Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
The MAD system allowed the subjects to push-off from fixed pads at
each stroke. Hence, power expended in giving the water a kinetic energy
change was 0 (Pk=0) as in free swimming, and thus Po=Pd. The 15 pushoff
pads were fixed 1.30m apart on a 23m horizontal rod 0.75m below
the water surface, making continuous swimming over the system possible.
At one end of the swimming pool, one rod was connected to a force
transducer. The force signal was processed and stored on the hard disk
of the notebook computer. Throughout the measurement, the swimmers
used their arms only; their legs were supported and fixed together by a
small buoy (buoyant force 15.7N) (ARN-100, ARENA).
The force signal was time-integrated, and yielded the average
force. The mean swimming velocity was computed from the time needed
to cover the distance between the second and fourteenth pads. The
power used to overcome drag (Pd) was calculated from the product of
the mean drag force and the mean velocity.
For the measurement of propelling efficiency (ep), each subject
swam 300m 6 times using front crawl arm stroke only, 3 times using the
MAD system, and 3 times in free swimming. The swimming velocities
were set at 80%, 85%, and 90% of the average velocity of 400m maximal
arm stroke swimming. These velocities were determined by the need to
ensure that all exercise was sub-maximal and also that subjects were
able to maintain normal swimming technique even at the lowest velocity.
During the measurements, subjects were aided to keep a constant
swimming velocity by a pacing device consisting of underwater lights
that was set at the bottom of swimming pool (SWIMMING PACE
MAKE MODEL PMS-103, TAKAGI). All measurements for each
subject were made in one day, taking enough rest to prevent the subjects
from becoming fatigued.
To determine energy expenditure, steady state oxygen uptake (VO 2 )
during the 300m swim was measured by the Douglas bag method. The
face mask used for collecting expired gas allowed unhindered movement
of the arms during swimming. In an earlier study the “streamlining”
of this design was such that there was no measurable increase in
drag (Toussaint et al., 1987). The expired gas collection to measure VO 2
was performed while the subject was swimming the final 50m (after
at least 3 min from beginning of the trial), by which time VO 2 had
reached a steady state. The O 2 and CO 2 fractions in the expired gas
were determined by an automatic gas analyzer (Vmax29c, Sensor medics
Corporation, California, USA). Expired gas volume was measured by a
dry gas meter (SHINAGAWA). The VO 2 was taken to reflect the rate
of energy expenditure at the sub-maximal exercise level studied, which
was confirmed by the observed respiratory exchange ratio (RER) values.
The rate of energy expenditure (PVO2) in Watts was calculated by the
oxygen uptake (l•min-1, STPD) and RER following the formula of
Carby et al., 1987:
PVO2=(4940RER+16040)•VO2/60 (Eq.1)
The rate of energy expenditure (PVO2) measured during swimming on
the MAD system was related to the total power output (Po), which
was equal to Pd, since the push-off was against the fixed pads (Pk=0).
Hence, gross efficiency (eg) in this experiment was computed as follows
(Toussaint et al., 1990);
eg=Po/ PVO2 (Eq.2)
Furthermore, the total power output (Po) of the free swimming was
calculated by the product of gross efficiency (eg) and energy expenditure
(PVO2 in W) of free swimming.
Po= PVO2•eg (Eq.3)
The Propelling efficiency (ep) is defined as the ratio of the propelling
power (used overcome drag, Pd) to the total power output (Po) (Toussaint
et al., 1988). Therefore, ep was calculated as Pd divided by Po in
free swimming at the same velocity.
ep=Pd/Po=Pd/(Pd+Pk (Eq.4)
202
The time trials of 50m, 100m, 200m and 400m front crawl were performed
on different days. Then, the average swimming velocity was
computed from each performance time.
results
The swimming performance (average velocity) of each distance for each
subject is presented in Table 1.
Measurements for ep were taken during free swimming and on the
MAD system in a range of matched velocities (range; 1.22 to 1.46 m•s -1 ).
PVO 2 calculated from the VO 2 data ranged from 388.5 to 917.7W (MAD
system), and from 553.1 to 1367.0W (free swim).The power used to overcome
drag (Pd) ranged from 40.7
50m
(m•s -1 100m
) (m•s -1 200m
) (m•s -1 400m
) (m•s -1 Table 1. Swimming performance (velocity) of each
distance
)
S.W. 1.82 1.71 1.61 1.55
K.W. 1.88 1.71 1.56 1.48
F.U. 1.89 1.71 1.47 1.4
K.A. 1.82 1.72 1.62 1.56
M.Y. 1.75 1.64 1.56 1.54
M.U. 1.77 1.67 1.58 1.52
S.K. 1.77 1.62 1.52 1.49
A.S. 1.85 1.75 1.67 1.62
E.T. 1.84 1.73 1.65 1.56
mean 1.82 1.70 1.58 1.52
SD 0.05 0.04 0.06 0.06
to 76.5W, and the total power output (Po) in free swimming ranged
from 54.1 to 103.4W. The mean value of eg calculated by the ratio of
Po and PVO2 was 10±1% (range; 6 to 11%). Finally, knowing the Po in
free swimming and Pd as determined on the MAD system at the same
velocity, the calculated ep was 71±6% (range; 56 to 80%) (Table 2).
velocity
(m･s -1 Table 2. Individual data dependent on velocity are given for power input (PiMAD, and Pifree), power out
(Pofree), drag force (Fd), power to overcome drag (PdAMD), power lost in moving water (Pk), the propelling
efficicency (ep), and gross efficiency (eg).
PiMAD PdMAD Fd Pofree Pifree Pk ep eg
) (W) (W) (N) (W) (W) (W) (%) (%)
S.W. 1.38 525.3 60.1 43.5 82.6 722.8 22.6 73% 11%
1.40 551.9 58.9 42.1 77.7 727.9 18.8 76% 11%
1.43 630.4 63.8 44.6 83.5 824.6 19.7 76% 10%
K.W. 1.22 388.5 41.2 33.8 63.1 595.0 21.9 65% 11%
1.28 453.2 49.7 38.8 75.5 688.7 25.8 66% 11%
1.32 491.0 51.8 39.3 77.9 738.6 26.1 66% 11%
F.U. 1.25 542.0 52.8 42.2 76.0 781.1 23.3 69% 10%
1.28 597.1 47.1 36.8 69.5 880.8 22.4 68% 8%
1.31 917.7 53.3 40.7 79.4 1367.0 26.1 67% 6%
K.A. 1.23 612.3 44.0 35.7 55.3 769.9 11.3 80% 7%
1.29 610.9 47.3 36.7 65.4 844.9 18.1 72% 8%
1.35 618.6 54.8 40.6 76.2 860.4 21.4 72% 9%
M.Y. 1.23 558.9 40.7 33.1 54.1 743.7 13.4 75% 7%
1.30 553.7 49.0 37.7 69.3 784.6 20.3 71% 9%
1.36 566.4 54.2 39.9 73.2 765.8 19.0 74% 10%
S.U. 1.23 441.8 45.3 36.8 56.7 553.1 11.4 80% 10%
1.29 471.0 47.7 37.0 61.1 604.2 13.5 78% 10%
1.35 491.6 53.8 39.8 95.3 871.6 41.6 56% 11%
S.K. 1.23 421.1 43.5 35.3 58.8 570.0 15.4 74% 10%
1.30 488.6 48.9 37.6 67.7 676.0 18.7 72% 10%
1.36 556.5 55.5 40.8 93.2 934.2 37.7 60% 10%
A.S. 1.39 528.7 57.9 41.7 89.2 726.3 24.3 73% 11%
1.43 602.7 64.9 45.4 103.4 814.5 26.9 74% 11%
1.46 773.2 76.5 52.4 103.3 1043.8 26.8 74% 10%
E.T. 1.25 408.7 42.4 33.9 59.2 570.8 16.8 72% 10%
1.28 420.2 47.1 36.8 64.2 573.2 17.2 73% 11%
1.36 497.9 55.6 41.0 76.5 685.1 20.9 73% 11%
mean 1.32 545.2 52.1 39.4 74.4 767.4 21.5 71% 10%
SD 0.07 112.6 8.2 4.2 13.9 170.3 6.9 6% 1%
When the relationship between ep and swimming performance for
different distances was examined, the individual ep values were significantly
related to individual swimming performance in 200m and 400m
(200m; r=0.72, P