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Rationale:
Swimming
is a technically demanding sport and a substantial proportion of training
time is devoted to the refinement of a swimmer's technique. A series of
7 x 50m swims of progressively increasing speed is used to establish the
relationship between swimming velocity (V), stroke rate (SR) and distance
per stroke (DPS). These relationship can be summarised (Costill et al.
1985, Craig and Pendergast 1979, Maw and Volkers 1996) as:
V
= SR x DPS
velocity (m.s-1)
= stroke rate (strokes.s-1) x distance per stroke (m.stroke-1)
distance per stroke (m) = (V (m.s-1) x 60) / SR (strokes
per minute)
In
practice, distance per stroke is difficult to measure in the pool without
sophisticated biomechanical analysis. Simply counting strokes per lap
may be inaccurate as this does not account for how much distance was travelled
underwater and whether the lap finished on a complete stroke. Distance
per stroke can be calculated from velocity and stroke rate by recording
stroke characteristics over a known distance in the pool (Maw and Volkers
1996), and this method is described below in sub-section 9.2 (vi) below.
Procedures:
- The
protocol for this test is 7 x 50m swims on a 2min cycle. All
swimmers use their main stroke. For IM swimmers the coach
should nominate the stroke to be used - the swimmer's weakest
stroke is suggested. A 50 m pool is mandatory for this test.
- The
target times for the test are determined as follows. The slowest
swim (ie swim no. 1) is undertaken approximately 12s slower
than the predicted best time on the day. Each of the following
swims is then undertaken approximately 2s faster than the
preceding swim, until the seventh and final (and maximal effort)
swim is completed. In colloquial terms, the protocol can be
summarised as 'add 12s to your predicted 50 m time and then
descend by 2'. A common mistake is for the swimmer to start
too fast on the first swim.
- All
swims utilise a push start.
- Using
manual timing the first observed movement is used as the starting
time and hand touch at the 50m as the finishing time.
- Record
all times to a tenth of a second.
- Record
stroke rate and distance per stroke for each repeat using
the following procedures:
- Stroke
data (DPS) should be recorded from between flags at
5m and 45m of each 50m swim. The time to swim this segment
is taken with a stopwatch. At approximately the 15m
mark (ie within the first 25m segment) and the 35 m
mark (ie within the second 25m segment) three complete
stroke cycles are recorded. The swimmer must be surfaced
from their push start by the 5m point to accurately
take these measurements. Timing the head as it goes
through the 5 and 45 m points is recommended as the
best method to record the time taken.
- Stroke
rate (strokes.min-1) is measured using the base three
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 time. Alternatively
the stroke cycles can be timed and stroke rate calculated
using the equation (Maw and Volkers 1996):
SR
= (60 x 3) / time for three strokes (seconds)
For
example, if three consecutive strokes takes 4.25s,
then SR = (60 x 3) / 4.08 = 44.1 strokes/min, while
for three strokes in 3.90s the SR = (60 x 3) / 3.90
= 46.2 strokes/min
- For
breaststroke, it is often easier to use the point where
the head comes up rather than the hand entry. The average
of the two stroke rates (ie at the 15 and 35m points)
is used to represent the stroke rate for that swim.
- Distance
per stroke is calculated using the equation DPS = (V
x 60) / SR (strokes per minute) which converts the units
from strokes per second to strokes per minute.
- Plot
on separate graphs stroke rate and distance per stroke (y-axis)
against swimming speed (x-axis).
Data
Presentation:
The following example is given for a female 100m breaststroke swimmer.
Table 6: A typical
example of results from the 7 x 50m stroke mechanics test
for a trained female breaststroke swimmer.
Figure
4 (below): Stroke rate relationship to swimming speed derived from the
7 x
50m stroke mechanics test
Figure
5 (below): Distance per stroke (m) relationship to swimming speed derived
from the 7
x 50m stroke mechanics test
Interpretation:
The
basic premise of this test is to provide a qualitative analysis of stroke
mechanics during a series of progressively faster swims (Craig and Pendergast
1979, Maw and Volkers 1996). This information should be used in conjunction
with the subjective assessment of the technical quality of the stroke
by the coach (Wakayoshi et al. 1995). The most important point to consider
is that each swimmer will have a different combination of distance per
stroke and stroke rate for their particular stroke.
It
is desirable for good technique to be maintained from the slowest to fastest
swim. Better performed swimmers are able to 'hold their stroke together'
at the fastest speeds while less-skilled performers lose control evidenced
by non-linear changes in stroke rate and/or distance per stroke. Inspection
of the graph should indicate the speed at which control of stroke mechanics
starts to deteriorate.
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