Biomechanics and Medicine in Swimming XI

for displacing the body over a given unit of distance (Zamparo et al, 2005).
Furthermore, it is accepted as an important bioenergetical determinant
of swimming performance (Wakayoshi et al, 1995; Kjendlie et al., 2004;
Fernandes et al., 2006). However, the body of scientific literature needs
approaches on the relationships between the IdC and the C in trying to
understand how these two variables may be connected. The present study
aimed at assessing relationships between the IdC and the C in front crawl,
especially at intensities ranging between ~70 % and 100% of the maximal
oxygen consumption ( V � O 2 max). We hypothesised that if velocity is
controlled, IdC and C are inversely related.
Methods
Seven high-level swimmers (17.0 ± 1.8 years; 168.0 ± 8.8 cm; 58.4 ± 8.2
kg) participant in national swimming championships were tested. Mean
(± SD) main physiological characteristics were: 18.0 (6.9) % of fat mass,
54.9 (10.1) ml.kg -1 .min -1 of V � O 2 max and 7.5 (2.4) of blood lactate
concentrations ([La - ]) at intensities corresponding to V � O 2 max. In an
indoor 25 m swimming pool, the participants performed an intermittent
incremental protocol, with increments of 0.05 m·s -1 each 200 m stage (and
30 s intervals), until exhaustion (Fernandes et al., 2003). Initial velocity
was established according to the individual level of fitness and was set
at the swimmer’s individual performance on the 400 m freestyle minus
seven increments of velocity. Swimming velocity was controlled using a
visual pacer (TAR 1.1, GBK-electronics, Aveiro, Portugal) with successive
flashing lights, 2.5 m apart, on the bottom of the pool.
V � O 2 was measured through direct breath-by-breath oximetry (K4
b 2 , Cosmed, Rome, Italy) connected to the swimmer by a respiratory snorkel
and valve system (Keskinen et al., 2003). Capillary blood samples (25
µl) for [La - ] analysis were collected from the earlobe at rest, in the 30 s rest
interval, at the end of exercise and during the recovery period (YSI1500L-
Sport auto-analyser, Yellow Springs Incorporated, Ohio, USA). The C was
calculated by dividing total energy expenditure (Ė) by velocity (v) and
converted to SI units, were 1 mlO 2 is equivalent to 20.1 J (Zamparo et al.,
2005; Fernandes et al., 2006):
C = Ė /v (1)
The Ė corrected for body mass was calculated using the V � O 2 net (difference
between the value measured in the end of the stage and the rest
value), and the blood lactate net (difference between the value measured
in two consecutive stages) transformed into V � O 2 equivalents using a
2.7mlO 2 kg -1 mmol -1 proportionality constant and by Equation (2) (cf.
Fernandes et al., 2006)
Ė = V� O2net + [La-]net (2)
Two video cameras (JVC GR-SX1 SVHS and JVC GR-SXM 25 SVHS)
were fixed on the lateral wall of the pool at a 10 m distance perpendicular
to the swimmers’ plane of movement. The cameras were connected to
a double entry and edited on a mixing table (Panasonic Digital Mixer
WJ-AVE55 VHS), providing a dual-media image (Panasonic AG 7355),
below and above the water surface (Vilas-Boas et al., 2006), at a frequency
of 50 Hz (1:250/s shutter speed).
For each step of the incremental protocol, two arm strokes were analysed
in every 50 m of the 200 m. Arm stroking coordination was obtained
through IdC (Chollet et al., 2000), being each arm stroke broken down
into four phases: (i) entry and catch (corresponding to the time between
the entry of the hand into the water and the beginning of its backward
movement); (ii) pull (corresponding to the time between the beginning
of the hand’s backward movement and its arrival in a vertical plane to the
shoulder); (iii) push (corresponding to the time from the position of the
hand below the shoulder to its release from the water) and (iv) recovery
(corresponding to the point of water release to water re-entry of the arm,
i.e., the above water phase). The duration of each phase was measured
for each arm-stroke cycle with a precision of 0.02 s. The duration of the
propulsive phases was the addition of the pull and the push phases, and
the duration of the non-propulsive phases was obtained by the sum of
chaPter2.Biomechanics
the catch and the recovery phases (the duration of a complete arm-stroke
was the sum of the propulsive and non-propulsive phases). The IdC was
calculated as the time gap between the propulsion of the two arms as a
percentage of the duration of the complete arm stroke cycle. Higher negative
percentage values expressed an evident discontinuity in the inter-arm
propulsion, tending to IdC=0% as the time gap was diminishing.
Mean ± SD computations for descriptive analysis were obtained in
each stage for all variables (all data were checked for distribution normality
with the Shapiro-Wilk test). Pearson correlation coefficient and partial
correlation were applied. Level of significance was established at 5%.
results
The mean ± SD values of velocity, % V � O 2 max, C, and IdC, obtained in
each step during the intermittent incremental test, are presented in Table
1. An increase of swimming intensity implies an increase of both C and
IdC (Table 1).
Table 1. Mean values of velocity, % V� O2max, IdC and C obtained in
each 200 m step of the incremental protocol (n=7).
Step velocity (m·s-1 ) % V� O2max C ( J·kg-1 ·m-1 1 1.15 ± 0.1 72.1 ± 8.7
)
9.4 ± 2.5
IdC (%)
-12.5 ± 2.5
2 1.20 ± 0.1 76.5 ± 9.1 10.3 ± 2.8 -12.1 ± 2.7
3 1.25 ± 0.1 77.8 ± 5.3 10.1 ± 3.0 -11.8 ± 2.6
4 1.30 ± 0.1 85.5 ± 3.3 11.5 ± 3.2 -10.9 ± 2.6
5 1.35 ± 0.1 90.9 ± 3.2 12.7 ± 2.8 -9.7 ± 2.7
6 1.40 ± 0.1 97.3 ± 3.2 13.7 ± 2.4 -8.2 ± 2.7
7 1.45 ± 0.1 100.0 ± 0.0 14.0 ± 4.2 -6.8 ± 2.5
The relationships between velocity and C, and velocity and IdC are
shown in Fig. 1 (left panel), being possible to observe a high correlation
value between these variables (r=0.98 and r=0.99, respectively, both for
p