An elite runner's running technique is shaped by a number of physical characteristics, the influence of previous training (volume, methods of training) and racing. Hence, the running style of each individual is very specific. The purpose of this study is to point to some important kinematic variables of the running stride of Jolanda Ceplak, the indoor world record holder over 800 metres. From the 3-D kinematic analysis it is possible to draw the following conclusions: The plant is close to the vertical projection of the body's CM (Center of Mass). Vertical displacement of CM is optimal, which can help to improve running economy. Great plantar flexation range, high angular velocity of plantar flexation in the ankle joint and explosive knee extension enable Ceplak to produce a substantial propulsive force and adds to the length of her stride. The. amplitude of the thigh swing of the swing leg is greater than this parameter in comparable studies. Several kinematic parameters of Ceplak's running are quite similar to parameters of longer sprint events (200m and 400m) especial/y during the onset of fatigue.
Yolanda Ceplak's competitive performances during the 2002 and 2003 seasons certainly go down in the history of the 800 metres. She is the indoor world record holder (1:55.82) and her outdoor PB 1:55.19, is the seventh best performance of all times.
Running technique contributes to the competitive edge of a long or middle distance runner. Efficient running biomechanics helps to keep injuries at bay and ensure that the runner's neuro-muscular potential is fully exploited. It also helps to save the energy, which in turn results in better racing.
An elite runner's running technique is shaped by a number of physical characteristics such as flexibility, power, neuro-muscular function, body composition etc., the influence of previous training (volume, methods of training) and racing. Hence the running style of each individual is very specific. However, there are general modelling laws that determine optimal running stride, and these are important starting points in the teaching and improving young runners' running technique.
The running cycle (double stride) consists of the support phase ("braking" phase: foot strike, midsupport and "propulsion" phase or takeoff) and flight phase (follow-through or float, forward swing and foot descent)7. Studies show that running stride efficiency depends to a large extent on how the runner plants his or her foot and how he or she uses the time during the support phase.1, 5, 10, 11 This in turn affects the speed, the onset of tiredness and running economy.
The purpose of the study is to show kinematic parameters of Jolanda Ceplak's running cycle during the finishing stages of the 800m. We focused our attention on parameters that describe dynamic of support phase.
We studied the kinematic parameters of Ceplak's running stride using a video of her competitive effort at European Athletic Association meeting held in Velenje. Her winning time for the race was 1:59.52 (1st 400m - 61.57, 2nd 400m - 57.95). The kinematic analysis covers the distance between 738 and 743m of the race.
3D kinematic parameters were measured with two synchronised Sony DVCAM DSR-300 PK cameras with a frequency of 50Hz. The cameras had an internal synchronisation system. They were placed at an angle of 90° with respect to the object recorded. Spatial calibration was done with eight reference points of two cubes with 1 m sides.
For a 3-D kinematic analysis of running technique, we used APAS kinematic systems (Ariel Dynamics Inc., USA) and our own software. CM (centre of mass) of separate body segments and the total body CM were calculated using a 15-segment anthropometric model.4 Using this model we studied trajectories, velocities, angles and angular velocities of each point and segment. All numeric data were smoothed with a 7Hz digital filter.
Results and discussion
The basic aim of this study was to define and show the stride cycle kinematic parameters that influence the efficiency of Ceplak's running to the greatest extent.
The results (see Figures 1-4 and Table 1) show basic kinematic variables of Ceplak's running stride as she is coming off the last turn and into the finishing straight. Running velocity at this stage was 7.10m/s'. Average stride length was 197cm, but in the section analysed it varied from 190 to 204cm. Relative stride length (stride length / height of body) was 1.17m. Stride frequency was 3.6Hz.
Figure 1: Kinematic parameters of running stride -footstrike
Figure 2: Kinematic parameters of running stride - midsupport
Figure 3: Kinematic parameters of running stride - takeoff
Figure 4: Angles (above) and hip, knee and ankle angular velocity (below) of Jolanda Ceplak's running stride (left leg)
An important factor of efficient running technique is a support phase generating as little deceleration as possible. The braking phase must be as short as possible. A short braking phase and only a slight braking impulse of the ground reaction force (very little loss of horizontal velocity) can be achieved by planting the foot close to the vertical projection of the body's CM on the ground (see Figure1). The distance between the first contact and the projection of the CM must be as short as possible; at the same time, the angle of foot placement on the ground must not be too narrow. The distance of 0.32m at foot strike is similar to corresponding values of other top female runners: Cathy Freeman during a 200m race (average velocity 8.44m/s-1), Marita Koch (0.28m) and Jarmila Kratochvilova (0.27m) in a 400m race (velocity 7.77/ 8.12m/s-1). The angle of 70° at foot strike was also similar2,9. In comparison to sprinting, the distance between foot strike and vertical projection of body's CM is much longer while the angle of foot plant is narrower3.
Apart from the method of planting the foot, the contact time and the appropriateness of the evaluation angle in the takeoff also depend on the execution of midsupport and the swing of the swing leg.
The braking phase and takeoff, which represent eccentric-concentric muscular contractions at the ankle, knee and hip joints, represent the phase of converting the runner's potential energy into kinetic energy6.
During the braking phase, suitable pre- activation and muscle stiffness enable the runner to keep the range of dorsal flexion of the ankle, as well as knee and hip flexion, as small as possible and the braking phase as short as possible (see Figures 2 and 4).
Despite tiredness in the closing stages of the 800m race, the ranges of dorsal flexion of the ankle at 21° and knee flexion at 7° (the widest angle of knee flexion during the support phase is 30°) are relatively very small and comparable (20° and 9°) to the corresponding ranges of top female runners in the closing stages (onset of fatigue) of a 400m race9.
This rather slight "give" in the ankle and knee joints points to the runner maintaining neuro-muscular potential (the ability to maintain muscle stiffness) even with the onset of tiredness. Over the running cycle the hips remain tall, which is reflected in the wide angle (165°) between the trunk and the thigh of the support leg in the braking phase.
From the magnitude of ankle plantar flexion at takeoff (80°), the high angular velocity of the foot (1374°/s-1). a high angular velocity (more than 1000°/s-1) and acceleration in the knee extension, a high forward swing of the recovery leg (63°), the takeoff angle of 62° (the angle between the lower leg and the ground) and the evaluation angle (7°), we can draw the conclusion that this runner's takeoff action is very efficient and explosive (see Figures 3 and 4). The values are comparable with the parameters of Cathy Freeman's sprinting and with the results of a group of elite middle distance runners2,8.
The movement of the swing leg significantly contributes to a runner's efficiency. The swing leg (thigh, lower leg and foot) is the only segment which in the braking phase of the running stride produces the propulsive force acting in the direction of running2,12. Efficient running stride is determined both by the speed of the swing leg, especially the foot, and the trajectory of the foot.
The speed of the swing leg foot during the braking phase is determined by an explosive takeoff and the runner's relaxation, which contribute to a greater range of knee flexion of the swing leg. This enables the foot to move at high speed as close to the thigh (buttocks) as possible. A shorter lever enhances the swing leg velocity and transition from follow-through to forward swing.
At footstrike, the horizontal velocity of the swing foot was 11.90m/s-1 and during forward swing it reached its peak with 14.25m/s-1 (see Figure 5). These values are comparable with foot velocities in longer sprint events (200m and 400m) - particularly in conditions of fatigue. In the 200m, Cathy Freeman's recovery leg foot velocity at footstrike of the opposite leg was 13.80mjs' while in the forward swing phase it was 14.72m/s-1. The best Slovene sprinters (100m) recorded 13.03m/s-1 and 16.30m/s-1 respectively2.3.
Figure 5; Horizontal (above) and vertical velocity (below) of CM, of Jolanda Ceplak's left and right feet
The efficiency of Ceplak's follow-through is reflected in the high position of her foot and a very narrow angle in the flexed knee (148°) of the swing leg in the midsupport (see Figure 1 and Table 1).
An important parameter of running economy is vertical displacement of the body's CM. The apex of the trajectory of the body's CM depends mainly on the takeoff angle (the narrower the better) and the relationship between the vertical and horizontal velocities of the CM at push-off. Ceplak's vertical displacement of CM is 0.08m (see Fig. 6); similar to Cathy Freeman (0.08m) and a group of elite female middle distance runners (0.076m)2,12.
Table 1 - Kinematic parameters of 800 meters running - Jolanda Ceplak
Figure 6: Vertical displacement of body's CM during running stride
Strength and power training is reflected in the technique of 800m runners. Several kinematic variables of 800m running appear to be quite similar to the parameters of longer sprint events, particularly in conditions of fatigue.
On the basis of the kinematic analysis of Jolanda Ceplak's running, we can draw the following conclusions:
FROM IAAF/NSA 1-04