Biomechanics and Medicine in Swimming XI

Oxygen Uptake Kinetics Around the Respiratory
Compensation Point in Swimming
chaPter3.PhysioLogyandBioenergetics
study was to describe VO2 kinetics throughout the heavy and severe
exercise domains during front-crawl swimming, considering RCP as the
transition parameter between them.
Pessôa Filho, d.M.
215
1 , reis, J.F. 2 , Alves, F.B. 2 , denadai, B.s. 1
1Paulista State University, Brazil
2Faculty of Human Kinetics, Technical University of Lisbon, Portugal
The purpose of this study was to describe VO2 kinetics throughout the
heavy and severe domains during swimming. Nine swimmers completed
two swimming tests to measure the conditioning indexes (ventilatory
threshold (VT), respiratory compensation point (RCP), and VO2max )
and VO2 kinetics (two trials intensities set at 2.5% below and above the
crawl velocity at RCP, lasting 420s). In both cases, a portable breathby-breath
system connected to a respiratory snorkel and valve was used.
The trial below RCP elicited only a sub-maximal rate (91.6±5.7%VO-
2max ), with a slow component of 391ml·min-1 beginning after 154s. The
trial above RCP showed a time delay of 188s for the slow component
(399ml·min-1 Method
Subjects: Nine well-trained male swimmers (21.0 ± 7.2 yr, 68.6 ± 9.2 kg,
178.2 ± 6.4 cm, 13.2 ± 4.1% body fat, and ~4.0 ± 0.7 L.min
), eliciting a rate of 104.6±9.5%VO2max . Thus, expected
VO2 kinetics for heavy and severe domains was characterized
around RCP.
Key-word: Vo2 kinetics, heavy and severe domains, respiratory compensation
point
IntroductIon
The boundary between heavy and severe exercise denotes a considerable
change in exercise tolerance. According to Jones & Poole (2005), the
upper boundary for the heavy domain is defined as the highest exercise
intensity in which oxygen uptake (VO2 ) and blood lactate concentration
([lactate]) can be maintained at an elevated but steady-state level.
By definition, both critical power (CP: the asymptote of the power (P)
–time (t) relationship, represents the limiting parameter to the aerobic
supply, comprising the notion that if P ≤ CP, the anaerobic supply is
never required, and endurance time is infinitely long – Morton, 2006)
and maximal lactate steady-state (MLSS: highest constant workload
that can be maintained over time without continuous blood lactate accumulation
– Beneke, 2003) match the physiological responses encompassed
in the upper boundary of the heavy domain.
However, CP intensity cannot be maintained without a substantial
increase in blood lactate concentration, and other physiological parameters
(Pringle & Jones, 2002; Dekerle et al., 2003). Comparisons between
the CP and power associated to MLSS suggest that both are different
and should not be used interchangeably (Pringle & Jones, 2002). Moreover,
the critical swimming velocity (CV), corresponding to the slope
of the distance–time relationship (Sd–t), lies within the severe intensity
domain with the physiological responses characterizing the heavy and
severe intensity domains when swimming 5% slower and 5% faster than
Sd-t, respectively (Dekerle et al., 2009). The dependence of the P-t relationship
on the choice of predictive trials may explain the misinterpretation
of its mathematical definition as the highest work rate that can be
maintained for a very long time without fatigue (Dekerle et al., 2009).
Exercising at 50% of the difference between the mode-specific LT
and VO2max (50%ΔVO2) is an alternative index to the transition between
heavy and severe domains ( Jones & Poole, 2005). Surprisingly,
whereas the LT has been estimated from gas-exchange responses as
ventilatory threshold (VT: rising in the VE/VO2 curve with no change
in the VE/VCO2 curve – Beaver et al., 1986), the respiratory compensation
point (RCP: point in the plot of VE vs. VCO2 where VE rises
more rapidly in a phase of relative hyperventilation - Beaver et al., 1986)
for metabolic acidosis and buffering events in the tissues, has not clearly
demarcated the upper boundary of the heavy domain. Although no significant
differences were obtained between VO2 and power output at
CP and RCP in cycling (Dekerle et al., 2003). Thus, the purpose of this
-1 VO2max )
participated of this study. All subjects were advised to tests protocols
and gave written consent. This research was approved by the local Ethics
Committee.
Experimental design: The subjects were required to perform three
stages of experimentation. The first stage involved the determination
of VT, RCP and VO2max . The second stage involved two swimming
sessions with the subjects performing two repetitions of square-wave
transitions, from rest to one of two exercise intensities set at 2.5% below
(v-2.5% ) and above (v +2.5% ) the velocity at RCP, corresponding to 36.3 ±
7.0% and 74.1 ± 11.4% of the delta between velocity at VT and VO2max .
No more than two transitions were completed in one day, with at least
1h of recovery between transitions. All the procedures were not extended
beyond 3–4 weeks for each subject, and the study was completed in
about eight weeks. All tests were performed in a 50-m indoor swimming
pool. During the exercise tests, pulmonary gas exchange was determined
breath-by-breath with a portable automated system (K4b2, Cosmed),
which was calibrated before each test, and connected to the swimmer
by a special respiratory snorkel and valve system, previously validated by
Keskinen et al. (2002).
Incremental protocol: Subjects performed an intermittent incremental
test (300-m stages) to exhaustion. The velocity increments were delineated
to four or five percentages designed to attain the 400-m maximal swimming
velocity at the last stage. The breath-by-breath VO2 responses were
smoothed and averaged every 30s. VO2max was calculated as the highest
30s value achieved during the incremental test. The swimming velocity
related to the VO2max (vVO2max ) was defined as the lowest velocity that
elicited VO2max (Demarie et al. 2001). The lower and upper boundary for
heavy intensity domains were determined from gas exchange responses at
VT and RPC respectively, following the recommendations of Beaver et
al. (1986). VT was examined visually using plots of VE /VCO2 , VE /VO2 ,
end-tidal PCO2 (PETCO2 ) and end-tidal PO2 (PETO2 ). The criteria used
for determination of VT and RCP were a non-linear increase in VE/VO2 and PETO2 curves without a corresponding change in VE/VCO2 and
PETCO2 curves; and an increase in both VE/VO2 and VE/VCO2 and a
decrease in PETCO2 , respectively. VT and RCP location point were estimated
by two independent observers. The highest 30-s average VO2 for
these steps was considered the VO2 at VT and RCP.
VO2 kinetic modeling: Subjects performed two repetitions of squarewave
transitions of 7 min duration at the two exercise intensities on
separate days. After a 3-4 min warm-up at a low swimming velocity
followed by 5 min of rest, the subjects were instructed to perform the
required intensity. Intensities were set at 2.5% below and above the velocity
at RCP, which corresponded to 1.35 ± 0.05 m·s-1 and 1.28 ± 0.05
m·s-1 67
instructed to perform the required intensity. Intensities were set at 2.5% below and
, respectively. For each exercise transition, the breath-by-breath
above the velocity at RCP, which corresponded to 1.35 ± 0.05 m·s
data were interpolated to give second-by-second values. For every each
intensity, the transitions were then synchronized with the start of exercise
and averaged to enhance the underlying response characteristics.
Nonlinear regression techniques were used to fit VO2 data after the onset
of exercise with a bi-exponential model (Equation 1) that provided
an estimate of the on-transients: amplitudes (A1 and A2 ), time delays
(TD1 and TD2 ) and time constants (t1 and t2 ). The initial cardiodynamic
component was not considered by eliminating the first 20s of data after
the onset of exercise. The baseline VO2 was defined as the average VO2 measured during resting 30s before the start of each transition.
(1)
-1 and 1.28 ± 0.05
m·s -1 , respectively. For each exercise transition, the breath-by-breath data were
interpolated to give second-by-second values. For every each intensity, the transitions
were then synchronized with the start of exercise and averaged to enhance the
underlying response characteristics. Nonlinear regression techniques were used to fi
VO2 data after the onset of exercise with a bi-exponential model (Equation 1) tha
provided an estimate of the on-transients: amplitudes (A1 and A2), time delays (TD1 and
TD2) and time constants (t1 and t2). The initial cardiodynamic component was no
considered by eliminating the first 20s of data after the onset of exercise. The baseline
VO2 was defined as the average VO2 measured during resting 30s before the start of
each transition.
⎛ −
⎛ −
⎡ −
t TD1
⎞ ⎤ ⎡ −
t TD2
⎞
⎜ ⎟
⎜ ⎟ ⎤
⎝ τ1
⎠
⎝ τ 2 ⎠
VO2 ( t)
= VO2b
+ A1
⎢1
− l ⎥ + A2
⎢1
− l ⎥
⎣ ⎦ ⎣ ⎦
(1)
The physiologically relevant increase in VO2 is the amplitude of phase I (A1’), or
primary component, which was calculated from:
⎛ ( )
⎜
⎛ −
TD2−TD1
⎟
⎞
'
⎞
⎝
τ 1⎠
A = ⎜ −
⎟
1 A1
1 l
⎝
⎠
(2)
Because the asymptotic value (A2) may represent a higher value than that actually