Biomechanics and Medicine in Swimming XI

arm coordination was observed exclusively. For the front crawl, the use
of a catch-up coordination mode is usually considered by coaches and
instructors as a technical fault (Seifert and Chollet, 2008) and is observed
in less skilled swimmers (Seifert et al., 2008). This coordination
mode does seem to be efficient at slow paces, as it favors a glide phase
following propulsive actions (Seifert et al., 2004b). These authors found
that when the velocity increases above a critical value, a transition from
catch-up to superposition mode is seen. In the present study swimmers
performed a maximal intensity protocol and the use of catch-up coordination
appears to be indicative of a less proficient technique. Interestingly,
Seifert et al. (2004a) showed that women have more negative IdC
values than men due to their higher fat mass values, different fat mass
distribution, lower arm strength, and as a result greater difficulty in overcoming
forward resistance. These are also characteristics of individuals
with DS (Aleixo et al., 2009). Other physical characteristics, such as a
smaller propulsive surface, also found in swimmers with loco-motor disabilities,
can also influence their inter-arm coordination (Satkunskiene
et al., 2005). The direct relationship found between the IdC and the
push phase and propulsive phases, also described in the literature on
able bodied swimmers (Figueiredo et al., in press) emphasizes the importance
of the propulsive phase duration in an arm stroke.
In backstroke, the catch-up coordination mode is the only pattern
of arm coordination used, with IdC values varying between -25% and
-5% (Seifert and Chollet, 2008). This fact seems to be due to the limited
shoulder range of movement and to the alternating body-roll (Chollet
et al., 2008), which impose a particular arm coordination and an additional
stroke phase - clearing phase (Lerda and Cardelli, 2003). This
clearing phase prevents continuity between the propulsive phases of the
two arms. This is only found when a three-peak stroke pattern is used,
creating some propulsion in the beginning of the upsweep (Maglisho,
2003). This three-peak stroke pattern was not seen in the present study.
On the contrary, a hand lag time phase was found in all swimmers in
accordance with Chollet et al. (2006) and Chollet et al. (2008). These
authors pointed out that this arm phase can affect the arm coordination
in backstroke, since it leads to propulsive discontinuity, explaining why
elite swimmers limit their hand lag time to approximately 2% of the
stroke cycle duration (a much lower value than found in the present
study). The very existence of this phase is, however, controversial because
some studies (e.g. Lerda and Cardelli, 2003; Lerda et al., 2005) did not
report this.
Although the participants in this study are international level Down
Syndrome swimmers, their arm coordination does not correspond to the
values of typical elite swimmers without DS, suggesting the presence
of technical faults or physical shortcomings (e.g. higher hand lag time).
The IdC values of the present swimmers are closer to those found by
Cardelli (2003) for less expert swimmers (-11.3%) compared to more
expert backstrokers (-9.7%). The inverse correlation between IdC and
velocity was also found by Chollet et al. (2008), corroborating the findings
elsewhere of higher (less negative) IdC values at higher swimming
velocities.
conclusIon
International level swimmers with DS presented a catch-up arm coordination
mode in front crawl, which may be associated with less proficient
arm coordination. Trained swimmers usually change from catch-up to
superposition with increasing velocities. The catch-up coordination mode
was also found in all swimmers for the backstroke. This is in concordance
with the literature on less skilled swimmers and for skilled swimmers at
low velocities. The high values of hand lag time contributed to this.
It can also be pointed out that this instrument can be very helpful
to coaches in better understanding underwater stroke phases. These
findings also emphasize the importance of augmenting the propulsive
phases of the arms and, with this, diminishing the lag time of the swimmers.
Technical mistakes can also be detected through the study of the
arm coordination.
chaPter2.Biomechanics
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