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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 (mVO2) 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 mVO2 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 (mVO2, 0.054 ± 0.010 vs. 0.038 ± 0.012 mLO2/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. [ABSTRACT FROM AUTHOR]

This study quantified performance and physiological responses during multi-set resistance exercise to failure at light versus moderate loads in normoxia and systemic hypoxia. On separate visits, fifteen resistance-trained adults performed barbell biceps curl exercise trials (6 sets to failure, 2 min rest between sets) in four separate randomised conditions; i.e. in normoxia at 380 m above sea level or systemic hypoxia at ∼3800 m simulated altitude (inspired oxygen fraction = 20.9% and 12.9%, respectively) combined with two different intensity levels (30% and 70% of 1 repetition maximal or 1RM). Muscle activation (root mean square value calculated from surface electromyography) and oxygenation (integrated-tissue saturation index derived from near-infrared spectroscopy) were monitored for the biceps brachii muscle. The total number of repetitions before failure at 30% 1RM (122 ± 5 vs. 131 ± 5; P = 0.021), but not 70% 1RM (39 ± 1 vs. 41 ± 2; P = 0.313), was lower in hypoxia compared to normoxia. Root mean square activity of the biceps brachii muscle was higher for 70% 1RM compared to 30% 1RM (P < 0.001), while the increase in muscle activation from the first to the last set (P < 0.001) occurred independently of altitude (P > 0.158). Deoxygenation and reoxygenation responses were higher under hypoxic versus normoxic conditions at 70% 1 RM (P = 0.013 and P = 0.015) but not 30% 1RM (P = 0.528 and P = 0.384). During upper-limb multi-set resistance exercise to failure, exposure to acute normobaric hypoxia negatively impacts performance at light, but not moderate, loads. Overall, external resistance has more profound effects on physiological strain than hypoxic exposure per se. Highlights The addition of acute systemic hypoxia negatively affects work performed at low, but not moderate, loads during upper-limb resistance exercise to failure. Hypoxic exposure, however, does not fundamentally alter muscle activation and oxygenation patterns. Muscle activation and oxygenation responses in turn are more largely influenced by load lifted. [ABSTRACT FROM AUTHOR]

Background: Repetitive electrically‐evoked muscle contractions lead to the early onset of muscle fatigue. This study assessed the relationship between muscle mechanomyography (%RMS‐MMG) and tissue oxygen saturation (%TSI) in extensor carpi radialis (ECR) during electrically‐evoked fatiguing exercise in individuals with tetraplegia. Methods: Skin‐surface mechanomyography (MMG) and near‐infrared spectroscopy (NIRS) sensors were placed on the ECR of seven individuals with tetraplegia. All participants performed repetitive electrically‐evoked wrist extension to fatigue while their muscle MMG and NIRS responses were monitored against their power output (PO). Findings: One out of seven participants showed no changes in %TSI throughout the repeated wrist FES‐evoked contraction. The other six participants' %TSI was positively correlated with %PO before fatigue onset. At 50%POpeak, %TSI was negatively correlated (0.489) significantly with declining %PO as the ability of the muscle to take up oxygen became limited. The %RMS‐MMG behaved analogously during pre and post‐fatigue against declining %PO, whereby both displayed positive correlations of 0.443 and 0.214, respectively, (%RMS‐MMG decreased) throughout the exercise session. Regression analysis revealed that %TSI was proportional to pre‐fatigue and inversely proportional to %RMS‐MMG during post‐fatigue. Conclusion: The significant changes in muscle mechanomyography and tissue oxygenation correlations after 50%POpeak implied that the muscle contraction mechanical‐and‐physiological behavior association had been altered following FES‐evoked fatigue. [ABSTRACT FROM AUTHOR]

Whole‐body vibration (WBV) is an exercise mimetic that elicits beneficial metabolic effects. This study aims to investigate the effects of WBV amplitude on metabolic, inflammatory, and muscle oxygenation responses. Forty women and men were assigned to a high (HI; n = 20, Age: 31 ± 6 y) or a low‐amplitude group (LO; n = 20, Age: 33 ± 6 y). Participants engaged in 10 cycles of WBV [1 cycle =1 min of vibration followed by 30 s of rest], while gastrocnemius muscle oxygen consumption (mVO2) was assessed using near‐infrared spectroscopy (NIRS). Blood samples were collected PRE, POST, 1H, 3Hs, and 24H post‐WBV and analyzed for insulin, glucose, and IL‐6. In the LO group, Homeostatic Model Assessment for Insulin Resistant (HOMA‐IR) at 3 h (0.7 ± 0.2) was significantly lower compared to PRE (1.1 ± 0.2; p = 0.018), POST (1.3 ± 0.3; p = 0.045), 1H (1.3 ± 0.3; p = 0.010), and 24H (1.4 ± 0.2; p < 0.001). In addition, at 24H, HOMA‐IR was significantly lower in the LO when compared to the HI group (LO: 1.4 ± 0.2 vs. HI: 2.2 ± 0.4; p = 0.030). mVO2 was higher (p = 0.003) in the LO (0.93 ± 0.29 ml/min/100 ml) when compared to the HI group (0.63 ± 0.28 ml/min/100 ml). IL‐6 at 3H (LO: 13.2 ± 2.7 vs. HI: 19.6 ± 4.0 pg·ml−1; p = 0.045) and 24H (LO: 4.2 ± 1.1 vs. HI: 12.5 ± 3.1 pg·ml−1; p = 0.016) was greater in the HI compared to the LO group. These findings indicate that low‐amplitude WBV provides greater metabolic benefits compared to high‐amplitude WBV. [ABSTRACT FROM AUTHOR]

Key points: Inhibition of pancreatic ATP‐sensitive K+ (KATP) channels is the intended effect of oral sulphonylureas to increase insulin release in diabetes.However, pertinent to off‐target effects of sulphonylurea medication, sex differences in cardiac KATP channel function exist, whereas potential sex differences in vascular KATP channel function remain unknown.In the present study, we assessed vascular KATP channel function (topical glibenclamide superfused onto fast‐twitch oxidative skeletal muscle) supporting blood flow and interstitial O2 delivery‐utilization matching (PO2is) during twitch contractions in male, female during pro‐oestrus and ovariectomized female (F+OVX) rats.Glibenclamide decreased blood flow (convective O2 transport) and interstitial PO2 in male and female, but not F+OVX, rats. Compared to males, females also demonstrated impaired diffusive O2 transport and a faster fall in interstitial PO2.Our demonstration, in rats, that sex differences in vascular KATP channel function exist support the tentative hypothesis that oral sulphonylureas may exacerbate exercise intolerance and morbidity, especially in premenopausal females. Vascular ATP‐sensitive K+ (KATP) channels support skeletal muscle blood flow (Q̇m), interstitial O2 delivery (Q̇O2)‐utilization (V̇O2) matching (i.e. interstitial‐myocyte O2 flux driving pressure; PO2is) and exercise tolerance. Potential sex differences in skeletal muscle vascular KATP channel function remain largely unexplored. We hypothesized that local skeletal muscle KATP channel inhibition via glibenclamide superfusion (5 mg kg–1 GLI; sulphonylurea diabetes medication) in anaesthetized female Sprague–Dawley rats, compared to males, would demonstrate greater reductions in contracting (1 Hz, 7 V, 180 s) fast‐twitch oxidative mixed gastrocnemius (97% type IIA+IID/X+IIB) Q̇m (15 μm microspheres) and PO2is (phosphorescence quenching), resulting from more compromised convective (Q̇O2) and diffusive (DO2) O2 conductances. Furthermore, these GLI‐induced reductions in ovary‐intact females measured during pro‐oestrus would be diminished following ovariectomy (F+OVX). GLI similarly impaired mixed gastrocnemius V̇O2 in both males (↓28%) and females (↓33%, both P < 0.032) via reduced Q̇m (male: ↓31%, female: ↓35%, both P < 0.020), Q̇O2 (male: 5.6 ± 0.5 vs. 4.0 ± 0.5, female: 6.4 ± 1.1 vs. 4.2 ± 0.6 mL O2 min–1 100 g tissue–1, P < 0.022) and the resulting PO2is, with females also demonstrating a reduced DO2 (0.40 ± 0.07 vs. 0.30 ± 0.04 mL O2 min–1 100 g tissue–1, P < 0.042) and a greater GLI‐induced speeding of PO2is fall (mean response time: Sex × Drug interaction, P = 0.026). Conversely, GLI did not impair the mixed gastrocnemius of F+OVX rats. Therefore, in patients taking sulphonylureas, these results support the potential for impaired vascular KATP channel function to compromise muscle Q̇m and therefore exercise tolerance. Such an effect, if present, would likely contribute to adverse cardiovascular events in premenopausal females more than males. Key points: Inhibition of pancreatic ATP‐sensitive K+ (KATP) channels is the intended effect of oral sulphonylureas to increase insulin release in diabetes.However, pertinent to off‐target effects of sulphonylurea medication, sex differences in cardiac KATP channel function exist, whereas potential sex differences in vascular KATP channel function remain unknown.In the present study, we assessed vascular KATP channel function (topical glibenclamide superfused onto fast‐twitch oxidative skeletal muscle) supporting blood flow and interstitial O2 delivery‐utilization matching (PO2is) during twitch contractions in male, female during pro‐oestrus and ovariectomized female (F+OVX) rats.Glibenclamide decreased blood flow (convective O2 transport) and interstitial PO2 in male and female, but not F+OVX, rats. Compared to males, females also demonstrated impaired diffusive O2 transport and a faster fall in interstitial PO2.Our demonstration, in rats, that sex differences in vascular KATP channel function exist support the tentative hypothesis that oral sulphonylureas may exacerbate exercise intolerance and morbidity, especially in premenopausal females. [ABSTRACT FROM AUTHOR]

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 (VO2max) (RW30); and 1-min RW at 90% of VO2max (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 VO2max or 3-min at 30% of VO2max, increased the subsequent intermittent sprint performance. [ABSTRACT FROM AUTHOR]

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 (VO2max) 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 (ΔO2Hb) (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 ΔO2Hb was lower in the EIH group than in the NEIH group (p = 0.03). At VO2max, hypoxia was associated with a smaller cerebral ΔO2Hb 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 O2 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. [ABSTRACT FROM AUTHOR]

Aims: The main mechanism behind caffeine's ergogenicity lies in its tendency to bind to adenosine receptors, although other mechanisms might be involved. The aim of this investigation was to analyse the effects of caffeine on muscle oxygen saturation during exercise of increasing intensity. Methods: Thirteen healthy and active individuals volunteered to participate in a randomized, double blind, placebo‐controlled crossover trial. During 2 different trials, participants either ingested a placebo (cellulose) or 3 mg/kg of caffeine. After waiting for 60 min to absorb the substances, participants underwent a maximal ramp cycle ergometer test (25 W/min). Near infrared spectrometers were positioned on each leg's vastus lateralis to monitor tissue O2 saturation. Blood lactate concentration was measured 1 min after the end of the exercise test. Results: In comparison to the placebo, the ingestion of caffeine improved the maximal wattage (258 ± 50 vs 271 ± 54 W, respectively, P <.001, effect size [ES] = 0.27; 95% confidence interval [CI] 0.14–0.35) and blood lactate concentration (11.9 ± 3.8 vs 13.7 ± 3.5 mmol/L, P =.029, ES = 0.38; 95% CI 0.14–0.75) at the end of the test. Caffeine increased muscle oxygen saturation at several exercise workloads with a main effect found in respect to the placebo (F = 6.28, P =.029; ES = 0.30 to 0.54; 95% CI 0.01–0.78). Peak pulmonary ventilation (124 ± 29 vs 129 ± 23 L/min, P = 0.035, ES = 0.25; 95% CI 0.07–0.40) and peak oxygen uptake (3.18 ± 0.70 vs 3.33 ± 0.88 L/min, P = 0.032, ES = 0.26; 95% CI 0.08–0.51) were also increased with caffeine. Conclusion: Acute ingestion of 3 mg/kg of caffeine improved peak aerobic performance and increased peak pulmonary ventilation. In addition, caffeine induced changes in muscle oxygen saturation during submaximal workloads, suggesting that this mechanism might also contribute to caffeine's ergogenic effect. [ABSTRACT FROM AUTHOR]

Keywords: exercise performance; exhaustion; muscle oxygenation; oxygen uptake kinetics; quadriceps EMG; severe-intensity exercise; slow component EN exercise performance exhaustion muscle oxygenation oxygen uptake kinetics quadriceps EMG severe-intensity exercise slow component 336 337 2 03/03/23 20230301 NES 230301 I Fatigue makes cowards of us all i . Skeletal muscle fatigue precedes the slow component of oxygen uptake kinetics during exercise in humans. Exercise performance, exhaustion, muscle oxygenation, oxygen uptake kinetics, quadriceps EMG, severe-intensity exercise, slow component. [Extracted from the article]

Background and objective: We hypothesized that by reducing respiratory work and improving gas exchange, nasal high flow (NHF) would improve exercise tolerance in patients with chronic obstructive pulmonary disease (COPD) following respiratory exacerbation. Methods: This was a monocentric, randomized, controlled crossover study. Patients with severe to very severe COPD carried out two high‐intensity constant work‐rate exercise tests (CWRET) with and without NHF on two consecutive days. The primary outcome was the mean difference in endurance time between both conditions. The secondary aims included vastus lateralis oxygenation (StO2), dyspnoea, leg discomfort, maximal inspiratory pressure (MIP), transcutaneous CO2 pressure (PtcCO2), respiratory rate (RR), heart rate (HR) and pulsed O2 saturation (SpO2), as well as the patients' opinions of the device. Results: A total of 19 patients were included (mean forced expiratory volume in 1 s = 28.7 ± 10.8%, age = 62.1 ± 9.1 years). No significant differences in endurance time during the CWRET were found between the two test conditions (−66.58 (95% CI: −155.9 to 22.7) s, P = 0.12). StO2, PtCO2 and HR were reduced at the end of the exercise with NHF (−2.1% (95% CI: −4.3 to −0.0); −1.3 mm Hg (95% CI: −2.5 to −0.2); −2.7 bpm (95% CI: −5.0 to −0.5), respectively, P ≤ 0.05). No significant differences were found for any of the other secondary outcomes. Half of the patients evaluated the device as being moderately to very uncomfortable. Conclusion: NHF during exercise did not increase endurance time in patients with COPD following exacerbation. Clinical trial registration: NCT03058081 at clinicaltrials.gov [ABSTRACT FROM AUTHOR]

Summary: Commonly, the near‐infrared spectroscopy (NIRS) devices are used to measure muscle oxygenated hemoglobin (HBO) concentration and total hemoglobin (HBT) concentration with a single channel, which can obtain the temporal HBO and HBT signals. Lacking of the spatial information of muscle oxygenation will limit the exploration of the heterogeneity of muscle activities. In this study, a multichannel NIRS recording system was used to measure the muscle oxygenation with an attempt to simultaneously provide the temporal and spatial HBO and HBT concentration. In the experiment, the influences of four motor tasks, including active, passive, imaginary movement, and the control task (no movement), on muscle oxygenation were investigated in eight normal subjects. Our results showed that both amplitude and spatial heterogeneity associated with variation in muscle oxygenation during active and passive motor tasks were significantly different between the motor time and rest time (P < 0.05). Furthermore, the region where HBO concentration decreased during the active motor task was in accordance with the anatomical position of contracted muscle, which cannot be observed from the results of the passive task. Considering the imaginary and control tasks in which the muscle was in a fixed/stationary state, the amplitude and spatial heterogeneity associated with variations in muscle oxygenation only exhibited slight changes (P > 0.05). This pilot study suggested that the spatiotemporal information obtained from multichannel NIRS devices might be potential for accurate measurement of the variation in muscle oxygenation during motor tasks, which would be useful for different clinical applications. [ABSTRACT FROM AUTHOR]

Key points: The reduced oxygen tension of high altitude compromises performance in lowlanders. In this environment, Sherpa display superior performance, but little is known on this issue.Sherpa present unique genotypic and phenotypic characteristics at the muscular level, which may enhance resistance to peripheral fatigue at high altitude compared to lowlanders.We studied the impact of gradual ascent and exposure to high altitude (5050 m) on peripheral fatigue in age‐matched lowlanders and Sherpa, using intermittent electrically‐evoked contractions of the knee extensors.Peripheral fatigue (force loss) was lower in Sherpa during the first part of the protocol. Post‐protocol, the rate of force development and contractile impulse recovered faster in Sherpa than in lowlanders. At any time, indices of muscle oxygenation were not different between groups.Muscle contractile properties in Sherpa, independent of muscle oxygenation, were less perturbed by non‐volitional fatigue. Hence, elements within the contractile machinery contribute to the superior physical performance of Sherpa at high altitude. Altitude‐related acclimatisation is characterised by marked muscular adaptations. Lowlanders and Sherpa differ in their muscular genotypic and phenotypic characteristics, which may influence peripheral fatigability at altitude. After gradual ascent to 5050 m, 12 lowlanders and 10 age‐matched Sherpa (32 ± 10 vs. 31 ± 11 years, respectively) underwent three bouts (separated by 15 s rest) of 75 intermittent electrically‐evoked contractions (12 pulses at 15 Hz, 1.6 s between train onsets) of the dominant leg quadriceps, at the intensity which initially evoked 30% of maximal voluntary force. Trains were also delivered at minutes 1, 2 and 3 after the protocol to measure recovery. Tissue oxygenation index (TOI) and total haemoglobin (tHb) were quantified by a near‐infrared spectroscopy probe secured over rectus femoris. Superficial femoral artery blood flow was recorded using ultrasonography, and delivery of oxygen was estimated (eDO2). At the end of bout 1, peak force was greater in Sherpa than in lowlanders (91.5% vs. 84.5% baseline, respectively; P < 0.05). Peak rate of force development (pRFD), the first 200 ms of the contractile impulse (CI200), and half‐relaxation time (HRT) recovered faster in Sherpa than in lowlanders (percentage of baseline at 1 min: pRFD: 89% vs. 74%; CI200: 91% vs. 80%; HRT: 113% vs. 123%, respectively; P < 0.05). Vascular measures were pooled for lowlanders and Sherpa as they did not differ during fatigue or recovery (P < 0.05). Mid bout 3, TOI was decreased (90% baseline) whereas tHb was increased (109% baseline). After bout 3, eDO2 was markedly increased (1266% baseline). The skeletal muscle of Sherpa seemingly favours repeated force production at altitude for similar oxygen delivery compared to lowlanders. Key points: The reduced oxygen tension of high altitude compromises performance in lowlanders. In this environment, Sherpa display superior performance, but little is known on this issue.Sherpa present unique genotypic and phenotypic characteristics at the muscular level, which may enhance resistance to peripheral fatigue at high altitude compared to lowlanders.We studied the impact of gradual ascent and exposure to high altitude (5050 m) on peripheral fatigue in age‐matched lowlanders and Sherpa, using intermittent electrically‐evoked contractions of the knee extensors.Peripheral fatigue (force loss) was lower in Sherpa during the first part of the protocol. Post‐protocol, the rate of force development and contractile impulse recovered faster in Sherpa than in lowlanders. At any time, indices of muscle oxygenation were not different between groups.Muscle contractile properties in Sherpa, independent of muscle oxygenation, were less perturbed by non‐volitional fatigue. Hence, elements within the contractile machinery contribute to the superior physical performance of Sherpa at high altitude. [ABSTRACT FROM AUTHOR]

Summary: Blood flow (BF) in exercising muscles is an important factor for exercise capacity. Recently, a non‐invasive method to estimate capillary BF (Qcap) was introduced. Using this method, the Fick principle is re‐arranged by using relative differences in deoxygenated haemoglobin (ΔHHb) as a surrogate for arteriovenous O2 difference and pulmonary oxygen uptake (VO2) instead of muscular oxygen uptake. The aim of this study was to examine (I) the relationship between Qcap and exercise intensity during and following exercise, and (II) to critically reflect the Qcap approach. Seventeen male subjects completed six bouts of cycling exercise with different exercise intensities (40–90% peak oxygen uptake, VO2peak) in randomized order. VO2 and ΔHHb were monitored continuously during the trail. Qcap was modelled bi‐exponentially, and mean response time (MRT) was calculated during recovery as well as the dissociation of modelled VO2 and Qcap recovery kinetics (MRT/τVO2). End‐exercise Qcap increased continuously with exercise intensity. This also applied to MRT. Postexercise MRT/τVO2 increased from 40 to 60% VO2peak but remained stable thereafter. The results show that Qcap response to exercise is linearly related to exercise intensity. This is presumably due to vasoactive factors like shear‐stress or endothelial‐mediated vasodilation. MRT/τVO2 shows that postexercise Qcap is elevated for a longer period than VO2, which is representative for metabolic demand following exercise ≥70% VO2peak. This is a hint for prolonged local vasodilation. According to previous studies, Qcap could not be modelled properly in some cases, which is a limitation to the method and therefore has to be interpreted with caution. [ABSTRACT FROM AUTHOR]

Summary: 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. [ABSTRACT FROM AUTHOR]

Aim To evaluate whether muscle vasodilatation plays a role for hypotension developed during central hypovolaemia, muscle oxygenation (SmO2) was examined during (pre)syncope induced by head-up tilt ( HUT). Skin blood flow (Sk BF) and oxygenation (SskinO2) were determined because evaluation of SmO2 may be affected by superficial tissue oxygenation. Furthermore, we evaluated cerebral oxygenation (ScO2) and middle cerebral artery mean blood flow velocity ( MCAvmean). Methods Twenty healthy male volunteers (median age 24 years; range 19-38) were subjected to passive 50° HUT for 1 h or until (pre)syncope. ScO2 and SmO2 (near-infrared spectroscopy), MCAvmean (transcranial Doppler) along with mean arterial pressure ( MAP), heart rate ( HR), stroke volume ( SV), cardiac output ( CO) and total peripheral resistance ( TPR) (Modelflow®) were determined. Results (Pre)syncopal symptoms appeared in 17 subjects after 11 min (median; range 2-34) accompanied by a decrease in MAP, SV, CO and TPR, while HR remained elevated. During (pre)syncope, ScO2 decreased [73% (71-76; mean and 95% CI) to 68% (65-71), P < 0.0001] along with MCAvmean [40 (37-43) to 32 (29-35) cm s−1, P < 0.0001]. In contrast, SmO2 increased [63 (56-69)% to 71% (65-78), P < 0.0001], while SskinO2 [64% (58-69) to 53% (47-58), P < 0.0001] and Sk BF [71 (44-98) compared to a baseline of 99 (72-125) units, P = 0.020] were reduced. Conclusion We confirm that the decrease in MAP during HUT is associated with a reduction in indices of cerebral perfusion. (Pre)syncope was associated with an increase in SmO2 despite reduced SskinO2 and Sk BF, supporting that muscle vasodilation plays an important role in the circulatory events leading to hypotension during HUT. [ABSTRACT FROM AUTHOR]

Increased local blood supply is thought to be one of the mechanisms underlying oxidative adaptations to interval training regimes. The relationship of exercise intensity with local blood supply and oxygen availability has not been sufficiently evaluated yet. The aim of this study was to examine the effect of six different intensities (40-90% peak oxygen uptake, VO2peak) on relative changes in oxygenated, deoxygenated and total haemoglobin (ΔO2Hb, Δ HHb, Δ THb) concentration after exercise as well as end-exercise Δ HHb/Δ VO2 as a marker for microvascular O2 distribution. Seventeen male subjects performed an experimental protocol consisting of 3 min cycling bouts at each exercise intensity in randomized order, separated by 5 min rests. ΔO2Hb and Δ HHb were monitored with near-infrared spectroscopy of the vastus lateralis muscle, and VO2 was assessed. Δ HHb/Δ VO2 increased significantly from 40% to 60% VO2peak and decreased from 60% to 90% VO2peak. Post-exercise Δ THb and ΔO2Hb showed an overshoot in relation to pre-exercise values, which was equal after 40-60% VO2peak and rose significantly thereafter. A plateau was reached following exercise at ≥80% VO2peak. The results suggest that there is an increasing mismatch of local O2 delivery and utilization during exercise up to 60% VO2peak. This insufficient local O2 distribution is progressively improved above that intensity. Further, exercise intensities of ≥80% VO2peak induce highest local post-exercise O2 availability. These effects are likely due to improved microvascular perfusion by enhanced vasodilation, which could be mediated by higher lactate production and the accompanying acidosis. [ABSTRACT FROM AUTHOR]

New Findings What is the central question of this study? What are the distinct and interactive effects of a 10 day exposure to hypoxia and horizontal bedrest on the whole-body peak oxygen uptake and on the regional cerebral and skeletal muscle tissue oxygenation during upright cycle ergometry in male lowlanders?, What is the main finding and its importance? A 10 day sustained exposure to hypoxia aggravates the bedrest-induced reduction in peak oxygen uptake during dynamic exercise engaging large muscle groups, but mitigates the skeletal muscle oxidative capacity impairment elicited by bedrest., The study examined the interactive effects of a 10 day exposure to hypoxia and bedrest on the whole-body peak oxygen uptake ( [ABSTRACT FROM AUTHOR]

SUMMARY 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. [ABSTRACT FROM AUTHOR]

Whole-body vibration ( WBV) training is commonly practiced and may enhance peripheral blood flow. Here, we investigated muscle morphology and acute microcirculatory responses before and after a 6-week resistive exercise training intervention without ( RE) or with ( RVE) simultaneous whole-body vibrations (20 Hz, 6 mm peak-to-peak amplitude) in 26 healthy men in a randomized, controlled parallel-design study. Total haemoglobin (t Hb) and tissue oxygenation index ( TOI) were measured in gastrocnemius muscle ( GM) with near-infrared spectroscopy ( NIRS). Whole-body oxygen consumption ( VO2) was measured via spirometry, and skeletal muscle morphology was determined in soleus ( SOL) muscle biopsies. Our data reveal that exercise-induced muscle deoxygenation both before and after 6 weeks training was similar in RE and RVE ( P = 0·76), although VO2 was 20% higher in the RVE group ( P<0·001). The RVE group showed a 14%-point increase in reactive hyperaemia ( P = 0·007) and a 27% increase in blood volume ( P<0·01) in GM after 6 weeks of training. The number of capillaries around fibres was increased by 15% after 6 weeks training in both groups ( P<0·001) with no specific effect of superimposed WBV ( P = 0·61). Neither of the training regimens induced fibre hypertrophy in SOL. The present findings suggest an increased blood volume and vasodilator response in GM as an adaptation to long-term RVE, which was not observed after RE alone. We conclude that RVE training enhances vasodilation of small arterioles and possibly capillaries. This effect might be advantageous for muscle thermoregulation and the delivery of oxygen and nutrients to exercising muscle and removal of carbon dioxide and metabolites. [ABSTRACT FROM AUTHOR]

Needle biopsies are being extensively used in clinical trials addressing muscular adaptation to exercise and diet. Still, the potential artifacts due to biopsy sampling are often overlooked. Healthy volunteers ( n = 9) underwent two biopsies through a single skin incision in a pretest. Two days later ( posttest) another biopsy was taken 3 cm proximally and 3 cm distally to the pretest incision. Muscle oxygenation status (tissue oxygenation index [TOI]) was measured by near-infrared spectroscopy. Biopsy samples were analyzed for 40 key markers (mRNA and protein contents) of myocellular O2 sensing, inflammation, cell proliferation, mitochondrial biogenesis, protein synthesis and breakdown, oxidative stress, and energy metabolism. In the pretest, all measurements were identical between proximal and distal biopsies. However, compared with the pretest, TOI in the posttest was reduced in the proximal (−10%, P < 0.05), but not in the distal area. Conversely, most inflammatory markers were upregulated at the distal (100-500%, P < 0.05), but not at the proximal site. Overall, 29 of the 40 markers measured, equally distributed over all pathways studied, were either up- or downregulated by 50-500% ( P < 0.05). In addition, 19 markers yielded conflicting results between the proximal and distal measurements ( P < 0.05). This study clearly documents that prior muscle biopsies can cause major disturbances in myocellular signaling pathways in needle biopsies specimens sampled 48 h later. In addition, different biopsy sites within identical experimental conditions yielded conflicting results. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effects of wearing compression socks (CS) on performance indicators and physiological responses during prolonged trail running. Eleven trained runners completed a 15.6 km trail run at a competition intensity whilst wearing or not wearing CS. Counter movement jump, maximal voluntary contraction and the oxygenation profile of vastus lateralis muscle using near-infrared spectroscopy (NIRS) method were measured before and following exercise. Run time, heart rate (HR), blood lactate concentration and ratings of perceived exertion were evaluated during the CS and non-CS sessions. No significant difference in any dependent variables was observed during the run sessions. Run times were 5681.1±503.5 and 5696.7±530.7 s for the non-CS and CS conditions, respectively. The relative intensity during CS and non-CS runs corresponded to a range of 90.5–91.5% HRmax. Although NIRS measurements such as muscle oxygen uptake and muscle blood flow significantly increased following exercise (+57.7% and + 42.6%,+59.2% and + 32.4%, respectively for the CS and non-CS sessions, P<0.05), there was no difference between the run conditions. The findings suggest that competitive runners do not gain any practical or physiological benefits from wearing CS during prolonged off-road running. [ABSTRACT FROM AUTHOR]

While the effect of lower body compression garments on performance and physiological responses are well documented, no studies have examined the effect of upper body compression garments (UBCG) on upper-body dominant exercise. This study examined the effects of wearing UBCG on performance and physiological responses during simulated flat-water kayaking. Five male (mean values±s: 21.8±2.8 years; 83.5±9.2 kg; 63.0±5.5 ml·kg−1·min−1) and two female (mean values±s: 25.0±4.2 years; 71.4±2.7 kg; 51.0±4.8 ml·kg-1·min-1) elite flat-water kayakers completed a six-step incremental test followed by a four-minute maximal performance test (4minPT) in both UBCG and control (no shirt or sports training bra) conditions in a randomized counter-balanced order. Heart rate and oxygen consumption (O2) as well as performance measures (power, distance covered, stroke rate) were recorded during the tests, and blood lactate was measured immediately after each incremental step and three minutes following the 4minPT. Near-infrared spectroscopy-derived measures of blood flow and oxygenation of the flexor carpi radialis were monitored continuously for all tests. No significant differences between the UBCG and control conditions were evident for any performance, cardiorespiratory or oxygenation measure across the incremental step test and 4minPT. It was concluded that wearing UBCG did not provide any significant physiological or performance benefits during simulated flat-water kayaking. [ABSTRACT FROM AUTHOR]

Near-infrared spectroscopy (NIRS) is a non-invasive method for monitoring oxygen availability and utilization by the tissues. In intact skeletal muscle, NIRS allows semi-quantitative measurements of haemoglobin plus myoglobin oxygenation (tissue O2 stores) and the haemoglobin volume. Specialized algorithms allow assessment of the oxidation–reduction (redox) state of the copper moiety (CuA) of mitochondrial cytochrome c oxidase and, with the use of specific tracers, accurate assessment of regional blood flow. NIRS has demonstrated utility for monitoring changes in muscle oxygenation and blood flow during submaximal and maximal exercise and under pathophysiological conditions including cardiovascular disease and sepsis. During work, the extent to which skeletal muscles deoxygenate varies according to the type of muscle, type of exercise and blood flow response. In some instances, a strong concordance is demonstrated between the fall in O2 stores with incremental work and a decrease in CuA oxidation state. Under some pathological conditions, however, the changes in O2 stores and redox state may diverge substantially. [ABSTRACT FROM AUTHOR]