|Start Technique - Recent Findings|
Race analysis of the 1999 Pan Pacific Championships (Mason and Cossor, 2000) has revealed that start times (time to 15m) are significantly related to race times in most events regardless of the stroke. This would be expected for short distance events but, surprisingly, includes the men's and women's 400m freestyle events.
In events other than relays, the grab start has become favored over the 'arm swing' or conventional start among elite competitive swimmers. At the 2000 Sydney Olympics the arm swing start was not used by any finalist. The general explanation is that the grab start permits the center of mass to be further forward and thereby reduces the time required to attain a position in which large horizontal forces can be applied to generate motion horizontally. The track start is basically a variant of the grab start. In the track start one foot is further forward than the other. Within track starts two variants have been identified. These are the forward weighted track start and the rear weighted 'slingshot' track start. Recently, Welcher et al. (1999) compared the grab start, forward weighted track start and rear weighted track start (slingshot), and found that there were no significant differences between the three techniques for time to 5m.
Blanksby, Nicholson, and Elliott (accepted, 2001) conducted an intervention study to determine whether any of the Grab, track or handle swimming starts yielded a faster time to 10m among elite swimmers. No significant differences between dive groups in time to 10m were revealed pre- or post-training. However, during the training period, time to 10m, reaction, movement, block and flight times all improved irrespective of the technique used. This indicates that it doesn't really matter which technique is used. The important aspect is that swimmers can improve with any technique with some intensive practice. The researchers stated that the fact that the handled start group improved the most, and was not practiced previously, supported the Pearson et al. (1998) conclusion that the handled start may yield an advantage once the swimmer becomes highly skilled in its use.
Vilas Boas et al. (2000) compared the two variants of the track start technique. Eleven Portugese top-level swimmers were trained in both variants. Although the track start with a rearward placement of the CG resulted in greater horizontal impulses and thereby greater horizontal velocity than the start with the forward placement of the CG, this advantage was offset by an increased block time. However, the researchers observed that any advantage in horizontal velocity at entry was quickly lost during immersion and gliding.
A study at The University of Edinburgh (Bonnar, 2001) compared the track and grab starts of two groups with equivalent 50m times. No significant differences were found between the two groups in time to 9.5m or in block time, flight time, time to entry, horizontal velocity at takeoff, or vertical velocity at takeoff. A very important finding was that 96% of the variance in time to 9.5m was explained by the duration of the period between from first water contact to 9.5m. This was very similar to the findings of Guimaeres and Hay (1985) that glide time accounted for 95% of the variance in starting time. The implication is that the better starters spent less time from entry to 9.5m than the less competent starters. These findings are also supported by data obtained from race analysis of finalists and semi-finalists during the 2000 Olympics by Cossor and Mason (accepted, 2001). They found that one of the variables commonly significantly related to time to 15m was the underwater distance. The findings from the Bonnar, Guimaeres and Hay, and Cossor and Mason studies all suggest that the underwater phase of a start is highly important in start performance.
In order to interpret why this is so, one needs to look at the factors that would affect the time spent under the water. These are: .• Horizontal Speed .• Distance Traveled
Thus, a logical explanation would be that the better starters have a greater horizontal speed at entry and are therefore going faster at the beginning of the underwater period or
Better starters enter the water further out from the block and therefore have less distance to travel under the water.
However, the correlation between the horizontal speed at takeoff and the time from entry to 9.5m was very low (r =0.245). Further, the correlation was positive, that is, the correlation indicated that, if anything, an increased horizontal speed resulted in an increased time from entry to 9.5m.
This leaves us with the second logical explanation, that is, the better starters entered further out so that there was less distance to travel. One would expect a strong negative correlation. However, the correlation between distance to entry and time from entry to 9.5m was very low (r =0.046) and it was positive rather than negative.
Therefore, the study by Bonnar has indicated that the underwater phase is critical to dive performance and that this is relatively independent of variables affecting flight from the block. One should not draw definite conclusions based on this single study with only sixteen swimmers. However, the results suggest that to determine how swimmers should optimize their start performance, research should focus on what the swimmer does in the underwater phase rather than on the issue of whether to use a track or grab start.
Given that differences in horizontal speed at takeoff appear to have little bearing on the period from entry to 9.5m, differences must be related to swimmers' ability to minimise resistance and maximize propulsion during the underwater phase. Thus, attention should be paid to streamlining and to kicking. With regard to the latter, the timing of initiation of the kick is important. As explained in the article on turns , the kick should not commence until the swimmer's speed is less than that which can be generated by kicking. It may be that many swimmers are kicking too soon. Swimmers should concentrate on adopting and holding a streamlined glide position until this time.
Another interesting finding in the study by Bonnar was that height and weight were significantly related to the time from entry to 9.5m (r = -.550 p =0.027; r = -.50 p =0.05 respectively). Thus, it may be that longer swimmers have hydrodynamic advantages in reducing drag and producing propulsion. As far as mass is concerned, possible explanations include the fact that the deceleration caused by any resistive force is proportional to mass i.e a =F/m (from F=ma) and that differences among subjects in mass may be partly due to differences in musculature. Muscular swimmers may be able to generate more propulsive force from kicking. Obviously, much work must be conducted to investigate these possible explanations.
Based on the findings of recent research, the following conclusions and implications can be drawn: