Biomechanics and Medicine in Swimming XI

TABLE 1. Performances during competition events
(5000-m, 1500-m, 800-m) expressed in real time and as
percent of world record.
S LP T5000-m
(h:min:s)
T1500-m
(min:s)
1500-m
(% wr)
T-800-m
(min:s)
800-m
(% wr)
1 N 55:31 16:25 88.7 8 :31 89.7
2 N 53:57 16:12 89.9 8 :17 92.2
3 N 55:07 16:12 89.9 8 :32 89.6
4 I 53:46 15:51 91.9 8 :12 93.1
5 I 54:37 16:05 90.6 8 :28 90.3
6 I 54:46 16:01 91.1 8 :16 92.4
7 N 55:44 16:08 90.3 8 :22 91.3
M 55:18 16:03 90:3 8 :37 91.2
SE 00 :44 00 :15 1.1 0 :07 1.3
All swimmers completed an incremental test performed to exhaustion.
This test was composed of five consecutive 300-m swims separated by
30s of rest. The speed of each increment was determined from the best
time performance of each swimmer in a 400-m freestyle event achieved
during the month preceding the test. The speed for the first 300m was
30s slower than the best 400-m time: this time was reduced by increments
of 5s for each consecutive 300m until the final 300m performed
maximally. Swimming speeds were monitored with Aquapacer ‘Solo’
(Challenge and Response, Inverurie, UK) so that each swimmer could
match auditory signals with visual markers positioned every 12.5m
along the border of the pool. Blood lactate level (expressed in mM/L)
was determined from a fingertip blood sample which was analyzed immediately
using a portable lactate analyzer (Lactate Pro, Arkray, Japan).
Breath-by-breath respiratory data were collected with a portable gas
analyzer (Cosmed K4b2, Rome, Italy) connected to an Aquatrainer
snorkel (Cosmed, Rome, Italy). Heart rate (HR) was recorded during
the K 4 b 2 exercise using a belt system (Polar Electro, Finland). The lactate
threshold (LT) was mathematically determined using the DMax
method (Cheng et al., 1992). HRpeak (expressed in beats·min -1 ) was
defined as the highest 15-s averaged HR value.
The interval training session consisted in a 500-m interval set. The
swimmers were informed of their velocity using the protocol described
above. Because they were wearing a snorkel, the swimmers used open
turns between 50-m bouts. During a pilot run, the time needed to execute
a turn with the snorkel was estimated individually at 1±0.37 s compared
with a conventional kick-off turn. Swimmers were instructed to perform
an open turn, always performed to the same lateral wall side, without underwater
gliding and breathing continually. The velocity (m·s-1) was calculated
by dividing the length of the 500-m by the time with individual
correction for number of turns. Expired gases collected breath-by-breath
was monitored continuously and recorded every 5-s. Serum lactate level
was measured at the end of the IT session. The parameters of · VO 2 kinetics
were calculated for the first 500m of the IT6x500 session. Since the
intensity of the exercise was equal to LT, breath-by-breath data were fitted
to two distinct models (Bell et al., 2001): a single exponential model
(equation 1) and a double-exponential model (equation 2).
·
VO 2 (t) = A 0 + A 1 × [1 – e – (t – TD 1 )/τ 1 )] (1)
Where A 0 is the baseline value (mL.min -1 ), A 1 is the asymptotic amplitude
for the exponential term (mL.min -1 ), τ 1 is the time constant (sec),
TD 1 is the time delay from the onset of exercise (sec)
·
VO 2 (t) = A 0 + A 1 × [1 – e – (t – TD 1 )/τ 1 )]*u 1 + A 2 × [1- e -(t – TD 2 )/
τ 2 (2)
·
where A 1 is the baseline value, TD 1 and τ 1 respectively the time delay
and the time constant for the first exponential term which is the rapid
phase of oxygen uptake adjustment and TD 2 (about 120 sec) and τ 2 are
respectively the delay and the time constant for the second exponential
chaPter3.PhysioLogyandBioenergetics
term which is the slow phase of oxygen uptake adjustment. Since the
first phase is unaffected by cardiodynamic factors (Bell et al., 2001), it
was not modeled in this study. As a consequence, the first 20sec of data
recording was removed from the analysis to ensure that the early initial
component would not influence the result (Bell et al., 2001). The parameters
of the model were determined by interaction minimization of
the sum of the mean squares of the differences between modeled VO
·
2
and measured · VO2 (Bell et al., 2001). The measured · VO2 values differing
by more than three standard deviations from the modeled · VO2 were excluded from the analysis. This exclusion was performed before
determining the final parameters for the model and accounted for only
2.5% of collected data. If the amplitude of the slow component was 0,
the second exponential term was removed and ·
VO2 kinetics was modeled
with the first exponential term (Bell et al., 2001). A Fisher test was
used to determine the significance of the exponential model. Linear and
non-linear regressions were used to analyze the distribution of residual
errors between measured and modeled · VO2 over time. The determination
coefficient was calculated and the Cp score computed as comparison
criteria to confirm accuracy and sensitivity of the modeling.
results
Swimming velocity (vLT), oxygen uptake ( · VO 2 LT), and blood lactate
concentration ([La]b) at LT were 1.46 ± 0.01 m·sec -1 , 352 ± 17-s, 60.1
± 6.4 mL·kg -1 .min -1 and 3.1 ± 1.2 mmol·L -1 , respectively. · VO 2 LT was
86.8 ± 1.7% of · VO 2 max and v LT was 96.7 ± 0.5% of v · VO 2 max . v · VO 2 max
was 91.1 ± 1.4 m·sec -1 of the 400-m best performance (with diving start,
without snorkel and with kick-off turns). · VO 2 max , HR peak , RPE and [La]
b obtained at v · VO 2 max during the increment test were 68.7 ± 5.2 mL·kg -1 .
min -1 , 196.3 ± 7.3 b·min -1 , 18.4 ± 3.2 a.u., 6.9 ± 1.4 mmol·L -1 respectively.
The fit was statistically superior for the two-term exponential model
compared with the one-term model (r²= 0.62 ± 0.18 vs. 0.52 ± 0.21, P
< 0.01). Furthermore, the Cp score was lower for the bi-exponential
model indicating a lesser prediction error (Cp=33.5±20.8 vs. 35.4±20.5,
p