Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
first in front crawl (non breathing cycles) and the second in backstroke.
Two digital cameras (Sony ® DCR-HC42E), placed inside a sealed
housing (SPK - HCB), recorded two complete underwater arm stroke
cycles in the lateral and frontal views. The lateral camera was placed at a
depth of 2 m and 11.5 m from the lane in which the participant swum.
The frontal camera was placed at 0.5 m depth. A rigid calibration frame
(2.10x0.70-m) was recorded at the beginning of the trials for calibration
purposes. Subsequently, each frame (50Hz) was digitized manually
using the APASystem (Ariel Dynamics Inc., USA). Nine anatomical
points were used: the hip (femoral condyle), and on both sides of the
body, the longest finger tips, wrist, elbow and shoulder of each swimmer.
After bi-dimensional reconstruction using a DLT procedure (Abel-Aziz
and Karara, 1978), a low pass filter of 5 Hz was used.
The front crawl arm stroke was divided into four phases (Chollet et
al., 2000): (i) entry and catch (time between the entry of the hand into
the water and the beginning of its backward movement); (ii) pull (time
between the beginning of the hand’s backward movement and when it
reaches a vertical plane with the shoulder); (iii) push (time from the position
of the hand below the shoulder to its release from the water) and
(iv) recovery (time from the point of water release to water re-entry of
the arm, i.e., the above water phase). In backstroke, each arm stroke was
divided into 6 phases (Chollet et al, 2006): (i) entry and catch (time between
the entry of the hand into the water and the start of its backward
movement that is followed by a diagonal hand sweep); (ii) pull (time
between the beginning of the hand’s backward movement and when the
line shoulder-hand is at 90° to the truck); (iii) push (time from the point
hand at shoulder level and the end of the hand’s backward movement);
(iv) hand lag time (time during which the hand stops at the thigh after
the push phase and before starting to move upward to clear the water);
(v) clearing (time from the beginning of the hand release upward to the
beginning of its exit from the water) and (vi) recovery (time corresponding
to the point of water release to water re-entry of the arm).
The duration of the propulsive phases of front crawl and backstroke
was the sum of the pull and the push phases. The duration of the nonpropulsive
phases was obtained by the sum of the catch and the recovery
phases (for front crawl) and the addition of the catch, hand lag
time, clearing and recovery phases (for backstroke). The duration of a
complete arm-stroke was the sum of the propulsive and non-propulsive
phases. The IdC was considered as the time gap between the propulsion
of the two arms and expressed as a percentage of the duration of the
complete arm stroke cycle.
Mean ± SD were calculated for all variables (all data were checked
for distribution normality with the Shapiro-Wilk test). Pearson correlation
coefficient was applied and the level of significance was established
at 95% (p