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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 – 3rd 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·APn
: tn x 60
where
APn
– 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 tn - 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·AP1 (from 7.5 to 25)
/t1
· 60; SL1
= (25-7.5)/
SR1
;
SR2=
0.5·AP2
(from
25
to 47.5)
/t2
·
60; SL2=
(47.5-25)
/SR2
;
SR3=0.5·AP3
(from
55
to 75)
/t3
·
60;
SL3=(75-55)/SR3;
SR4=0.5·AP4
(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).
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