|A Biomechanical Comparison of Elite Swimmers Start Performance Using the Traditional Track Start and the New Kick Start|
Honda, K.E.1, 2, Sinclair, P.J.1, Mason, B.R. 2 & Pease, D.L.2
The international governing body for swimming ‘FINA’ has approved the development of a new starting block (Omega, OSB11) with an in-clined kick plate at the rear of the block. The purpose of this study was to determine the effects of the new start platform on performance relative to that of the traditional track start. Fourteen elite swimmers completed three ‘dive and glide’ starts using the kick plate and three traditional track starts. Results indicated the kick start to be a significantly faster start than the track start. The kick start was significantly faster off the block with a higher horizontal velocity at take off and an increased on block horizontal force. This advantage was maintained through the time to 5 m and 7.5 m. It is recommended coaches and athletes should spend time adapting to the new block and this new starting technique.
The goal of a swimming race is to complete the required distance in the least amount of time, with races being won or lost by a hundredth of a second. A race is made up of a number of key components, the free swim (where the athlete is stroking), starts, turns and finishes. The velocity achieved by a swimmer is greatest during the starting phase, therefore it is important for a swimmer to maintain the velocity achieved off the start block for as long as possible before slowing to race pace (Welcher, Hinrichs, & George, 2008). Although the time a swimmer spends start-ing is less than in the free swim and turning phases, an effective start is important for success (Miller, Hay, & Wilson, 1984).
Researchers have broken down the swimming start into three phases (Guimaraes & Hay 1985; Schnabel & Kuchler 1998). Block time (start signal until toes off block) flight time (time spent in the air), and un-derwater or glide time (from water entry until first kick). Swimmers can only attain maximum performances during the start phase if they are able to skilfully execute all three phases (Schnabel & Kuchler 1998).
The performance measure of a start is usually set to time to 15 m (Cossor & Mason 2001), incorporated in this is the block time, flight time and the water time (Guimaraes & Hay 1985). Ruschel et al, (2007) suggest that water phase is intimately connected to the individual char-acteristics of each subject, like the streamline position and the underwa-ter stroke technique used, being influenced by several factors and actions that happen from the instant of entry in the water to the beginning of the first kicking and the first stroke movements. A study by Guimaraes and Hay (1985) observed 94% of the variance in start time was attrib-uted to the water time.
The requirements for a superior start include a fast reaction time, significant jumping power, a high take-off velocity and a decrease in drag force during entry. A low resistance streamline position during un-derwater gliding to minimize the loss of horizontal velocity as well as an increase in propulsive efficiency during the transition stage can assist in a superior start (Schnabel & Kuchler 1998; Breed & Young 2003). Over the last 40 years, the swim start technique has continued to evolve, from the conventional or arm swing start to the grab start and the track start. In the late 1970’s the track start debuted and has gained in popularity and proven successful in international competition. The track start has one foot at the front edge of the block, the other placed towards the back on the starting platform with hands grabbing the front edge of the block. Due to these changes in the swimmers foot place-ment, the track start employs a wider base of support than the grab start resulting in greater stability for the swimmer (Shin & Groppel, 1986; Breed & McElroy, 2000).
In 2009 a new starting technique has developed with the introduction of an incline or ‘kick’ plate mounted to the start platform. This newly designed start block by Omega (OSB11, Corgémont, Switzerland, Fig-ure 1), has the international governing body for swimming ‘FINA’ ap-proval and has allowed the development of the kick start. The kick start is essentially a modified track start that allows the rear foot to be raised off the platform and placed upon a kick plate. The kick plate is angled at 30 deg to the surface of the block and can be moved through five different locations on the starting platform. Omega claims that “tests undertaken by top level swimmers showed faster races versus a standard block” however no data was provided to support this statement. To date, no study has examined the biomechanical factors associated with a suc-cessful start using the OSB11. Hence the purpose of this study was to determine the effects of the new angled start platform on performance relative to that of the traditional track start. This study hypothesized that the kick start would increase the amount of horizontal force being applied, enabling faster start times and greater horizontal velocity when compared to the track start.
The subject cohort for this study consisted of fourteen elite swimming subjects (9 male aged 20.8 ± 3.0 years, 5 female aged 21.4 ± 2.8 years) all of which were members of the Australian Institute of Sport (AIS) Swim Team. All participants had personal best times which attained a minimum of 850 FINA points. The experimental procedure was approved by the AIS ethics committee.
The participants completed a warm up, based around their pre-race routine which consisted of some sprint and dive drills to ensure the ath-lete was ready to perform at their maximal capacity. Before the com-mencement of the testing session their weight was obtained using the force platform built into the start block. This was used to normalise the force data.
Normal competitive starting procedures were used for each trail. The participants were instructed to perform a maximal effort dive and glide until their forward momentum ceased, while not kicking or swimming. The participants completed three ‘dive and glide’ starts using the kick plate in their preferred position and three traditional track starts, in a randomised sequence.
‘Wetplate’ is the proprietary system used to analyse the starts. It is comprised of an instrumented start block constructed using a Kistler force platform (Z20314, Winterthur, Switzerland, figure 2). Wetplate not only allows for the determination of the overall force profile of the start itself but also allows measurement of the grab force through two Kistler tri-axial transducers (9601A) placed in a bar at the front of the start block. The contribution of the rear foot is also measured on a second instrumented incline plate by 4 Kistler tri-axial transducers (9251A) developed to the specifications of the OSB11 start platform. The system includes a series of calibrated high speed digital cameras (Pulnix, TMC-6740GE), one above water to capture the start and entry with 3 underwater to obtain vision from 0m to 15m. The tim-ing to 5m and 7.5m was assessed using ‘SwimTrak’ an analogue video camera timing system in which the cameras (Samsung, SCC-C4301P) were located perpendicular to the plane of motion at 0m, 5m and 7.5m. Deinterlacing the video signal allowed for the respective split times to be determined to a resolution of 1/50th of a second. All calculations were timed from when the participants head passed the specified points.
Figure 2: The AIS Wetplate Instrumented Starting Platform with Grab bar and Kick Plate
Data was collected for a total of 12 seconds, 1 second prior to and 11 seconds after the start signal. The start signal is integrated into the anal-ysis system and triggers the data collection from the force plates and the cameras. A 10Hz Butterworth low pass digital filter was applied to the force data collected through Wetplate.
A two way repeated measures analysis of variance (ANOVA) was performed to assess the main effects of style (Kick Start vs. Track Start) and gender (male vs. female). When the assumption of equal variances was violated, significance was adjusted using the Greenhouse-Geisser procedure (Vincent, 1995). All presented values are expressed as mean ± SD, and P values less than or equal to 0.05 were considered as statisti-cally significant.resultsThe performance differences between the kick start and traditional track start are presented in Table 1. Males recorded faster times and higher velocities than females for both the track start and the kick start. How-ever there were no significant interactions between gender and the style of the start for any of the variables and so results were pooled in Table 1. All force data presented has been normalised to the participant’s weight and expressed in Body Weights (BW).
This study hypothesized that the kick start would increase the amount of horizontal force being applied when compared to the track start, enabling shorter start times and greater horizontal velocity off the block. Results showed the kick start was the significantly superior method when looking at performance indicators of time to 5 m and time to 7.5 m.
This study included nine male subjects, but only five females. It is possible the different subject numbers may have masked differences be-tween genders owing to a reduced statistical power. The main intent of this study, however, was to investigate differences between the start techniques, not to determine whether strategies would be different for males and females.
The new block allows the kick start to achieve an average on block time of 0.77s compared to the track starts of 0.80s. This was significant (p<0.01) as the kick start had shorter off block times by 0.03 second. Breed and McElroy (2000) have previously found a 0.03 second dif-ference in on block time between the Grab and the Track start to be insignificant, as the variance between their starts was high (0.06s, 0.07s standard deviations for the grab and track start respectively). Their study utilised novice swimmers, whereas the present study was conducted with elite swimmers in which variance was significantly smaller than that of 0.01s for both the kick and track starts. Shin and Groppel (1986) found the take-off time of the track start was significantly faster (p<0.05) than that of the grab start. This further highlights the benefit the kick start has, not only over the track start, but also other starts.
The advantage which was provided by the kick start over the track start was able to carry through to 5 m and 7.5 m, where it held a sig-nificant 0.04 second gain at both distances. This consistent difference indicated the improvement was established on the block and not greatly enhanced thereafter. No prior study has found the track start to be sig-nificantly faster than the grab start to a set distance ranging from 5 m to 11 m (Breed and McElroy, 2000); however most researchers have suggested that the track start is a viable and equally effective alternate to the grab start, depending on the individual. The track start has been reported as equivalent to the grab start due to trade-offs in take-off ve-locity and block time (Allen et. al, 1999), yet others have found the track start superior to the grab start when solely comparing performance times (Counsilman et. al., 1988). The fact that all participants found the kick start to be their faster start to 5 m and 7.5m showed its superiority compared to the track start.
Counsilman et al. (1988) stated that, for the track start, maximal momentum is sacrificed for a decreased time on block. In the present study, however, the average horizontal force was significantly higher for the kick start compared to the track start, allowing both a faster time to leave the block and higher velocity off the block. This indicated that having the kick plate allowed block time to be reduced without sacrific-ing horizontal impulse. The advantage of having the back foot raised and able to apply force in a more horizontal direction allows for direct force application to drive the body forward with an increased horizontal velocity. The attainment of greater horizontal velocity has been seen as a benefit to overall dive performance (Galbraith et al, 2008)
There was a significantly greater horizontal velocity when leaving blocks, however this was not the case for the average velocity between 5 m and 7.5 m. This suggests that swimmers’ decelerate more from the kick start; however this should not be surprising because this was only a dive and glide study. Higher velocity leads to a larger drag force, as the drag force acting on a body moving through a fluid is proportional to the square of its velocity (Guimaraes & Hay 1985). In a start which enabled the use of kicking, the athlete may be better able to maintain a higher velocity.
The use of the dive and glide allowed for the comparison of the starts without the influence of other underwater variables such as kick-ing technique and the transition to stroking, however this does limit the research. Further testing of the kick start with the full dive parameters to 15m, including analysis of flight, entry and underwater movements, is needed to encompass the start as a whole.
The results of this study indicated that the kick start on the new OSB11 start platform to be significantly faster start than the traditional track start. Prior research into swimming starts has tended to suggest that “what one does most, one does best” (Pearson et. al 1998). Despite the participants own bias towards their preferred and experienced tech-nique, the track start, the kick start was significantly faster off the block with a higher horizontal velocity and an increased on block horizontal force. This advantage was maintained through the time to 5 m and 7.5 m. Even though further research is needed into the kick start to look at the full start to 15 m, including the effect of the underwater kick and transition to stroking, it is recommended that coaches and athletes should spend time in adapting to these new blocks and this new starting technique.
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The authors would like to gratefully acknowledge the support and as-sistance of the AIS, Aquatics Testing, Training and Research Unit for their contribution to the testing procedure, the AIS, Technical Research Laboratory for their continued effort to produce world class equipment and the AIS, Swim team for their participation.