Biomechanics and Medicine in Swimming XI

The aims of this study were to: (1) investigate co-ordination changes
during a 100 m short course breaststroke swim and (2) compare kinematic
variables between each of the four laps of the100 m swim.
Method
Twenty six specialist breaststroke participants (8 females: mean age, 19.1
+ 2.3 yrs; mean body mass, 70.0 + 8.0 kg; mean height, 1.70 + 0.05 m;
18 males: mean age 18.9 + 2.2 yrs.; mean body mass 69.3 + 7.3 kg;
height 1.78 + 0.06 m; short course 100 m breaststroke mean best times
females 88.7 + 5.4 s and males 77.0 + 5.5 s) volunteered to participate in
this study. The selection criterion for the study was that participants had
to be competitive in the 100 m breaststroke event at County standard
or above within that season. The study was approved by the Coventry
University Ethics Committee. The requirements of the study were explained
to participants and each participant provided written informed
consent. Twelve body landmarks (lateral malleolus, lateral femoral condyle,
greater femoral trochanter, styloid process, epicondyle of humerus
and acromion process) were marked using black vinyl tape.
Each swimmer performed a self-selected 800 m warm-up in a 25 m
pool. They were then instructed to perform a maximal effort 100 m swim
from a water start without the use of race strategy. Three cameras operating
at 50 Hz were used to record the 100 m swim. Two cameras (Sony
video DCR-TRV460E) were submerged in waterproof housings, one
at each end of the swimmer’s lane, to record frontal and rear views. The
third camera, a waterproof bullet camera, was connected to a visual display
unit (Sony digital video cassette recorder GV-D800E), which was
attached to a trolley. The trolley was moved manually to maintain the
swimmer’s hip marker in the centre of the visual display unit throughout
the entire 100 m swim.
Time to complete 100 m was recorded via a video analysis package
(Dartfish Trainer 2.5.2.19, Fribourg, Switzerland) as the time from
when the feet left the wall at the start until the double hand touch on
the wall at the end. Clean swim speed, stroke rate and stroke length
were determined over a 10 m section of the pool that was not affected
by starting, turning or finishing technique. The time taken for the hip
marker to travel this 10 m distance from the 15 m marker to the 5 m
marker from the end of the pool was determined from the video. Stroke
length was calculated from the mean clean swim speed and stroke rates
for each of the four laps, over the 10 m section of pool.
Stroke cycle time was calculated as the mean of the last three full
strokes completed in the 10 m section of each lap from the frontal and
sagittal camera views. To quantify co-ordination, five stroke phases were
identified: 1) Arm Propulsion - from the initial separation of the arms
from the extended position in front of the body until the first forward
movement of the elbows when the hands were under the head; 2) Arm
Recovery - from the end of the arm propulsion phase until the start of
the separation of the hands from the extended position; 3) Leg Propulsion
- from the start of the first backwards movement of the feet relative
to the body (the point where the knees were maximally flexed at the
start) until the instant when the knees were fully extended ; 4) Leg recovery
– from the end of the leg propulsion phase until the frame prior
to the first backwards movement of the feet in relation to the body; 5)
Transition phase - from the end of the leg propulsion phase until the
start of the arm propulsion phase. Each of the arm and leg phases were
expressed as a percentage of a complete arm or leg stroke respectfully.
Transition phase was expressed as a percentage of a complete leg stroke.
The complete arm and leg strokes were calculated as the mean of three
complete strokes. Means and standard deviations were calculated for
all the data. Analysis of variance with Bonferroni post-hoc tests were
used to compare laps (1, 2, 3 and 4) using selected variables at the same
point of each lap (clean swim speed, stroke rate, stroke length, stroke
cycle time, arm recovery, arm propulsion, leg propulsion, leg recovery
and transition time). Correlation coefficients were determined among
selected variables. The level of significance was set at p