Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
Methods
Twenty-one young female water polo players participated to the study.
They were divided into two groups: G-12: 11 players, their average age,
stature and body mass were, respectively: 11.9 ± 1.4 years; 1.59 ± 0.07 m;
48.4 ± 5.3 kg; and G-16: 10 players, their average age, stature and body
mass were, respectively: 16.5 ± 1.3 years; 1.64 ± 0.04 m; 65.2 ± 9.5 kg.
The G-12 players had a practice of water polo of 3.3 ± 0.5 years whereas
the G-16 players of 4.8 ± 0.6 years. The subjects were informed about
the methods and aims of the study and gave their written informed consent
to participate; parental consent was obtained for under age subjects.
The experiments were performed in an indoor 25 m swimming pool.
The subjects were requested to swim at constant speed and stroke rate
starting, without diving, from the pool wall. The experiments were repeated
at 4 speeds (self selected by the swimmers as slow, moderate, fast
and maximal) and with the two styles (HOS: head out swimming and
FCS: front crawl swimming) in two separate days.
In the central 10 m of the pool the average speed (V, m . s -1 ), the
stroke frequency (SF, Hz) and the kick frequency (KF, Hz) were measured
by means of a stopwatch. The stroke length (SL, m) was then calculated
as V/ SF.
The arm stroke efficiency was calculated according to the simple
model proposed by Zamparo et al. (2005). The model is based on the assumption
that the arm is a rigid segment of length l, rotating at constant
angular speed about the shoulder and yields the average efficiency for
the underwater phase only, as follows:
188
η p = ((V . 0.9) / (2π . SF . l)) . (2 / π) (2)
where V is the average speed of the swimmer, SF is the stroke frequency
and l is the average shoulder to hand distance. In turn, l can be calculated
trigonometrically by measuring the upper limb length (0.49 ± 0.02 m
in G-12 and 0.50 ± 0.02 m in G-16) and the average elbow angle (EA)
during the in-sweep of the arm pull. In this study, EA was not directly
measured but calculated on the basis of the subject’s age based on data
published by Zamparo (2006). Finally, in equation 7, the speed was multiplied
by 0.9 to take into account that, in the front crawl, about 10% of
forward propulsion is produced by the legs (e. g. Hollander et al. 1988).
For a detailed discussion about the pro and cons of this model the reader
is referred to Zamparo et al. (2005) and Zamparo (2006).
During the experiments video records were taken, with a sampling
rate of 50 Hz, by means of a video-camera (TS-6031PSC, CANO-
PUS, UK) positioned 0.5 m below the water surface, perpendicular to
the swimmer’s direction (the subjects swam in the second lane, at a distance
of 7-8 m from the camera). After the experiments, the data were
downloaded to a PC and analyzed using a commercial software package
(Twin pro, SIMI, G). In FCS trunk incline (TI, degrees) was measured
from the angle with the horizontal of the segment between the shoulder
(acromion) and the hip (great trochanter) whereas in HOS, instead of
the shoulder, the margin of the axilla was marked instead (since the
shoulder joint is outside the water in this condition). The measurement
of TI was taken, for a single passage, at the end of the in-sweep (when
the hand is directly below the shoulder) since in this position the rotation
around the sagittal axis is the least and has the smaller influence on
the degree of rotation (see also Kjendlie et al. 2004).
Finally, the subjects were equipped with a waterproof heart rate
monitoring system (RS800sd, Polar, Fi) so their heart rate (HR, bpm)
at the end of each trial was recorded as well. These data should indicate,
albeit indirectly, whether the differences in the kinematical/biomechanical
parameters between styles and groups do indeed lead to differences
in the energetics of swimming.
Statistical analysis was carried out by means of an ANOVA test
(SPSS v17.0, SPSS Inc., Chicago Ill., USA) for repeated measures: two
groups (G-12 and G-16), four speeds (V1 –V4) and two conditions
(FCS: front crawl swimming and HOS: head out swimming).
measurement of TI was taken, for a single passage, at the end of the in-sweep (when the
hand is directly below the shoulder) since in this position the rotation around the sagittal
axis is the least and has the smaller influence on the degree of rotation (see also
Kjendlie et al. 2004).
Finally, the subjects were equipped with a waterproof heart rate monitoring system
(RS800sd, Polar, Fi) so their heart rate (HR, bpm) at the end of each trial was recorded
as well. These data should indicate, albeit indirectly, whether the differences in the
kinematical/biomechanical parameters between styles and groups do indeed lead to
results
differences in the energetics of swimming.
In tables 1 and 2 are reported the average ± 1 SD values of all the inves-
Biomechanics and Medicine in Swimming XI Chapter 2 Biomechanics b
tigated parameters for the two groups (Table 1: G-12; Table 2: G-16)
at swimming). the four speeds and in the two conditions (FCS and HOS). In both
conditions RESULTS (HOS and FCS) and for both groups (G-12 and G-16), with
increasing speed (from V1: slow to V4: maximal) KF and SF increase
while SL and ηp decrease; moreover, with increasing speed TI decreases
while HR increases (ANOVA, F (3, 57) , p < 0.001 in all cases).
Statistical analysis was carried out by means of an ANOVA test (SPSS v17.0, SPSS
Inc., Chicago Ill., USA) for repeated measures: two groups (G-12 and G-16), four 188
speeds (V1 –V4) and two conditions (FCS: front crawl swimming and HOS: head out
were downloaded to a PC and analyzed using a commercial software package (Twin
In pro, tables SIMI, 1 G). and In 2 FCS are trunk reported incline the (TI, average degrees) ± was 1 SD measured values from of all the the angle investigated with the
parameters horizontal for of the two segment groups between (Table 1: the G-12; shoulder Table 2: (acromion) G-16) at the and four the speeds hip and (great in
the trochanter) two conditions whereas (FCS in HOS, and HOS). instead In of both the conditions shoulder, the (HOS margin and FCS) of the and axilla for both was
groups marked (G-12 instead and (since G-16), the with shoulder increasing joint speed is outside (from V1: the water slow to in V4: this maximal) condition). KF The and
SF
measurement
increase while
of TI
SL
was
and
taken, for
ηp decrease;
a single
moreover,
passage, at
with
the
increasing
end of the in-sweep
speed TI
(when
decreases
the
while hand is HR directly increases below (ANOVA, the shoulder) since F(3, 57), p < 0.001 in this in position all cases). the rotation around the sagittal
axis is the least and has the smaller influence on the degree of rotation (see also
Table 1. Average values ± 1 SD of the investigated parameters for the
Kjendlie et al. 2004).
G-12 group
Table 1. Average values ± 1 SD of the investigated parameters for the G-12 group
V (m
FCS
. s -1 ) SF (Hz) SL (m ) KF(Hz) ηp TI (deg) HR (bpm)
V1 0.94 ± 0.06 0.45 ± 0.12 2.22 ± 0.57 1.85 ± 0.37 0.45 ± 0.08 23.4 ± 3.99 149 ± 17
V2 1.07 ± 0.11 0.59 ± 0.05 1.81 ± 0.21 1.86 ± 0.73 0.38 ± 0.04 21.0 ± 3.85 162 ± 12
V3 1.15 ± 0.13 0.76 ± 0.10 1. 54 ± 0.18 2.01 ± 0.60 0.32 ± 0.04 18.1 ± 3.91 169 ± 11
V4 1.25 ± 0.16 0.85 ± 0.13 1.49 ± 0.26 2.50 ± 0.60 0.31 ± 0.06 13.5 ± 4.51 165 ± 11
V1 0.95 ± 0.09 0.69 ± 0.07 1.39 ± 0.18 1.56 ± 0.71 0.29 ± 0.04 33.7 ± 9.08 159 ± 14
HOS V2 1.00 ± 0.12 0.73 ± 0.07 1.38 ± 0.20 1.76 ± 0.85 0.29 ± 0.04 28.7 ± 4.62 167 ± 15
V3 1.12 ± 0.15 0.89 ± 0.15 1.30 ± 0.26 1.85 ± 0.84 0.27 ± 0.05 30.2 ± 4.97 174 ± 16
V4 1.16 ± 0.18 0.93 ± 0.16 1.28 ± 0.25 2.04 ± 0.76 0.27 ± 0.05 22.2 ± 8.06 176 ± 16
Table 2. Average values ± 1 SD of the investigated parameters for the G-16 group
V (m . s -1 Finally, the subjects were equipped with a waterproof heart rate monitoring system
(RS800sd, Polar, Fi) so their heart rate (HR, bpm) at the end of each trial was recorded
as well. These data should indicate, albeit indirectly, whether the differences in the
kinematical/biomechanical parameters between styles and groups do indeed lead to
differences in the energetics of swimming.
Statistical analysis was carried out by means of an ANOVA test (SPSS v17.0, SPSS
Inc., Chicago Ill., USA) for repeated measures: two groups (G-12 and G-16), four
speeds (V1 –V4) and two conditions (FCS: front crawl swimming and HOS: head out
swimming).
RESULTS
In tables 1 and 2 are reported the average ± 1 SD values of all the investigated
parameters for the two groups (Table 1: G-12; Table 2: G-16) at the four speeds and in
the two conditions (FCS and HOS). In both conditions (HOS and FCS) and for both
groups (G-12 and G-16), with increasing speed (from V1: slow to V4: maximal) KF and
SF increase while SL and ηp decrease; moreover, with increasing speed TI decreases
while HR increases (ANOVA, F(3, 57), p < 0.001 in all cases).
Table 2. Average values ± 1 SD of the investigated parameters for the
G-16 Biomechanics group and Medicine in Swimming XI Chapter 2 Biomechanics b 189
) SF (Hz) SL (m ) KF(Hz) ηp TI (deg) HR (bpm)
Table 1. Average values ± 1 SD of the investigated parameters for the G-12 group
V (m . s -1 ) SF (Hz) SL (m ) KF(Hz) ηp TI (deg) HR (bpm)
V1 0.94 1.01 ± 0.06 0.08 0.45 0.48 ± 0.12 0.07 2.22 2.13 ± 0.57 0.34 1.85 1.43 ± 0.37 0.48 0.45 0.43 ± 0.08 0.07 23.4 24.0 ± 3.99 5.62 149 131 ± 17 13
V2 1.07 1.15 ± 0.11 0.08 0.59 ± 0.05 0.15 1.81 2.04 ± 0.21 0.56 1.86 1.82 ± 0.73 0.31 0.38 0.39 ± 0.04 0.07 21.0 21.4 ± 3.85 5.20 162 141 ± ± 12 8
FCS
FCS V3 1.15 1.27 ± 0.13 0.76 0.66 ± 0.10 0.12 1. 1.97 54 ± 0.18 0.32 2.01 2.03 ± 0.60 0.53 0.32 0.40 ± 0.04 0.06 18.1 20.0 ± 3.91 5.49 169 157 ± 11
V4 1.25 1.37 ± 0.16 0.12 0.85 0.74 ± 0.13 0.10 1.49 1.88 ± 0.26 0.27 2.50 2.40 ± 0.60 0.31 0.38 ± 0.06 13.5 14.6 ± 4.51 3.71 165 166 ± ± 11 8
V1 0.95 1.01 ± 0.09 0.12 0.69 0.60 ± 0.07 0.09 1.39 1.70 ± 0.18 0.23 1.56 1.30 ± 0.71 0.52 0.29 0.34 ± 0.04 0.05 33.7 34.4 ± 9.08 3.39 159 153 ± 14 15
HOS V2 1.00 1.13 ± 0.12 0.09 0.73 0.70 ± 0.07 0.11 1.38 1.66 ± 0.20 0.33 1.76 1.55 ± 0.85 0.55 0.29 0.34 ± 0.04 0.07 28.7 27.6 ± 4.62 3.81 167 160 ± 15 14
V3 1.12 1.24 ± 0.15 0.11 0.89 0.78 ± 0.15 0.08 1.30 1.62 ± 0.26 0.25 1.85 1.78 ± 0.84 0.69 0.27 0.33 ± 0.05 30.2 30.9 ± 4.97 3.33 174 165 ± 16 13
V4 1.16 1.33 ± 0.18 0.13 0.93 0.84 ± 0.16 0.08 1.28 1.59 ± 0.25 0.23 2.04 2.10 ± 0.76 0.61 0.27 0.32 ± 0.05 22.2 ± 8.06 4.43 176 175 ± ± 16 9
The comparison between styles (both groups considered, at all swim-
Table 2. Average values ± 1 SD of the investigated parameters for the G-16 group
V (m . s -1 The comparison between styles (both groups considered, at all swimming speeds)
indicates that all parameters are significantly different in the two conditions (HOS and
ming FCS) (ANOVA, speeds) indicates F(1, 19), p < that 0.05 all in all parameters cases). Swimming are significantly with the head different out leads in to a
the small two (2%), conditions albeit ) significant, (HOS SF (Hz) reduction and SL (m FCS) ) of the (ANOVA, KF(Hz) self select speed F in comparison ηp TI (deg) HR to (bpm) FCS.
(1, 19) , p < 0.05 in all
During HOS the players have a larger (32%) inclination of the trunk with the horizontal
cases). Swimming with the head out leads to a small (2%), albeit signifi-
and a higher heart rate (7%) compared to FCS. Moreover, in HOS, SL and ηp are
cant, significantly reduction reduced of the (21% self in both select cases) speed whereas in comparison SF is increased to (17%) FCS. in During respect to
HOS FCS. Finally, the players KF is 10% have lower a larger during (32%) HOS than inclination during FCS. of the trunk with the
The comparison between groups (both styles considered, at all swimming speeds)
horizontal indicates that and there a higher are no significant heart rate differences (7%) compared between groups to FCS. (G-12 Moreover, and G-16) in in TI
and KF. However, players of G-12 swim at a significantly lower pace than those of G-
HOS, SL and ηp are significantly reduced (21% in both cases) whereas
SF is increased (17%) in respect to FCS. Finally, KF is 10% lower during
HOS than during FCS.
The comparison between groups (both styles considered, at all swim-
16 (9%), with a lower SL (14%), a higher SF (8%) and a lower ηp (11%) (ANOVA, F(1,
19), p < 0.05 in all cases). Finally, HR is 5% lower in G-16 than in G-12 albeit this
difference does not reach a significant level (p = 0.06).
DISCUSSION
ming speeds) indicates that there are no significant differences between
Data reported in this study indicate that HOS is characterized by relevant differences in
groups the biomechanics (G-12 and of swimming G-16) in in TI comparison and KF. with However, FCS. The players need of keeping G-12 swim the head
at out a of significantly the water does lower indeed pace lead than to an increase those of G-16 TI (and (9%), thus to with an increase a lower of frontal SL
area and hydrodynamic resistance) whereas the need of keeping the elbows high does
(14%), indeed a lead higher to an SF increase (8%) of and SF a and lower thus ηto p (11%) a reduction (ANOVA, of the distance F (1, 19) , covered p < 0.05 per
in stroke all cases). (and of Finally, the arm stroke HR is efficiency). 5% lower Both in needs G-16 do than indeed in result, G-12 as albeit hypothesized, this
in an increase of the energy requirement of this peculiar “form of locomotion in water”
difference does not reach a significant level (p = 0.06).
as confirmed, albeit indirectly, by the higher HR in HOS than in FCS at any given
speed.
Interestingly, KF is lower during HOS than FCS and this suggests that these players
are not able to contrast the larger trunk incline with a more frequent/forceful leg kick.
dIscussIon
Moreover, KF and TI do not change with the years of practice (no differences are
Data observed reported between in the this two study groups indicate for these two that parameters) HOS is characterized and this suggests by that rel- more
experienced swimmers essentially rely on a better arm stroke efficiency to overcome the
evant differences in the biomechanics of swimming in comparison with
challenges of this “swimming style”.
FCS. The need of keeping the head out of the water does indeed lead
to an increase of TI (and thus to an increase of frontal area and hydrodynamic
resistance) whereas the need of keeping the elbows high does
indeed lead to an increase of SF and thus to a reduction of the distance
covered per stroke (and of the arm stroke efficiency). Both needs do
indeed result, as hypothesized, in an increase of the energy requirement
of this peculiar “form of locomotion in water” as confirmed, albeit indirectly,
by the higher HR in HOS than in FCS at any given speed.
CONCLUSIONS
This study suggests that while training young water polo players is necessary to
improve as much as possible the efficiency of the arm stroke. Moreover, it indicates the
importance to teach them how to perform a continuous and regular leg kick to raise, as