The Gliding and Push-off Technique of Male and Female Olympic Speed Skaters

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1 ORIGINAL INVSTIGATIONS INTRNATIONAL JOURNAL OF SPORT BtOMCANICS, 1989, 5, The Gliding and Push-off Technique of Male and Female Olympic Speed Skaters Ruud W. de Boer and im L. Nilsen The 1988 Winter Olympic Games provided a unique opportunity to study large numbers of optimally prepared speed skaters during ideal ice and weather conditions for all the competitors (indoor Olympic Oval in Calgary). In this study a kinematic analysis was conducted of the gliding and push-off technique during the Men's and Ladies' 1,5-m and 5,-m races. Statistical analysis showed that factors such as trunk position, preextension knee angle, and peak knee and hip angular velocities failed to correlate with mean lap speed. Within such a homogeneous group of elite athletes it was found that the higher work per stroke of the faster skaters was correlated to a longer gliding phase and a more horizontally directed push-off. All skaters showed plantar flexion at the end of the stroke, which is undesirable and indicates the complex nature of the gliding and push-off technique in speed skating. Biomechanical investigations on speed skating have provided a number of objective parameters that are important for coaches of competitive skaters. On the one hand, aspects concerning trunk position, knee angle, suit, air density, weather conditions, and body composition that influence frictional losses have been explored (Ingen Schenau, 1982). On the other hand, analyses of elite and nonelite male and female skaters have shown which technical parameters are of essential significance for performance in speed skating (de Boer, ttema, van Gorkurn, de Groot, & van Ingen Schenau, 1987; de Boer, Schermerhorn, Gademan, de Groot, & van Ingen Schenau, 1986; Ingen Schenau, de Groot, & de Boer, 1985; de oning, de Boer, de Groot, & van Ingen Schenau, 1987). The scientific literature on speed skating has been reviewed recently by van Ingen Schenau, de Boer, and de Groot (1987) and by de Groot, ollander, Sargeant, van Ingen Schenau, and de Boer (1987). The most important technical parameters for speed skating can be summarized as follows: 1. Skating position: Speed in skating can be seen as the ultimate result of a balance between (minimal) frictional losses and (maximal) power production. Ruud W. de Boer, formerly with Vnje Universiteit, Amsterdam, is now with Rijksuniversiteit Utrecht, Fysiologisch laboratorium, Vondellaan 24, 3521 GG Utrecht, The Netherlands. im L. Nilsen is with the Biomechanics Laboratory, University of Calgary, 25 University Drive N.W., Calgary, Alberta, Canada T2N 1N4.

2 12 D BOR AND NILSN Skating position is extremely important with respect to frictional losses (Ingen Schenau, 1982) and the potential for power production (Ingen Schenau et al., 1987). 2. Push-off mechanics: Previous studies show that the most important technical factor in speed skating is the amount of mechanical work per stroke. This is particularly true for skating the curves. Important parameters that determine this amount of work per stroke are effectiveness of push-off (direction of pushoff force), extension velocity in hip and knee joint, and preextension knee angle (de Boer et al., 1986; Djatschkow, 1977; Ingen Schenau et al., 1985). 3. Stroke frequency: It has been shown (Ingen Schenau et al., 1985) that stroke frequency is used primarily to control speed (like an accelerator pedal). The stroke frequency in the curves cannot be chosen freely by the skaters. Due to the sideward push-off characteristics in speed skating and the geometry of the speed skating oval, the stroke frequency is a constraint frequency dependent on speed, work per stroke, and the radius of the curve (de Boer, ttema, van Gorkurn, de Groot, & van Ingen Schenau, 1988). Considerations for This Study All the results described in the literature have been derived from studies with small samples of selected all-around skaters, during races with relatively uncontrolled external conditions (ice, wind). Moreover, at present most of the technical parameters are related to mean speed per lap. It is to be expected that phases of acceleration and deceleration within one lap are also related to technique of the skater. The geometrical model of speed skating the curves (de Boer et al., 1988), for example, predicts that better skaters (higher work per stroke) can increase their speed in the curves more than less skilled skaters. The XV Winter Olympic Games provided a unique opportunity to study large numbers of optimally prepared male and female world class speed skaters. It was the first time ever that the races were held indoors (standardized ice and weather conditions for all competitors). It was our purpose to investigate relations between speed and variation in speed on the one hand with kinematic parameters of speed skating technique on the other. It is expected that even within such a group of world class athletes, performance in skating will be determined by differences in coordination and timing of the complicated speed skating technique. Subjects Methods Data were collected during the 1988 Winter Olympic Games held in Calgary. All male and female athletes who participated in the 1,5-m and 5,-m races served as subjects. These athletes were considered the best speed skaters in the world and, in contrast to all-around meets such as the uropean and World Championships, skated only their strongest events (only one race per day). eight and body mass were derived from the athletes' data base provided by the Olympic organization (OCO 88). A total of 28 women ( kg, m) participated in the 1,5-m and 24 women (62.3f 5.3 kg, m) in the 5,-m races. A total of 37 men ( kg, 1.79f.8 m) participated in the 1,5-m and 29 men ( kg, 1.78k.8 m) in the 5,-m races.

3 GLIDING AND PUS-OFF TCNIQU 121 Measurements The races were organized at the indoor Olympic Oval in Calgary at an altitude of 1,1 m. The Men's and Ladies' 1,5-m and 5,-m events were selected in this study to allow several measurements of each skater in the same race for both the straightaways and the curves. Two sets of two panning 16-mm highspeed film cameras (LOCAM 5 1-2, Angenieux mm zoom lens, battery pack operated, nominal film speed 1 z) were used to record the technique of the skaters. Using one set of cameras, we filmed a couple of strides of the skater in the outside lane on the straightaways from two positions. The other set of cameras filmed the same skater in the outside lane of the following curve, also for a couple of strides from two positions. The cameras were placed outside the track on tripods at known positions and orientations (see Figure I), and were synchronized electronically using the internal LD system. odak color highspeed daylight negative film 7297 was used. Two video cameras (VS, 3 z) mounted on tripods and placed at known positions (Figure 1) followed the skater during the entire lap. Film and Video Analysis Data analysis of the speed skating technique was conducted according to previous studies by de Boer et al. (1986), de Boer, ttema, et al. (1987), and Ingen Schenau et al. (1987). The stride of the right leg closest to the lateral camera was analyzed. The positions of neck, hip, knee, and ankle were manually digi- Figure 1 - xperimental set-up in the Olympic Oval. The thick lines indicate the six segments used for the speed analysis: 1. Lateral frlm camera straights; 2. Posterior fh =era straights; 3. Lateral film camera curves; 4. Anterior fi camera curves; 5. Video camera; 6. Video camera.

4 122 D BOR AND NILSN tized using a ewlett Packard 9874a digitizer and Vanguard m-16c motion analyzer (see Figure 2). From these data the trunk angle (TI), hip angle (T), and knee angle (T) were calculated. From the posterior film the positions of hip and heel were digitized and the push-off angle (AL) was calculated (see Figure 2). For the curves a similar set-up was used, but the posterior camera was replaced by an anterior camera for organizational reasons. The angles derived from film analysis were smoothed using a digital filter (low pass Butterworth, fourth-order zero lag, cutoff frequency = 9.6 z, as described by Winter, 1979). The angles were corrected for optical distortion (de Boer et al., 1986), and the results presented are kinematic data in the real plane of motion. Angular velocity was obtained with a Lanczos 5-point differentiating filter (Lees, 198). All calculations were done on a SUN computer (programmed using C and UNIX). The time phases of a speed skating stroke were defined as follows: B = beginning of stride (contralateral skate is lifted from the ice), = start of hip extension (smoothed hip angular velocity remains > 5O.s-'), = start of knee extension (smoothed knee angular velocity remains > 5" s-'), = end of stride (skate is partially lifted from the ice). These instants determine the gliding phase (from B to ), the push-off phase (from to ), and the repositioning of the leg phase (from to B of the next stride). The repositioning phase was not considered in this study. A skater's technique was operationally defined as the trunk, knee, and push-off angles at the above mentioned instants within a stroke (see Table 1). Video recordings provided information about speed and stroke frequency (F). Video frame counting (accuracy = 1/6 s) yielded time of the skater crossing known positions on the ice. From these data, speed over six segments (see LATRAL POSTRIOR F'igure 2 - Film analysis method. The neck, hip, knee, and ankle (lateral view) and hip and heel (posterior) were manually digitized.

5 GLIDING AND PUS-OFF TCNIQU Table 1 Description of Selected inematic Variables Derived From Film and Video Analysis Name Units Description TI B Ti TI T T ALB AL TV VL DVS DVC F AF S s S. s-' O.s-' rn-s-' mas-' mgs-' s-' J kg-' Instant of final explosive extension in hip joint lnstant of final explosive extension in knee joint nd of stride (instant skate is lifted from ice) Trunk angle (TI) at beginning of stride Trunk angle (TI) at start of final knee extension Trunk angle (TI) at end of stride nee angle (T) at beginning of stride nee angle (T) at beginning of final knee extension nee angle (T) at end of stride Push-off angle (AL) at beginning of stride Push-off angle (AL) at start of final knee extension Push-off angle (AL) at end of stride Maximal hip angular velocity Maximal knee angular velocity Average lap speed derived from electronic timing Change in speed on straights Change in speed in curves Stroke frequency Mechanical work per stroke per kg body mass Figure 1) and the derived changes in speed (Table 1) were calculated (de Boer & Nilsen, 1989). Power PF necessary to overcome friction was calculated using a model of air and ice friction losses (Ingen Schenau, 1982). This model predicts power as a function of trunk position, knee angle, body weight, body length, and speed of center of mass. Air frictional losses were corrected for altitude and measured barometric pressure. Ice friction coefficients were derived from the measured ice temperature and pre-olympic experiments on ice friction during speed skating in the Olympic Oval (de Boer & de oning, 1987). Mechanical work per stroke AF was calculated as AF=PF/F and divided by body weight. This work-perstroke AF can be seen as the mechanical result of the push-off and is also equal to the increase of kinetic energy of center of mass due to this push-off (de Boer et al., 1986; Ingen Schenau et al., 1985). Statistics Values of the parameters were averaged over three laps (1,5 m : two laps) to obtain a representative picture of the skaters' individual technique. These averaged values were correlated with lap speed, changes in speed within one lap, and mechanical work per stroke using the BMDP statistical package (Dixon, 1985). A significance level (two-tailed) of.5 was used.

6 124 D BOR AND NILSN Results A typical example of the movements of a speed skater is shown with the diagrams in Figure 3a (1-msec intends). The data are derived from the films of a male top skater skating on the straightaways at the beginning of a 5,-m race. Stick diagrams of the trunk, upper and lower leg segments (lateral view), and leg (posterior view) form the mechanical basis of the present analysis. After synchronization and correction for optical distortion, the time series of knee angle, hip angle, and push-off angle can be presented as in Figure 3b. The top part shows the hip angle (solid line) and hip angular velocity (dotted line) as a function of time. Time has been defined as the beginning of the stride. The middle part shows the knee angle (solid line) and knee angular velocity (dotted line) versus time, and the bottom part shows the push-off angle versus time. A speed skating stride on the straightaways (for a detailed discussion about the differences with the technique in the curves, see de Boer, ttema, et al., 1987) can be divided into three phases: gliding, push-off, and repositioning. During the gliding phase the skater more or less maintains his or her static body position in the hip and knee joint (hip and knee angle are constant or slightly increasing or decreasing). The duration is dependent on the skater's forward speed and skills, but usually lasts sec. After the gliding phase, a fast explosive extension in hip and knee joint can be obsened. This is mainly the result of rotation of the upper leg. This push-off phase usually lasts sec. The peak extension velocity in the hip joint is smaller than in the knee joint. During both the gliding phase and the push-off phase, the skater also shows a rotating movement around the skate in the frontal plane (see Figures 3a and 3b). This is a continuous movement with a constant push-off angular velocity of 5-75" s-l. At the beginning of the stride the skater leans on the outside edge of the skate (push-off angle AL > 9"). Until lift off of the push-off skate (time ), push-off angle AL decreases. At time, push-off angle AL is about 55" (skater is leaning on the inside edge of hislher skate). After lift off the repositioning phase starts: The skater is bending hislher leg and trunk, glides and pushes off with the other skate, and is preparing for the next stride of the right leg. The mean speeds, based on electronic timing, attained by the skaters during the Olympics were very high because of the optimal conditions (indoor, 1,1-m altitude): m*s-i for the Men's 5, m; 11.2f.31 m=s-i for the Women's 5, m; 13.23f.33 m=s-l for the Men's 1,5 m; and k.44 m=s-' for the Women's 1,5 m. The variation in speed within such an elite group of Olympic skaters was very small: The standard deviations varied from only 1.65% in the Men's 5, m to 3.68% in the Women's 1,5 m. The variation in speed within one lap, based on video analysis, was very small. Although a general tendency to decelerate at the transitions from straights to curves and from curves to straights was observed, the speeds on the different segments never exceeded the mean lap speed by more than 3 % (group values). For details of the variation in speed and the control of speed in relation to technique (stroke frequency and work per stroke) on the straights and in the curves, refer to de Boer and Nilsen (1989). The kinematic parameters describing speed skating technique (Table 1) were derived for eight situations. The results were subdivided into distance (1,5 m and 5, m), gender, and straights or curves (Tables 2 through 9). The mean values and standard deviations of the kinematic variables for the Men's 1,5-m

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8 126 D BOR AND NILSN Table 2 Means and Standard Deviations of Selected inematic Variables: Men's 1,5-m Straights (n = 37) Correlation coefficients Name Units M SD VL DVS AF TI B TI TI T T AL TV Note. Significant correlations with lap speed (VL), change in speed on straights (DVS), and work per stroke (AF). Table 3 Means and Standard Deviations of Selected inematic Variables: Men's 1,5-m Curves (n r 22) Correlation coefficients Name Units M SD VL DVC AF TI 6 TI T1 T T ALB AL TV Note. Significant correlations with lap speed (VL), change in speed in curves (DVC), and work per stroke (AF).

9 GLIDING AND PUS-OFF TCNIQU 127 Table 4 Means and Standard Deviations of Selected inematic Variables: Women's 1,5-m Straights (n = 28) Correlation coefficients Name Units M SD VL DVS AF T1 B TI T1 T T ALB AL TV Note. Significant correlations with lap speed (VL), change in speed on straights (DVS), and work per stroke (AF). Table 5 Means and Standard Deviations of Selected inematic Variables: Women's 1,5-m Curves (n = 18) Correlation coefficients Name Units M SO VL DVC AF TI B TI TI T T ALB AL TV Note. Significant correlations with lap speed (VL), change in speed in curves (DVC), and work per stroke (AF).

10 128 D BOR AND NiLSN Table 6 Means and Standard Deviations of Selected inematic Variables: Men's 5,8-m Straights (n = 29) Correlation coefficients Name Units M SD VL DVS AF TI B TI TI T T ALB AL TV Note. Significant correlations with lap speed (VL), change in speed on straights (DVS), and work per stroke (AF). Table 7 Means and Standard Deviations of Selected inematic Variables: Men's 5,-m Curves (n = 28) Correlation coefficients Name Units M SD VL DVC AF T1 B TI TI T T ALB AL TV Note. Significant correlations with lap speed (VL), change in speed in curves (DVC), and work per stroke (AF).

11 GLIDING AND PUS-OFF TCNIQU 129 Table 8 Means and Standard Deviations of Selected inematic Variables: Women's 5,-m Straights (n = 24) Correlation coefficients Name Units M SD VL DVS AF TI B TI TI T T ALB AL TV Note. Significant correlations with lap speed (VL), change in speed on straights (DVS), and work per stroke (AF). Table 9 Means and Standard Deviations of Selected inematic Variables: Women's 5,-m Curves (n = 22) Correlation coefficients Name Units M SD VL DVC AF TI B TI TI T T ALB AL TV Note. Significant correlations with lap speed (VL), change in speed in curves (DVC), and work per stroke (AF).

12 13 D BOR AND NILSN straights are shown in Table 2. The signifcant correlation coefficients of these variables with mean lap speed, change in speed on the straights, and mechanical work per stroke are indicated in the three columns at the right of Table 2. Similar results for the other analyses are shown in Tables 3 through 9. Note the lack of significant correlations of kinematic variables with lap speed and with changes in speed within one lap. The magnitude of the significant correlation coefficients with work per stroke varies between.4 and.6. ven in the situation of the highest correlation coefficient (Table 9), only about 5% of the variance in work per stroke can be explained by the kinematic variable. Comparing the information of the eight analyses yielded the following systematic result: The higher mechanical work per stroke of the faster skaters is correlated with a longer gliding phase (time ), a longer stride (time ), and a smaller push-off angle at the start of the push-off phase (angle AL). Some more detailed statistical analyses were done in order to get a better understanding of the relation between kinematic variables and the performance of a speed skater. But an analysis of the individual laps of each skater and the difference in speed and technique between the beginning and end of the race yielded no new information. Also, a multiple regression analysis (BMDP 9R; Dixon, 1985) did not lead to new findings. These analyses were not incorporated into the results of this study. Discussion The most noticeable result of the statistical analysis was the lack of significant correlations between kinematic variables of technique and performance (mean lap speed: VL). ven parameters that were important in previous investigations on speed skating technique (de Boer et al., 1986; Ingen Schenau et al., 1985; Ingen Schenau & Bakker, 198) such as trunk position, preextension knee angle, and knee and hip angular velocities failed to show any correlation with forward speed. It should be realized, however, that these studies were done with groups of skaters with a large interindividual difference in performance level. During the Winter Olympic Games the groups were very homogeneous with respect to performance, resulting in a small variation in speed (standard deviations were less than 4%). From these results, however, it cannot be concluded that trunk position, preextension knee angle, and peak extension velocities in hip and knee joint are not important for a proper speed skating technique. But within an elite group of Olympic speed skaters these are no longer discriminating factors in performance. Also, the changes in speed on the and in the were not systematically correlated to speed skating technique, mostly because the skaters hardly changed their speed within one lap. This unexpected result contrasted with studies by uhlow (1974, 1976), who did measure variation in speed within one lap during sprint races. It was hypothesized that skaters in the present study would accelerate in the curves and decelerate on the straights. Moreover, it was expected that these phases of acceleration and deceleration were correlated to kinematic variables. The speed within one lap was remarkably constant, however. In two previous studies (5,-m races, outdoor), a change in speed in the curves was measured: a decrease of -.58f.17 m*s-i (de Boer, ttema, et al., 1987) and an increase of.92f.41 m*s-i (de Boer et al., 1988). These large changes were most likely the result of external wind conditions. Apparently

13 GLIDING AND PUS-OFF TCNIQU 131 the windless conditions in the indoor Olympic Oval allowed skaters to maintain a constant cruising speed. Details on the control of speed and the relation with technique are discussed by de Boer and Nilsen (1989). Speed skating is truly a threedimensional movement. The body center of mass accelerates with respect to the forward gliding push-off skate by extension of the knee and hip in the sagittal plane, while the center of mass rotates from the lateral to the medial side of the skate in the posterior plane. It is important to realize that there is continuous movement in these two planes (shown in the stick diagrams in Figure 3a). The increase in kinetic energy-of the center of mass due to the push-off is equal to the mechanical work per stroke AF (Ingen Schenau et al., 1985). As demonstrated by Ingen Schenau et al. (1985) and by de Boer et al. (1986), the amount of useful work per stroke is determined by the horizontal (propulsive) component of the push-off force. It is easy to understand that the mechanics of the push-off angle AL determines the magnitude of the effective (horizontal) component of the push-off force. In experimental studies (de Boer et al., 1986; de Boer, ttema, et al., 1987; Ingei Schenau et al., 1985) it was found that the faster skaters demonstrate a higher work per stroke due to a smaller push-off angle (a more horizontal directed push-off). In a follow-up study (de Boer, Cabri, et al., 1987) it was shown that muscle coordination patterns (MG) confirm these kinematic findings. The results of the present study are in agreement with the above mentioned mechanics of the speed skating technique. Comparing the results of eight analyses (Tables 2-9), and summarizing which kinematic variables are systematically correlated to mechanical workper stroke, yields the following description of the optimal gliding and push-off technique in speed skating: The higher work per stroke of the faster skaters results from a better gliding technique and a more effectively directed push-off. The stroke time and the time of the gliding phase are higher for the better skaters. In the gliding phase the center of mass is rotated from the lateral to the medial side of the skate. Because of the longer gliding phase of the better skaters, at the onset of the final explosive knee extension the push-off leg has a more horizontal position with respect to the ice (more rotation in the posterior plane). This will result in a higher horizontal component of the push-off force, and consequently in a higher velocity of the center of mass due to the push-off. Comparing the results of the kinematic analysis, as expressed by the group means and standard deviations in Tables 2 through 9, with results of similar experiments (e.g., 1,5 m and 5, m at the 1983 World Championships for women) yields slightly higher standard deviations for the present study. Assuming an equal error due to the analysis (same set-up, equipment, and digitizing procedure), this might reflect a larger variation in speed skating style in the present study. Previous studies concentrated on West uropean skaters whereas the Olympic races included many Oriental skaters as well. Speed skating coaches agree that these skaters show a different way of skating. Some aspects (sway of trunk, curvature of the back) were not properly incorporated into the current biomechanical analyzing model. This might be another reason for the lack of correlations with performance. A real three-dimensional model should be used in future experiments to cover these and other aspects of the speed skating movement in detail (exorotation in hip joint, movement of arms, and contralateral leg). Such a method was used in a study on the start in speed skating and appears promising (de oning, de Groot, & van Ingen Schenau, 1989).

14 132 D BOR AND NILSN When studying stroke mechanics in detail (e.g., Men's 5,-m straights), it was found that in the gliding phase the trunk angle decreased by 4" (flexion), the upper leg angle increased by 23" (extension), and the lower leg angle decreased by 15" (flexion). In an attempt to understand these changes, we estimated the x-, y-, and z-positions of the body center of mass using frlm data and data derived from Clauser, McConville, and Young (1969) and Dempster (1955). Positions were expressed with respect to the ankle joint, with z the vertical, y the forward, and x the sideward component. A typical result of such calculations is shown in Figure 4 (same skater as in Figures 3a and 3b). The vertical position (z) remains more or less constant during the entire stroke. The sideward position (x) shows the rotational movement from the lateral to the medial side of the skate in the posterior plane. The forward (y) position shows an unexpected shift. At the beginning of the stride the y position of the center of mass is negative (behind ankle joint). During the stroke the y position is shifted forward to 25 cm in front of the ankle joint. Group mean values of such calculations for the Men's and Women's 1,5 m and 5, m (straights) are shown in Table 1 (standard deviations of 4 to 5 cm are omitted). These results confm the forward shift of the center of mass in y direction during the stroke. ven these elite Olympic speed skaters cannot suppress plantar flexion at the end of the stroke. This will result in an excessive increase in ice friction when the tip of the skate blade pricks into the ice (flying pieces of ice can be seen on the film). The Y values in Table 1 even suggest that this occurs more at the higher speeds of the 1,5 m. These kinematic results are confirmed by measurements of the push-off forces in speed skating. Both Ingen Schenau (1981) and de Boer, Cabri, et al. (1987) found a forward shift in the point of application of the push-off force. Apparently the unnatural gliding and push-off technique in speed skating differs so much from the more normal movements like walking and running that the human locomotor system has difficulty suppressing the undesirable plantar flexion. time (s) Figure 4 - The x- (solid line), y- (dotted line), and z- (intermittent line) position of the center of mass in time. For details, see Discussion.

15 GLIDING AND PUS-OFF TCNIQU Table 1 Position of Center of Mass in X-, Y-, and 2-Direction at Beginning (B) and nd () of Stroke While Skating the Straightaways Distance XB X YB Y ZB Z Men's 5, m Men's 1,5 m Women's 5, m Women's 1,5 m Concluding Remarks It is concluded that within a homogeneous group of Olympic skaters, trunk position, preextension knee angle, and peak knee and hip extension velocities do not correlate with performance. A biomechanical analysis of the optimal gliding and push-off technique shows that the faster skaters show a higher work per stroke. This is due to a longer gliding phase and a more horizontal position of the pushoff leg just before the final explosive knee extension phase. It was found that even these elite Olympic athletes cannot suppress plantar flexion, resulting in an increase of ice friction when the tip of the skate blade pricks into the ice. Real three-dimensional analyzing methods should be used in further studies to enable a better understanding of the complicated speed skating technique. References Boer, R.W. de, Cabri, J., Vaes, W., Claxys, J.P., ollander, A.P., de Groot, G., & Ingen Schenau, G.J. van (1987). Moments of force, power and muscle coordination in speed skating. International Journal of Sports Medicine, 8, Boer, R.W. de, tterna, G.J.C., Gorkum,. van, de Groot, G., & Ingen Schenau, G.J. van (1987). Biomechanical aspects of push-off technique in speed skating the curves. Internatl'onal Journal of Sport Biomechanics, 3, Boer, R.W. de, ttema, G.J.C., Gorkum,. van, de Groot, G., & Ingen Schenau, G.J. van (1988). A geometrical model of speed skating the curves. Jouml of Biomechanics, 21, Boer, R.W. de, & de oning, J.J. (1987). Ice fiction during speed skating in the Olympic Oval. Unpublished research report, Free University of Amsterdam and University of Calgary. Boer, R.W. de, & Nilsen,.L. (1989). Work per stroke and stroke frequency regulation in Olympic speed skating. Intem'oml Jouml of Sport Biomechanics, 5, Boer, R.W. de, Schermerhorn, P., Gademan, J., de Groot, G., & Ingen Schenau, G.J. van (1986). Characteristic stroke mechanics of elite and trained male speed skaters. International Journal of Sport Biomechanics, 2,

16 134 D BOR AND NILSN Clauser, C.., McConville, J.T., & Young, J.W. (1969). Weight, volume and center of mass segments of the human body (AMRL-TR-69-7). Dayton, O: Wright- Patterson Air Force Base. Dempster, W.T. (1955). Space requirements of the seated operator (WADC Tech. Rep ). Dayton, O: Wright-Patterson Air Force Base. Dixon, W.J. (1985). BMDP statistical soware, printing. Berkeley: University of California Press. Djatschkow, W.M. (1977). Steuering und optimierung des Trainingsprozesses. Ausdauersporten mit zyklischer Bewegungsstruktur [Control and optimization of training. ndurance sports with cyclic movement patterns]. Berlin: Sportverlag. Groot, G. de, ollander, A.P., Sargeant, A.J., Ingen Schenau, G.J. van, & de Boer, R.W. (1987). Applied physiology of speed skating. Journal of Sport Sciences, 5, Ingen Schenau, G.J. van, & Bakker,. (198). A biomechanical model of speed skating. Journal of uman Movement Studies, 6, Ingen Schenau, G.J. van (1981). A power balance applied to speed skating. Doctoral thesis, Free University, Rodopi, Amsterdam. Ingen Schenau, G.J. van (1982). The influence of air friction in speed skating. Journal of Biomechanics, 15, Ingen Schenau, G.J. van, de Groot, G., & de Boer, R.W. (1985). The control of speed in elite female speed skaters. Journal of Biomechanics, 18, Ingen Schenau, G.J. van, de Boer, R.W., & de Groot, G. (1987). On the technique of speed skating. Zntemational Journal of Sport Biomechanics, 3, oning, J.J. de, de Boer, R.W., de Groot, G., & Ingen Schenau, G.J. van (1987). Pushoff force in speed skating. ZnternationalJourna~ of Sport Biomechanics, 3, oning, J.J. de, de Groot, G., & van Ingen Schenau, G.J. (1989). Mechanical aspects of the sprint start in Olympic speed skating. International Journal of Sport Biomechanics, 5, uhlow, A. (1974). Analysis of competitors in world speed skating championship. In R.C. Nelson & C.A. Morehouse (ds.), Biomechanics W@p ). Baltimore: University Park Press. uhlow, A. (1976). Running economy in long-distance speed skating. In P.V. omi (d.), Biomechanics ). Baltimore: University Park Press. Lees, A. (198). An optirnised film analysis method based on fhte difference techniques. Journal of uman Movement Studies, 6, Winter, D.A. (1979). Biomechanics of human movement. New York: Wiley. Acknowledgments This study was made possible through the IOC Medical Commission's Subcommittee on Biomechanics and Sport Physiology, Red Lake Corporation, XV Olympic Winter Games Organizing Committee (OCO '88), and The University of Calgary. Data analysis was supported by a grant from Sport Canada, applied research program. Also gratefully acknowledged is the help of the Olympic speed skating research group-gemt Jan van Ingen Schenau, Gert de Groot, Jos J. de oning, Maarten Bobbert, Marge artfel, Yasuo Yoshihuku, and Todd Allinger.