Muscle oxygenation profiles between active and inactive muscles with nitrate supplementation under hypoxic exercise

L-Citrulline Supplementation Improves Arterial Blood Flow and Muscle Oxygenation during Handgrip Exercise in Hypertensive Postmenopausal Women

Endothelial dysfunction decreases exercise limb blood flow (BF) and muscle oxygenation. Acute L-Citrulline supplementation (CIT) improves muscle tissue oxygen saturation index (TSI) and deoxygenated hemoglobin (HHb) during exercise. Although CIT improves endothelial function (flow-mediated dilation [FMD]) in hypertensive women, the impact of CIT on exercise BF and muscle oxygenation (TSI) and extraction (HHb) are unknown. We examined the effects of CIT (10 g/day) and a placebo for 4 weeks on blood pressure (BP), arterial vasodilation (FMD, BF, and vascular conductance [VC]), and forearm muscle oxygenation (TSI and HHb) at rest and during exercise in 22 hypertensive postmenopausal women. Compared to the placebo, CIT significantly (p < 0.05) increased FMD (Δ-0.7 ± 0.6% vs. Δ1.6 ± 0.7%) and reduced aortic systolic BP (Δ3 ± 5 vs. Δ-4 ± 6 mmHg) at rest and improved exercise BF (Δ17 ± 12 vs. Δ48 ± 16 mL/min), VC (Δ-21 ± 9 vs. Δ41 ± 14 mL/mmHg/min), TSI (Δ-0.84 ± 0.58% vs. Δ1.61 ± 0.46%), and HHb (Δ1.03 ± 0.69 vs. Δ-2.76 ± 0.77 μM). Exercise BF and VC were positively correlated with improved FMD and TSI during exercise (all p < 0.05). CIT improved exercise artery vasodilation and muscle oxygenation via increased endothelial function in hypertensive postmenopausal women.

Five Days of Tart Cherry Supplementation Improves Exercise Performance in Normobaric Hypoxia

Previous studies have shown tart cherry (TC) to improve exercise performance in normoxia. The effect of TC on hypoxic exercise performance is unknown. This study investigated the effects of 5 days of tart cherry (TC) or placebo (PL) supplementation on hypoxic exercise performance. Thirteen healthy participants completed an incremental cycle exercise test to exhaustion (TTE) under two conditions: (i) hypoxia (13% O2) with PL and (ii) hypoxia with TC (200 mg anthocyanin per day for 4 days and 100 mg on day 5). Pulmonary gas exchange variables, peripheral arterial oxygen saturation (SpO2), deoxygenated hemoglobin (HHb), and tissue oxygen saturation (StO2) assessed by near-infrared spectroscopy in the vastus lateralis muscle were measured at rest and during exercise. Urinary 8-hydro-2′ deoxyguanosine (8-OHdG) excretion was evaluated pre-exercise and 1 and 5 h post-exercise. The TTE after TC (940 ± 84 s, mean ± standard deviation) was longer than after PL (912 ± 63 s, p < 0.05). During submaximal hypoxic exercise, HHb was lower and StO2 and SpO2 were higher after TC than PL. Moreover, a significant interaction (supplements × time) in urinary 8-OHdG excretion was found (p < 0.05), whereby 1 h post-exercise increases in urinary 8-OHdG excretion tended to be attenuated after TC. These findings indicate that short-term dietary TC supplementation improved hypoxic exercise tolerance, perhaps due to lower HHb and higher StO2 in the working muscles during submaximal exercise.

Dietary Nitrate Supplementation Does Not Alter Exercise Efficiency at High Altitude - Further Results From the Xtreme Alps Study

Introduction

Nitrate supplementation in the form of beetroot juice (BRJ) ingestion has been shown to improve exercise tolerance during acute hypoxia, but its effect on exercise physiology remains unstudied during sustained terrestrial high altitude exposure. We hypothesized that performing exercise at high altitude would lower circulating nitrate and nitrite levels and that BRJ ingestion would reverse this phenomenon while concomitantly improving key determinants of aerobic exercise performance.

Methods

Twenty seven healthy volunteers (21 male) underwent a series of exercise tests at sea level (SL, London, 75 m) and again after 5-8 days at high altitude (HA, Capanna Regina Margherita or "Margherita Hut," 4,559 m). Using a double-blind protocol, participants were randomized to consume a beetroot/fruit juice beverage (three doses per day) with high levels of nitrate (∼0.18 mmol/kg/day) or a nitrate-depleted placebo (∼11.5 μmoles/kg/day) control drink, from 3 days prior to the exercise trials until completion. Submaximal constant work rate cycle tests were performed to determine exercise efficiency and a maximal incremental ramp exercise test was undertaken to measure aerobic capacity, using breath-by-breath pulmonary gas exchange measurements throughout. Concentrations of nitrate, nitrite and nitrosation products were quantified in plasma samples collected at 5 timepoints during the constant work rate tests. Linear mixed modeling was used to analyze data.

Results

At both SL and HA, plasma nitrate concentrations were elevated in the nitrate supplementation group compared to placebo (P < 0.001) but did not change throughout increasing exercise work rate. Delta exercise efficiency was not altered by altitude exposure (P = 0.072) or nitrate supplementation (P = 0.836). V̇O₂peak decreased by 24% at high altitude (P < 0.001) and was lower in the nitrate-supplemented group at both sea level and high altitude compared to placebo (P = 0.041). Dietary nitrate supplementation did not alter other peak exercise variables or oxygen consumption at anaerobic threshold. Circulating nitrite and S-nitrosothiol levels unexpectedly rose in a few individuals right after cessation of exercise at high altitude.

Conclusion

Whilst regularly consumed during an 8 days expedition to terrestrial high altitude, nitrate supplementation did not alter exercise efficiency and other exercise physiological variables, except decreasing V̇O₂peak. These results and those of others question the practical utility of BRJ consumption during prolonged altitude exposure.

Effects of arm cranking exercise on muscle oxygenation between active and inactive muscles in people with spinal cord injury

Objective: We investigated the effects of the incremental arm-cranking exercise (ACE) on tissue oxygen saturation (StO₂) between active and inactive muscles, and the relationship between peak oxygen uptake (VO_2peak) and changes in the StO₂ in inactive muscles.Design: Observational study.Setting: Community-based supervised intervention.Participants: The participants were individuals with motor and sensory complete spinal cord injury (complete SCI; n = 8) and motor complete but sensory incomplete SCI (incomplete SCI; n = 8), and able-bodied (AB) individuals (n = 8) matched for age, height, and body mass index.Intervention: The ACE was performed at a rate increasing by 10 watts min^-1 until exhaustion.Outcome Measures: VO_2peak, heart rate (HR), and StO₂.Results: While VO_2peak was similar among the groups, peak HR was significantly higher in both SCI groups than in the AB (P < 0.05). In active muscles (biceps brachii), no differences in the StO₂ were observed among the groups (P > 0.05). In inactive muscles (vastus lateralis), the StO₂ in the AB and the incomplete SCI began to decrease at approximately 40% of the peak work rate; however, they remained unchanged in the complete SCI. The reductions in StO₂ in the AB were significantly greater than in the incomplete SCI.Conclusions: These results suggest that sympathetic vasoconstriction occurred in the incomplete SCI and AB, although it did not occur in the complete SCI, probably due to a reduction in sympathetic nerve activity. Sympathetic vasoconstriction in inactive muscles may not contribute to an individual's VO_2peak regardless of their group.

Association between pulmonary oxygen uptake on-kinetics and acute cardiovascular responses to resistance exercise in patients with coronary artery disease: a preliminary study

[Purpose] This study aimed to examine whether pulmonary oxygen uptake on-kinetics at the onset of moderate-intensity exercise can predict acute cardiovascular responses to resistance exercise. [Participants and Methods] The association between pulmonary oxygen uptake on-kinetics and acute cardiovascular responses to a single resistance exercise session was investigated in seven patients with low-risk coronary artery disease who underwent revascularization through percutaneous coronary intervention. The participants performed a cardiopulmonary exercise test on a cycle ergometer and a single resistance exercise session at 30% of maximum voluntary contraction on a bilateral leg-extension machine 1 week after surgery. We measured the ventilatory anaerobic threshold and pulmonary oxygen uptake on-kinetics during the cardiopulmonary exercise test; left ventricular ejection fraction at rest; and heart rate, systolic blood pressure, and rate pressure product during the single resistance exercise session. [Results] Pulmonary oxygen uptake on-kinetics showed a positive association with the amount of increase in systolic blood pressure and rate pressure product during the single resistance exercise session, but had no association with the amount of increase in heart rate. Ventilatory anaerobic threshold and left ventricular ejection fraction were not associated with these parameters. [Conclusion] These data suggested that pulmonary oxygen uptake on-kinetics can be a useful evaluation index for predicting acute systolic blood pressure and rate pressure product responses to low-intensity resistance exercise 1 week after percutaneous coronary intervention in patients with low-risk coronary artery disease.

Acute Effects of Dietary Nitrate on Exercise Tolerance, Muscle Oxygenation, and Cardiovascular Function in Patients With Peripheral Arterial Disease

Previous studies have used supplements to increase dietary nitrate intake in clinical populations. Little is known about whether effects can also be induced through vegetable consumption. Therefore, the aim of this study was to assess the impact of dietary nitrate, through nitrate-rich vegetables (NRV) and beetroot juice (BRJ) supplementation, on plasma nitrate and nitrite concentrations, exercise tolerance, muscle oxygenation, and cardiovascular function in patients with peripheral arterial disease. In a randomized crossover design, 18 patients with peripheral arterial disease (age: 73 ± 8 years) followed a nitrate intake protocol (∼6.5 mmol) through the consumption of NRV, BRJ, and nitrate-depleted BRJ (placebo). Blood samples were taken, blood pressure and arterial stiffness were measured in fasted state and 150 min after intervention. Each intervention was followed by a maximal walking exercise test to determine claudication onset time and peak walking time. Gastrocnemius oxygenation was measured by near-infrared spectroscopy. Blood samples were taken and blood pressure was measured 10 min after exercise. Mean plasma nitrate and nitrite concentrations increased (nitrate; Time × Intervention interaction; p < .001), with the highest concentrations after BRJ (494 ± 110 μmol/L) compared with NRV (202 ± 89 μmol/L) and placebo (80 ± 19 μmol/L; p < .001). Mean claudication onset time and peak walking time did not differ between NRV (413 ± 187 s and 745 ± 220 s, respectively), BRJ (392 ± 154 s and 746 ± 176 s), and placebo (403 ± 176 s and 696 ± 222 s) (p = .762 and p = .165, respectively). Gastrocnemius oxygenation, blood pressure, and arterial stiffness were not affected by the intervention. NRV and BRJ intake markedly increase plasma nitrate and nitrite, but this does not translate to improved exercise tolerance, muscle oxygenation, and/or cardiovascular function.

Ergogenic Effect of Nitrate Supplementation: A Systematic Review and Meta-analysis

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Although over 100 studies and reviews have examined the ergogenic effects of dietary nitrate (NO₃⁻) supplementation in young, healthy men and women, it is unclear if participant and environmental factors modulate the well-described ergogenic effects—particularly relevant factors include biological sex, aerobic fitness, and fraction of inspired oxygen (F_iO₂) during exercise. To address this limitation, the literature was systematically reviewed for randomized, crossover, placebo-controlled studies reporting exercise performance outcome metrics with NO₃⁻ supplementation in young, healthy adults. Of the 2033 articles identified, 80 were eligible for inclusion in the meta-analysis. Random-effects meta-analysis demonstrated that exercise performance improved with NO₃⁻ supplementation compared with placebo (d = 0.174; 95% confidence interval (CI), 0.120–0.229; P < 0.001). Subgroup analyses conducted on biological sex, aerobic fitness, and F_iO₂ demonstrated that the ergogenic effect of NO₃⁻ supplementation was as follows: 1) not observed in studies with only women (n = 6; d = 0.116; 95% CI, −0.126 to 0.358; P = 0.347), 2) not observed in well-trained endurance athletes (≥65 mL·kg⁻¹·min⁻¹; n = 26; d = 0.021; 95% CI, −0.103 to 0.144; P = 0.745), and 3) not modulated by F_iO₂ (hypoxia vs normoxia). Together, the meta-analyses demonstrated a clear ergogenic effect of NO₃⁻ supplementation in recreationally active, young, healthy men across different exercise paradigms and NO₃⁻ supplementation parameters; however, the effect size of NO₃⁻ supplementation was objectively small (d = 0.174). NO₃⁻ supplementation has more limited utility as an ergogenic aid in participants with excellent aerobic fitness that have optimized other training parameters. Mechanistic research and studies incorporating a wide variety of subjects (e.g., women) are needed to advance the study of NO₃⁻ supplementation; however, additional descriptive studies of young, healthy men may have limited utility.

Effects of compression stockings on lower-limb venous and arterial system responses to prolonged sitting: A randomized cross-over trial

Exposure to prolonged sitting increases blood pooling and the risk of lower-extremity vascular arterial and venous complications, including deep vein thrombosis. Compression garment stockings (CGS) may prevent pooling, thereby mitigating the associated vascular complications. Three aims were addressed: (i) does use of CGS help to prevent blood pooling; (ii) does blood pooling correlate with decreased stroke volume; and (iii) does use of CGS preserve leg arterial flow-mediated dilation and reactive hyperemia response. Twenty inactive participants (22 ± 4 years, 30% female, 22.1 ± 2.0 kg/m2) were randomized to sit for 3 hours with (CGS) and without use of CGS. Blood pooling was determined using medial gastrocnemius total hemoglobin. Stroke volume was estimated using finger photoplethysmography, respectively. Macrovascular and microvascular function were measured using popliteal artery flow-mediated dilation and reactive hyperemia, respectively. In response to 3 hours of sitting: (i) there was an interaction effect for total hemoglobin ( p < 0.001); the condition without use of CGS increased 10.5% (95% CI: 6.7 to 14.3) and CGS increased 4.3% (95% CI: 0.1 to 7.7); (ii) blood pooling was negatively associated with stroke volume ( r = −0.58, 95% CI: −0.68 to −0.45); (iii) reactive hyperemia and flow-mediated arterial dilation was impaired after prolonged sitting, and use of CGS was not associated with attenuation of this impairment. Use of CGS decreases blood pooling but does not preserve arterial macrovascular and microvascular responses to prolonged sitting. Further study is warranted to determine whether CGS has additive benefits when combined with sitting interruption strategies.

The benefits and risks of beetroot juice consumption: a systematic review

Beetroot juice (BRJ) has become increasingly popular amongst athletes aiming to improve sport performances. BRJ contains high concentrations of nitrate, which can be converted into nitric oxide (NO) after consumption. NO has various functions in the human body, including a vasodilatory effect, which reduces blood pressure and increases oxygen- and nutrient delivery to various organs. These effects indicate that BRJ may have relevant applications in prevention and treatment of cardiovascular disease. Furthermore, the consumption of BRJ also has an impact on oxygen delivery to skeletal muscles, muscle efficiency, tolerance and endurance and may thus have a positive impact on sports performances. Aside from the beneficial aspects of BRJ consumption, there may also be potential health risks. Drinking BRJ may easily increase nitrate intake above the acceptable daily intake, which is known to stimulate the endogenous formation of N-nitroso compounds (NOC's), a class of compounds that is known to be carcinogenic and that may also induce several other adverse effects. Compared to studies on the beneficial effects, the amount of data and literature on the negative effects of BRJ is rather limited, and should be increased in order to perform a balanced risk assessment.

Dietary Nitrate and Physical Performance

Nitric oxide (NO) plays a plethora of important roles in the human body. Insufficient production of NO (for example, during older age and in various disease conditions) can adversely impact health and physical performance. In addition to its endogenous production through the oxidation of l-arginine, NO can be formed nonenzymatically via the reduction of nitrate and nitrite, and the storage of these anions can be augmented by the consumption of nitrate-rich foodstuffs such as green leafy vegetables. Recent studies indicate that dietary nitrate supplementation, administered most commonly in the form of beetroot juice, can ( a) improve muscle efficiency by reducing the O₂ cost of submaximal exercise and thereby improve endurance exercise performance and ( b) enhance skeletal muscle contractile function and thereby improve muscle power and sprint exercise performance. This review describes the physiological mechanisms potentially responsible for these effects, outlines the circumstances in which ergogenic effects are most likely to be evident, and discusses the effects of dietary nitrate supplementation on physical performance in a range of human populations.

Pulmonary oxygen uptake on-kinetics can predict acute physiological responses to resistance exercise training in healthy young men

PURPOSE

To clarify whether pulmonary oxygen uptake kinetics ( τ V ˙ O 2 p ) at the onset of moderate-intensity exercise can predict acute physiological responses to resistance exercise training (RET).

METHODS

We investigated the relationship between τ V ˙ O 2 p and acute metabolic and hemodynamic responses to a single RET session in 27 healthy young adult men. Cardiopulmonary exercise was on a cycle ergometer, and a single RET at 30% or 60% of one-repetition maximum was on a bilateral leg-extension machine. We measured the anaerobic threshold, peak V ˙ O 2 and τ V ˙ O 2 p while cardiopulmonary exercising, and the rates of increase in blood lactate (Bla), heart rate (HR), systolic blood pressure (SBP) and rate pressure product (RPP) for a single RET.

RESULTS

There were significant positive associations between τ V ˙ O 2 p and the rates of increase in Bla, HR, SBP and RPP during a single RET session (P<0·05). However, the anaerobic threshold and peak V ˙ O 2 did not significantly affect these parameters.

CONCLUSION

The τ V ˙ O 2 p is a useful evaluation index for predicting acute physiological responses to RET.

A single dose of beetroot juice improves endothelial function but not tissue oxygenation in pregnant women: a randomised clinical trial

Beetroot juice (BJ) consumption has been associated with improved cardiovascular health owing to an increase in NO bioconversion. This study evaluates the effect of BJ consumption on macrovascular endothelial function (flow-mediated dilation (FMD)) and muscle oxygen saturation (StO2) parameters in pregnant women within a randomised, crossover, double-blind design in which twelve pregnant women consumed a single dose (140 ml) of BJ or placebo (PLA). Urinary nitrate was assessed before (T0) and 150 min after BJ/PLA consumption. FMD was used to evaluate macrovascular endothelial function, and near-IR spectroscopy was used to evaluate muscle StO2 parameters during the occlusion and reperfusion phases, which were taken at baseline (PRE) and 120 and 140 min after BJ/PLA consumption, respectively. A significant increase in urinary nitrate was observed at 150 min after BJ consumption when compared with T0 (BJ: 0·20 (sd 0·13) v. T0: 0·02 (sd 0·00), P=0·000) and PLA intervention (PLA: 0·02 (sd 0·00), P=0·001). FMD improved after BJ consumption when compared with PRE (BJ: 11·00 (sd 1·67) v. PRE: 5·53 (sd 1·17), P=0·000) and PLA (5·34 (sd 1·31), P=0·000). No significant difference between PLA and PRE in FMD (P=1·000) was observed. In StO2 parameters, a difference was not observed after BJ consumption compared with PRE and PLA intervention. The data demonstrate that a single dose of 140 ml of BJ consumption improves macrovascular endothelial function, but not StO2 parameters.

Limitation of Maximal Heart Rate in Hypoxia: Mechanisms and Clinical Importance

The use of exercise intervention in hypoxia has grown in popularity amongst patients, with encouraging results compared to similar intervention in normoxia. The prescription of exercise for patients largely rely on heart rate recordings (percentage of maximal heart rate (HR_max) or heart rate reserve). It is known that HR_max decreases with high altitude and the duration of the stay (acclimatization). At an altitude typically chosen for training (2,000-3,500 m) conflicting results have been found. Whether or not this decrease exists or not is of importance since the results of previous studies assessing hypoxic training based on HR may be biased due to improper intensity. By pooling the results of 86 studies, this literature review emphasizes that HR_max decreases progressively with increasing hypoxia. The dose–response is roughly linear and starts at a low altitude, but with large inter-study variabilities. Sex or age does not seem to be a major contributor in the HR_max decline with altitude. Rather, it seems that the greater the reduction in arterial oxygen saturation, the greater the reduction in HRmax, due to an over activity of the parasympathetic nervous system. Only a few studies reported HR_max at sea/low level and altitude with patients. Altogether, due to very different experimental design, it is difficult to draw firm conclusions in these different clinical categories of people. Hence, forthcoming studies in specific groups of patients are required to properly evaluate (1) the HR_max change during acute hypoxia and the contributing factors, and (2) the physiological and clinical effects of exercise training in hypoxia with adequate prescription of exercise training intensity if based on heart rate.

Muscle oxygenation profiles between active and inactive muscles with nitrate supplementation under hypoxic exercise

Whether dietary nitrate supplementation improves exercise performance or not is still controversial. While redistribution of sufficient oxygen from inactive to active muscles is essential for optimal exercise performance, no study investigated the effects of nitrate supplementation on muscle oxygenation profiles between active and inactive muscles. Nine healthy males performed 25 min of submaximal (heart rate ~140 bpm; EX_sub) and incremental cycling (EX_max) until exhaustion under three conditions: (A) normoxia without drink; (B) hypoxia (FiO₂ = 13.95%) with placebo (PL); and (c) hypoxia with beetroot juice (BR). PL and BR were provided for 4 days. Oxygenated and deoxygenated hemoglobin (HbO₂ and HHb) were measured in vastus lateralis (active) and biceps brachii (inactive) muscles, and the oxygen saturation of skeletal muscle (StO₂; HbO₂/total Hb) were calculated. During EX_sub, BR suppressed the HHb increases in active muscles during the last 5 min of exercise. During EX_max, time to exhaustion with BR (513 ± 24 sec) was significantly longer than with PL (490 ± 39 sec, P < 0.05). In active muscles, BR suppressed the HHb increases at moderate work rates during EX_max compared to PL (P < 0.05). In addition, BR supplementation was associated with greater reductions in HbO₂ and StO₂ at higher work rates in inactive muscles during EX_max. Collectively, these findings indicate that short‐term dietary nitrate supplementation improved hypoxic exercise tolerance, perhaps, due to suppressed increases in HHb in active muscles at moderate work rates. Moreover, nitrate supplementation caused greater reductions in oxygenation in inactive muscle at higher work rates during hypoxic exercise.

Beetroot supplementation improves the physiological responses to incline walking

PURPOSE

We investigated the effects of an acute 24-h nitrate-rich beetroot juice supplement (BR) on the energy cost, exercise efficiency and blood pressure responses to intermittent walking at different gradients.

METHODS

In a double-blind, cross-over design, eight participants were provided with a total of 350 ml of nitrate-rich (~ 20.5 mmol nitrate) BR or placebo (PLA) across 24 h before completing intermittent walking at 3 km/h on treadmill at gradients of 1, 5, 10, 15 and 20%.

RESULTS

Resting mean arterial pressure (MAP) was ~ 4.1% lower after BR (93 vs. 89 mmHg; P = 0.001), as well as during exercise (102 vs. 99 mmHg; P = 0.011) and recovery (97 vs. 94 mmHg; P = 0.001). Exercising (1227 vs. 1129 ml/min P < 0.001) and end-stage (1404 vs. 1249 ml/min; P = 0.002) oxygen uptake ([Formula: see text]O₂) was lower in BR compared to PLA, which was accompanied by an average reduction in phase II [Formula: see text]O₂ amplitude (1067 vs. 940 ml/min; P = 0.025). Similarly, recovery [Formula: see text]O₂ (509 vs. 458 ml/min; P = 0.001) was lower in BR. Whole blood potassium concentration increased from pre-post exercise in PLA (4.1 ± 0.3 vs. 4.5 ± 0.3 mmol/L; P = 0.013) but not BR (4.1 ± 0.31 vs. 4.3 ± 0.2 mmol/L; P = 0.188).

CONCLUSIONS

Energy cost of exercise, recovery of [Formula: see text]O₂, MAP and blood markers were ameliorated after BR. Previously-reported mechanisms explain these findings, which are more noticeable during less-efficient walking at steep gradients (15-20%). These findings have practical implications for hill-walkers.