Methodological considerations on near-infrared spectroscopy derived muscle oxidative capacity.

PURPOSE: Different strategies for near-infrared spectroscopy (NIRS)-derived muscle oxidative capacity assessment have been reported. This study compared and evaluated (I) approaches for averaging trials; (II) NIRS signals and blood volume correction equations; (III) the assessment of vastus lateralis (VL) and tibialis anterior (TA) muscles in two fitness levels groups. METHODS: Thirty-six participants [18 chronically trained (CT: 14 males, 4 females) and 18 untrained (UT: 10 males, 8 females)] participated in this study. Two trials of twenty transient arterial occlusions were performed for NIRS-derived muscle oxidative capacity assessment. Muscle oxygen consumption ([Formula: see text]O2m) was estimated from deoxygenated hemoglobin (HHb), corrected for blood volume changes following Ryan (HHbR) and Beever (HHbB) equations, and from oxygen saturation (StO2) in VL and TA. RESULTS: Superimposing or averaging [Formula: see text]O2m or averaging the rate constants (k) from the two trials resulted in equivalent k values [two one-sided tests (TOST) procedure with 5% equivalence margin-P < 0.001]. Whereas HHbR (2.35 ± 0.61 min-1) and HHbB (2.34 ± 0.58 min-1) derived k were equivalent (P < 0.001), StO2 derived k (2.81 ± 0.92 min-1) was greater (P < 0.001) than both. k values were greater in CT vs UT in both muscles (VL: + 0.68 min-1, P = 0.002; TA: + 0.43 min-1, P = 0.01). CONCLUSION: Different approaches for averaging trials lead to similar k. HHb and StO2 signals provided different k, although different blood volume corrections did not impact k. Group differences in k were detected in both muscles.

Heavy-, Severe-, and Extreme-, but not Moderate-Intensity Exercise Increase V̇o2max and Thresholds after 6 Weeks of Training.

INTRODUCTION: This study assessed the effect of individualized, domain-based exercise intensity prescription on changes in maximal oxygen uptake (V̇O2max) and submaximal thresholds. METHODS: Eighty-four young healthy participants (42 Females, 42 Males) were randomly assigned to six age, sex, and V̇O2max-matched groups (14 participants each). Groups performed continuous cycling in the 1) moderate (MOD)-, 2) lower heavy (HVY1)-, and 3) upper heavy-intensity (HVY2)- domain; interval cycling, in the form of 4) high-intensity interval training (HIIT) in the severe-intensity domain, or 5) sprint-interval training (SIT) in the extreme-intensity domain; or no exercise for, 6) control (CON). All training groups except SIT, were work-matched. Training participants completed three sessions per week for six weeks with physiological evaluations performed at PRE, MID and POST intervention. RESULTS: Compared to the change in V̇O2max (∆V̇O2max) in CON (0.1 ± 1.2 mL·kg-1·min-1), all training groups except MOD (1.8 ± 2.7 mL·kg-1·min-1), demonstrated a significant increase (p < 0.05). HIIT produced the highest increase (6.2 ± 2.8 mL·kg-1·min-1) followed by HVY2 (5.4 ± 2.3 mL·kg-1·min-1), SIT (4.7 ± 2.3 mL·kg-1·min-1), and HVY1 (3.3 ± 2.4 mL·kg-1·min-1), respectively. The Δ PO at the estimated lactate threshold (θLT) was similar across HVY1, HVY2, HIIT and SIT which were all greater than CON (p < 0.05). The Δ V̇O2 and Δ PO at θLT for MOD was not different from CON (p > 0.05). HIIT produced the highest Δ PO at maximal metabolic steady state, which was greater than CON, MOD, and SIT (p < 0.05). CONCLUSIONS: This study demonstrated that i) exercise intensity is a key component determining changes in V̇O2max and submaximal thresholds and ii) exercise intensity domain-based prescription allows for a homogenous metabolic stimulus across individuals.

Transient speeding of V̇O2 kinetics following acute sessions of sprint interval training: Similar exercise dose but different outcomes in older and young adults.

An acute session of sprint interval training (SIT) is a potent stimulus for the metabolic and cardiovascular systems. However, the feasibility of SIT in older adults and its effectiveness to acutely improve aerobic function by transiently accelerating the rate of adjustment of oxidative phosphorylation quantified by V̇O2 kinetics (τV̇O2) are unknown. This study evaluated the time course of changes of τV̇O2 in response to different doses of SIT in older inactive adults compared to their young counterparts. Eight older (age: 67 ± 3 years) and eight young (age: 30 ± 3 years) adults completed three separate SIT sessions consisting of either one (SIT1), three (SIT3), or five (SIT5) consecutive bouts of SIT. Each SIT intervention was interspersed by a two-week recovery phase. The bike resistance during the sprints was set at 0.065 kg·kg-1 body mass for older and 0.075 kg·kg-1 body mass for young adults. Moderate-intensity step-transitions were performed to assess τV̇O2 before (PRE) and one (1d), two (2d) and three (3d) days post each SIT intervention. Older adults attained lower peak power outputs, average power output, and blood lactate concentrations across all sprints of each SIT intervention compared to young (P < 0.01). Following SIT1, τV̇O2 was faster at 1d (-13.6%; P = 0.008) and 2d (-12.7%; P = 0.017) and returned to values similar to PRE at 3d (+0.4%; P > 0.05) in both older and young. Following SIT3, τV̇O2 was faster at 1d (-20.6%; P < 0.001), 2d (-18.5%; P = 0.011), and 3d (-14.5%; P = 0.045) compared to PRE in both older and young. Following SIT5, τV̇O2 became faster in older (at 1d, 2d, and 3d; ~25%; P < 0.05) but remained unchanged in young with respect to PRE (P > 0.05). These findings indicate that SIT has the potency to acutely improve aerobic function by speeding the rate of adjustment of oxidative phosphorylation. However, only older adults were able to maintain these beneficial effects when the volume of SIT was maximized (SIT5). Future studies are warranted to evaluate the long-term feasibility of SIT in older adults.

Fitness Level- and Sex-Related Differences in Macrovascular and Microvascular Responses during Reactive Hyperemia.

PURPOSE: 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.

Evaluating the Accuracy of Using Fixed Ranges of METs to Categorize Exertional Intensity in a Heterogeneous Group of Healthy Individuals: Implications for Cardiorespiratory Fitness and Health Outcomes.

BACKGROUND: Appropriate quantification of exertional intensity remains elusive. OBJECTIVE: To compare, in a large and heterogeneous cohort of healthy females and males, the commonly used intensity classification system (i.e., light, moderate, vigorous, near-maximal) based on fixed ranges of metabolic equivalents (METs) to an individualized schema based on the exercise intensity domains (i.e., moderate, heavy, severe). METHODS: A heterogenous sample of 565 individuals (females 165; males 400; age range 18-83 years old) were included in the study. Individuals performed a ramp-incremental exercise test from which gas exchange threshold (GET), respiratory compensation point (RCP) and maximum oxygen uptake (VO2max) were determined to build the exercise intensity domain schema (moderate = METs ≤ GET; heavy = METs > GET but ≤ RCP; severe = METs > RCP) for each individual. Pearson's chi-square tests over contingency tables were used to evaluate frequency distribution within intensity domains at each MET value. A multi-level regression model was performed to identify predictors of the amplitude of the exercise intensity domains. RESULTS: A critical discrepancy existed between the confines of the exercise intensity domains and the commonly used fixed MET classification system. Overall, the upper limit of the moderate-intensity domain ranged between 2 and 13 METs and of the heavy-intensity domain between 3 and 18 METs, whereas the severe-intensity domain included METs from 4 onward. CONCLUSIONS: Findings show that the common practice of assigning fixed values of METs to relative categories of intensity risks misclassifications of the physiological stress imposed by exercise and physical activity. These misclassifications can lead to erroneous interpretations of the dose-response relationship of exercise and physical activity.

Association between [Formula: see text]O2 kinetics and [Formula: see text]O2max in groups differing in fitness status.

PURPOSE: This study evaluated (i) the relationship between oxygen uptake ([Formula: see text]O2) kinetics and maximal [Formula: see text]O2 ([Formula: see text]O2max) within groups differing in fitness status, and (ii) the adjustment of [Formula: see text]O2 kinetics compared to that of central [cardiac output (Q̇), heart rate (HR)] and peripheral (deoxyhemoglobin over [Formula: see text]O2 ratio ([HHb]/[Formula: see text]O2)] 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. Q̇ and HR kinetics were measured in 18 participants (9 untrained; 9 trained). RESULTS: No significant correlation between τ̇[Formula: see text]O2 and [Formula: see text]O2max 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) and all participants (r = - 0.82; p < 0.05). τQ̇ (18.8 ± 5.5 s) and τHR (20.1 ± 6.2 s) were significantly greater than τ[Formula: see text]O2 (13.9 ± 2.7 s) for trained (p < 0.05). No differences were found between τQ̇ (22.8 ± 8.45 s), τHR (21.2 ± 8.3 s) and τ[Formula: see text]O2 (28.9 ± 5.7 s) for untrained (p > 0.05). τQ̇ demonstrated a significant strong positive correlation with τHR in trained (r = 0.76; p < 0.05) but not untrained (r = 0.61; p > 0.05). A significant overshoot in the [HHb]/[Formula: see text]O2 ratio was found in the untrained groups (p < 0.05) but not in the trained groups (p > 0.05) CONCLUSION: The results indicated that when comparing participants of different fitness status (i) there is a point at which greater V̇O2max values are not accompanied by faster [Formula: see text]O2 kinetics; (ii) central delivery of O2 does not seem to limit the kinetics of [Formula: see text]O2; and (iii) O2 delivery within the active tissues might contribute to the slower [Formula: see text]O2 kinetics response in untrained participants.

Rolling massage acutely improves skeletal muscle oxygenation and parameters associated with microvascular reactivity: The first evidence-based study.

Although it has been claimed that rolling massage (RM), may lead to improvements in skeletal muscle oxygenation, metabolism, blood flow, and vascular function, scientific evidence has not yet been provided. Thus, the current study investigated the effects of 30 s and 2 min of RM on forearm muscle oxygenation, parameters associated with oxidative metabolism, and microvascular reactivity as well as brachial artery endothelial function. Forearm skeletal muscle parameters were assessed in 12 healthy young men (26 ± 6 yrs) using near-infrared spectroscopy (NIRS) combined with a 5-min vascular occlusion test. Additionally, brachial artery endothelial function was simultaneously assessed by measuring the relative change in brachial artery diameter normalized to the hyperemic blood flow (Normalized %FMD). These measurements were performed before and after the RM interventions performed on the anterior forearm muscles. Forearm muscle oxygenation increased after 30 s of RM (62 ± 7 to 71 ± 11%; p = 0.02) while there was no change from baseline to post-intervention after 2 min of RM. No change was observed for oxidative metabolism, however, the significant main effect (p = 0.02) for NIRS-derived reperfusion slope (%·s-1) indicated that microvascular function improved after both 30 s (2.30 ± 0.5 to 2.61 ± 0.70%·s-1) and 2 min of RM (2.33 ± 0.4 to 2.60 ± 0.85%·s-1). The lack of significant effects of RM on Normalized %FMD suggest that the RM did not acutely improve brachial artery endothelial function. These findings provide, for the first time, evidence that RM improves skeletal muscle oxygenation and parameters associated with microvascular reactivity. Additionally, RM increased brachial artery blood flow, but not upstream brachial artery endothelial function.

Hypoxia equally reduces the respiratory compensation point and the NIRS-derived [HHb] breakpoint during a ramp-incremental test in young active males.

This study investigated the effect of reduced inspired fraction of O2 (FiO2 ) in the correspondence between the respiratory compensation point (RCP) and the breakpoint in the near-infrared spectroscopy-derived deoxygenated hemoglobin signal ([HHb]bp ) during a ramp-incremental (RI) test to exhaustion. Eleven young males performed, on two separated occasions, a RI test either in normoxia (NORM, FiO2  = 20.9%) or hypoxia (HYPO, FiO2  = 16%). Oxygen uptake ( V˙ O2 ), and [HHb] signal from the vastus lateralis muscle were continuously measured. Peak V˙ O2 (2.98 ± 0.36 vs. 3.39 ± 0.26 L min-1 ) and PO (282 ± 29 vs. 310 ± 19 W) were lower in HYPO compared to NORM condition, respectively. The V˙ O2 and PO associated with RCP and [HHb]bp were lower in HYPO (2.35 ± 0.24 and 2.34 ± 0.26 L min-1 ; 198 ± 37 and 197 ± 30 W, respectively) when compared to NORM (2.75 ± 0.26 and 2.75 ± 0.28 L min-1 ; 244 ± 29 and 241 ± 28 W, respectively) (p < .05). Within the same condition, the V˙ O2 and PO associated with RCP and [HHb]bp were not different (p > .05). Bland-Altman plots mean average errors between RCP and [HHb]bp were not different from zero in HYPO (0.01 L min-1 and 1.1 W) and NORM (0.00 L min-1 and 3.6 W) conditions. The intra-individual changes between thresholds associated with V˙ O2 and PO in HYPO from NORM were strongly correlated (r = .626 and 0.752, p < .05). Therefore, breathing a lower FiO2 during a RI test resulted in proportional reduction in the RCP and the [HHb]bp in terms of V˙ O2 and PO, which further supports the notion that these physiological responses may arise from similar metabolic changes reflecting a common phenomenon.

A "Step-Ramp-Step" Protocol to Identify the Maximal Metabolic Steady State.

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.

Training-Induced Changes in the Respiratory Compensation Point, Deoxyhemoglobin Break Point, and Maximal Lactate Steady State: Evidence of Equivalence.

PURPOSE: 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). V˙O2 at MLSS also increased from PRE to POST (delta: 0.17 [12] L·min-1) (P < .05). V˙O2 was not different at RCP, [HHb]BP, and MLSS at PRE (3.74 [0.34], 3.64 [0.40], 3.78 [0.23] L·min-1) or POST (3.96 [0.25], 3.95 [0.32], 3.94 [0.18] L·min-1) respectively, and RCP (3.98 [0.33] L·min-1) and [HHb]BP (3.97 [0.34] L·min-1) were not different at MID (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 Critical Evaluation of Current Methods for Exercise Prescription in Women and Men.

Common methods to prescribe exercise intensity are based on fixed percentages of maximum rate of oxygen uptake (V˙O2max), peak work rate (WRpeak), maximal HR (HRmax). However, it is unknown how these methods compare to the current models to partition the exercise intensity spectrum. PURPOSE: Thus, the aim of this study was to compare contemporary gold-standard approaches for exercise prescription based on fixed percentages of maximum values to the well-established, but underutilized, "domain" schema of exercise intensity. METHODS: One hundred individuals participated in the study (women, 46; men, 54). A cardiopulmonary ramp-incremental test was performed to assess V˙O2max, WRpeak, HRmax, and the lactate threshold (LT), and submaximal constant-work rate trials of 30-min duration to determine the maximal lactate steady-state (MLSS). The LT and MLSS were used to partition the intensity spectrum for each individual in three domains of intensity: moderate, heavy, and severe. RESULTS: V˙O2max in women and men was 3.06 ± 0.41 L·min and 4.10 ± 0.56 L·min, respectively. Lactate threshold and MLSS occurred at a greater %V˙O2max and %HRmax in women compared with men (P < 0.05). The large ranges in both sexes at which LT and MLSS occurred on the basis of %V˙O2max (LT, 45%-74%; MLSS, 69%-96%), %WRpeak (LT, 23%-57%; MLSS, 44%-71%), and %HRmax (LT, 60%-90%; MLSS, 75%-97%) elicited large variability in the number of individuals distributed in each domain at the fixed-percentages examined. CONCLUSIONS: Contemporary gold-standard methods for exercise prescription based on fixed-percentages of maximum values conform poorly to exercise intensity domains and thus do not adequately control the metabolic stimulus.

The effect of the fraction of inspired oxygen on the NIRS-derived deoxygenated hemoglobin "breakpoint" during ramp-incremental test.

During ramp-incremental (RI) exercise to exhaustion, the near-infrared spectroscopy-derived deoxygenated hemoglobin ([HHb]) signal in the vastus lateralis muscle shows a linear increase up to a point at which a plateau-like response is manifested ([HHb]bp). This study investigated if 1) the [HHb]bp is affected by different fractions of inspired O2 (FIO2) [hypoxia (16%; HYPO); normoxia (21%; NORM); hyperoxia (30%; HYPER)]; and 2) an abrupt change to hyperoxic-inspired gas just before the occurrence of the [HHb]bp (HYPERSWITCH) would affect the [HHb] plateau-like response. Ten physically active male participants reported to the laboratory on four separate occasions to perform an RI test to exhaustion in NORM, HYPO, and HYPER and an RI test to exhaustion with an abrupt increase in FIO2 (30%; HYPERSWITCH) 15 W before the power output (PO) associated with [HHb]bp in normoxia. PO, [HHb], tissue O2 (StO2), and pulse O2 saturation (SpO2) were recorded continuously. Peak PO was significantly lower in HYPO (290 ± 21 W) and higher in HYPER (321 ± 22 W) and HYPERSWITCH (320 ± 19 W) compared with NORM (311 ± 18 W). The PO associated with [HHb]bp was not different between NORM and HYPER (246 ± 23 vs. 247 ± 24 W), but it was lower in HYPO (198 ± 31 W) than NORM and HYPER. The PO associated with the [HHb]bp in HYPERSWITCH (240 ± 23) was not different compared with NORM. HYPER and HYPERSWITCH resulted in greater StO2 and SpO2 compared with NORM. These results suggest that the [HHb]bp response is not dependent of O2 driving pressure and that other physiological mechanisms might determine its occurrence.

Maximal Lactate Steady State Versus the 20-Minute Functional Threshold Power Test in Well-Trained Individuals: "Watts" the Big Deal?

PURPOSE: 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.

Evaluating the NIRS-derived microvascular O2 extraction "reserve" in groups varying in sex and training status using leg blood flow occlusions.

It 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.

Reliability of microvascular responsiveness measures derived from near-infrared spectroscopy across a variety of ischemic periods in young and older individuals.

BACKGROUND: Cardiovascular disease (CVD) is associated with impairments in microvascular responsiveness. Therefore, reliably assessing microvascular function is clinically relevant. Thus, this study aimed to examine the reliability of the near-infrared spectroscopy (NIRS)-derived oxygen saturation (StO2) reperfusion slope, a measure of microvascular responsiveness, to four different vascular occlusion tests (VOT) of different durations in young and older participants. METHODS: Eight healthy young (29 ±â€¯5 yr) and seven older (67 ±â€¯4 yr) men participated in four NIRS combined with VOT (NIRS-VOT; 30 s, 1, 3, and 5 min) in the leg microvasculature on two visits separated by 1-2 weeks. Vascular responsiveness was determined by the StO2 reperfusion slope. The coefficient of variation (CV), repeatability, reliability (ICC), and the limits of agreement (LOA) were calculated for the NIRS-derived reperfusion slopes for each occlusion duration and visit. RESULTS: CV for the StO2 reperfusion slope following 30 s, 1, 3 and 5 min of occlusion were 33 ±â€¯29%, 19 ±â€¯21%, 14 ±â€¯12%, and 12 ±â€¯10%, respectively. Repeatability values following 30 s, 1, 3 and 5 min occlusions were 20%, 1%, 4% and 21%, respectively. The ICC for the StO2 reperfusion slopes for each occlusion duration were 0.29, 0.42, 0.84, and 0.88 following 30 s, 1, 3 and 5 min of occlusion, respectively. LOA values between visit 1 and 2 for occlusions were not different from zero. There were no age-related differences for all variables of the study. CONCLUSION: NIRS-derived StO2 reperfusion slope, has good reliability across a range of occlusion durations with the strongest reliability during longer occlusion durations.

Metabolic and performance-related consequences of exercising at and slightly above MLSS.

Exercising at the maximal lactate steady state (MLSS) results in increased but stable metabolic responses. We tested the hypothesis that even a slight increase above MLSS (10 W), by altering the metabolic steady state, would reduce exercise performance capacity. Eleven trained men in our study performed: one ramp-incremental tests; two to four 30-minute constant-load cycling exercise trials to determine the PO at MLSS (MLSSp ), and ten watts above MLSS (MLSSp+10 ), which were immediately followed by a time-to-exhaustion test; and a time-to-exhaustion test with no-prior exercise. Pulmonary O2 uptake V.O2 ) and blood lactate concentration ([La- ]b ) as well as local muscle O2 extraction ([HHb]) and muscle activity (EMG) of the vastus lateralis (VL) and rectus femoris (RF) muscles were measured during the testing sessions. When exercising at MLSSp+10 , although V.O2 was stable, there was an increase in ventilatory responses and EMG activity, along with a non-stable [La- ]b response (P < 0.05). The [HHb] of VL muscle achieved its apex at MLSSp with no additional increase above this intensity, whereas the [HHb] of RF progressively increased during MLSSp+10 and achieved its apex during the time-to-exhaustion trials. Time-to-exhaustion performance was decreased after exercising at MLSSp (37.3 ± 16.4%) compared to the no-prior exercise condition, and further decreased after exercising at MLSSp+10 (64.6 ± 6.3%) (P < 0.05). In summary, exercising for 30 min slightly above MLSS led to significant alterations of metabolic responses which disproportionately compromised subsequent exercise performance. Furthermore, the [HHb] signal of VL seemed to achieve a "ceiling" at the intensity of exercise associated with MLSS.

An equation to predict the maximal lactate steady state from ramp-incremental exercise test data in cycling.

OBJECTIVES: 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.

Blood flow occlusion-related O2 extraction "reserve" is present in different muscles of the quadriceps but greater in deeper regions after ramp-incremental test.

It was recently demonstrated that an O2 extraction reserve, as assessed by the near-infrared spectroscopy (NIRS)-derived deoxygenation signal ([HHb]), exists in the superficial region of vastus lateralis (VL) muscle during an occlusion performed at the end of a ramp-incremental test. However, it is unknown whether this reserve is present and/or different in magnitude in other portions and depths of the quadriceps muscles. We tested the hypothesis that an O2 extraction reserve would exist in other regions of this muscle but is greater in deep compared with more superficial portions. Superficial (VL-s) and deep VL (VL-d) as well as superficial rectus femoris (RF-s) were monitored by a combination of low- and high-power time-resolved (TRS) NIRS. During the occlusion immediately post-ramp-incremental test there was a significant overshoot in the [HHb] signal ( P < 0.05). However, the magnitude of this increase was greater in VL-d (93.2 ± 42.9%) compared with VL-s (55.0 ± 19.6%) and RF-s (47.8 ± 14.0%) ( P < 0.05). The present study demonstrated that an O2 extraction reserve exists in different pools of active muscle fibers of the quadriceps at the end of a ramp exercise to exhaustion. The greater magnitude in the reserve observed in the deeper portion of VL, however, suggests that this portion of muscle may present a greater surplus of oxygenated blood, which is likely due to a greater population of slow-twitch fibers. These findings add to the notion that the plateau in the [HHb] signal toward the end of a ramp-incremental exercise does not indicate the upper limit of O2 extraction. NEW & NOTEWORTHY Different portions of the quadriceps muscles exhibited an untapped O2 extraction reserve during a blood flow occlusion performed at the end of a ramp-incremental exercise. In the deeper portion of the vastus lateralis muscle, this reserve was greater compared with superficial vastus lateralis and rectus femoris. These data suggest that the O2 extraction reserve may be dependent on the vascular and/or oxidative capacities of the muscles.