Biomechanics and Medicine in Swimming XI

was used in addition to arm-strokes. During the ARM test a floating
device was used to keep legs together in a horizontal position. A zero
velocity was maintained in all tests.
The force for SW and ARM tests was averaged for 15 s. In addition,
the force for each right and each left arm-stroke was measured for the
first five stroke cycles during the SW and ARM tests and during five
strokes of the 1ARM-R and 1ARM-L tests. Additionally, a qualitative
representation of force variation during the fourth stroke cycle of the
SW and ARM test was applied. All tests were applied at maximum
intensity and completed within two consecutive days. Each test started
with slow swimming and with countdown from three. The swimmers
applied maximum intensity after the examiner’s commands and the start
always coincided with the entry of the right hand in the water, while using
the front crawl style in all tests. A standard warm-up was applied before
each test (400-m swim, 4x50-m progressively increasing intensity,
2x6s tethered swimming sprints). All swimmers had been familiarized
with the procedures on a previous day.
During tethered swimming tests a piezoelectric force transducer
connected to an analog to digital (A/D) converter system (MuscleLab,
Ergotest) with a sampling frequency 100Hz was used for force measurement.
A trigger was used to insert a signal synchronized with force
recordings into the system, and separated the arm-strokes. The button of
the hand-held trigger was pressed by the experimenter at the moment
of each arm-stroke entry in the water. In a separate experiment a female
swimmer performed 10x20-arm-stroke trials videotaped above water
and 6x20-arm-stroke trials videotaped underwater in order to validate
the accuracy of stroke separation using the hand-held trigger. Using
a small LED emitting light, the signal of the hand-held trigger was
synchronized with a camera (Sony DCR-HC14 E, Sony Corporation,
Japan) operating in interlaced scan mode (50Hz), which was located
perpendicular to the swimmer. A different group of swimmers (n=7, age:
13.8±1.5 years, body mass: 58.5±7.6 kg, height: 1.67±0.08 m) was used
to test the reliability of force output for each arm-stroke. The swimmers
performed a 15 s sprint with the same procedure as described above (test
1) and repeated the test within seven days (test 2). The force of the first
ten arm-strokes of the two tests was compared.
Analysis of variance for repeated measures on two factors (tests x
arms) was used to examine force differences between tests and between
arms. Differences between means were located using a Tukey post-hoc
test. The Pearson correlation coefficient was used to test the relationship
between variables and the intraclass correlation coefficient (ICC) was
used to examine the reliability of the procedures. The results are presented
as mean±SD and the accepted level of significance was set at p0.05). The
R and L arm-stroke ICC confirmed the reliable force reproduction in
each arm-stroke (R arm-stroke, ICC=0.985; L arm-stroke, ICC=0.975
p0.05, Figure 1). The average time to complete
each arm-stroke calculated by video recording, by the LED emitting
time and by the hand-held trigger was no different (video time overwater:
0.752±0.065 s, LED time: 0.748±0.070 s, hand-held trigger time:
0.747±0.069 s, p>0.05). In addition, the reliability of the hand-held trigger
use was confirmed with the over-water and underwater video recordings
(ICC=0.939 and 0.974, p0.05). The absolute difference between video-recorded stroke time
(under-water and over-water) versus the trigger hand-held time measure
was not significant (under-water video recorded stroke time vs. hand-held
trigger time: 0.024±0.026 s and over-water video recorded stroke time vs.
hand-held trigger time: 0.018±0.022 s, p>0.05).
Force (N)
180
160
140
120
100
80
60
R
Test1 Test 2
chaPter4.trainingandPerformance
L R L R L R L R L
1 2 3 4 5 6 7 8 9 10
Arm-stroke number
Figure 1. The force produced by each arm-stroke during 10 front-crawl
strokes during two successive tests performed within a week. R and L:
right and left arm-stroke.
The mean force produced during the 15 s sprint SW was higher compared
to ARM test (SW: 93±6, ARM: 68±4 N, p