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Messung von Frequenz und Zugzahl

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By David Pyne, B App Sc M App Sc

Introduction

One of the oldest but most valuable coaching tools available to swimming coaches is the measurement of stroke rate and stroke count. Coaches Gennadi Touretski and Jim Fowlie have extensively used stroke rate analysis in their coaching at the Australian Institute of Sport. We reported on this work with the 1992 Olympic 50m and 100m Freestyle Gold Medallist, Aleksandre Popov, in a previous issue of Australian Swim Coach (Vol.10 No.5). In this article, I wish to further examine the issue of measuring stroke rate and stroke count.

There are a number of ways to measure stroke rate and stroke count. The most accurate is by filming and computer analysis, although this is obviously not available to most coaches. There are several more practical methods available to measure these factors in the pool using a stopwatch and swimming over a measured distance. To simplify this process even further, a revised method has recently been proposed. A series of six 50m swims of progressively increasing intensity is used to establish the relationship between swimming velocity (V), stroke rate (SR) and stroke length (SL) or distance per stroke (DPS). This relationship can be summarised as…

Velocity (V) = Stroke Rate (SR) x Distance Per Stroke (DPS)

 

In practice, distance-per-stroke is difficult to measure and requires a time-consuming test protocol or the use of biomechanical filming. By measuring stroke count (i.e. the number of strokes required to swim 50m) we can substitute this as an indicator of distance per stroke … e.g. as the stroke count increases we assume that the distance per stroke is decreasing.

How to Measure Stroke Rate and Stroke Count

1. The protocol for this test is 6x50m swims on a 2-minute cycle. All swimmers are to use their preferred stroke. For Individual Medley swimmers, the coach should nominate the stroke to be used. A 50m pool is preferred for this test.

2. The target times for the test are determined as follows. The slowest swim (i.e. swim No.1 is undertaken approximately 10 seconds slower than the predicted best time on the day. Each of the following swims is then undertaken approximately two seconds faster than the preceding swim, until the sixth and final (and maximal effort) swim is completed.

3. All swims utilise a push start.

4. Using manual timing, the first observed movement is used as the starting time and hand touch at the 50m is used as the finishing time.

5. Record all times to a tenth of a second.

6. Record stroke rate and count.

 

Stroke rate is measured using the base 3-stroke rate facility on the stopwatch. The stopwatch is started as the swimmer’s hand enters the water to commence a stroke. At the completion of three complete stroke cycles, the stopwatch is stopped as the same hand enters the water for the fourth stroke cycle (Figure 1). Alternatively the stroke cycles can be timed and stroke rate calculated using the above equation. For Breaststroke, it is often easier to use the point where the head comes up rather than the hand entry.

Figure 1. In this example the stopwatch is started on the entry of the right hand (0). Three complete stroke cycles are timed (R-L-R, R-L-R, R-L-R).

 

 

Right

Hand

Left

Hand

0

x

x

1

x

x

2

x

x

3

x

 

On the completion of the third cycle … i.e. when the right hand enters the water for the fourth time (3) … the stopwatch is stopped.

The stroke rate should be measured twice in each 50m swim: in the first 25m and again in the second 25m. The value should be similar and, if not, then averaged to give a representative figure.

5. Calculate velocity and plot stroke rate and stroke count against velocity.

The following example is given for a male 100m Freestyle swimmer. His predicted fastest time for 50m on the day is around 26 seconds. In this case, he will be asked to swim his series of six at the following speeds…

 

1. 36 (26+10) seconds

2. 34.0

3. 32.0

4. 30.0

5. 28.0

6. 26.0

 

Here we see the results with the initial time a little slow (37.5), but then an even descent and a pleasing final time of 26.0, which equalled the predicted time.

 

Swim

No.

Time

(Secs)

Velocity

(M/s)

Stroke Rate

(Cycles/min)

Stroke Count

(Strokes/50)

1

37.5

1.37

27

28

2

34.5

1.45

31

28

3

32.5

1.54

35

28

4

30.5

1.64

39

28

5

28.5

1.75

43

29

6

26.0

1.92

47

29

 

Figure 2 shows a graphical representation of this data showing the linear increase in stroke rate. The stroke count is held relatively constant through the set indicating that distance per stroke was maintained.

 

Stroke Rate (cyc/min

Rat Strokecount1

Stroke Count (per 50m)

Velocity – Metres per Second

 

Data Interpretation

The basic premise of this test is to provide a qualitative analysis of stroke mechanics during a series of progressively faster swims. This information should be used in conjunction with the subjective assessment of the technical quality of the stroke by the coach (using video tapes analysis if possible). It is desirable for good quality stroke mechanics to be maintained from the slowest to fastest swim. Elite swimmers are able to "hold their stroke together" at the fastest speeds whilst less skilled performers lose control, evidenced by a significant increase in stroke count … i.e. a decrease in distance per stroke. The aim should be to hold the same or similar stroke count throughout the test and increase swimming velocity by simply accelerating the stroke rate. Inspection of the graph should indicate the speed at which control of stroke mechanics is lost. Data can be viewed on a group basis, although the most appropriate interpretation is achieved by comparing an individual’s result to his or her previous data.

 

Stroke Analysis at the 1993 Pan Pacific Championships

 

The best means to familiarise yourself with the interpretation of stroke rates and counts is, of course, to practice on your own swimmers. However, a great deal of information can be gained from analysis of results from elite swimmers. The following is from the 1993 Pan Pacific Championships held in Kobe, Japan. For interest and information, here are some results for Australian swimmers, kindly provided by the Medical and Scientific Committee of the Japan Amateur Swimming Federation (averaged in some instances).

Kieren Perkins 800m FS, 1st place, 7:50.51

Velocity 1.65 metres/sec

Stroke Rate 45-50 strokes/min

Stroke Length 2.10-2.23 metres

 

Susan O’Neill 100m FS, 2nd place, 55.80

Velocity 1.74 metres/sec

Stroke Rate 55 strokes/min

Stroke Length 1.85 metres

 

Darren Lange 50m FS, 4th place, 23.17

Velocity 2.001 metres/sec

Stroke Rate 63 strokes/min

Stroke Length 1.91 metres

 

Philip Rogers 100m BR, 1st place, 1.01.56

Velocity 1.53 metres/sec

Stroke Rate 58 strokes/min

Stroke Length 1.59 metre

 

Rebecca Brown 200m BR, 2nd place, 2.28.42

Velocity 1.30 metres/sec

Stroke Rate 49 strokes/min

Stroke Length 1.64 metres

A comparison between Rebecca Brown (AUS) and Anita Nail (USA) in the Women’s Final of the 200m Breaststroke – one of the best races at the 1993 Pan Pacs.

 

Anita Nail, USA, 1st place

Lap

Stroke

Length

Time

Split

(m/s)

Velocity

(s/min)

Stroke

Rate

(m)

0-50m

33.57

33.57

1.38

46.3

1.79

50-100m

1.11.47

37.90

1.27

40.7

1.88

100-150m

1.50.03

38.56

1.27

40.5

1.84

150-200m

2.28.40

38.37

1.26

41.1

1.84

 

Rebecca Brown, AUS, 2nd place

Lap

Stroke

Length

Time

Split

(m/s)

Velocity

(s/min)

Stroke

Rate

(m)

0-50m

34.20

34.20

1.37

39.5

1.66

50-100m

1.12.37

38.17

1.29

46.9

1.64

100-150m

1.50.25

37.88

1.28

48.7

1.58

150-200m

2.28.42

38.17

1.27

52.4

1.46

 

Summary

The preceding results indicate that there is a great deal of variation in the stroke patterns of elite swimmers. Apart from different style, the stroke mechanics will depend on several factors including body size (height and limb length), tactics, and fitness. There is, of course, no perfect stroke pattern. Each individual swimmer will have their own stroke and stroke mechanics – the more important feature is consistency. As every wise coach will confirm the ability to "hold the stroke together" is a telling one. Armed with a stopwatch, every coach is able to check their swimmers stroking patterns during training and competition.

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