ST 3 / cet 1 / 
Swimming Speed, Stroke Rate and Stroke Length During
Maximal 100 M Freestyle Swim in Boy-Swimmers 11-16 Years of Age

ORIGINAL ARTICLE

Vorontsov, A.R. and Binevsky, D.A. (2002). Swimming Speed, Stroke Rate and Stroke Length
               DuringMaximal 100 M Freestyle Swim in Boy-Swimmers 11-16 Years of Age.
               IX International Symposium "Biomechanics and Medicine in Swimming",
               University of Saint-Etienne (France), 21-23 June 2002.

1.  Abstract

2.  Introduction
            
3.  Methods and Subjects

4.  Results and Discussion

5.  Conclusions
          
References

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Swimming Speed, Stroke Rate and Stroke Length
During Maximal 100 M Freestyle Swim
in Boy-Swimmers 11-16 Years of Age




1) Andrei R.Vorontsov, 2) Dimitry A.Binevsky

1) Amateur Swimming Federation of Great Britain, Bath, UK.
2) Russian State Academy of Physical Education, Moscow.

Vorontsov's presentation:
IX International Symposium "Biomechanics and Medicine in Swimming",
University of Saint-Etienne (France), 21-23 June 2002.

1. Abstract

The purpose of this study was to establish the age dynamics of stroke rate (SR), stroke length (SL) and swimming speed (V) during maximal 100m freestyle swimming in boy-swimmers aged 11-16 years. The subjects of this study were 225 boy-swimmers from 3 swimming schools and the State College of Olympic Reserves (Moscow). Each swimmer performed maximal 100m freestyle swim from a dive. The swim was recorded using a video camera (frequency 50 Hz) and VHS-VCR installed on a trolley, which accompanied a swimmer along the pool deck throughout the entire swim. Video records of swimming with electronic time data were processed and velocity of “pure” swimming at 4 different sections of the 100m race, as well as SR and SL for each lap of “pure” swimming were calculated. No age-related differences were found for average and lap-by-lap values of SR. In all ages the uniformed lap-to-lap decrease of SR was established. SL during the race changed insignificantly. The decrease of V toward the end of 100m race in all age cohorts should be attributed primarily to the decrease of SR.

Key words: young swimmers, stroke rate, stroke distance, swimming velocity.

2. Introduction

Stroke rate (SR) and stroke length (SL) ratio as well as changes of racing speed (V) during competitive swimming are widely regarded as macro characteristics of  sport  technique and its efficiency. The dynamics of these characteristics during competitive swimming was the subject of numerous investigations (Haljand et al., 1984; Lipsky, Abramov, 1988, Wakayoshi et al., 1992; Wirtz W., Wilke K. & Zimmermann F., 1992; Pyne & Trewin, 2001 and many others). The subjects of those studies were physically matured elite athletes able to control and voluntary change the SR and SL during the race in order to reduce the decrease of the swimming speed due to accumulation of fatigue.

Young swimmers learn to control the structure and efficiency of the movement  while they grow up and mature in the process of  a 5-7- year training program. During that time they pass through pre-pubescent and pubescent stages of ontogenesis when rapid physical growth and motor development take place. Significant changes in body build, motor abilities and fitness may be reflected in the “macro” structure and efficiency of sport techniques. Knowledge of the age particulars and year-by-year dynamics of technical characteristics may allow us to control and correct the process of technical preparation in young swimmers.

The purpose of this study was to establish the age dynamics of SR, SL and swimming speed in young swimmers (boys aged 11-16 years) during a maximal swimming 100m freestyle and thus to establish the formation of special swimming skills during the growth from 11 to 16 years of age.

3. Methods and Subjects

The subjects of this study were 225 boy-swimmers 11 to 16 years of age from 3 swimming schools and the State College of Olympic Reserves (Moscow). The experiment was held in the 50m swimming pool of the Russian State Academy of Physical Education. Each swimmer performed a maximal 100m freestyle swim from a dive. Only those swims with a time less than PB+2 s (personal best time + 2 s) were taken into consideration.

For the purpose of this study the entire distance was conditionally split into 4 sections:
0-25m, 25-50m, 50-75m and 75-100m.  Both sides of the swimming lane  (in all cases it was the same lane – 3^rd lane from the camera) were marked with pairs of black buoys – 7.5 meters from starting edge and 5m and 2.5m before the turning wall. This was done in order to exclude the effect of the starting dive, turn and gliding on calculation of the speed of “pure” swimming, SR and SL.

Each swim was recorded using a video camera (recording frequency 50 Hz) and VHS-VCR with TV display installed on a trolley. The trolley, towed by operator-camera men, accompanied each swimmer along the pool deck throughout the entire swim. During recording operator kept swimmer’s image in the middle of TV display. The optical axis of the camera was perpendicular to the swimming direction. The starting sound signal was synchronized with a flashlight to indicate the beginning of the race on videotape. A signal from an electronic timer was recorded on the same videotape as the swimming race throughout the time of video recording.

Video records of swimming with electronic time data were processed and the following characteristics were calculated:

-          velocity of “pure” swimming (V) in 4 different sections within the 100m swim,

-          SR and SL at each lap of “pure” swimming.

SR (cycles · min^-1) for each lap was determined as:

0.5·AP_n : t_n   x 60    

where  AP_n – the number of arm pulls (each arm pull constitutes a half of freestyle’s swimming cycle) completed by a swimmer at each segment of “pure” swimming and t_n - time of “pure” swimming  at every “quarter” of the race.                                               

SL at every lap of “pure” swimming were determined as length of lap divided by SR.

Hence:

SR₁= 0.5·AP_{1 (from 7.5 to 25)} /t₁ · 60;        SL₁ = (25-7.5)/ SR₁ ; 

SR₂= 0.5·AP_{2 (from 25 to 47.5)} /t₂ · 60;      SL₂= (47.5-25) /SR₂ ;

SR₃=0.5·AP_{3 (from 55 to 75)} /t₃ · 60;         SL₃=(75-55)/SR₃;

SR₄=0.5·AP_{4 (from 75 to 100)} /t₄ · 60;        SL₄=(100-75) /SR₄.

Average values of V, SR and SL per distance were calculated based on individuals’ average values. T-statistics (ANOVA, SPSS) was used to establish significance of the differences in V, SR, and SL between age cohorts and lap-by-lap changes of V, SR, and SL within each age cohort (results of analysis are given in Supplementum, tables 4 and 5).

1. Dynamics of the  “pure” swimming speed during 100-m swimming.

The data in table 1 contains the values of “pure” swimming speed (V) in each of the 4 sections and the average “pure” V during 100m freestyle race in boy-swimmers  11-16 years of age.

Within each age group the same tendency was revealed - swimming speed decreased from the first lap to the last (p<0.01-0.001). Comparison of the data for consecutive ages shows that swimming speed values at every lap of “pure” swimming and average racing speed in the 100m freestyle event increased with the age of the swimmer. On the basis of year-by-year differences we assume that the most rapid growth of the V occurs from 11 to 13 years of age. A slow increase of V at 13-14 years is followed by a second acceleration from 14 to 16 years of age.

Table 1. Swimming speed (V (m·s^-1)) at consecutive laps during maximal 100-m freestyle swim 
              in boy-swimmers 11-16 years of age. Values are mean + SD.

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2. Dynamics of the SR during 100-m swimming.

The age dynamics of  the values of SR and SL during competitive swimming in 100m freestyle represents high interest because swimming speed is the derivative namely from SR and SL. The values of SR during 100m swimming for each age group are shown in Table 2. It should be noted that the mean values of swimming tempo are almost identical in all age cohorts. The values of SR found in boys 11-16 years of age were much higher than those reported by Pyne and Trewin (2001) for the finalists of the Sydney Olympic Games competing in the 100m freestyle, but very close to the values of SR demonstrated by Olympians in the 50m freestyle. As we assumed before these studies, SR in young swimmers should decrease with the age due to somatic growth and the increase of strength and endurance. Nevertheless, we did not establish any consistent and significant decrease of average SR with age (see Supplementum, table 4). In every age cohort we found young swimmers with high as well as low SR.

Table 2. Stroke Rate (cycles · min^-1) at consecutive laps during maximal 100-m freestyle swim
              in boy-swimmers 11-16 years of age. Values are mean + SD.

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It looks like swimmers choose their own most “comfortable” stroke rate at earlier ages (at the age of 11-12 years). Hence it should become a prime concern for coaches to help age groupers to produce a more economical stroke rate and to teach them to concentrate more on increasing the stroking distance to an optimal level.

We found consistent decreases of SR from lap to lap for boy-swimmers of all age cohorts.

Decrease of SR from lap 1 to lap 2, lap 2 to lap 4, lap 1 to laps 3 and 4 was significant  (p<0.01-0.001, see Supplementum, table 5). It follows from the results of our studies that the decrease of swimming velocity is related to the reduction of SR due to fatigue. This supports the data of Barden and Rorke (1999), who found that changes in swimming velocity only affected stroke rate, not stroke length and a decreased stroke rate might serve as a useful indicator of loss of anaerobic power. Earlier MacArdle and Reilly (1992) suggested that a fall in SR during competitive racing is a consequence of the decrease in pulling velocity.

During a 100m race young swimmers did not demonstrate any compensatory increase of SR in order to prevent slowing down of swimming speed. It is interesting that similar lap-by-lap decrease of SR was found for the male finalists at the Pan Pacific Swimming Championships (1999) reported by a research group from the Australian Institute of Sport (the winner had stroke rate respectively 57.3-53.3-52.9-51.3. Total decrease of SR was 10.5%!).

3. Dynamics of the SL during 100-m swimming.

The average value of SL (Table 3) increased from the 11 to 16 years of age cohorts with periods of fast gain between 11-13 (p<0.001) and 15-16 years (p<0.05). Minor slow down in the growth rate of SL took place between 13 and 14 years of age.  These results are in agreement with our previous research related to the growth  of the dynamic parameters of pulling actions in young swimmers (Vorontsov, Binevsky, 1991). In accordance with that data at the age of 11-12 years occurs a significant increase of pulling power and efficiency related to improvement of core swimming skills at the early stages of multi-year training.

Following increase of the SL at the age of 15-16 years, as we assumed, may be connected with a period of fast increase of muscle mass and power (Vorontsov et al, 1999).

Table 3. Stroke length at consecutive laps during maximal 100-m freestyle swim in
              boy-swimmers 11-16 years of age. Values are mean + SD.

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       With regards to the change of SL from lap to lap we did not find any significant fall in that parameter during the race in all age cohorts. An increase of SL at the last 25-m section in 11-12 year old boys may reflect the contribution of leg kick with the onset of fatigue, but the role of the leg kick was beyond our attention in this study.

The highest value of SL for boy-swimmers of 13-16 years age was produced in the 2nd 25m section, where despite a much lower SR than during the first lap, swimming speed was still higher than average racing V. Exactly the same tendency was found in finalists of the 1999 Pan Pacific Championships (AIS Biomechanics, 1999) - 7 of the 8 elite swimmers had the largest StD in the 2^nd 25m section. During swimming at the 3rd and 4th 25-m sections of the race, young swimmers demonsrated a non-significant decrease of SL which together with a significant reduction of SR caused significant decrease in swimming speed (p<0.001).

We suggest  than the quality of arm pulls during swimming in the second 25m section is the best and the SR/SL ratio is optimal (moderate SR, maximal SL while swimming speed is above average distance speed).  It may be used as a model in the process of technical preparation of age group swimmers. The accent on the maintenance of large SL and constant moderate SR will mean an introduction of reasonable physical difficulty into a process of technical preparation and, thus, will facilitate both physical and technical preparedness of young swimmers.

During the process of  growth and multi-years training, there occurs an increase of average V and average SL, V and SL in all 4 consecutive sections of the 100m distance. Periods of rapid increase of V and SL in boys (12-13 and 15-16 years of age) coincide with periods of rapid growth of maximal strength and anaerobic lactic ability (Vorontsov et al., 1999).

No significant age-related differences were found for average and lap-by-lap values of SR. In all age cohorts uniformed lap-to-lap decreases in SR was established. It seems that the individual rhythm of swimming movement is formed in boys already at the age of 11-12 years.

The decrease of V toward the end of 100-m distance in all age cohorts should be attributed to the decrease of SR. No temporal compensatory increase of SR in order to delay the decrease of V was found.

Further investigation of V, SR and SL dynamics at different competitive distances in young swimmers of different sexes and ages have considerable topical significance.

References

1. AIS Biomechanics (1999) Swim Competition Analysis: Pan Pacific Championships, Sydney, August 22-29 1999. (Scientific guidance by B.Mason), AIS, Sydney.

2. Barden, J. M., & Rorke, S. C. (1999). Stroke parameter relationships in a repeated swim interval training set. Medicine and Science in Sports and Exercise, 31(5), Supplement abstract 375.

3. Haljand R., Tamp T., Kaal P. (1984) Models of technique of the swimming strokes with methods of their perfection and control. Pedagogical Institute of E.Vilde, Tallin.

4. Lipsky E.V., Abramov A.B. (1988). Competitive performance of sprint-swimmers on the distance 50 m. In: Plavanie, (Editor L.P.Makarenko), pp.13-16. FiS, Moscow.

5. McArdle D., Reilly T. (1992) Consequences of altering stroke parameters in front crawl swimming and its simulation. In: Biomechanics and Medicine in Swimming. Swimming Science VI, (Editors: D.MacLaren, T.Reilly and A.Lees), E & FN SPON, Cambridge.

6. Pyne D., Trewin C. (2001). Analysis of stroke rates in freestyle events at 2000 Olympics. Swimming in Australia, January-February 2001, downloaded from http:/www.ascta.com (ASCTA Online Library).

7. Vorontsov A.R., Binevsky D.A. (1991) Time and dynamic parameters of front crawl arm pull in boy-swimmers 11-16 years of age. Annual scientific report of Swimming Department. Central State Institute of Physical Culture, Moscow.

8. Vorontsov A.R., Dyrco V.V., Binevsky D.A., Solomatin V.R., Sidorov N.N. (1999). Patterns of growth for some characteristics of physical development, functional and motor abilities in boy-swimmers 11-18 years. In: Biomechanics and Medicine in Swimming VIII. (Editors: K.L.Keskinen, P.V.Komi, A.P.Hollander), Gummerus Printing, Jyvaskyla.

9. Wakayoshi K., Nomura T., Takahashi G., Mutoh Y., Miyashito M. (1992) Analysis of swimming races in the 1989 Pan Pacific swimming championships and 1988 Japanese Olympic Trials. In: Biomechanics and Medicine in Swimming. Swimming Science VI, (Editors: D.MacLaren, T.Reilly and A.Lees), E & FN SPON, Cambridge, pp.135-141.

10. Wirtz W., Wilke K., Zimmermann F. (1992) Velocity, distance per stroke and stroke frequency of highly skilled swimmers in 50 m freestyle sprint in a 50 and 25 m pool.

In: Biomechanics and Medicine in Swimming. Swimming Science VI, (Editors: D.MacLaren, T.Reilly and A.Lees), E & FN SPON, Cambridge, pp.131-134

Supplementum.

Table 4. Significance of the year-by year increase of the mean values of 
 V, SR and SL in boy-swimmers from 11 to 16 years.

Table 5. Significance of lap-to-lap dynamics of mean values of 
V, SR and SL in boy-swimmers  of different age.