1,720,970 research outputs found
Association between V̇O2max and the kinetics of V̇O2 in groups differing in fitness status
No full textPurpose This study evaluated (i) the relationship between oxygen uptake ( ̇VO2) kinetics and maximal ̇VO2 ( ̇VO2max) within groups differing in fitness status, and (ii) the adjustment of ̇VO2 kinetics compared to that of central [cardiac output (Q), heart rate (HR)] and peripheral (deoxyhemoglobin over ̇VO2 ratio ([HHb]/̇VO2)] O2 delivery, during step-transitions to moderate-intensity exercise. Methods Thirty-six young healthy male participants (18 untrained; 18 trained) performed a ramp-incremental test to exhaustion and 3 step-transitions to moderate-intensity exercise. Q and HR kinetics were measured in 18 participants (9 untrained; 9 trained). Results No significant correlation between τ̇VO2 and ̇VO2max was found in trained participants (r = 0.29; p > 0.05) whereas a significant negative correlation was found in untrained (r = − 0.58; p 0.05). τQ demonstrated a significant strong positive correlation with τHR in trained (r = 0.76; p 0.05). A significant overshoot in the [HHb]/̇VO2 ratio was found in the untrained groups (p 0.05) Conclusion The results indicated that when comparing participants of different fitness status (i) there is a point at which greater VO2max values are not accompanied by faster ̇VO2 kinetics; (ii) central delivery of O2 does not seem to limit the kinetics of ̇VO2; and (iii) O2 delivery within the active tissues might contribute to the slower ̇VO2 kinetics response in untrained participants
Fitness level- and sex-related differences in macro- and micro-vascular responses during reactive hyperemia
No full textPurpose
Reactive hyperemia (RH) is widely used for the investigation of macrovascular (flow-mediated dilation, or FMD) and microvascular (near-infrared spectroscopy–vascular occlusion test, or NIRS-VOT) function. Mixed results have been reported on fitness level‐ and sex-related differences in FMD outcomes, and little is known about microvascular differences in untrained and chronically trained males and females.
Methods
Fifteen chronically trained (CT: 8 males, 7 females) and 16 untrained (UT: 8 males, 8 females) individuals participated in this study. Aerobic fitness (V ̇O2max) was assessed during a cycling incremental exercise test to volitional exhaustion. FMD and NIRS-VOT were performed simultaneously on the lower limb investigating superficial femoral artery and vastus lateralis muscle, respectively.
Results
%FMD was not different between groups (CT males, 4.62 ± 1.42; CT females, 4.15 ± 2.23; UT males, 5.10 ± 2.53; CT females, 3.20 ± 1.67). Peak blood flow showed greater values in CT versus UT (P ≤ 0.0001) and males versus females (P = 0.032). RH blood flow area under the curve was greater in CT versus UT (P = 0.001). At the microvascular level, desaturation and reperfusion rates were faster in CT versus UT (P = 0.018 and P = 0.013) and males versus females (P = 0.011 and P = 0.005). V ̇O2max was significantly correlated with reperfusion rate (P = 0.0005) but not with %FMD.
Conclusions
Whereas NIRS-VOT outcomes identified fitness- and sex-related differences in vascular responses, %FMD did not. However, when RH-related outcomes from the FMD analysis were considered, fitness- and/or sex-related differences were detected. These data highlight the importance of integrating FMD and NIRS-VOT outcomes for a more comprehensive evaluation of vascular function
Maximal Lactate Steady State Versus the 20-Minute Functional Threshold Power Test in Well-Trained Individuals: “Watts” the Big Deal?
No full textPurpose: To (1) compare the power output (PO) for both the 20-minute functional threshold power (FTP20) field test and the calculated 95% (FTP95%) with PO at maximal lactate steady state (MLSS) and (2) evaluate the sensitivity of FTP95% and MLSS to training-induced changes.
Methods: Eighteen participants (12 males: 37 [6] y and 6 females: 28 [6] y) performed a ramp-incremental cycling test to exhaustion, 2 to 3 constant-load MLSS trials, and an FTP20 test. A total of 10 participants returned to repeat the test series after 7 months of training.
Results: The PO at FTP20 and FTP95% was greater than that at MLSS (P = .00), with the PO at MLSS representing 88.5% (4.8%) and 93.1% (5.1%) of FTP and FTP95%, respectively. MLSS was greater at POST compared with PRE training (12 [8] W) (P = .002). No increase was observed in mean PO at FTP20 and FTP95% (P = .75).
Conclusions: The results indicate that the PO at FTP95% is different to MLSS, and that changes in the PO at MLSS after training were not reflected by FTP95%. Even when using an adjusted percentage (ie, 88% rather than 95% of FTP20), the large variability in the data is such that it would not be advisable to use this as a representation of MLSS
Training-induced changes in the RCP, [HHb]BP, and MLSS: Evidence of equivalence
No full textPurpose: To evaluate whether the coherence in the oxygen uptake (V ̇O2) associated with the respiratory compensation point (RCP), near-infrared spectroscopy-derived muscle deoxyhemoglobin ([HHb]) break point ([HHb]BP), and maximal lactate steady state (MLSS) would persist at the midpoint and endpoint of a 7-month training and racing season.
Methods: Eight amateur male cyclists were tested in 3 separate phases over the course of a cycling season (PRE, MID, and POST). Testing at each phase included a ramp-incremental test to exhaustion to determine RCP and [HHb]BP. The PRE and POST phases also included constant power output rides to determine MLSS.
Results: Compared with PRE, V ̇O2 at both RCP and [HHb]BP was greater at MID (delta: RCP 0.23 [0.14] L·min-1, [HHb]BP 0.33 [0.17] L·min-1) and POST (delta: RCP 0.21 [0.12], [HHb]BP 0.30 [0.14] L·min-1) (P .05). PRE-MID and PRE-POST changes in V ̇O2 associated with RCP, [HHb]BP, and MLSS were strongly correlated (range: r = .85-.90) and demonstrated low mean bias (range = -.09 to .12 L·min-1).
Conclusions: At all measured time points, V ̇O2 at RCP, [HHb]BP, and MLSS were not different. Irrespective of phase comparison, direction, or magnitude of V ̇O2 changes, intraindividual changes between each index were strongly related, indicating that interindividual differences were reflected in the group mean response and that their interrelationships are beyond coincidental
A “step-ramp-step” protocol to identify the maximal metabolic steady state
No full textThe oxygen uptake (V[Combining Dot Above]O2) at the respiratory compensation point (RCP) closely identifies with the maximal metabolic steady state. However, the power output (PO) at RCP cannot be determined from contemporary ramp-incremental exercise protocols.
Purpose: This study aimed to test the efficacy of a "step-ramp-step" (SRS) cycling protocol for estimating the PO at RCP and the validity of RCP as a maximal metabolic steady-state surrogate.
Methods: Ten heathy volunteers (5 women; age: 30 ± 7 yr; V[Combining Dot Above]O2max: 54 ± 6 mL·kg·min) performed in the following series: a moderate step transition to 100 W (MOD), ramp (30 W·min), and after 30 min of recovery, step transition to ~50% POpeak (HVY). Ventilatory and gas exchange data from the ramp were used to identify the V[Combining Dot Above]O2 at lactate threshold (LT) and RCP. The PO at LT was determined by the linear regression of the V[Combining Dot Above]O2 versus PO relationship after adjusting ramp data by the difference between the ramp PO at the steady-state V[Combining Dot Above]O2 from MOD and 100 W. Linear regression between the V[Combining Dot Above]O2-PO values associated with LT and HVY provided, by extrapolation, the PO at RCP. Participants then performed 30-min constant-power tests at the SRS-estimated RCP and 5% above this PO.
The oxygen uptake (V[Combining Dot Above]O2) at the respiratory compensation point (RCP) closely identifies with the maximal metabolic steady state. However, the power output (PO) at RCP cannot be determined from contemporary ramp-incremental exercise protocols.
Purpose: This study aimed to test the efficacy of a "step-ramp-step" (SRS) cycling protocol for estimating the PO at RCP and the validity of RCP as a maximal metabolic steady-state surrogate.
Methods: Ten heathy volunteers (5 women; age: 30 ± 7 yr; V[Combining Dot Above]O2max: 54 ± 6 mL·kg·min) performed in the following series: a moderate step transition to 100 W (MOD), ramp (30 W·min), and after 30 min of recovery, step transition to ~50% POpeak (HVY). Ventilatory and gas exchange data from the ramp were used to identify the V[Combining Dot Above]O2 at lactate threshold (LT) and RCP. The PO at LT was determined by the linear regression of the V[Combining Dot Above]O2 versus PO relationship after adjusting ramp data by the difference between the ramp PO at the steady-state V[Combining Dot Above]O2 from MOD and 100 W. Linear regression between the V[Combining Dot Above]O2-PO values associated with LT and HVY provided, by extrapolation, the PO at RCP. Participants then performed 30-min constant-power tests at the SRS-estimated RCP and 5% above this PO.
Results: All participants completed 30 min of constant-power exercise at the SRS-estimated RCP achieving steady-state V[Combining Dot Above]O2 of 3176 ± 595 mL·min that was not different (P = 0.80) from the ramp-identified RCP (3095 ± 570 mL·min) and highly consistent within participants (bias = -26 mL·min, r = 0.97, coefficient of variation = 2.3% ± 2.8%). At 5% above the SRS-estimated RCP, four participants could not complete 30 min and all, but two exhibited non-steady-state responses in blood lactate and V[Combining Dot Above]O2.
Conclusions: In healthy individuals cycling at their preferred cadence, the SRS protocol and the RCP are capable of accurately predicting the PO associated with maximal metabolic steady state
Evaluating the NIRS-derived microvascular O2 extraction "reserve" in groups varying in sex and training status using leg blood flow occlusions.
No full textIt has been demonstrated that the plateau in the near-infrared spectroscopy (NIRS) derived deoxygenated hemoglobin and myoglobin (deoxy[Hb+Mb]) signal (i.e., deoxy[Hb+Mb]PLATEAU) towards the end of a ramp-incremental (RI) test does not represent the upper-limit in O2 extraction of the vastus lateralis (VL) muscle, given that an O2 extraction reserve has been recently observed. This study aimed to investigate whether this O2 extraction reserve was present in various populations and whether it exhibited sex- and/or training- related differences.Sixteen men- 8 untrained (27±5 years; 83±11 kg; 179±9 cm), 8 trained (27±4 years; 82±10 kg; 182±8 cm) and 9 trained women (27±2 years; 66±10 kg; 172±6 cm) performed a RI cycling test to exhaustion. The NIRS-derived deoxy[Hb+Mb] signal was measured continuously on the VL as a proxy for O2 extraction. A leg blood flow occlusion (i.e., ischemia) was performed at rest (LBFOCC 1) and immediately post the RI test (LBFOCC 2).No significant difference was found between the deoxy[Hb+Mb] amplitude during LBFOCC 1 and the deoxy[Hb+Mb]PLATEAU (p>0.05) nor between baseline (bsln) deoxy[Hb+Mb] values. deoxy[Hb+Mb] amplitude during LBFOCC 2 was significantly greater than LBFOCC 1 and at deoxy[Hb+Mb]PLATEAU (p<0.05) with group means ~30-45% higher than the deoxy[Hb+Mb]PLATEAU and LBFOCC 1 (p<0.05). No significant differences were found between groups in O2 extraction reserve, regardless of sex- or training-statusThe results of this study demonstrated the existence of an O2 extraction reserve in different populations, and that neither sex- nor training-related differences affect the amplitude of the reserve
The plateau in the NIRS-derived [HHb] signal near the end of a ramp incremental test does not indicate the upper limit of O<sub>2</sub> extraction in the vastus lateralis
No full text This study aimed to examine, at the level of the active muscles, whether the plateau in oxygen (O2) extraction normally observed near the end of a ramp incremental (RI) exercise test to exhaustion is caused by the achievement of an upper limit in O2 extraction. Eleven healthy men (27.3 ± 3.0 yr, 81.6 ± 8.1 kg, 183.9 ± 6.3 cm) performed a RI cycling test to exhaustion. O2 extraction of the vastus lateralis (VL) was measured continuously throughout the test using the near-infrared spectroscopy (NIRS)-derived deoxygenated hemoglobin [HHb] signal. A leg blood flow occlusion was performed at rest (LBFOCC1) and immediately after the RI test (LBFOCC2). The [HHb] values during the resting occlusion (108.1 ± 21.7%; LBFOCC1) and the peak values during exercise (100 ± 0%; [HHb]plateau) were significantly greater than those observed at baseline (0.84 ± 10.6% at baseline 1 and 0 ± 0% at baseline 2) ( P < 0.05). No significant difference was found between LBFOCC1 and [HHb]plateau ( P > 0.05) or between the baseline measurements ( P > 0.05). [HHb] values at LBFOCC2 (130.5 ± 19.7%) were significantly greater than all other time points ( P < 0.05). These results support the existence of an O2 extraction reserve in the VL muscle at the end of a RI cycling test and suggest that the observed plateau in the [HHb] signal toward the end of a RI test is not representative of an upper limit in O2 extraction. </jats:p
An equation to predict the maximal lactate steady state from ramp-incremental test data
No full textObjectives: The maximal lactate steady state (MLSS) represents the highest exercise intensity at which an elevated blood lactate concentration ([Lac]b) is stabilized above resting values. MLSS quantifies the boundary between the heavy-to-very-heavy intensity domains but its determination is not widely performed due to the number of trials required.
Design: This study aimed to: (i) develop a mathematical equation capable of predicting MLSS using variables measured during a single ramp-incremental cycling test and (ii) test the accuracy of the optimized mathematical equation.
Methods: The predictive MLSS equation was determined by stepwise backward regression analysis of twelve independent variables measured in sixty individuals who had previously performed ramp-incremental exercise and in whom MLSS was known (MLSSobs). Next, twenty-nine different individuals were prospectively recruited to test the accuracy of the equation. These participants performed ramp-incremental exercise to exhaustion and two-to-three 30-min constant-power output cycling bouts with [Lac]b sampled at regular intervals for determination of MLSSobs. Predicted MLSS (MLSSpred) and MLSSobs in both phases of the study were compared by paired t-test, major-axis regression and Bland-Altman analysis.
Results: The predictor variables of MLSS were: respiratory compensation point (Wkg-1), peak oxygen uptake (V ̇O2peak) (mlkg-1min-1) and body mass (kg). MLSSpred was highly correlated with MLSSobs (r=0.93; p<0.01). When this equation was tested on the independent group, MLSSpred was not different from MLSSobs (234±43 vs. 234±44W; SEE 4.8W; r=0.99; p<0.01).
Conclusions: These data support the validity of the predictive MLSS equation. We advocate its use as a time-efficient alternative to traditional MLSS testing in cycling
- …
