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Significance: Near-infrared spectroscopy (NIRS) measurement is a widely used technique to measure muscle oxygenation. A knowledge of the reproducibility of NIRS measurements is essential for the correct interpretation of data., Aim: Our aim was to test the reproducibility and sex differences of NIRS measurements during brachial artery occlusion in healthy participants., Approach: An NIRS device was used to measure muscle oxygenation and microvascular function during a 5 min brachial occlusion. Muscle oxygen consumption (mVO 2 ) and tissue saturation index (TSI%) were used. The occlusion test was performed three times on separate days for males (n = 13, 28 ± 8 years) and females (n = 13, 29 ± 7 years)., Results: During the occlusion phase, the reproducibility of mVO 2 was excellent (intraclass correlation; ICC = 0.90). During the reperfusion phase, the maximal change in TSI% revealed the best reproducibility (ICC = 0.77). There were no sex differences in reproducibility. Male participants had higher muscle oxygenation during occlusion (mVO 2 , 0.054 ± 0.010 vs. 0.038 ± 0.012 mLO 2 /min/100 g, p = 0.001, male and female, respectively). There were no sex differences during the reperfusion phase., Conclusion: The reproducibility of NIRS to measure muscle oxygenation and microvascular function during circulation occlusion and reperfusion is good to excellent. Muscle oxygen capacity measured during occlusion is higher in males compared to females, and there are no sex differences in microvascular function during the reperfusion phase., (© 2024 The Authors. Clinical Physiology and Functional Imaging published by John Wiley & Sons Ltd on behalf of Scandinavian Society of Clinical Physiology and Nuclear Medicine.)

Long-term hyperglycemia in individuals with type 2 diabetes (T2D) can detrimentally impact pulmonary function and muscle oxygenation. As a result, these factors can impede the body's adaptation to physical exertion. We aimed to evaluate the oxygen pathway during maximal exercise among overweight/obese individuals with type 2 diabetes free from complications, in comparison with a group of matched overweight/obese individuals without diabetes, specifically concentrating on the effects on pulmonary function and muscle oxygenation. Fifteen overweight/obese adults with type 2 diabetes [glycated hemoglobin (HbA1c) = 8.3 ± 1.2%] and 15 matched overweight/obese adults without diabetes underwent pre- and post exercise lung function assessment. A maximal incremental exercise test was conducted, monitoring muscle oxygenation using near-infrared spectroscopy and collecting arterial blood gas samples. Both groups exhibited normal lung volumes at rest and after exercise. Spirometric lung function did not significantly differ pre- and post exercise in either group. During maximal exercise, the type 2 diabetes group showed significantly lower augmentation in total hemoglobin and deoxygenated hemoglobin compared with the control group. Despite comparable usual physical activity levels and comparable heart rates at exhaustion, the type 2 diabetes group had a lower peak oxygen consumption than controls. No significant differences were found in arterial blood gas analyses ([Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]) between the groups. Individuals with type 2 diabetes free from complications displayed normal pulmonary function at rest and post exercise. However, impaired skeletal muscle oxygenation during exercise, resulting from reduced limb blood volume and altered muscle deoxygenation, may contribute to the lower V̇o 2peak observed in this population. NEW & NOTEWORTHY Individuals with type 2 diabetes free from micro- and macrovascular complications have normal resting pulmonary function, but their V̇o 2peak is impaired due to poor skeletal muscle oxygenation during exercise. Tailoring exercise regimes for this population should prioritize interventions aimed at enhancing muscle oxygenation and blood flow improvement.

The oxygen partial pressure within the interstitial space (PO 2 is; mmHg) provides the driving force for oxygen diffusion into the myocyte thereby supporting oxidative phosphorylation. We tested the hypothesis that potentiation of the nitric oxide pathway with sildenafil (phosphodiesterase type 5 inhibitor) would enhance PO 2 is during muscle metabolic transitions, thereby slowing PO 2 is on- and accelerating PO 2 is off-kinetics. The rat spinotrapezius muscle (n = 17) was exposed for PO 2 is measurements via phosphorescence quenching under control (CON), low-dose sildenafil (1 mg/kg i.a., SIL1) and high-dose sildenafil (7 mg/kg i.a., SIL7). Data were collected at rest and during submaximal twitch contractions (1 Hz, 4-6 V, 3 min) and recovery (3 min). Mean arterial blood pressure (MAP; mmHg) was reduced with both SIL1 (pre:132 ± 5; post:99 ± 5) and SIL7 (pre:111 ± 6; post:99 ± 4) (p < 0.05). SIL7 elevated resting PO 2 is (18.4 ± 1.1) relative to both CON (15.7 ± 0.7) and SIL1 (15.2 ± 0.7) (p < 0.05). In addition, SIL7 increased end-recovery PO 2 is (17.7 ± 1.6) compared to CON (12.8 ± 0.9) and SIL1 (13.4 ± 0.8) (p < 0.05). The overall PO 2 is response during recovery (i.e., area under the PO 2 is curve) was greater in SIL7 (4107 ± 444) compared to CON (3493 ± 222) and SIL1 (3114 ± 205 mmHg s) (p < 0.05). Contrary to our hypothesis, there was no impact of acute SIL (1 or 7 mg/kg) on the speed of the PO 2 is response during contractions or recovery (p > 0.05). However, sildenafil lowered MAP and improved skeletal muscle interstitial oxygenation in healthy rats. Specifically, SIL7 enhanced PO 2 is at rest and during recovery from submaximal muscle contractions. Potentiation of the nitric oxide pathway with sildenafil enhances microvascular blood-myocyte O 2 transport and is expected to improve repeated bouts of contractile activity., Competing Interests: Declaration of competing interest No conflicts of interest, financial or otherwise, are declared by the authors., (Copyright © 2023 Elsevier Inc. All rights reserved.)

We investigated the relationship between muscle microvascular responses during reactive hyperemia as assessed using near-infrared spectroscopy (NIRS) with changes in skeletal muscle oxygen saturation during exercise. Thirty young untrained adults (M/W: 20/10; 23 ± 5 years) completed a maximal cycling exercise test to determine exercise intensities performed on a subsequent visit separated by seven days. At the second visit, post-occlusive reactive hyperemia was measured as changes in NIRS-derived tissue saturation index (TSI) at the left vastus lateralis muscle. Variables of interest included desaturation magnitude, resaturation rate, resaturation half-time, and hyperemic area under the curve. Afterwards, two 4-minute bouts of moderate intensity cycling followed by one bout of severe intensity cycling to fatigue took place while TSI was measured at the vastus lateralis muscle. TSI was averaged across the last 60-s of each moderate intensity bout then averaged together for analysis, and at 60-s into severe exercise. The change in TSI (∆TSI) during exercise is expressed relative to a 20 W cycling baseline. On average, the ΔTSI was -3.4 ± 2.4 % and -7.2 ± 2.8 % during moderate and severe intensity cycling, respectively. Resaturation half-time was correlated with the ΔTSI during moderate (r = -0.42, P = 0.01) and severe (r = -0.53, P = 0.002) intensity exercise. No other reactive hyperemia variable was found to correlate with ΔTSI. These results indicate that resaturation half-time during reactive hyperemia represents a resting muscle microvascular measure that associates with the degree of skeletal muscle desaturation during exercise in young adults., Competing Interests: Declaration of competing interest The authors (JD, AF, and JG) have no conflicts of interest, financial or otherwise, to declare., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The aim of this study was to investigate the longitudinal relationship between the slopes of systemic and quadriceps muscle O 2 dynamics in subjects without attenuation point in deoxygenated hemoglobin concentration at vastus lateralis (AP deoxy-Hb@VL ) during high-intensity cycling. Seven young men without AP deoxy-Hb@VL performed ramp cycling exercise until exhaustion before and after 8 weeks, while continuing recreational physical activities throughout that period. Muscle O 2 saturation (SmO 2 ) and deoxy-Hb were monitored at the vastus lateralis (VL) and rectus femoris (RF) by near infrared spectroscopy oximetry during exercise. Cardiac output (CO) was also continuously assessed. During high-intensity exercise, at VL, a significantly steeper slope of deoxy-Hb was found after 8 weeks compared with before, while the slopes of deoxy-Hb at RF were not significantly changed. Though a decrease in the slope of CO after 8 weeks did not reach significance (p = 0.12), the change in the slope of CO was significantly related to the change in the slopes of deoxy-Hb at VL (r s  = -0.89, p < 0.01) and RF (r s  = -0.86, p < 0.05). Our data reinforces the idea that, in subjects without AP deoxy-Hb@VL , the slope of muscle deoxygenation at VL during high-intensity cycling exercise may partly be explained by systemic O 2 supply, rather than O 2 balance in other thigh muscles., (© 2023. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

The effects of sympathetic activity on vasoconstriction are dampened in active skeletal muscle during exercise, a phenomenon termed functional sympatholysis. Limited work has examined the influence of sex on the magnitude of sympatholysis or the test-retest reliability of measurements. In 16 women and 15 men, forearm blood flow (FBF; Doppler ultrasound), muscle oxygenation (near-infrared spectroscopy, NIRS), and beat-to-beat mean arterial pressure (MAP; photoplethysmography) were measured during lower-body negative pressure (LBNP; -20 mmHg) at rest and simultaneously during rhythmic handgrip exercise (30% maximum contraction). Measures were taken twice within the same visit (separated by 15 min) and repeated on a second visit. Forearm vascular conductance (FVC) was calculated as FBF/MAP. The magnitude of sympatholysis was calculated as the difference of LBNP-induced changes between handgrip and rest. LBNP decreased FBF (Δ-45 ± 15%), FVC (Δ-45 ± 16%), and muscle oxygenation (Δ-14 ± 11%); however, these responses were attenuated when LBNP was applied during rhythmic handgrip exercise (Δ-7 ± 9%, Δ-9 ± 10%, and Δ-6 ± 9%, respectively). The magnitude of sympatholysis was not different between men and women (FBF: 40 ± 16% vs. 35 ± 9%, P = 0.37; FVC: 38 ± 16% vs. 35 ± 11%, P = 0.53; muscle oxygenation: 5 ± 9% vs. 11 ± 10%, P = 0.11). Furthermore, sympatholysis measurements demonstrated good to excellent intraday (intraclass-correlation coefficients; ICC ≥ 0.85) and interday (ICC ≥ 0.72) test-retest reliability (all P ≤ 0.01) in both sexes. The coefficients of variation were larger with NIRS (68-91%) than with Doppler ultrasound (16%-22%) assessments of functional sympatholysis. Collectively, these findings demonstrate that assessments of functional sympatholysis are not impacted by biological sex and that Doppler ultrasound-derived measures of sympatholysis have better within-subject reliability than NIRS-derived measures in young healthy adults.

The intensity of large muscle mass exercise declines at altitude due to reduced oxygen delivery to active muscles. The purpose of this investigation was to determine if the greater limb blood flow during single-leg cycling prevents the reduction in tissue oxygenation observed during traditional double-leg cycling in hypoxic conditions. Ten healthy individuals performed bouts of double and single-leg cycling (4, four-minute stages at 50−80% of their peak oxygen consumption) in hypoxic (15% inspired O2) and normoxic conditions. Heart rate, mean arterial pressure, femoral blood flow, lactate, oxygenated hemoglobin, total hemoglobin, and tissue saturation index in the vastus lateralis were recorded during cycling tests. Femoral blood flow (2846 ± 912 mL/min) and oxygenated hemoglobin (−2.98 ± 3.56 au) during single-leg cycling in hypoxia were greater than double-leg cycling in hypoxia (2429 ± 835 mL/min and −6.78 ± 3.22 au respectively, p ≤ 0.01). In addition, tissue saturation index was also reduced in the double-leg hypoxic condition (60.2 ± 3.1%) compared to double-leg normoxic (66.0 ± 2.4%, p = 0.008) and single-leg hypoxic (63.3 ± 3.2, p < 0.001) conditions. These data indicate that while at altitude, use of reduced muscle mass exercise can help offset the reduction in tissue oxygenation observed during larger muscle mass activities allowing athletes to exercise at greater limb/muscle specific intensities.

The present study sought to investigate if faster upper body oxygen uptake (VO 2 ) and hemoglobin/myoglobin deoxygenation ([HHb]) kinetics during heavy intensity exercise were associated with a greater upper body repeated-sprint ability (RSA) performance in a group of judokas and in a group of individuals of heterogenous fitness level. Eight judokas (JT) and seven untrained healthy participants (UT) completed an incremental step test, two heavy intensity square-wave transitions and an upper body RSA test consisting of four 15 s sprints, with 45 s rest, from which the experimental data were obtained. In the JT group, VO 2 kinetics, [HHb] kinetics and the parameters determined in the incremental test were not associated with RSA. However, when the two groups were combined, the amplitude of the primary phase VO 2 and [HHb] were positively associated with the accumulated work in the four sprints (ΣWork). Additionally, maximal aerobic power (MAP), peak VO 2 and the first ventilatory threshold (VT 1 ) showed a positive correlation with ΣWork and an inverse correlation with the decrease in peak power output (Dec-PPO) between the first and fourth sprints. Faster VO 2 and [HHb] kinetics do not seem to be associated with an increased upper body RSA in JT. However, other variables of aerobic fitness seem to be associated with an increased upper body RSA performance in a group of individuals with heterogeneous fitness level.

Aims: Skeletal muscle dysfunction is a systemic consequence of heart failure (HF) that correlates with functional capacity. However, the impairment within the skeletal muscle is not well established. We investigated the effect of exercise training on peripheral muscular performance and oxygenation in HF patients., Methods and Results: HF patients with ejection fraction ≤40% were randomized 2:1 to exercise training or control for 12 weeks. Muscle tissue oxygen was measured noninvasively by near-infrared spectroscopy (NIRS) during rest and a symptom-limited cardiopulmonary exercise test (CPET) before and after intervention. Measurements included skeletal muscle oxygenated hemoglobin concentration, deoxygenated hemoglobin concentration, total hemoglobin concentration, VO 2 peak, VE/VCO 2 slope, and heart rate. Muscle sympathetic nerve activity by microneurography, and muscle blood flow by plethysmography were also assessed at rest pre and post 12 weeks. Twenty-four participants (47.5 ± 7.4 years, 58% men, 75% no ischemic) were allocated to exercise training (ET, n = 16) or control (CG, n = 8). At baseline, no differences between groups were found. Exercise improved VO 2 peak, slope VE/VCO 2 , and heart rate. After the intervention, significant improvements at rest were seen in the ET group in muscle sympathetic nerve activity and muscle blood flow. Concomitantly, a significant decreased in Oxy-Hb (from 29.4 ± 20.4 to 15.7 ± 9.0 μmol, p = 0.01), Deoxi-Hb (from 16.3 ± 8.2 to 12.2 ± 6.0 μmol, p = 0.003) and HbT (from 45.7 ± 27.6 to 27.7 ± 13.4 μmol, p = 0.008) was detected at peak exercise after training. No changes were observed in the control group., Conclusion: Exercise training improves skeletal muscle function and functional capacity in HF patients with reduced ejection fraction. This improvement was associated with increased oxygenation of the peripheral muscles, increased muscle blood flow, and decreased sympathetic nerve activity., (Copyright © 2021 Elsevier B.V. All rights reserved.)

This study tested the hypothesis that muscle blood flow restriction reduces muscle and cerebral oxygenation at rest. In 26 healthy males, aged 33 ± 2 yrs, physiological variables were continuously recorded during a 10-min period in 2 experimental conditions: a) with muscle blood flow restriction through thigh cuffs application inflated at 120 mm Hg (With Cuffs, WC) and b) without restriction (No Cuffs, NC). Muscle and cerebral oxygenation were reduced by muscle blood flow restriction as suggested by the increase in both muscle and cerebral deoxygenated hemoglobin (Δ[HHb]; p  < 0.01) and the decrease of muscle and cerebral oxygenation index (Δ[HbDiff]; p  < 0.01). Hemodynamic responses were not affected by such muscle blood flow restriction, whereas baroreflex sensitivity was reduced ( p  = 0.009). The perception of leg discomfort was higher ( p  < 0.001) in the WC than in the NC condition. This study suggests that thigh cuffs application inflated at 120 mm Hg is an effective method to reduce muscle oxygenation at rest. These changes at the muscular level seem to be sensed by the central nervous system, evoking alterations in cerebral oxygenation and baroreflex sensitivity. Novelty: Thigh cuffs application inflated at 120 mm Hg effectively reduces muscle oxygenation at rest. Limiting muscle oxygenation appears to reduce cerebral oxygenation, and baroreflex sensitivity, at rest. Even in healthy subjects, limiting muscle oxygenation, at rest, affects neural integration.

Dietary nitrate (NO 3 - ) supplementation via beetroot juice (BR) has been reported to lower oxygen cost (i.e., increased exercise efficiency) and speed up oxygen uptake (VO 2 ) kinetics in untrained and moderately trained individuals, particularly during conditions of low oxygen availability (i.e., hypoxia). However, the effects of multiple-day, high dose (12.4 mmol NO 3- per day) BR supplementation on exercise efficiency and VO 2 kinetics during normoxia and hypoxia in well-trained individuals are not resolved. In a double-blinded, randomized crossover study, 12 well-trained cyclists (66.4 ± 5.3 ml min -1 ∙kg -1 ) completed three transitions from rest to moderate-intensity (~70% of gas exchange threshold) cycling in hypoxia and normoxia with supplementation of BR or nitrate-depleted BR as placebo. Continuous measures of VO 2 and muscle (vastus lateralis) deoxygenation (ΔHHb, using near-infrared spectroscopy) were acquired during all transitions. Kinetics of VO 2 and deoxygenation (ΔHHb) were modeled using mono-exponential functions. Our results showed that BR supplementation did not alter the primary time constant for VO 2 or ΔHHb during the transition from rest to moderate-intensity cycling. While BR supplementation lowered the amplitude of the VO 2 response (2.1%, p = 0.038), BR did not alter steady state VO 2 derived from the fit (p = 0.258), raw VO 2 data (p = 0.231), moderate intensity exercise efficiency (p = 0.333) nor steady state ΔHHb (p = 0.224). Altogether, these results demonstrate that multiple-day, high-dose BR supplementation does not alter exercise efficiency or oxygen uptake kinetics during normoxia and hypoxia in well-trained athletes., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Previous studies have reported that the reduced scattering coefficient (μ s ') in the vastus lateralis changes during ramp-incremental exercise due to blood volume changes or accumulation of metabolic by-products. We aimed to clarify the influences of deoxygenation and blood volume changes during exercise on μ s ' dynamics in subjects with various aerobic capacities. Twenty-three healthy young men participated in this study. All subjects performed a ramp-incremental cycling exercise until exhaustion and were divided into two groups: lower (Low: n = 12; peak pulmonary oxygen uptake per kg of fat-free mass (VO 2peak ), 54.2 ± 5.3 mL/kg/min) and higher aerobic capacity group (High: n = 11; VO 2peak , 69.7 ± 5.2 mL/kg/min) by median of VO 2peak . Deoxygenated hemoglobin and myoglobin concentrations (deoxy[Hb + Mb]) and total [Hb + Mb] (total[Hb + Mb]) in the vastus lateralis were monitored during the exercise by three-wavelength (760, 800, and 830 nm) time-resolved NIRS. Similarly, μ s ' at each wavelength was continuously monitored. With increasing exercise intensity, deoxy[Hb + Mb] and total[Hb + Mb] significantly increased in both groups, and the average values of the peak amplitudes of deoxy[Hb + Mb] and total[Hb + Mb] during exercise showed a 106.4% increase and a 17.9% increase from the start of the exercise, respectively. Furthermore, the peak amplitude of total[Hb + Mb] was significantly greater in High. Conversely, there were no changes in μ s ' at any wavelength during exercise and no differences between two groups, suggesting that the great deoxygenation and blood volume changes during incremental exercise have little effect on μ s ' dynamics.

HIV-1 proteins and highly active antiretroviral therapy (HAART) have been associated with microvascular endothelial dysfunction. Although nitrate-rich beetroot juice (NR-BJ) consumption has been shown to improve endothelial function in clinical population, its effects in HIV-infected patients has not been addressed. We investigated the effect of a single dose of NR-BJ on muscle oxygen saturation parameters in response to a handgrip exercise in HIV-infected patients. Fifteen HIV-infected patients received NR-BJ or nitrate-depleted beetroot juice (ND-BJ) in a double-blind cross-over design. Near-IR spectroscopy was utilised to assess muscle oxygen saturation parameters during rhythmic handgrip exercise after NR-BJ or ND-BJ supplementation. A significant faster muscle oxygen desaturation rate during exercise (-7·97 (sd 5·00) v. -5·45 (3·94) %/s, P = 0·005) and muscle oxygen resaturation rate during exercise recovery (0·43 (0·24) v. 0·28 (0·24) %/s, P = 0·030) after NR-BJ ingestion was found. However, no significant difference in exercise time until fatigue was observed. Salivary nitrite and urinary nitrate concentration were analysed after NR-BJ or ND-BJ. A significant increase in salivary nitrite and urinary nitrate in NR-BJ was observed compared with ND-BJ (P < 0·05). Our findings suggest that NR-BJ consumption may acutely improve muscle oxygen saturation during exercise and exercise recovery in HIV-infected patients undergoing HAART and who are expected to present microvascular damage. Thus, future studies investigating the chronic effects of NR-BJ are warranted to delineate a better nutritional strategy based on nitrate-rich foods.

This study investigated the effect of high-intensity cycling re-warm up (RW) within a very short time-frame on the subsequent intermittent sprint performance. Twelve active males completed three trials in random order: control (CON); 3-min RW at 30% of maximal oxygen uptake (VO 2max ) (RW30); and 1-min RW at 90% of VO 2max (RW90). During the experimental trials, participants performed 40-min intermittent cycling exercise followed by 15-min rest. During the rest period, participants completed CON, RW30, or RW90. After the rest period, participants performed the Cycling Intermittent-Sprint Protocol (CISP), which consisted of 10-s rest, 5-s maximal sprint, and 105-s active recovery with the cycles repeated over 10 min. The mean work during sprint for the CISP was significantly higher in both RW trials than in the CON trial (mean±standard deviation; CON: 3539±698 J; RW30: 3724±720 J; RW90: 3739±736 J; p <0.05). The mean electromyogram amplitude during the sprint for the CISP was higher in the RW30 trial than in the CON trial; however, there was no significant difference between the two trials ( p =0.06). The mean median frequency during sprint for the CISP was significantly higher in the RW90 trial than in the other trials ( p <0.05). Rectal temperature did not differ among the three trials. Oxygenated haemoglobin during the initial 30 s of the CISP was significantly higher in the RW90 trial than in the CON trial ( p <0.05). Compared with seated rest, RW, irrespective of whether it comprised 1-min at 90% of VO 2max or 3-min at 30% of VO 2max , increased the subsequent intermittent sprint performance.

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., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The objective of the present study was to evaluate the influence of exercise-induced hypoxemia (EIH) on muscle and cerebral oxygenation responses during maximal exercise in normoxia and in acute moderate hypoxia (fraction of inspired oxygen: 15.3%, 2400 m). EIH was defined as a drop in hemoglobin saturation of at least 4% for at least three consecutive minutes during maximal exercise at sea level. Twenty-five athletes performed incremental treadmill tests to assess maximal oxygen consumption (VO 2max ) in normoxia and in hypoxia. Oxygenation of the vastus lateralis muscle and the left prefrontal cortex of the brain was monitored using near-infrared spectroscopy. During the normoxic test, 15 athletes exhibited EIH; they displayed a larger change in muscle levels of oxyhemoglobin (ΔO 2 Hb) ( p  = 0.04) and a greater change in cerebral levels of deoxyhemoglobin (ΔHHb) ( p  = 0.02) than athletes without EIH (NEIH group). During the hypoxic test, muscle ΔO 2 Hb was lower in the EIH group than in the NEIH group ( p  = 0.03). At VO 2max , hypoxia was associated with a smaller cerebral ΔO 2 Hb in both groups, and a greater cerebral ΔHHb compared to normoxia in the NEIH group only ( p  = 0.02). No intergroup differences in changes in muscle oxygenation were observed. The severity of O 2 arterial desaturation was negatively correlated with changes in total muscle hemoglobin in normoxia ( r  = -0.48, p  = 0.01), and positively correlated with the cerebral ΔHHb in normoxia ( r  = 0.45, p  = 0.02). The occurrence of EIH at sea level was associated with specific muscle and cerebral oxygenation responses to exercise under both normoxia and moderate hypoxia.

This study assessed the intra-individual reliability of oxygen saturation in intercostal muscles (SmO 2 - m.intercostales ) during an incremental maximal treadmill exercise by using portable NIRS devices in a test-retest study. Fifteen marathon runners (age, 24.9 ± 2.0 years; body mass index, 21.6 ± 2.3 kg·m -2 ; V̇O 2 -peak, 63.7 ± 5.9 mL·kg -1 ·min -1 ) were tested on two separate days, with a 7-day interval between the two measurements. Oxygen consumption (V̇O 2 ) was assessed using the breath-by-breath method during the V̇O 2 -test, while SmO 2 was determined using a portable commercial device, based in the near-infrared spectroscopy (NIRS) principle. The minute ventilation (VE), respiratory rate (RR), and tidal volume (Vt) were also monitored during the cardiopulmonary exercise test. For the SmO 2 - m.intercostales , the intraclass correlation coefficient (ICC) at rest, first (VT1) and second ventilatory (VT2) thresholds, and maximal stages were 0.90, 0.84, 0.92, and 0.93, respectively; the confidence intervals ranged from -10.8% - +9.5% to -15.3% - +12.5%. The reliability was good at low intensity (rest and VT1) and excellent at high intensity (VT2 and max). The Spearman correlation test revealed ( p ≤ 0.001) an inverse association of SmO 2 - m.intercostales with V̇O 2 ( ρ  = -0.64), VE ( ρ  = -0.73), RR ( ρ  = -0.70), and Vt ( ρ  = -0.63). The relationship with the ventilatory variables showed that increased breathing effort during exercise could be registered adequately using a NIRS portable device.

It is unclear if the exaggerated exercise pressor reflex observed in peripheral arterial disease (PAD) patients facilitates Oxygen (O 2 ) transport during presymptomatic exercise. Accordingly, this study compared O 2 transport between PAD patients and healthy controls during graded presymptomatic work. Seven PAD patients and seven healthy controls performed dynamic plantar flexion in the bore of a 3T MRI scanner. Perfusion, T 2 * (an index of relative tissue oxygenation), and SvO 2 (a measure of venous oxygen saturation) were collected from the medial gastrocnemius (MG) during the final 10 seconds of each stage. Blood pressure was also collected during the final minute of each stage. As expected, the pressor response to presymptomatic work (4 kg) was exaggerated in PAD patients compared to controls (+14 mmHg ± 4 and +7 mmHg ± 2, P ≤ 0.034). When normalized to changes in free water content (S 0 ), T 2 * was lower at 2 kg in PAD patients compared to controls (-0.91 Δms/ΔAU ± 0.3 and 0.57 Δms/ΔAU ± 0.3, P ≤ 0.008); followed by a greater increase in perfusion at 4 kg in the PAD group (+18.8 mL/min/100g ± 6.2 vs. -0.21 mL/min/100g ± 3.2 in PAD and controls, P ≤ 0.026). Lastly, SvO 2 decreased at 4 kg in both groups (-13% ± 4 and -2% ± 4 in PAD and controls, P ≤ 0.049), suggesting an increase in O 2 extraction in the PAD group. Based on these findings, O 2 transport appears to be augmented during graded presymptomatic work in PAD patients, and this may be partially mediated by an exaggerated pressor response., (© 2019 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.)

The oxygen partial pressure in the interstitial space (Po 2 is ) drives O 2 into the myocyte via diffusion, thus supporting oxidative phosphorylation. Although crucial for metabolic recovery and the capacity to perform repetitive tasks, the time course of skeletal muscle Po 2 is during recovery from contractions remains unknown. We tested the hypothesis that Po 2 is would recover to resting values and display considerable on-off asymmetry (fast on-, slow off-kinetics), reflective of asymmetric capillary hemodynamics. Microvascular Po 2 (Po 2 mv ) was also evaluated to test the hypothesis that a significant transcapillary gradient (ΔPo 2  = Po 2 mv - Po 2 is ) would be sustained during recovery. Po 2 mv and Po 2 is (expressed in mmHg) were determined via phosphorescence quenching in the exposed rat spinotrapezius muscle during and after submaximal twitch contractions ( n = 12). Po 2 is rose exponentially ( P < 0.05) from end-contraction (11.1 ± 5.1), such that the end-recovery value (17.9 ± 7.9) was not different from resting Po 2 is (18.5 ± 8.1; P > 0.05). Po 2 is off-kinetics were slower than on-kinetics (mean response time: 53.1 ± 38.3 versus 18.5 ± 7.3 s; P < 0.05). A significant transcapillary ΔPo 2 observed at end-contraction (16.6 ± 7.4) was maintained throughout recovery (end-recovery: 18.8 ± 9.6; P > 0.05). Consistent with our hypotheses, muscle Po 2 is recovered to resting values with slower off-kinetics compared with the on-transient in line with the on-off asymmetry for capillary hemodynamics. Maintenance of a substantial transcapillary ΔPo 2 during recovery supports that the microvascular-interstitium interface provides considerable resistance to O 2 transport. As dictated by Fick's law (V̇o 2  = Do 2 × ΔPo 2 ), modulation of O 2 flux (V̇o 2 ) during recovery must be achieved via corresponding changes in effective diffusing capacity (Do 2 ; mainly capillary red blood cell hemodynamics and distribution) in the face of unaltered ΔPo 2 . NEW & NOTEWORTHY Capillary blood-myocyte O 2 flux (V̇o 2 ) is determined by effective diffusing capacity (Do 2 ; mainly erythrocyte hemodynamics and distribution) and microvascular-interstitial Po 2 gradients (ΔPo 2  = Po 2 mv - Po 2 is ). We show that Po 2 is demonstrates on-off asymmetry consistent with Po 2 mv and erythrocyte kinetics during metabolic transitions. A substantial transcapillary ΔPo 2 was preserved during recovery from contractions, indicative of considerable resistance to O 2 diffusion at the microvascular-interstitium interface. This reveals that effective Do 2 declines in step with V̇o 2 during recovery, as per Fick's law.

Background: We assess whether the lower exercise tolerance in children with univentricular heart (UVH) after Fontan operation is associated with altered peripheral muscular and cerebral tissue oxygenation., Methods: 18 children with UVH and 20 healthy subjects performed an incremental ramp exercise test. Changes in the cerebral and muscular pattern of oxygenated (O 2 Hb) and deoxygenated hemoglobin (HHb) and local tissue oxygenation (TOI) were analyzed by means of Near Infrared Spectroscopy (NIRS). Correlations between arterial saturation during exercise and tissue oxygenation were evaluated., Results: In UVH, maximal oxygen consumption (VO 2 peak/kg, 28.9 ± 7.9 vs. 46.3 ± 11.9 ml/min/kg, P < 0.001), heart rate (HRpeak, 168 ± 13 vs. 193 ± 12 bpm, P < 0.001) and load (Ppeak, 73 ± 19 vs. 133 ± 68 W, P < 0.001) were lower, VE/VCO 2 slope was higher (34.5 ± 5.9 vs. 27.1 ± 3.9, P < 0.001). A faster and steeper course up to the same level of HHb and absent increase in O 2 Hb was seen at cerebral level in UVH; tissue oxygenation index (TOI) demonstrated a steady decrease from the start of exercise. At the muscular level, HHb curve has a similar pattern compared to controls, with an early cessation. O 2 Hb has a similar pattern, but with early discontinuation at a higher O 2 Hb-level. Muscular TOI has the same course throughout exercise, starting from a lower level. Lower arterial saturation and higher age correlated with lower VO 2 peak; higher amplitude of muscular TOI and lower amplitude cerebral TOI correlated with higher VO 2 peak., Conclusion: Children after Fontan procedure have different oxygenation mechanisms at muscular and cerebral level. This reflects a different balance between O 2 supply to O 2 demand which might contribute to the reduced exercise tolerance in this patient population., (Copyright © 2019. Published by Elsevier B.V.)

Purpose: The aim of this study was to assess the acute cardiorespiratory as well as muscle and cerebral tissue oxygenation responses to submaximal constant-load (CL) and high-intensity interval (HII) cycling exercise performed in normoxia and in hypoxia at similar intensity, reproducing whole-body endurance exercise training sessions as performed in sedentary and clinical populations., Methods: Healthy subjects performed two CL (30 min, 75% of maximal heart rate, n = 12) and two HII (15 times 1-min high-intensity exercise-1-min passive recovery, n = 12) cycling exercise sessions in normoxia and in hypoxia [mean arterial oxygen saturation 76 ± 1% (clamped) during CL and 77 ± 5% (inspiratory oxygen fraction 0.135) during HII]. Cardiorespiratory and near-infrared spectroscopy parameters as well as the rate of perceived exertion were continuously recorded., Results: Power output was 21 ± 11% and 15% (according to protocol design) lower in hypoxia compared to normoxia during CL and HII exercise sessions, respectively. Heart rate did not differ between normoxic and hypoxic exercise sessions, while minute ventilation was higher in hypoxia during HII exercise only (+ 13 ± 29%, p < 0.05). Quadriceps tissue saturation index did not differ significantly between normoxia and hypoxia (CL 60 ± 8% versus 59 ± 5%; HII 59 ± 10% versus 56 ± 9%; p > 0.05), while prefrontal cortex deoxygenation was significantly greater in hypoxia during both CL (66 ± 4% versus 56 ± 6%) and HII (58 ± 5% versus 55 ± 5%; p < 0.05) sessions. The rate of perceived exertion did not differ between normoxic and hypoxic CL (2.4 ± 1.7 versus 2.9 ± 1.8) and HII (6.9 ± 1.4 versus 7.5 ± 0.8) sessions (p > 0.05)., Conclusion: This study indicates that at identical heart rate, reducing arterial oxygen saturation near 75% does not accentuate muscle deoxygenation during both CL and HII exercise sessions compared to normoxia. Hence, within these conditions, larger muscle hypoxic stress should not be expected.

This study examined whether the point of accelerated deoxygenation of active muscle occurs during the 20-m shuttle run test (20mSRT) and, if so, whether it is associated with exercise performance in the test. Twenty-nine male subjects performed the 20mSRT, and concentration changes in oxyhaemoglobin (ΔOxy-Hb) and deoxyhaemoglobin (ΔDeoxy-Hb) in the m. vastus lateralis were measured using a portable near-infrared spectroscopy device. The difference between the relative concentration changes in ΔOxy-Hb and ΔDeoxy-Hb (Δ[Oxy-Hb - Deoxy-Hb]) was regarded as the muscle oxygenation index. Group-averaged Δ[Oxy-Hb - Deoxy-Hb] showed progressive decrease during the test. However, among the individuals, we found an accelerated point of decrease in Δ[Oxy-Hb - Deoxy-Hb] in 20 subjects, which revealed that the laps at the accelerated point correlated with the total laps (r = 0·78). These results demonstrate that the accelerated deoxygenation of active muscle occurs during the 20mSRT, but not in all cases. Our findings also indicate that if the accelerated point of muscle deoxygenation occurs, the timing of its appearance is related to 20mSRT performance., (© 2017 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.)

Phenylephrine increases mean arterial pressure (MAP) by enhanced total peripheral resistance (TPR) but near-infrared spectroscopy (NIRS) determined muscle oxygenation (S m O 2 ) increases. We addressed that apparent paradox during supine rest and head-up tilt (HUT). Variables were determined ± phenylephrine in males during supine rest (n = 17) and 40° HUT (n = 7). MAP, stroke volume (SV), heart rate (HR), and TPR were derived by Modelflow ® and NIRS determined biceps S m O 2 and (tibial) bone oxygenation (S tibial O 2 ). For ten subjects, cardiac filling and the diameter of the inferior caval vein (ICV collapsibility index: ((ICV expiration  - ICV inspiration )/ICV expiration ) × 100) were assessed by ultrasound. Pancreatic polypeptide (PP) and atrial natriuretic peptide (proANP) in plasma were determined by immunoassay. Brachial artery blood flow was assessed by ultrasound and skin oxygenation (S skin O 2 ) monitored by white light spectroscopy. Phenylephrine increased MAP by 34% and TPR (62%; P < 0.001) during supine rest. The ICV collapsibility index decreased (24%; P < 0.001) indicating augmented cardiac preload although volume of the left atrium and ventricle did not change. SV increased (18%; P < 0.001) as HR decreased (24%; P < 0.001). ProANP increased by 9% (P = 0.002) with unaffected PP. Brachial artery blood flow tended to decrease while S skin O 2 together with S tibial O 2 decreased by 11% (P = 0.026) and 20% (P < 0.001), respectively. Conversely, phenylephrine increased S m O 2 (9%) and restored the HUT elicited decrease in S m O 2 (by 19%) along with SV (P = 0.02). Phenylephrine reduces skin and bone oxygenation and tends to reduce arm blood flow, suggesting that the increase in S m O 2 reflects veno-constriction with consequent centralization of the blood volume.

Background: The impact of inspiratory muscle training (IMT) on respiratory and peripheral muscle oxygenation and perfusion during inspiratory muscle fatigue in patients with chronic heart failure (HF) has not been established., Methods and Results: Twenty-six patients with chronic HF were randomly assigned to either 8 weeks of IMT or a control group. Inspiratory fatigue was induced by means of a progressive inspiratory resistive loading protocol until there was an inability to sustain inspiratory pressure, when the inspiratory muscle metaboreflex should be activated. The main outcomes were intercostal and forearm muscle oxygen saturation and deoxygenation as measured by means of near-infrared spectroscopy (NIRS) and blood lactate levels. Inspiratory muscle strength was increased by 78% (P <.001) after 8 weeks of participation in the IMT group. IMT attenuated the reduction of oxygen saturation in intercostal and forearm muscles and the increase in blood lactate during respiratory fatigue (P <.001 and P <.05, respectively). These changes were different from the control group (P <.01, P <.05, and P <.05, respectively). After 8 weeks, similar increases in oxygen consumption, mean arterial pressure, heart rate, stroke volume, and cardiac output were observed in both groups during respiratory fatigue., Conclusions: This randomized controlled clinical trial demonstrates that IMT attenuates the respiratory muscle oxygen demand-delivery mismatch during respiratory fatigue in patients with chronic HF., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Objective: To assess the potential utility of a novel non-invasive muscle oxygen measurement to determine the presence of muscle hypoxia in patients with anaemia., Background: Recent assessment of the risk/benefit ratio of blood transfusion has led to clinical strategies optimising transfusion decisions. These decisions are primarily based on haematocrit (Hct) but not oxygen delivery, the primary function of red blood cells (RBCs). We hypothesised that muscle oxygenation (MOx) would correlate with Hct in patients with anaemia and may be a physiologically relevant determinant of the transfusion threshold., Methods/materials: MOx was non-invasively determined in children in the Cancer and Blood Disorders Center ambulatory clinic at Seattle Children's Hospital using a custom-designed optical probe and spectrometer. MOx was compared with contemporaneous Hct. In subjects receiving RBCs, MOx and Hct were also determined following transfusion., Results: MOx ranged from 36·7 to 100%, and Hct ranged from 17·0 to 38·6% in 27 measurements from 16 patients. High MOx values were associated with high Hct. Mean MOx for patients with normal Hct for age (n = 5) was 95·9 ± 2·9%. RBC transfusion increased mean Hct from 19·1 ± 1·5% to 29·3 ± 2·0 and mean MOx from 67·9 ± 21·1% to 89·9 ± 9·8%. Among six transfusion episodes (in five patients) with initial Hct < 22, only three had a pre-transfusion MOx of <70%. Patients with the lowest pre-transfusion MOx had the largest increase in MOx after transfusion., Conclusions: These preliminary data suggest that MOx may aid in making transfusion decisions when used in combination with Hct., Competing Interests: Drs. Schenkman and Arakaki and Mr. Ciesielski have a significant financial interest in Opticyte, Inc., which is not directly or significantly related to the research. None of the other authors have disclosed that they have any potential conflicts of interest., (© 2017 British Blood Transfusion Society.)

We examined the effect of heavy-intensity 'priming' exercise on the rate of adjustment of pulmonary O 2 uptake (τV˙O 2p ) initiated from elevated intensities. Fourteen men (separated into two groups: τV˙O 2p ≤25s [Fast] or τV˙O 2p >25s [Slow]) completed step-transitions from 20W to 45% lactate threshold (LT; lower-step, LS) and 45% to 90%LT (upper-step, US) performed (i) without; and (ii) with US preceded by heavy-intensity exercise (HUS). Breath-by-breath V˙O 2p and near-infrared spectroscopy-derived muscle deoxygenation ([HHb+Mb]) were measured. Compared to LS, τV˙O 2p was greater (p<0.05) in US in both Fast (LS, 19±4s; US, 30±4s) and Slow (LS, 25±5s; US, 40±11s) with τV˙O 2p in US being lower (p<0.05) in Fast. In HUS, τV˙O 2p in Slow was reduced (28±8s, p<0.05) and was not different (p>0.05) from LS or Fast group US. In Slow, τ[HHb+Mb] increased (p<0.05) in US relative to HUS; this finding coupled with a reduced τV˙O 2p indicates a priming-induced improvement in matching of muscle O 2 delivery-to-O 2 utilization during transitions from elevated intensities in those with Slow but not Fast V˙O 2p kinetics., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Unlabelled: The purpose of the study was to determine muscle metabolism adaptation to exercise in facioscapulohumeral muscular dystrophy patients (FSHD) and to study the correlation with clinical functional status (6-min walk test). 8 FSHD patients and 15 age-matched healthy controls (Controls) performed two isokinetic constant-load knee extension exercises: (1) at 20% of their maximal extensors' peak torque (i.e., the same relative workload) and (2) at (20N⋅m) (the same absolute workload) for up to 4 min. All exercises consisted of rhythmic, voluntary, isokinetic, concentric contractions of the quadriceps femoris at 90°/s, whereas the flexion was performed passively at the same speed. Muscle oxygenation in the vastus lateralis was evaluated using near-infrared spectroscopy (NIRS). The FSHD patients displayed a lower maximal peak torque than controls (-41%, p < 0.05). During the two-exercise modalities, deoxygenated haemoglobin (HHb) and total haemoglobin volume (tHb) were lower in the FSHD patients (p < 0.05). The initial muscle deoxygenation time delay was shorter in the control group (FSHD: 15.1 ± 4.1 s vs., Controls: 10.4 ± 2.1 s, p < 0.05). Mean response time and maximal peak torque were both correlated with functional impairment (walking endurance). The results suggest that FSHD patients present an impairment in their capacity to deliver or to use oxygen., (Copyright © 2015 Elsevier B.V. All rights reserved.)

We investigated whether muscle and ventilatory responses to incremental ramp exercise would be influenced by aerobic fitness status by means of a cross-sectional study with a large subject population. Sixty-four male students (age: 21.2 ± 3.2 years) with a heterogeneous peak oxygen uptake (51.9 ± 6.3 mL·min(-1)·kg(-1), range 39.7-66.2 mL·min(-1)·kg(-1)) performed an incremental ramp cycle test (20-35 W·min(-1)) to exhaustion. Breath-by-breath gas exchange was recorded, and muscle activation and oxygenation were measured with surface electromyography and near-infrared spectroscopy, respectively. The integrated electromyography (iEMG), mean power frequency (MPF), deoxygenated [hemoglobin and myoglobin] (deoxy[Hb+Mb]), and total[Hb+Mb] responses were set out as functions of work rate and fitted with a double linear function. The respiratory compensation point (RCP) was compared and correlated with the breakpoints (BPs) (as percentage of peak oxygen uptake) in muscle activation and oxygenation. The BP in total[Hb+Mb] (83.2% ± 3.0% peak oxygen uptake) preceded (P < 0.001) the BP in iEMG (86.7% ± 4.0% peak oxygen uptake) and MPF (86.3% ± 4.1% peak oxygen uptake), which in turn preceded (P < 0.01) the BP in deoxy[Hb+Mb] (88.2% ± 4.5% peak oxygen uptake) and RCP (87.4% ± 4.5% peak oxygen uptake). Furthermore, the peak oxygen uptake was significantly (P < 0.001) positively correlated to the BPs and RCP, indicating that the BPs in total[Hb+Mb] (r = 0.66; P < 0.001), deoxy[Hb+Mb] (r = 0.76; P < 0.001), iEMG (r = 0.61; P < 0.001), MPF (r = 0.63; P < 0.001), and RCP (r = 0.75; P < 0.001) occurred at a higher percentage of peak oxygen uptake in subjects with a higher peak oxygen uptake. In this study a close relationship between muscle oxygenation, activation, and pulmonary oxygen uptake was found, occurring in a cascade of events. In subjects with a higher aerobic fitness level this cascade occurred at a higher relative intensity.

Purpose: The aim of this study was to compare the muscle oxygenation between trained and untrained subjects during heavy exercise until exhaustion at two extreme pedaling cadences using a NIRS system., Methods: Nine untrained male subjects and nine male competitive triathletes cycled until exhaustion at an intensity corresponding to 90 % of the power output achieved at peak oxygen uptake at 40 and 100 rpm. Gas exchanges were measured breath-by-breath during each exercise. Muscle (de)oxygenation was monitored continuously by near-infrared spectroscopy on the Vastus Lateralis., Results: Muscle deoxygenation (∆deoxy[Hb + Mb], i.e., O2 extraction) and ∆total[Hb + Mb] were significantly higher at 40 rpm compared to 100 rpm during the exercise in untrained subjects but not in triathletes (p < 0.05). The time performed until exhaustion was significantly higher at 40 than at 100 rpm in untrained subjects (373 ± 55 vs. 234 ± 37 s, respectively) but not in triathletes (339 ± 69 vs. 325 ± 66 s)., Conclusions: These results indicate that high aerobic fitness (1) allows for better regulation between [Formula: see text]O2M and VO2M following the change in pedaling cadence, and (2) is the most important factor in the relationship between pedaling cadence and performance.

Background: Routine oropharyngeal suctioning in term vigorous neonates immediately after birth is a questionable practice. Current recommendations favor suctioning only in the presence of considerable obstruction due to secretions, blood or other matter. We aimed to analyze the influence of oropharyngeal suctioning on cerebral and peripheral muscle oxygenation in term neonates during transition immediately after birth., Methods: We included term neonates after elective cesarean section for this prospective observational study. Oropharyngeal suctioning was performed based on the clinicians' judgment of threatening airway obstruction. From a total of 138 enrolled neonates, 36 were suctioned and then compared to 36 controls matched for gestational age. Heart rate (HR) and pre/postductal arterial oxygen saturation (SpO2pre/SpO2post) were measured by pulse oximetry. Cerebral (rSO2brain) and pre/postductal peripheral muscle tissue oxygenation (rSO2pre/rSO2post) were measured by near infrared spectroscopy during the first 15min of life., Results: All neonates in both groups experienced normal postnatal transition with normal Apgar scores (Apgar 9/10/10) and with no events of apnea or bradycardia induced by suctioning. SpO2pre values were slightly lower at 2 and 4min after birth. Suctioning had no main and interaction effect on HR, SpO2post, rSO2brain, rSO2pre and rSO2post in the first 15min after birth., Conclusion: In the present study we were able to show that, in term neonates, when correctly indicated, immediate postnatal oropharyngeal suctioning does not compromise cerebral and peripheral muscle tissue oxygenation. However, any suction maneuver must be performed with caution and strict indication during neonatal transition., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Recent research has suggested that dietary nitrate (NO3(-)) supplementation might alter the physiological responses to exercise via specific effects on type II muscle. Severe-intensity exercise initiated from an elevated metabolic rate would be expected to enhance the proportional activation of higher-order (type II) muscle fibers. The purpose of this study was, therefore, to test the hypothesis that, compared with placebo (PL), NO3(-)-rich beetroot juice (BR) supplementation would speed the phase II VO2 kinetics (τ(p)) and enhance exercise tolerance during severe-intensity exercise initiated from a baseline of moderate-intensity exercise. Nine healthy, physically active subjects were assigned in a randomized, double-blind, crossover design to receive BR (140 ml/day, containing ~8 mmol of NO3(-)) and PL (140 ml/day, containing ~0.003 mmol of NO3(-)) for 6 days. On days 4, 5, and 6 of the supplementation periods, subjects completed a double-step exercise protocol that included transitions from unloaded to moderate-intensity exercise (U→M) followed immediately by moderate to severe-intensity exercise (M→S). Compared with PL, BR elevated resting plasma nitrite concentration (PL: 65 ± 32 vs. BR: 348 ± 170 nM, P < 0.01) and reduced the VO2 τ(p) in M→S (PL: 46 ± 13 vs. BR: 36 ± 10 s, P < 0.05) but not U→M (PL: 25 ± 4 vs. BR: 27 ± 6 s, P > 0.05). During M→S exercise, the faster VO2 kinetics coincided with faster near-infrared spectroscopy-derived muscle [deoxyhemoglobin] kinetics (τ; PL: 20 ± 9 vs. BR: 10 ± 3 s, P < 0.05) and a 22% greater time-to-task failure (PL: 521 ± 158 vs. BR: 635 ± 258 s, P < 0.05). Dietary supplementation with NO3(-)-rich BR juice speeds VO2 kinetics and enhances exercise tolerance during severe-intensity exercise when initiated from an elevated metabolic rate.

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Use of muscle oxygen saturation (SmO2) has been validated as a performance factor during incremental exercise with portable near-infrared stereoscopy (NIRS) technology. However, there is little knowledge about the use of SmO2 to identify training zones. The objective of this study was to evaluate the metabolic zones by SmO2: maximum lipid oxidation zone (Fatmax), ventilatory thresholds (VT1 and VT2) and maximum aerobic power (MAP) during a graded exercise test (GXT). Forty trained cyclists and triathletes performed a GXT. Output power (W), heart rate (HR), oxygen consumption (VO2), energy expenditure (kcal/min) and SmO2 were measured. Data were analysed using the ANOVA test, ROC curves and multiple linear regressions. Significance was established at p ≤ 0.05. SmO2 decreases were observed from baseline (LB) to Fatmax (Δ = -16% p < 0.05), Fatmax to VT1 (Δ = -16% p < 0.05) and VT1 to VT2 (Δ = -45% p < 0.01). Furthermore, SmO2 together with weight, HR and output power have the ability to predict VO2 and energy expenditure by 89% and 90%, respectively. We conclude that VO2 and energy expenditure values can be approximated using SmO2 together with other physiological parameters and SmO2 measurements can be a complementary parameter to discriminate aerobic workload and anaerobic workload in athletes. [ABSTRACT FROM AUTHOR]

Use of muscle oxygen saturation (SmO2) has been validated as a performance factor during incremental exercise with portable near-infrared stereoscopy (NIRS) technology. However, there is little knowledge about the use of SmO2 to identify training zones. The objective of this study was to evaluate the metabolic zones by SmO2: maximum lipid oxidation zone (Fatmax), ventilatory thresholds (VT1 and VT2) and maximum aerobic power (MAP) during a graded exercise test (GXT). Forty trained cyclists and triathletes performed a GXT. Output power (W), heart rate (HR), oxygen consumption (VO2), energy expenditure (kcal/min) and SmO2 were measured. Data were analysed using the ANOVA test, ROC curves and multiple linear regressions. Significance was established at p ≤ 0.05. SmO2 decreases were observed from baseline (LB) to Fatmax (Δ = -16% p < 0.05), Fatmax to VT1 (Δ = -16% p < 0.05) and VT1 to VT2 (Δ = -45% p < 0.01). Furthermore, SmO2 together with weight, HR and output power have the ability to predict VO2 and energy expenditure by 89% and 90%, respectively. We conclude that VO2 and energy expenditure values can be approximated using SmO2 together with other physiological parameters and SmO2 measurements can be a complementary parameter to discriminate aerobic workload and anaerobic workload in athletes.

ter Beek, F, Jokumsen, PS, Sloth, BN, Thomas Stevenson, AJ, and Larsen, RG. Ischemic preconditioning attenuates rating of perceived exertion but does not improve maximal oxygen consumption or maximal power output. J Strength Cond Res 36(9): 2479–2485, 2022—Brief consecutive periods of limb ischemia and reperfusion, known as ischemic preconditioning (IPC), have been reported to increase maximal power output (MPO) during cycling. However, the underlying mechanisms are unclear. Therefore, the purpose of the study was to investigate the effects of IPC on MPO, maximal oxygen consumption (V̇ o 2max), muscle oxygenation, and rating of perceived exertion (RPE) during an incremental cycling test. Fourteen healthy young men participated in this double-blinded, randomized crossover study, involving IPC (250 mm Hg; four 5-minute cycles of ischemia) and sham (20 mm Hg) treatment followed by an incremental cycling test to exhaustion. During the cycling test, V̇ o 2, RPE, heart rate (HR), blood lactate (BL), and muscle oxygenation and deoxygenation (near-infrared spectroscopy) were measured. MPO, V̇ o 2max, HRmax, and muscle deoxygenation did not change with IPC (all p -values > 0.13). Furthermore, IPC had no significant effect on V̇ o 2, HR, or muscle oxygenation during the incremental cycling test (all p -values > 0.18). However, IPC attenuated RPE during cycling at 210 W (IPC: median 17.0 [interquartile range 15.3–19.0]; sham: 17.5 [17.0–19.0]; p = 0.007) and 245 W (IPC: 18.0 [17.0–18.8]; sham: 19.0 [18.0–19.8]; p = 0.011). A single session of IPC did not improve MPO, V̇ o 2max, or measures of oxygen consumption during the cycling test. However, IPC lowered RPE at 210 and 245 W, suggesting that IPC may attenuate the perception of effort at higher submaximal exercise intensities. [ABSTRACT FROM AUTHOR]

Purpose: The objective of the study was to describe and compare the acute response of muscle oxygen saturation (SmO2) and hemoglobin concentration (Hgb) in the vastus lateralis (VL) during resistance exercise protocols until failure. Methods: Sixteen males were considered (mean ± SD, age = 36.12 ± 6.40 years). Two familiarization sessions and one evaluation session were carried out where three force protocols were executed in the VL, one of them was isometric load (P1) and two of dynamic load (P2 and P3). SmO2 [%] and Hgb [g/dL] were measured before and after each of these protocols. For P1, three series of 8 s of maximum isometric strength with the rest of 60 s between each set, the average isometric strength (AIS), and the isometric peak strength (IPS) were also recorded. After five minutes, P2 was performed, with an initial load of 40% of AIS. Then, at 30 minutes, P3 was performed considering an initial load of 40% of IPS. Results: The results suggest (I) minimum levels of SmO2 (66.31 ± 9.38%) and Hgb (12.22 ± 0.55 g/dL) during P2, (II) no significant differences were observed between the average loads of the respective protocols for SmO2 and (III) muscle Hgb differed significantly between rest with P1 and P3. Conclusions: Exercises of increasing intensity and of short duration do not significantly modify SmO2. However, Hgb increases substantially compared baseline values. [ABSTRACT FROM AUTHOR]

This study aimed to profile the physiological characteristics of junior sprint kayak athletes (n = 21, VO2max 4.1 ± 0.7 L/min, training experience 2.7 ± 1.2 y) and to establish the relationship between physiological variables (VO2max, VO2 kinetics, muscleoxygen kinetics, paddling efficiency) and sprint kayak performance. VO2max, power at VO2max, power:weight ratio, paddling efficiency, VO2 at lactate threshold, and whole-body and muscle oxygen kinetics were determined on a kayak ergometer in the laboratory. Separately, on-water time trials (TT) were completed over 200 m and 1000 m. Large to nearly perfect (-.5 to -.9) inverse relationships were found between the physiological variables and on-water TT performance across both distances. Paddling efficiency and lactate threshold shared moderate to very large correlations (-.4 to -.7) with 200- and 1000-m performance. In addition, trivial to large correlations (-.11 to -.5) were observed between muscle-oxygenation parameters, muscle and whole-body oxygen kinetics, and performance. Multiple regression showed that 88% of the unadjusted variance for the 200-m TT performance was explained by VO2max, peripheral muscle deoxygenation, and maximal aerobic power (P < .001), whereas 85% of the unadjusted variance in 1000-m TT performance was explained by VO2max and deoxyhemoglobin (P < .001). The current findings show that well-trained junior sprint kayak athletes possess a high level of relative aerobic fitness and highlight the importance of the peripheral muscle metabolism for sprint kayak performance, particularly in 200-m races, where finalists and nonfinalists are separated by very small margins. Such data highlight the relative aerobic-fitness variables that can be used as benchmarks for talent-identification programs or monitoring longitudinal athlete development. However, such approaches need further investigation. [ABSTRACT FROM AUTHOR]

In resistance training squats are often used to strengthen the muscles of the lower extremities and core muscles. There are two common forms of squats that use a barbell for loading, the back squat and the front squat. The technique and loading of each squat differ markedly. However, the energetic demands on the muscle between the two forms are not well understood. The purpose of this study was to investigate the difference in energy demands between front and back squats by measuring the change in skeletal muscle oxygen saturation (SmO2) through the use of near infrared spectroscopy (NIRS). Methods: Eleven resistance trained individuals, (5 female, 6 male) with an average age of 23.7 ± 1.4, completed 3 sets of 15 repetitions at 70% of their 1-RM weight for both back and front squats. Skeletal muscle oxygen saturation (SmO2) of the vastus lateralis was measured using a wireless NIRS device. Results: The △SmO2 was not significantly different between back and front squats but was different between sets 1-3 (44.76 ± 3.24% vs. 55.19 ± 2.75% vs. 56.30 ± 2.63%), main effect p = 0.0001. The recovery of SmO2 was significantly different between back (42.5 ± 3.4 sec) and front squats (30.9 ± 2.8 sec), main effect p = 0.05. Conclusions: The findings of this study suggest that the energetic demands placed on the vastus lateralis during both front and back squats are similar with a slower recovery of energetics in the back squat. [ABSTRACT FROM AUTHOR]

BACKGROUND: The ergogenic effect of ischemic preconditioning (IPC) has been widely approved, but the mechanisms underlying the beneficial effects are still not fully clarified. OBJECTIVE: The aim of this study was to examine the effects of IPC on human isokinetic muscular function and hemodynamics during exercise. METHODS: In a counterbalanced, crossover study, 14 healthy non-athletic males (26.0 ± 3.5 years) performed isokinetic muscle strength and endurance tests of the dominant leg on an isokinetic dynamometer, preceded by either IPC on bilateral thighs (3 × 5-min compression/5-min reperfusion cycles at 50 mmHg greater than the participant's systolic blood pressure) or SHAM (10 mmHg) intervention. Participants underwent strength testing by performing three maximum isokinetic knee extensions and flexions at the angular velocities of 30 ⋅ ∘ s - 1 , 150 ⋅ ∘ s - 1 , and 270 ⋅ ∘ s - 1 . An endurance test was also conducted over 30 repetitions at 180 ∘ /s. Hemodynamics of the vastus lateralis muscle were monitored before and after the interventions and during exercise tests by near-infrared spectrometer (NIRS). RESULTS: Resting total hemoglobin significantly increased after IPC (p = 0.048, d = 0.15). During the endurance testing, the oxygen uptake was significantly improved after IPC as shown by the change of oxygenated hemoglobin, deoxygenated hemoglobin, and oxygen saturation, at small to moderate effect size. However, both muscular strength and endurance were found unchanged. CONCLUSION: IPC improves the local oxygenation status without altering maximal muscle strength and endurance in young non-athletic males. [ABSTRACT FROM AUTHOR]

The objective of the study was to develop a better understanding of the capillary circulation in contracting muscles. Ten subjects were measured during a submaximal fatiguing isometric muscle action by use of the O2C spectrophotometer. In all measurements the capillary-venous oxygen saturation of hemoglobin (SvO2) decreased immediately after the start of loading and leveled off into a steady state. However, two different patterns (type I and type II) emerged. They differed in the extent of deoxygenation (-10.37 ±2.59 percent points (pp) vs. -33.86 ±17.35 pp, p = .008) and the behavior of the relative hemoglobin amount (rHb). Type I revealed a positive rank correlation of SvO2 and rHb (p = 0.735, p <.001), whereas a negative rank correlation (p = -0.522, p <.001) occurred in type II, since rHb decreased until a reversal point, then increased averagely 13% above the baseline value and leveled off into a steady state. The results reveal that a homeostasis of oxygen delivery and consumption during isometric muscle actions is possible. A rough distinction in two types of regulation is suggested. [ABSTRACT FROM AUTHOR]

International Journal of Exercise Science 12(2): 444-455, 2019. L-arginine is used as a nitric oxide related supplement intended to improve sports performance, and to enhance muscular recovery during exercise. However, the literature is inconclusive. The aim of this study was to determine the effects of acute oral L-arginine supplementation on O2 consumption kinetics and local muscle blood volume and oxygenation during treadmill running at two different intensities. Using a double-blind, crossover and placebo-controlled design, 11 young healthy male adults were randomly assigned to 6 g of L-arginine (ARG) or placebo (PLA) supplementation that was ingested 60 min before the exercise test. Tests consisted of treadmill run at two different intensities (5 min each; moderate, 90% of ventilatory threshold, VT; and heavy, 50% of the difference between VT and VO2peak) interspersed by 1-min walking. Respiratory gas exchange variables were measured continuously with an automated metabolic cart. Near infrared spectroscopy (NIRS) was used to continuously monitor muscle oxyhemoglobin and deoxyhemoglobin and total hemoglobin. Blood samples were collected before supplementation and 6 min after exercise. Two-way repeated measures ANOVA did not show differences in plasma nitrite concentrations between ARG or PLA conditions during the running tests. No significant differences were observed between ARG and PLA conditions for O2 kinetics as well as for NIRS variables. ARG supplementation does not improve physiological responses associated with oxygen cost and NIRS variables during running treadmill tests. Hence, our results do not support the use of L-arginine as an ergogenic aid for running performance in young healthy males. [ABSTRACT FROM AUTHOR]

Purpose: Although ischaemic preconditioning (IPC), induced by cycles of transient limb ischaemia and reperfusion, seems to improve exercise performance, the optimal duration of ischaemia-reperfusion cycles is not established. The present study investigated the effect of ischaemia-reperfusion duration within each IPC cycle on performance in a 2000-m rowing ergometer test.Methods: After incremental and familiarization tests, 16 trained rowers (mean ± SD: age, 24 ± 11 years; weight, 74.1 ± 5.9 kg; [Formula: see text] peak, 67.2 ± 7.4 mL·kg-1·min-1) were randomly submitted to a 2000-m rowing test preceded by intermittent bilateral cuff inflation of the lower limbs with three cycles of ischaemia-reperfusion, lasting 5 min (IPC-5) or 10 min (IPC-10) at 220 or 20 mmHg (control). Power output, [Formula: see text], heart rate, blood lactate concentration, pH, ratings of perceived exertion (RPE), and near-infrared spectroscopy-derived measurements of the vastus lateralis muscle were continuously recorded.Results: No differences among treatments were found in the 2000-m test (control: 424 ± 17; IPC-5: 425 ± 16; IPC-10: 424 ± 17 s; P = 0.772). IPC-10 reduced the tissue saturation index and oxy-haemoglobin concentration during exercise compared with control. The power output during the last 100-m segment was significantly lower with IPC-10. The IPC treatments increased the heart rate over the first 500 m and decreased the pH after exercise. No alterations were observed in [Formula: see text], blood lactate, or RPE among the trials.Conclusion: In conclusion, IPC does not improve the 2000-m rowing ergometer performance of trained athletes regardless of the length of ischaemia-reperfusion cycles. [ABSTRACT FROM AUTHOR]

Purpose: The study examined the effects of short-term field-based military training with partial sleep deprivation on whole-body endurance performance in well-trained individuals.Methods: Before and after a 2-day sustained operations (SUSOPS), 14 cadets performed a 15-min constant-load cycling at 65% of peak power output (PPO; CLT65), followed by an exhaustive constant-load trial at 85% of PPO (CLT85). Physiological [oxygen uptake ([Formula: see text]O2), heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), and regional oxygenation (TOI) in the frontal cerebral cortex and vastus lateralis muscle] and psychological [effort perception (RPE), affective valence (FS), and perceived activation (FAS)] variables were monitored during exercise.Results: SUSOPS reduced time to exhaustion in CLT85 by 29.1% (p = 0.01). During the CLT65 trial, SUSOPS potentiated the exercise-induced elevations in [Formula: see text]O2 and HR (p < 0.05), and blunted MAP (p = 0.001). CO did not differ between trials. Yet, towards the end of both CLT85 trials, CO tended to decline (p ≤ 0.08); a response that occurred at an earlier stage in the SUSOPS trial. During CLT65, SUSOPS altered neither cerebral nor muscle TOI. The SUSOPS CLT85 trial, however, was terminated at similar leg-muscle deoxygenation (p > 0.05) and lower prefrontal cortex deoxygenation (p < 0.01). SUSOPS increased RPE at submaximal intensities (p = 0.05), and suppressed FAS and FS throughout (p < 0.01).Conclusions: The present findings indicate, therefore, that a brief period of military sustained operations with partial sleep deprivation augment cardiorespiratory and psychological strain, limiting high-intensity endurance capacity. [ABSTRACT FROM AUTHOR]

Objective: To examine the effects of beetroot juice (BRJ) on (i) in vivo skeletal muscle O2 consumption (mVO2) and microvascular reactivity at rest and (ii) muscle performance, muscle oxygenation, and mVO2 during sustained isometric handgrip exercise (IHG).Methods: Sixteen young males consumed, randomly, a nitrate-rich (8.1 mmol BRJnitrate) or nitrate-depleted (BRJplacebo) BRJ. After 2.5 hours, they performed an occlusion-reperfusion maneuver at rest, a 3-minute sustained IHG, and a sustained IHG to exhaustion with arterial occlusion. Changes in muscle oxygenated hemoglobin (O2Hb), deoxygenated hemoglobin (HHb), microvascular red blood cell content (tHb), and mVO2 were measured using near-infrared spectroscopy. Force output was recorded.Results: During occlusion, the O2Hb decline did not differ between BRJnitrate and BRJplacebo (magnitude: -30.3 ± 1.6 vs. -31.1 ± 1.5 ΔμΜ; slope: -0.107 ± 0.007 vs. -0.111 ± 0.007 μΜ second-1). During reperfusion, all microvascular reactivity indices were not altered after BRJnitrate (e.g., O2Hbslope: 1.584 ± 0.093 vs. 1.556 ± 0.072 μΜ second-1). During the second and third minute of IHG, O2Hb and tHb were higher in BRJnitrate versus BRJplacebo (p < 0.05), and force output was higher during the third minute (10.8 ± 0.7 vs. 9.5 ± 1.2 kg; p < 0.05); HHb did not differ between trials. In IHG with arterial occlusion, BRJnitrate prolonged the time to fatigue (94.1 ± 5.8 vs. 80.1 ± 3.3 seconds; p < 0.01), with no effects on O2Hb decline (O2Hbslope: -0.226 ± 0.015 vs. -0.230 ± 0.026 μΜ s-1) and mVO2 (14.1 ± 1.0 vs. 14.3 ± 1.6 μmol l-1 minute-1).Conclusion: Acute BRJ ingestion in moderately trained individuals (i) did not alter in vivo skeletal muscle microvascular reactivity (index of microvascular function at rest) and basal oxidative efficiency, (ii) increased muscle oxygenation during IHG (possibly via enhanced O2 delivery), and (iii) provided ergogenic benefits during sustained IHG with no effects on muscle oxidative efficiency. The ergogenic effects of BRJ appeared independent of its tissue perfusion benefits. [ABSTRACT FROM AUTHOR]