, pressing the front tip of the blade in the ice, was considered to be undesirable and even counterproductive. Therefore, in most kinematic studies of speed skating, the end of the (effective) push-off is defined as the instant that the rear end of the blade leaves the ice despite of additional contact between ice and front tip of the blade.
In less constrained movements, such as jumping and sprint running, the geometrical constraint is dealt with by executing an explosive plantar flexion at the instant the extension velocity of the hip relative to the ankle decreases. In this way, the extension velocity of the leg (the velocity at which the hip moves away from the surface) can be increased further and contact between the push-off leg and surface can be maintained. Thus, the ability to plantar flex the foot not only enables the ankle but also the knee extensor muscles to do additional work. It was hypothesized that by enabling the speed skater to plantar flex his foot while the full blade remained on the ice, a similar increase in work per stroke could be obtained. A skate was developed in which a hinge between shoe and blade enables the skater to plantar flex his foot while the blade remains gliding on the ice (8).
A remarkable progress in the performances of speed skaters switching to klapskates has been observed. Although the benefits of the klapskate are undisputed, limited data on the push-off mechanics using klapskates are available. In a kinematic analysis performed previously (3), the expected increase of push-off duration and range of knee and ankle joint extension was confirmed. However, a kinematic analysis does not elucidate the amount or source of power enhancement. Moreover, in that study, two different groups of skaters were studied, introducing possible confounding factors. In the present study, we have investigated the push-off mechanics within one group of skaters, skating with both conventional and klapskates. The purpose of this study was to gain insight into the differences in skating technique with conventional and klapskates, and to unveil the source of power enhancement using klapskates. The use of high-speed film, an instrumented skate recording push-off force, and EMG recordings enabled us to gain important insight into the benefits of the klapskate.