Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
Methods
The study involved 14 male top senior national level water polo players
(Age=21.5±5.1 yrs, Height=187.2±6.1 cm, Mass=84.5±11.9 kg, training
experience=11.7±3.6 yrs). The tests were conducted in the middle of the
national premier league preparation period for the 2006/07 competition
season. Egg beater kick pulling force was tested by the method of
tethered swimming (Sidney et al., 1996; Dopsaj et al., 2003). Before the
test the players warmed up swimming independently up to 400m, and
did 10 min of specific water polo warm-up in the vertical position with
the emphasis on eggbeater kick exercises. After a 10 min rest the testing
procedure started. On his turn, each player put on a belted harness
adjusting it to his body size. Then he hooked a 1cm-thick PVC rope to
the belt at back hip region. The other end of the 5m rope was attached to
a water-resistant high-resolution (100 kHz) tensiometric dynamometer
placed on a metal support fixed on the side of the pool (Dopsaj et al.,
2003). The dynamometer was connected to a PC. After they entered the
pool, the players did a 15s pre-test trial of eggbeater kick tethered swim
at self chosen intensity in order to get familiar with the equipment and
the testing procedure. After the 1 min rest, testing procedure started,
where the players had to realize the one test trial of maximal pull force of
10 seconds using eggbeater kicks only while in the chest-forward position,
with hands above the water wrist-high, in semi-flexed position and
in front of the shoulders, i.e. the chest. The following measurements of
the kinetic characteristics of pulling force at a single leg eggbeater kick
were taken: the duration (Time EBK ), expressed in ms; the realized maximal
(peak) force value (F maxEBK ), expressed in N; the average realized
force value (F avgEBK ), expressed in N; the impulse of force (I mp F EBK ),
expressed in N⋅s; the explosive rate of force production (RFD EBK ), expressed
in N⋅s -1 ; and the frequency (Hz EBK) , expressed in the numbers of
single leg kicks per minute (Slk⋅min -1 ). All data were treated in absolute
and relative values with the descriptive statistical method. Linear regression
analysis was used to define a model of variable change during the
testing time. Since the testing method had not been previously used for
eggbeater kick techniques, the reliability was determined by applying
reliability analysis with Split-half model criteria.
results
All descriptive data are shown in Table 1 (Mean, Standard Deviation
and Coefficient of Variation). The reliability analysis showed that the
resulting measurements of pulling force characteristics of 10s maximal
tethered egg beater kick were highly statistically significant at 96.81%
(Spearman-Brown rtt coefficient – 0.9681), with Interclass Correlation
Coefficient at single measurements IC= 0.918, F=157.63, p=0.000, and
at average measurements IC= 0.994, F=157.63, p=0.000.
Table 2 gives the results of the defined regression models showing
the dependence in the change of tethered pulling force characteristics
in 10s (where: y values are variable units; x values are observed time
intervals in ms). Statistical significance was determined in only two variables,
F maxEBK and F avgEBK at the level of F=26.21, p=0.000 and F=43.95,
p=0.000, respectively.
Figure 1 gives the F-t curve tethered eggbeater pulling force of two
players playing in different positions (central defender and peripheral
player), while Figure 2 is a graphic representation of the observed tethered
force pulling characteristics with the regression lines showing the
trend of change.
70
Table 1. The descriptive statistics of 10 s maximum chest-forward tethered
single leg eggbeater kick
Time EBK (ms) F maxEBK (N)
I mp F EBK
(N-s)
F avgEBK (N)
RFD EBK
(N-s -1 )
Hz EBK
(Slk-min -1 )
Mean 497.78 190.52 72.95 140.44 336.73 122.08
Sd 56.95 36.04 14.32 21.12 98.89 14.70
Cv% 11.44 18.92 19.64 15.04 29.37 12.04
Relative 10 s tethered eggbeater kick descriptive statistics
FrelEBK (N-kg-1 ImpFrelEBK ) (N-s-kg-1 FavgrelEBK ) (N-kg-1 RFDrelEBK ) (N-s-1-kg-1 )
Mean 2.295 0.880 1.689 4.105
Sd 0.534 0.214 0.327 1.610
Cv% 23.26 24.30 19.34 39.21
Egg beater kick tethered pulling force (N)
280
260
240
220
200
180
160
140
120
100
80
60
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000
Time (ms)
V. U.
N. J.
Figure 1. Tethered eggbeater 10 s maximal pulling force in the chestforward
position in the two players (central guard – red line; peripheral
– black line).
Egg Beater Kick Pulling Force Characteristics
700
600
500
400
300
200
100
0
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000
Time (ms)
Fmax (N)
ImpF (N·s)
Favg (N)
RFD (N·s-1)
t (ms)
HZ (kicks·min-1)
Figure 2. Linear regression trend line models of tethered eggbeater 10
s maximal pulling force characteristics in the chest-forward position in
the peripheral player.
Table 2. The linear regression model equation of 10 s maximum chestforward
tethered leg eggbeater kick for all observed pulling force variables
Model Adj. R2 F and p value
TimeEBK (ms) y = 0.0036x + 467.8573 R2 = 0.063 F=0.796, p=0.382
FmaxEBK (N) Y = -0.0037x + 205.9223 R2 = 0.512 F=26.21, p=0.000
ImpFEBK (N⋅s) y = -0.0010x + 75.7146 R2 = 0.086 F=2.71, p=0.113
FavgEBK (N) y = -0.0037x + 159.2081 R2 = 0.641 F=43.95, p=0.000
RFDEBK (N⋅s-1 ) y = 0.0035x + 328.7769 R2 = 0.018 F=0.573, p=0.457
HzEBK (Slk⋅min-1 ) y = -0.0006x + 140.1895 R2 = 0.0061 F=0.071, p=0.793
dIscussIon
In comparison with the absolute values, the variation coefficient showed
high homogeneity in all tested variables, with the value of all variables
below 30 % (from 11% with Time EBK to 29% with RFD EBK ). The rela-