Biomechanics and Medicine in Swimming XI

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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
average VO2 measured during resting 30s before the start of g the first 20s of data after the onset of exercise. The baseline average VO2 measured during resting 30s before the start of ⎡ ⎤ ⎡ ⎤ = VO − l − l ⎥ (1) BiomechanicsandmedicineinswimmingXi − ⎛ t−TD1 ⎞ − ⎛ t−TD2 ⎞ ⎜ ⎟ ⎜ ⎟ ⎝ τ1 ⎠ ⎝ τ 2 ⎠ 2b + A1 ⎢1 ⎥ + A2 ⎢1 ⎛ t−TD ⎛ − ⎡ − 1 ⎞ ⎤ ⎡ − t TD2 ⎞ ⎜ ⎟ ⎜ ⎟ ⎤ + ⎣ ⎝ τ1 ⎠ − + ⎦ −⎣ ⎝ τ 2 ⎠ 2b A1 1 A2 1 ) = VO ⎢ l ⎥ ⎢ l ⎥ ⎦ (1) The physiologically ⎣ relevant ⎦ increase ⎣ in VO2 is the ⎦ amplitude of phase I (A1’), or primary component, which was calculated from: h relevant was calculated increase in from: VO2 is the amplitude of phase I (A1’), or ch was calculated ⎛ from: ( ) ⎜ ⎛ − TD2−TD1 ⎟ ⎞ ' ⎞ ⎝ τ 1⎠ (2) = ⎜ − ⎟ 1 A⎛1 1 ( ) ⎜ ⎛ − TD2−TD1 ⎟ ⎞ ' ⎞ ⎝ τ 1⎠ A ⎜ ⎜⎝ ⎟ 1 = A1 1− l ⎠ (2) ⎝ ⎠ Because the asymptotic value (A2) may represent a higher value than otic value that (A2) actually may reached represent at the end a higher of the exercise, value than the value that of actually the VO2 exercise, slow the exponential value of term the at VO2 the end slow of exercise exponential was defined term as at (A2’): the end s (A2’): ⎛ ( ) ⎜ ⎛ − ED−TD2 ⎟ ⎞ ' ⎛ ( ) ⎜ ⎛ − ED−TD2 ⎟ ⎞ ⎞ (3) ' ⎝ ⎞ τ 2 ⎠ = ⎜ ⎝ τ 2 ⎠ A − ⎟ 2 = A2 ⎜ 1− ⎟ 2 A2 1 l (3) ⎝⎝ ⎠ ⎠ duration. where ED is the exercise duration. relevant increase in VO2 is the amplitude of phase I (A1’), or A l (2) tic value (A2) may represent a higher value than that actually exercise, the value of the VO2 slow exponential term at the end duration. A l (3) Statistical analysis: The values were expressed as mean ± SD. The normal- values were expressed as mean ± SD. The normality of data values were expressed as mean ± SD. The normality of data -Wilk test. ity of The data was statistical checked by difference Shapiro-Wilk between test. The two statistical means difference was -Wilk test. between The two statistical means was checked difference by a paired between Student’s t-test two (2-tailed). means was dent’s t-test (2-tailed). Bi-exponential analyses were performed ent’s t-test Bi-exponential duals method. (2-tailed). analyses The level of Bi-exponential were performed by significance was analyses the least squared set at p were residuals ≤ 0.05. performed method. The level of significance was set at p ≤ 0.05. All statistical analy- All performed uals method. by utilizing The level software of significance SPSS 17.0. was set at p ≤ 0.05. All ses were performed by utilizing software SPSS 17.0. erformed by utilizing software SPSS 17.0. RESULTS Variables presented in Table 1 describe the physiological and perfor- able 1 describe the physiological and performance parameters delimiting exercise domains. The RCP was observed to point between VT and VO2max, but substantial variability was ble 1. cremental test. n = 9. to BW Relative to Velocity 1 ) VO2max (%) (m·s -1 able 1 describe the physiological and performance parameters delimiting exercise domains. The RCP was observed to point between VT and VO2max, but substantial variability was able 1. ncremental test. n = 9. to BW Relative to Velocity -1 ) VO2max (%) (m·s Delta ) (%∆) 100 1.40 (±0.03) 100 70.5 (±8.0) 1.21 (±0.06) 0 -1 mance parameters related to the indices delimiting exercise domains. The RCP was observed to correspond with the midpoint between VT and VO2max , but substantial variability was observed, as shown on Table 1. Table 1: Parameters for incremental test. n = 9. VO Delta 2 relative to BW (ml ) (%∆) 100 1.40 (±0.03) 100 70.5 (±8.0) 1.21 (±0.06) 0 86.0 (±4.9) 1.32 (±0.05) 51.0 (±16.5) . min-1 .kg-1 Relative to Velocity ) VO2max (%) (m·s-1 Delta ) (%Δ) VO2max 58.0 (±5.1) 100 1.40 (±0.03) 100 VT 41.1 (±7.3) 70.5 (±8.0) 1.21 (±0.06) 0 RCP 49.9 (±5.5) 86.0 (±4.9) 1.32 (±0.05) 51.0 (±16.5) The trivial difference between predetermined and performed trials above (1.35 ± 0.05 m·s 86.0 (±4.9) 1.32 (±0.05) 51.0 (±16.5) -1 and 1.34 ± 0.05 m·s-1 , ρ = 0.54) and below (1.28 ± 0.05 m·s-1 and 1.28 ± 0.05 m·s-1 , ρ = 0.78) RCP ensured the effective control of the velocity under the test condition. The velocity measured during trials was closer to the defined velocity in both trials above (2.0 ± 1.2%) and below (-2.7 ± 0.8%) the RCP. Table 2: Parameters of VO2 on-kinetics around RCP. n = 9. 2.5% below RCP 2.5% above RCP VO2Baseline (ml.min-1 ) 474.90 ± 91.24 523.78 ± 79.08 TD1 (s) 17.6 ± 3.3 14.0 ± 5.6 † t1 (s) 17.8 ± 7.1 16.1 ± 4.9 A’ 1 (ml·min-1 ) 2.784.93 ± 616.02 3.247.04 ± 669.99 † R2 0.97 ± 0.02 0.93 ± 0.04 TD2 (s) 153.8 ± 42.5 188.4 ± 97.2 t2 (s) 99.5 ± 82.2 73.8 ± 67.4 A’ 2 (ml·min-1 ) 391.24 ± 236.61 399.40 ± 270.49 R2 0.69 ± 0.26 0.66 ± 0.23 EEVO2 (ml·min-1 ) 3.176.17 ± 647.01 3.646.45 ± 823.11 † A’ 2 %EEVO2 12.4 ± 7.3 10.5 ± 5.3 TotalVO2 (ml·min-1 ) 3.651.07 ± 660.36 4.170.23 ± 810.11 † %VO2max attained 92.0 ± 6.0 105.0 ± 9.5 † EEVO 2 is the increase in VO 2 above baseline at end of exercise. † Marked differences (p < 0.05) were observed in relation to 2.5% below RCP. 216 Time parameters of VO2 on-kinetics seems not to differ substantially between trials around RCP, with the exception of TD1 (p = 0.03) (Table 2). This scenario suggests that the response for the primary component begins early while swimming above rather than below RCP. The amplitude parameters account for the noticeable differences between trials in each condition. Primary amplitude, end-exercise VO2 (EEVO2 ), and entire VO2 (TotalVO2 ) showed difference for their paired values in each trial (p values of 0.001, 0.001, and 0.000, respectively) (Table 2). There was no tendency for the onset of the slow component (TDs) to occur earlier as exercising above (188.4s) and below (153.8s) RCP intensity, neither to differ in amplitude (399.4 and 391.2 ml.min-1 above and below RCP, respectively), or in relative contribution to the EEVO2 (10.5 and 12.4% above and below RCP, respectively) (Table 2). None of the subjects reached the exhaustion in either trial (above and below RCP), however because of the slow component, TotalVO2 eliciting 104.57 and 91.58% of VO2max while swimming above and below RCP, respectively. The on-transient for VO2 above and below RCP is illustrated for one swimmer in the Figure 1. VO2 (L x min -1 ) 6.0 5.0 4.0 3.0 2.0 1.0 2.5%RCP VO2max RCP VT -100 0 100 200 300 400 500 Time (s) Figure 1: On-transition oxygen uptake kinetics in the trials around RCP for subject 6. Baseline VO 2 in each trials is showed for 30-s before exercise beginning (at time zero). dIscussIon In swimming, heavy and severe domains of exercise intensity have not been studied by means of pulmonary VO 2 on-kinetics. In a recent study, Dekerle et al. (2009) concluded that CV lies on the boundary between the heavy and severe intensity domains within a range of ± 5%, since post exercise VO 2 (reaching only 87 ± 14%VO 2peak ) and [lactate] remained stable when swimming 5% below CV. In contrast, when swimming 5% above, both a rapid increase in [lactate] and quick attainment of peak VO 2 were observed. Data from the present study corroborates with these results in an even narrower range (less than 5% was the difference between slower and faster trials) around the RCP, by on-transient VO 2 kinetics. The trial ~2.7% below RCP was performed at v36.8 ± 8.5%∆ (about 1.28 ± 0.05 m·s -1 or 91 ± 2% of vVO 2max ), eliciting a submaximal VO 2 (about 92.0 ± 6.0%VO 2max ), after a delayed steady-state (154s) of an amplitude of 391 ml·min -1 . The VO 2 in the trial above ~2% of RCP (v71.1 ± 17.1%Δ, about 1.3 ± 0.05 m·s -1 or 96.1 ± 2.4% of vVO 2max ) presented a delayed (188s) amplitude of 399 ml·min -1 limited trunked at its maximum rate (105.0 ± 9.5%VO 2max ). Similar results were previously observed by Demarie et al. (2001) with pentathletes, whose VO2 slow component rose to 114 ± 10%VO- 2peak when swimming at a velocity corresponding to 96% of VO- 2peak. Swimming at previously determined vVO2max, high level male swimmers exhibited a VO2 slow component of 274.1 ± 152.8 ml·min -1 (Fernandes et al., 2003). These authors have analyzed the VO2 changes (ΔVO2) between the second minute to the end of exercise for determining the amplitude of VO2 slow component, arguing that (1) onset of slow component has an earlier time delay in the severe than in the heavy domain; (2) there is no consensus about the algorithm to fit VO2 slow component kinetic; and (3) there is a high variability in the ampli-
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Biomechanics and Medicine in Swimmi
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Bibliographic information: Biomecha
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Figure 1. General biomechanical par
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Figure 2. Repeatability of the LTin
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-ARM * 5 Biomechanicsandmedic
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• Without restriction; • Blinde
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etween experimental groups and cont
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Pahlen Norge AS Pahlen Norge AS Cha
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Biomechanics and Medicine in Swimming XI

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