Fitness Level and Not Aging per se, Determines the Oxygen Uptake Kinetics Response

NIRS-Derived Muscle-Deoxygenation and Microvascular Reactivity During Occlusion-Reperfusion at Rest Are Associated With Whole-Body Aerobic Fitness

Purpose: Near-infrared spectroscopy (NIRS) indices during arterial occlusion-reperfusion maneuver have been used to examine the muscle's oxidative metabolism and microvascular function-important determinants of whole-body aerobic-fitness. The association of NIRS-derived parameters with whole-body VO2max was previously examined using a method requiring exercise (or electrical stimulation) followed by multiple arterial occlusions. We examined whether NIRS-derived indices of muscle deoxygenation and microvascular reactivity assessed during a single occlusion-reperfusion at rest are (a) associated with maximal/submaximal indices of whole-body aerobic-fitness and (b) could discriminate individuals with different VO2max. We, also, investigated which NIRS-parameter during occlusion-reperfusion correlates best with whole-body aerobic-fitness. Methods: Twenty-five young individuals performed an arterial occlusion-reperfusion at rest. Changes in oxygenated- and deoxygenated-hemoglobin (O2Hb and HHb, respectively) in vastus-lateralis were monitored; adipose tissue thickness (ATT) at NIRS-application was assessed. Participants also underwent a maximal incremental exercise test for VO2max, maximal aerobic velocity (MAV), and ventilatory-thresholds (VTs) assessments. Results: The HHbslope and HHbmagnitude of increase (occlusion-phase) and O2Hbmagnitude of increase (reperfusion-phase) were strongly correlated with VO2max (r = .695-.763, p < .001) and moderately with MAV (r = .468-.530; p < .05). O2Hbmagnitude was moderately correlated with VTs (r = .399-.414; p < .05). After controlling for ATT, the correlations remained significant for VO2max (r = .672-.704; p < .001) and MAV (r = .407; p < .05). Individuals in the high percentiles after median and tritile splits for HHbslope and O2Hbmagnitude had significantly greater VO2max vs. those in low percentiles (p < .01-.05). The HHbslope during occlusion was the best predictor of VO2max. Conclusion: NIRS-derived muscle deoxygenation/reoxygenation indices during a single arterial occlusion-reperfusion maneuver are strongly associated with whole-body maximal indices of aerobic-fitness (VO2max, MAV) and may discriminate individuals with different VO2max.

Aerobic capacity and [Formula: see text] kinetics adaptive responses to short-term high-intensity interval training and detraining in untrained females

PURPOSE

This study investigated the physical fitness and oxygen uptake kinetics (τ[Formula: see text]) along with the O2 delivery and utilization (heart rate kinetics, τHR; deoxyhemoglobin/[Formula: see text] ratio, ∆[HHb]/[Formula: see text]) adaptations of untrained female participants responding to 4 weeks of high-intensity interval training (HIIT) and 2 weeks of detraining.

METHODS

Participants were randomly assigned to HIIT (n = 11, 4 × 4 protocol) or nonexercising control (n = 9) groups. Exercising group engaged 4 weeks of treadmill HIIT followed by 2 weeks of detraining while maintaining daily activity level. Ramp-incremental (RI) tests and step-transitions to moderate-intensity exercise were performed. Aerobic capacity and performance (maximal oxygen uptake, [Formula: see text]; gas-exchange threshold, GET; power output, PO), body composition (skeletal muscle mass, SMM; body fat percentage, BF%), muscle oxygenation status (∆[HHb]), [Formula: see text], and HR kinetics were assessed.

RESULTS

HIIT elicited improvements in aerobic capacity ([Formula: see text], + 0.17 ± 0.04 L/min; GET, + 0.18 ± 0.05 L/min, P < 0.01; PO-[Formula: see text], ± 23.36 ± 8.37 W; PO-GET, + 17.18 ± 3.07 W, P < 0.05), body composition (SMM, + 0.92 ± 0.17 kg; BF%, - 3.08% ± 0.58%, P < 0.001), and speed up the τ[Formula: see text] (- 8.04 ± 1.57 s, P < 0.001) significantly, extending to better ∆[HHb]/[Formula: see text] ratio (1.18 ± 0.08 to 1.05 ± 0.14). After a period of detraining, the adaptation in body composition and aerobic capacity, as well as the accelerated τ[Formula: see text] were maintained in the HIIT group, but the PO-[Formula: see text] and PO-GET declined below the post-training level (P < 0.05), whereas no changes were reported in controls (P > 0.05). Four weeks of HIIT induced widespread physiological adaptations in females, and the majority of improvements were preserved after 2 weeks of detraining except for power output corresponding to [Formula: see text] and GET.

Adaptations to 4 weeks of high-intensity interval training in healthy adults with different training backgrounds

PURPOSE

This study investigated the physical fitness and oxygen uptake kinetics ([Formula: see text]) along with the exercise-onset O₂ delivery (heart rate kinetics, τHR; changes in normalized deoxyhemoglobin/[Formula: see text] ratio, Δ[HHb]/[Formula: see text]) adaptations of individuals with different physical activity (PA) backgrounds responding to 4 weeks of high-intensity interval training (HIIT), and the possible effects of skeletal muscle mass (SMM) on training-induced adaptations.

METHODS

Twenty subjects (10 high-PA level, HIIT-H; 10 moderate-PA level, HIIT-M) engaged in 4 weeks of treadmill HIIT. Ramp-incremental (RI) test and step-transitions to moderate-intensity exercise were performed. Cardiorespiratory fitness, body composition, muscle oxygenation status, VO₂ and HR kinetics were assessed at baseline and post-training.

RESULTS

HIIT improved fitness status for HIIT-H ([Formula: see text], + 0.26 ± 0.07 L/min; SMM, + 0.66 ± 0.70 kg; body fat, - 1.52 ± 1.93 kg; [Formula: see text], - 7.11 ± 1.05 s, p < 0.05) and HIIT-M ([Formula: see text], 0.24 ± 0.07 L/min, SMM, + 0.58 ± 0.61 kg; body fat, - 1.64 ± 1.37 kg; [Formula: see text], - 5.48 ± 1.05 s, p < 0.05) except for visceral fat area (p = 0.293) without between-group differences (p > 0.05). Oxygenated and deoxygenated hemoglobin amplitude during the RI test increased for both groups (p < 0.05) except for total hemoglobin (p = 0.179). The Δ[HHb]/[Formula: see text] overshoot was attenuated for both groups (p < 0.05) but only eliminated in HIIT-H (1.05 ± 0.14 to 0.92 ± 0.11), and no change was observed in τHR (p = 0.144). Linear mixed-effect models presented positive effects of SMM on absolute [Formula: see text] (p < 0.001) and ΔHHb (p = 0.034).

CONCLUSION

Four weeks of HIIT promoted positive adaptations in physical fitness and [Formula: see text] kinetics, with the peripheral adaptations attributing to the observed improvements. The training effects are similar between groups suggesting that HIIT is effective for reaching higher physical fitness levels.

Metabolic and microvascular function assessed using near-infrared spectroscopy with vascular occlusion in women: age differences and reliability

NEW FINDINGS

What is the central question of this study? Can the near-infrared spectroscopy with vascular occlusion test (NIRS-VOT) reliably measure skeletal muscle metabolic and microvascular function in women? What is the main finding and its importance? The NIRS-VOT can be used as a reliable technique for the assessment of skeletal muscle metabolism and microvascular function in women, with reliability being generally greater in younger women. These findings have important implications for the planning and development of future studies employing the NIRS-VOT in women, and provide insights into the effects of age on these parameters in women specifically.

ABSTRACT

We investigated the test-retest reliability of, and age-related differences in, markers of skeletal muscle metabolism and microvascular function derived from the near-infrared spectroscopy with vascular occlusion test (NIRS-VOT) in younger women (YW) and middle-aged and older women (MAOW). Seventeen YW (age 23 ± 4 years) and 17 MAOW (age 59 ± 8 years) completed this study. Participants completed identical experimental visits separated by ∼4 weeks during which the NIRS-VOT was used to quantify the occlusion slope, minimum and maximum tissue saturation, ischaemic index, reperfusion magnitude, the reperfusion and 10-s reperfusion slopes (slope 2 and slope 210-s ), time to max tissue saturation, and area under the reperfusion curve using the local tissue oxygen saturation signal. Except for slope 210-s (intraclass correlation coefficient (ICC) = 0.37; coefficient of variation (CV) = 31%), time to max tissue saturation (ICC = 0.21), and ischaemic index (ICC = 0.37) for MAOW, all of the NIRS variables demonstrated good to excellent relative reliability for the YW (ICCs = 0.74-0.86) and the MAOW (ICCs = 0.51-0.87), with CVs of 2-21% and 2-22%, respectively. The occlusion slope was significantly lower, indicating accelerated deoxygenation, while maximum tissue saturation, reperfusion magnitude, and ischaemic index were significantly higher in YW versus MAOW. No other group differences were found. In conclusion, our data support the use of the NIRS-VOT as a simple, reliable, non-invasive technique for the assessment of peripheral skeletal muscle metabolism and microvascular function in women, with the reliability being generally greater in YW versus MAOW. Further, our data suggest that ageing is associated with lower skeletal muscle metabolism and microvascular hyperaemic responsiveness in women.

Similar Slow Component of Oxygen Uptake and Ventilatory Efficiency between an Aerobic Dance Session on an Air Dissipation Platform and a Constant-Load Treadmill Test in Healthy Women

There is a lack of evidence about the slow component of oxygen consumption (V.O2sc) and ventilatory efficiency (slope VE·VCO2−1) during an aerobic dance (AD) session on an air dissipation platform (ADP) despite the key role played in endurance exercises. This research was designed to assess V.O2sc, ventilatory efficiency, and blood lactate concentration by comparing two exercise modes: AD session on an ADP versus treadmill test at a constant-load intensity of the first ventilatory threshold (VT1). In the first session, an incremental treadmill test was completed. In sessions 2 and 3, the participants were randomly assigned to the AD session on an ADP or to a treadmill constant-load test at VT1 intensity to determine their cardioventilatory responses. In addition, their blood lactate levels and ratings of perceived exertion (RPE, CR-10) were evaluated. No significant differences were found between the constant-load treadmill test and AD session on an ADP with respect to V.O2sc, VE VCO2−1 slope, and RPE (p > 0.05). Higher blood lactate concentrations were observed in an AD session on an ADP than in a constant-load treadmill test at 10 min (p = 0.003) and 20 min (p < 0.001). The two different exercise modalities showed similar V.O2sc and VE·VCO2−1 slope, even though the blood lactate concentrations were different.

A Single Bout of Constant-Load Exercise Test for Estimating the Time Constant of Oxygen Uptake Kinetics in Individuals With Stroke

Objective

To examine the relationship between the time constant of oxygen uptake kinetics during the onset of exercise (τVO₂) estimated from a single exercise bout and that obtained from three averaged exercise bouts in individuals with stroke.

Methods

Twenty participants with stroke performed three bouts of a constant-load pedaling exercise at approximately 80% of the workload corresponding to the ventilatory threshold to estimate τVO₂. The VO₂ data from the first trial of three bouts were used to estimate τVO₂ for a single bout. Additionally, data collected from three bouts were ensemble-averaged to obtain τVO₂ for three averaged bouts as the criterion.

Results

There was a very high correlation between τVO₂ for a single bout (34.8±14.0 seconds) and τVO₂ for three averaged bouts (38.5±13.4 seconds) (r=0.926, p<0.001). However, τVO₂ for a single bout was smaller than that for three averaged bouts (p=0.006).

Conclusion

τVO₂ for a single bout could reflect the relative difference in τVO₂ for three averaged bouts among individuals with stroke. However, it should be noted that τVO₂ for a single bout may be underestimated compared to τVO₂ for three averaged bouts.

Cardiorespiratory responses to exercise related to post-stroke fatigue severity

Physical deconditioning after stroke may induce post-stroke fatigue. However, research on this association is limited. Our primary objective was to investigate the associations of post-stroke fatigue severity with oxygen uptake ([Formula: see text]O₂) at peak exercise and the time constant of [Formula: see text]O₂ kinetics (τ[Formula: see text]O₂) at exercise onset. The secondary objective was to examine the associations between fatigue and cardiorespiratory variables potentially affecting [Formula: see text]O₂ during exercise. Twenty-three inpatients from a subacute rehabilitation ward were enrolled in this study. The median (interquartile range) Fatigue Severity Scale (FSS) score, as a measure of fatigue, was 32 (range 27-42) points. The FSS score was not associated with [Formula: see text]O₂ at peak exercise during a symptom-limited graded exercise test (rho = - 0.264; p = 0.224), whereas it was significantly associated with τ[Formula: see text]O₂ during a submaximal constant-load exercise test (rho = 0.530; p = 0.009). A higher FSS score also significantly correlated with a longer time constant of cardiac output (CO) kinetics (rho = 0.476; p = 0.022). Our findings suggest that severe post-stroke fatigue is associated with delayed increases in [Formula: see text]O₂ and CO at the onset of exercise. Our findings can contribute to the development of an appropriate rehabilitation programme for individuals with post-stroke fatigue.

Cocoa-flavanols enhance moderate-intensity pulmonary [Formula: see text] kinetics but not exercise tolerance in sedentary middle-aged adults

INTRODUCTION

Cocoa flavanols (CF) may exert health benefits through their potent vasodilatory effects, which are perpetuated by elevations in nitric oxide (NO) bioavailability. These vasodilatory effects may contribute to improved delivery of blood and oxygen (O₂) to exercising muscle.

PURPOSE

Therefore, the objective of this study was to examine how CF supplementation impacts pulmonary O₂ uptake ([Formula: see text]) kinetics and exercise tolerance in sedentary middle-aged adults.

METHODS

We employed a double-blind cross-over, placebo-controlled design whereby 17 participants (11 male, 6 female; mean ± SD, 45 ± 6 years) randomly received either 7 days of daily CF (400 mg) or placebo (PL) supplementation. On day 7, participants completed a series of 'step' moderate- and severe-intensity exercise tests for the determination of [Formula: see text] kinetics.

RESULTS

During moderate-intensity exercise, the time constant of the phase II [Formula: see text] kinetics ([Formula: see text]) was decreased by 15% in CF as compared to PL (mean ± SD; PL 40 ± 12 s vs. CF 34 ± 9 s, P = 0.019), with no differences in the amplitude of [Formula: see text] (A[Formula: see text]; PL 0.77 ± 0.32 l min^-1 vs. CF 0.79 ± 0.34 l min^-1, P = 0.263). However, during severe-intensity exercise, [Formula: see text], the amplitude of the slow component ([Formula: see text]) and exercise tolerance (PL 435 ± 58 s vs. CF 424 ± 47 s, P = 0.480) were unchanged between conditions.

CONCLUSION

Our data show that acute CF supplementation enhanced [Formula: see text] kinetics during moderate-, but not severe-intensity exercise in middle-aged participants. These novel effects of CFs, in this demographic, may contribute to improved tolerance of moderate-activity physical activities, which appear commonly present in daily life.

TRIAL REGISTRATION

Registered under ClinicalTrials.gov Identifier no. NCT04370353, 30/04/20 retrospectively registered.

An update in toxicology of ageing

The field of ageing research has been rapidly advancing in recent decades and it had provided insight into the complexity of ageing phenomenon. However, as the organism-environment interaction appears to significantly affect the organismal pace of ageing, the systematic approach for gerontogenic risk assessment of environmental factors has yet to be established. This puts demand on development of effective biomarker of ageing, as a relevant tool to quantify effects of gerontogenic exposures, contingent on multidisciplinary research approach. Here we review the current knowledge regarding the main endogenous gerontogenic pathways involved in acceleration of ageing through environmental exposures. These include inflammatory and oxidative stress-triggered processes, dysregulation of maintenance of cellular anabolism and catabolism and loss of protein homeostasis. The most effective biomarkers showing specificity and relevancy to ageing phenotypes are summarized, as well. The crucial part of this review was dedicated to the comprehensive overview of environmental gerontogens including various types of radiation, certain types of pesticides, heavy metals, drugs and addictive substances, unhealthy dietary patterns, and sedentary life as well as psychosocial stress. The reported effects in vitro and in vivo of both recognized and potential gerontogens are described with respect to the up-to-date knowledge in geroscience. Finally, hormetic and ageing decelerating effects of environmental factors are briefly discussed, as well.

A clinical evaluation of VO2 kinetics in kidney transplant recipients

Purpose

Aerobic exercise capacity is reduced in patients with chronic kidney disease, partly due to alterations at the muscular and microvascular level. This study evaluated oxygen uptake (VO₂) kinetics as indicator of muscular oxidative metabolism in a population of Kidney Transplant Recipients (KTRs).

Methods

Two groups of KTRs enrolled 3 (n = 21) and 12 months (n = 14) after transplantation and a control group of healthy young adults (n = 16) underwent cardiopulmonary exercise testing on cycle-ergometer. The protocol consisted in two subsequent constant, moderate-load exercise phases with a final incremental test until exhaustion.

Results

The time constant of VO₂ kinetics was slower in KTRs at 3 and 12 months after transplantation compared to controls (50.4 ± 13.1 s and 43.8 ± 11.6 s vs 28.9 ± 8.4 s, respectively; P < 0.01). Peak VO₂ was lower in KTRs evaluated 3 months after transplantation compared to patients evaluated after 1 year (21.3 ± 4.3 and 26.4 ± 8.0 mL/kg/min; P = 0.04). Blood haemoglobin (Hb) concentration was higher in KTRs evaluated at 12 months (12.8 ± 1.7 vs 14.6 ± 1.7 g/dL; P < 0.01). Among KTRs, τ showed a moderate negative correlation with Peak VO₂ (ρ = − 0.52) and Oxygen uptake efficiency slope (OUES) (r = − 0.57) while no significant correlation with Hb and peak heart rate.

Conclusions

KTRs show slower VO₂ kinetics compared to healthy controls. Hb and peak VO₂ seem to improve during the first year after transplantation. VO₂ kinetics were significantly associated with indices of cardiorespiratory fitness, but less with central determinants of aerobic capacity, thus suggesting a potential usefulness of adding this index of muscular oxidative metabolism to functional evaluation in KTRs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-021-04672-x.

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]O_2max) 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]O_2max 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 V̇O_2max 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.

Cardiorespiratory mechanisms underlying the impaired oxygen uptake kinetics at exercise onset after stroke

BACKGROUND

Oxygen uptake (V˙O₂) kinetics at the onset of exercise is slower in patients with stroke than in healthy adults. However, little is known about the cardiorespiratory mechanisms underlying the impaired V˙O₂ kinetics.

OBJECTIVES

This study aimed to investigate the relative effect of impaired oxygen delivery and utilisation on V˙O₂ kinetics at the onset of submaximal exercise in patients with stroke by comparing the time constants of cardiac output (τCO) and V˙O₂ (τV˙O₂). In addition, we aimed to examine the association between the kinetics of cardiorespiratory variables and functional outcomes.

METHODS

We included 21 patients with stroke (15 males, mean [SD] age 58.7 [9.5] years, mean days post-stroke 67.9 [30.9]). A submaximal constant-load exercise test was performed to measure τV˙O₂, τCO, and the time constant of arterialvenous oxygen difference (τAVO₂diff). The ratio of τCO to τV˙O₂ was calculated to assess the matching of oxygen delivery and consumption. Fugl-Meyer lower-extremity motor scores, comfortable gait speeds, and Functional Independence Measure motor scores were used as functional variables.

RESULTS

Mean (SD) τAVO₂diff was markedly shorter than τV˙O₂ and τCO (26.1 [7.1] vs. 38.7 [10.2] and 46.6 [23.2 s], P<0.05), with no significant difference between τV˙O₂ and τCO (P=0.444). The greater ratio of τCO to τV˙O₂ was related to poorer motor function (rho=-0.484, P=0.026) and slower comfortable gait speed (r=-0.482, P=0.027).

CONCLUSIONS

An increase in CO was slower than that in AVO₂diff in patients with stroke. Therefore, V˙O₂ kinetics in patients with stroke appears to be affected by a delayed increase in CO rather than AVO₂diff. Furthermore, these patients with motor and gait impairments may have a poor matching of oxygen delivery and consumption during exercise onset.

Underlying mechanisms of oxygen uptake kinetics in chronic post-stroke individuals: A correlational, cross-sectional pilot study

Post-stroke individuals presented deleterious changes in skeletal muscle and in the cardiovascular system, which are related to reduced oxygen uptake ([Formula: see text]) and take longer to produce energy from oxygen-dependent sources at the onset of exercise (mean response time, MTRON) and during post-exercise recovery (MRTOFF). However, to the best of our knowledge, no previous study has investigated the potential mechanisms related to [Formula: see text] kinetics response (MRTON and MRTOFF) in post-stroke populations. The main objective of this study was to determine whether the MTRON and MRTOFF are related to: 1) body composition; 2) arterial compliance; 3) endothelial function; and 4) hematological and inflammatory profiles in chronic post-stroke individuals. Data on oxygen uptake ([Formula: see text]) were collected using a portable metabolic system (Oxycon Mobile®) during the six-minute walk test (6MWT). The time to achieve 63% of [Formula: see text] during a steady state (MTRON) and recovery (MRTOFF) were analyzed by the monoexponential model and corrected by a work rate (wMRTON and wMRTOFF) during 6MWT. Correlation analyses were made using Spearman's rank correlation coefficient (rs) and the bias-corrected and accelerated bootstrap method was used to estimate the 95% confidence intervals. Twenty-four post-stroke participants who were physically inactive took part in the study. The wMRTOFF was correlated with the following: skeletal muscle mass (rs = -0.46), skeletal muscle mass index (rs = -0.45), augmentation index (rs = 0.44), augmentation index normalized to a heart rate of 75 bpm (rs = 0.64), reflection magnitude (rs = 0.43), erythrocyte (rs = -0.61), hemoglobin (rs = -0.54), hematocrit (rs = -0.52) and high-sensitivity C-reactive protein (rs = 0.58), all p < 0.05. A greater amount of oxygen uptake during post-walking recovery is partially related to lower skeletal muscle mass, greater arterial stiffness, reduced number of erythrocytes and higher systemic inflammation in post-stroke individuals.

Evaluating the suitability of supra-POpeak verification trials after ramp-incremental exercise to confirm the attainment of maximum O2 uptake

During exhaustive ramp-incremental cycling tests, the incidence of O₂ uptake (V̇o₂) plateaus is low. To verify the attainment of maximum V̇o₂ (V̇o_2max), it is recommended that a trial at a power output (PO) corresponding to 110% of the ramp-derived peak (PO_peak) is performed. It remains unclear whether verification trials set at this PO can be tolerated for long enough to allow attainment of V̇o_2max. Eleven recreationally trained individuals performed five ramp tests of varying slope (5, 10, 15, 25, and 30 W/min), each followed, in series, by two verification trials: the first at 110% PO_peak of the 25 W/min ramp and the second at 110% PO_peak attained in the preceding ramp test. Exercise duration of the first verification trial was on average 81 ± 15 s (CV = 9 ± 3%) versus 162 ± 32, 121 ± 24, 103 ± 15, and 73 ± 10 s for the second verification trials at 110% of PO_peak of the 5, 10, 15, and 30 W/min ramp tests, respectively (P < 0.05). Compared with the highest V̇o₂ recorded during ramp tests, V̇o₂ from the subsequent verification trials was not different for the 5, 10, and 15 W/min ramp tests (P > 0.05) but was lower for the 25 and 30 W/min ramp tests (P < 0.05). Verification trials at 110% PO_peak of rapidly incrementing ramp tests (i.e., 25 W/min) were not sustained for long enough to allow the attainment of V̇o_2max. With commonly used rapidly incrementing ramp tests engendering exhaustion within 8-12 min, verification trials less than PO_peak should be preferred as they can be sustained sufficiently long to allow the attainment of V̇o_2max.

Better Executive Function Is Associated With Faster On-Transition Aerobic Metabolism Among Older Adults

The present study aimed to examine relationships between executive function (EF) and variables of aerobic fitness. Participants were 32 healthy older adults (M age = 65.1, SD = 6.6 years). We measured the first ventilatory threshold (VeT₁) and the kinetics of oxygen uptake (V˙O₂), heart rate (HR), and muscle deoxygenation [HHb] during treadmill walking of either constant, moderate intensity, or increasing intensity. We assessed EF with a computerized Stroop test and Stroop measures of correct answers, reaction time, and percent interference. We found the Stroop interference score to be negatively associated with the VeT₁ (r = -0.387, p = 0.031) and positively associated with the on-transition aerobic metabolism time constant (τ) of HR (r = 0.519, p = 0.003), V˙O₂ (r = 0.454; p = 0.010), and [HHb] (r = 0.644, p = 0.001). Correct responses were negatively related with τHR (r = -0.372, p = 0.039) and τV˙O₂ (r = -0.500, p = 0.004). The Stroop average reaction time, congruent reaction time and incongruent reaction time were positively related to τ[HHb] (r = 0.507, p = 0.010; r = 0.437, p = 0.029; r = 0.558, p = 0.004, respectively). Better EF was associated with faster on-transition aerobic metabolism and higher aerobic fitness among older adults.

The effect of age and training status on oxygen uptake kinetics in women

We examined the effect of age and training status on the oxygen uptake (V˙ O₂) kinetics of untrained and recreationally trained women. Young (20-35yr), middle-age (40-55yr) and older (58-71yr) recreationally trained (YTR, n = 10; MTR, n = 12; OTR, n = 9) and untrained (YUT, n = 12; MUT, n = 10; OUT, n = 9) women participated in this crossectional study. Breath-by-breath V˙ O₂ and near-infrared-spectroscopy-derived (NIRS) muscle deoxygenation [HHb] were monitored continuously during increasing and constant walking exercises. On-transition V˙ O₂ and [HHb] responses to moderate intensity walking were modeled as mono-exponential. The data were normalized for each subject (0%-100 %), and [HHb]/ V˙ O₂ ratio was calculated as the average [HHb]/ V˙ O₂ during the 20- to 120-s period after the onset of moderate intensity walking exercise. The time constant of V˙ O₂ (τ V˙ O₂) was longer in OUT(23.8 ± 2.4), MUT(25.4 ± 5.1), YUT(23.1 ± 3.4) than in YTR(16.2 ± 2.0), MTR(16.7 ± 3.9), OTR(16.3 ± 2.8) women (p < 0.05). The [HHb]/ V˙ O₂ ratio in OUT (1.31 ± 0.18) was higher than in YTR(1.08 ± 0.05), MTR(1.13 ± 0.09), YUT(1.12 ± 0.09) (p < 0.05). It is concluded that recreationally trained women had faster V˙ O₂ kinetics along with better matching of O₂ delivery and utilization at the site of gas exchange in the exercising muscles.

Microvascular responses during reactive hyperemia assessed by near-infrared spectroscopy and arterial stiffness in young, middle-aged, and older women

We investigated the effects of age on microvascular responses during reactive hyperemia and arterial stiffness in 13 young (22 ± 1 years), 12 middle-aged (42 ± 5 years), and 15 older (63 ± 2 years) women. During the vascular occlusion test (VOT), forearm tissue oxygen saturation (StO₂) was measured using near-infrared spectroscopy (NIRS). During reperfusion, the area under the curve (AUC) during hyperemia in young women (1123 ± 208% s) was significantly greater than that in middle-aged (771 ± 445% s, P = 0.024) and older women (619 ± 356% s, P = 0.001) with no differences between middle-aged and older women (P = 0.265). Cardio-ankle vascular index (CAVI) as an indicator of arterial stiffness was assessed using four-limb oscillometry. CAVI significantly increased with age (8.1 ± 0.7 in the older group, 6.0 ± 0.8 in the middle-aged group, and 5.8 ± 0.4 in the young group), with significant differences between older women and women in the other groups (P < 0.001); however, no differences in CAVI between young and middle-aged women (P = 0.484) were found. When the data of all groups were pooled, the AUC or upslope was associated with CAVI or body mass index or mean arterial pressure (all P < 0.05). To conclude, the AUC derived by NIRS measures of StO₂ during the reperfusion phase can be used as one of the evaluations of microvascular function, followed by the development of atherosclerosis in middle-aged and older women.

The effects of aging and cardiovascular risk factors on microvascular function assessed by near-infrared spectroscopy

This study aimed to evaluate whether NIRS-derived reperfusion rate would detect potential differences in the forearm microvascular responsiveness between young healthy adults, and older adults free from or with cardiovascular disease (CVD) risk factors. Fifteen healthy young (age: 24.8 ± 4.0 years), seventeen older adults free of CVD risk factors (age: 67.0 ± 6.8 years), and twenty-three older adults with CVD risk factors (age: 67.9 ± 8.0 years) participated this study. Individuals underwent a blood draw and vascular occlusion test (30 s of baseline, 5 min of occlusion, and 2 min of reperfusion) and microvascular responsiveness was evaluated by using NIRS-derived tissue oxygen saturation indexes during reperfusion. A significant slower reperfusion rate and lower reperfusion magnitude was observed in older adults with CVD risk factors compared to healthy young and older adults. Although no statistical differences were found between healthy young and older individuals, there was a small (d = 0.4) effect size for reperfusion rate and moderate (d = 0.7) effects size for reperfusion magnitude when comparing these groups. In conclusion, this study demonstrated that even though the effects of aging per se on microvascular function should not be completely neglected, the CVD risk factors seem to be determinant on microvascular responsiveness impairment associated with aging.

The association between near-infrared spectroscopy assessment of microvascular reactivity and flow-mediated dilation is disrupted in individuals at high risk for cardiovascular disease

OBJECTIVE

This study aimed to evaluate the correlation between the NIRS-derived reperfusion slope and %FMD in the arm of healthy and at high risk for CVD individuals.

METHODS

Twelve healthy (24 ± 4 years) and twelve at high risk for cardiovascular disease (65 ± 11 years) individuals participated in the study. The individuals were submitted to a conduit artery FMD followed by a NIRS-VOT microvascular function test in the arm. Microvascular responsiveness was calculated as the forearm reperfusion slope, and macrovascular function was assessed as the percent of change in FMD (%FMD) of the brachial artery.

RESULTS

There was a significant correlation between reperfusion slope and %FMD (R = 0.61, P < 0.05) in the healthy group; however, no significant correlation between FMD and reperfusion slope (R = -0.21, P > 0.05) was found in individuals at high risk for CVD.

CONCLUSION

The correlation between NIRS-derived reperfusion slope and %FMD was disrupted in the arm of individuals at high risk for cardiovascular disease compared to healthy individuals. The findings of the present study reinforce the importance of examining vascular function at microvasculature and conduit artery level, especially in populations with risk factors for CVD.

Skeletal muscle fiber characteristics in patients with chronic heart failure: impact of disease severity and relation with muscle oxygenation during exercise

INTRODUCTION

Skeletal muscle function in patients with heart failure and reduced ejection fraction (HFrEF) greatly determines exercise capacity. However, reports on skeletal muscle fiber dimensions, fiber capillarization, and their physiological importance are inconsistent.

METHODS

Twenty-five moderately-impaired patients with HFrEF and 25 healthy control (HC) subjects underwent muscle biopsy sampling. Type I and type II muscle fiber characteristics were determined by immunohistochemistry. In patients with HFrEF, enzymatic oxidative capacity was assessed, and pulmonary oxygen uptake (VO₂) and skeletal muscle oxygenation during maximal and moderate-intensity exercise were measured using near-infrared spectroscopy.

RESULTS

While muscle fiber cross-sectional area (CSA) was not different between patients with HFrEF and HC, percentage of type I fibers was higher in HC (46±15% versus 37±12%, respectively, P=0.041). Fiber type distribution and CSA were not different between patients in New York Heart Association (NYHA) class II and III. Type I muscle fiber capillarization was higher in HFrEF compared with controls (capillary-to-fiber perimeter exchange (CFPE) index: 5.70±0.92 versus 5.05±0.82, respectively, P=0.027). Patients in NYHA class III had slower VO₂ and muscle deoxygenation kinetics during onset of exercise, and lower muscle oxidative capacity than those in class II (P<0.05). Also, fiber capillarization was lower, but not compared with HC. Higher CFPE index was related to faster deoxygenation (r_spearman=-0.682, P=0.001), however, not to muscle oxidative capacity (r=-0.282, P=0.216).

CONCLUSIONS

Type I muscle fiber capillarization is higher in HFrEF compared with HC, but not in patients with greater exercise impairment. Greater capillarization may positively affect VO₂ kinetics by enhancing muscle oxygen diffusion.

Changes in pulmonary oxygen uptake and muscle deoxygenation kinetics during cycling exercise in older women performing walking training for 12 weeks

PURPOSE

This study examined the hypothesis that walking training (WT) could accelerate the slowed time constant (τ) of phase II in pulmonary oxygen uptake ([Formula: see text]O₂) on-kinetics in older women. Also, we aimed to demonstrate that O₂ delivery and O₂ utilization were better matched at the site of gas exchange in exercising muscles when τ[Formula: see text]O₂ was shortened.

METHODS

20 recreationally active older women underwent WT sessions of approximately 60 min, 3-4 times a week for 12 weeks. We assessed [Formula: see text]O₂, heart rate (HR) and deoxygenated-hemoglobin concentration ([HHb]) kinetics during a constant-load exercise test before training (0 week-Pre), and at 6 and 12 weeks (6 weeks-Mid, 12 weeks-Post) throughout the training period.

RESULTS

Maximal oxygen uptake ([Formula: see text]O_2max) was unchanged throughout the training program. τHR tended to decline at Mid (58.6 ± 22.0 s), and was significantly shorter at Post (51.7 ± 21.7 s, p = 0.01) compared to Pre (67.1 ± 23.8 s). τ[Formula: see text]O₂ significantly decreased from 38.9 ± 8.6 s for Pre, to 31.5 ± 7.9 s for Mid (p = 0.02), and 32.3 ± 10.5 s for Post (p = 0.03). The normalized [HHb] to [Formula: see text]O₂ ratio (Δ[HHb]/Δ[Formula: see text]O₂) at Pre (1.32 ± 0.93) gradually approached the perfectly matched value (= 1.0) at Mid (1.15 ± 0.61) and Post (1.07 ± 0.52).

CONCLUSIONS

The restoration to baseline (≒ 30 s) of the slower τ[Formula: see text]O₂ due to WT, which may reflect better matching of O₂ delivery and O₂ utilization at the site of gas exchange, suggests that a longer period of WT could be a useful tool for improving exercise tolerance in older individuals.