Muscle Oxygenation Kinetics Research Articles

Muscle oxygenation kinetics in Long COVID-19: Illness severity and clinical implications

Muscle oxygenation kinetics in Long COVID-19: Illness severity and clinical implications

Evaluation of the pulmonary and muscle oxygen kinetics in heart failure patients with reduced and preserved ejection fraction

Evaluation of the pulmonary and muscle oxygen kinetics in heart failure patients with reduced and preserved ejection fraction

Effects of Hypoxia Severity on Muscle Oxygenation Kinetics Using Statistical Parametric Mapping During Repeated Treadmill Sprints.

We examined the effects of increasing hypoxia severity on oxygenation kinetics in the vastus lateralis muscle during repeated treadmill sprints, using statistical parametric mapping (SPM). Ten physically active males completed 8 sprints of 5seconds each(recovery = 25s) on a motorized sprint treadmill in normoxia (sea level; inspired oxygen fraction = 0.21), moderate hypoxia (inspired oxygen fraction = 0.17), and severe hypoxia (SH; inspired oxygen fraction = 0.13). Continuous assessment of tissue saturation index (TSI) in the vastus lateralis muscle was conducted using near-infrared spectroscopy. Subsequently, TSI data were averaged for the sprint-recovery cycle of all sprints and compared between conditions. The SPM analysis revealed no discernible difference in TSI signal amplitude between conditions during the actual 5-second sprint phase. However, during the latter portion of the 25-second recovery phase, TSI values were lower in SH compared with both sea level (from 22 to 30s; P = .003) and moderate hypoxia (from 16 to 30s; P = .001). The mean distance covered at sea level (22.9 [1.0]m) was greater than for both moderate hypoxia (22.5 [1.2]m; P = .045) and SH (22.3 [1.4]m; P = .043). The application of SPM demonstrated that only SH reduced muscle oxygenation levels during the late portion of the passive (recovery) phase and not the active (sprint) phase during repeated treadmill sprints. These findings underscore the usefulness of SPM for assessing muscle oxygenation differences due to hypoxic exposure and the importance of the duration of the between-sprints recovery period.

A systematic review of the relationship between muscle oxygen dynamics and energy rich phosphates. Can NIRS help?

BackgroundPhosphocreatine dynamics provide the gold standard evaluation of in-vivo mitochondrial function and is tightly coupled with oxygen availability. Low mitochondrial oxidative capacity has been associated with health issues and low exercise performance.MethodsTo evaluate the relationship between near-infrared spectroscopy-based muscle oxygen dynamics and magnetic resonance spectroscopy-based energy-rich phosphates, a systematic review of the literature related to muscle oxygen dynamics and energy-rich phosphates was conducted. PRISMA guidelines were followed to perform a comprehensive and systematic search of four databases on 02-11-2021 (PubMed, MEDLINE, Scopus and Web of Science). Beforehand pre-registration with the Open Science Framework was performed. Studies had to include healthy humans aged 18–55, measures related to NIRS-based muscle oxygen measures in combination with energy-rich phosphates. Exclusion criteria were clinical populations, laboratory animals, acutely injured subjects, data that only assessed oxygen dynamics or energy-rich phosphates, or grey literature. The Effective Public Health Practice Project Quality Assessment Tool was used to assess methodological quality, and data extraction was presented in a table.ResultsOut of 1483 records, 28 were eligible. All included studies were rated moderate. The studies suggest muscle oxygen dynamics could indicate energy-rich phosphates under appropriate protocol settings.ConclusionArterial occlusion and exercise intensity might be important factors to control if NIRS application should be used to examine energetics. However, more research needs to be conducted without arterial occlusion and with high-intensity exercises to support the applicability of NIRS and provide an agreement level in the concurrent course of muscle oxygen kinetics and muscle energetics.Trial registrationhttps://osf.io/py32n/.Key points1. NIRS derived measures of muscle oxygenation agree with gold-standard measures of high energy phosphates when assessed in an appropriate protocol setting.2. At rest when applying the AO protocol, in the absence of muscle activity, an initial disjunction between the NIRS signal and high energy phosphates can been seen, suggesting a cascading relationship.3. During exercise and recovery a disruption of oxygen delivery is required to provide the appropriate setting for evaluation through either an AO protocol or high intensity contractions.

The Influence of Acute Hypoxia on Oxygen Uptake and Muscle Oxygenation Kinetics During Cycling Exercise in Prepubertal Boys.

To examine the effect of normobaric hypoxia on pulmonary oxygen uptake (V˙O2) and muscle oxygenation kinetics during incremental and moderate-intensity exercise in children. Eight prepubertal boys (9-11y)performed incremental cycle tests to exhaustion in both normoxia and hypoxia (fraction of inspired O2 of 15%) followed by repeat 6-minute transitions of moderate-intensity exercise in each condition over subsequent visits. Maximal oxygen uptake (V˙O2max) was reduced in hypoxia compared with normoxia (1.69 [0.20] vs 1.87 [0.26]L·min-1, P = .028), although the gas exchange threshold was not altered in absolute terms (P = .33) or relative to V˙O2max (P = .78). During moderate-intensity exercise, the phase II V˙O2 time constant (τ) was increased in hypoxia (18 [9] vs 24 [8]s, P = .025), with deoxyhemoglobin τ unchanged (17 [8] vs 16 [6], P ≥ .28). In prepubertal boys, hypoxia reduced V˙O2max and slowed V˙O2 phase II kinetics during moderate-intensity exercise, despite unchanged deoxyhemoglobin kinetics. These data suggest an oxygen delivery dependence of V˙O2max and moderate-intensity V˙O2 kinetics under conditions of reduced oxygen availability in prepubertal boys.

Load carriage physiology in normoxia and hypoxia

PurposeTo determine the effects of load carriage in normoxia and normobaric hypoxia on ventilatory responses, hemodynamics, tissue oxygenation, and metabolism.MethodsHealthy males (n = 12) completed 3 randomly ordered baseline graded exercise tests in the following conditions: (1) unloaded normoxic (U: FIO2 = 20.93%), (2) loaded (~ 30 kg) normoxic (LN), and (3) loaded hypoxic simulating ~ 3650 m (LH: FIO2 = ~ 13%). Thereafter, experimental exercise trials were completed in quasi-randomized order (i.e., U completed first) consisting of 3 × 10 min of walking (separated by 5 min seated rest) with stages matched with the U condition (in ascending order) for relative intensity, absolute oxygen consumption ([VO2]; 1.7 L min−1), and walking speed (1.45 ± 0.15 m s−1).ResultsLoad carriage increased perceived exertion and reduced VO2max (LN: − 7%; LH: − 32%; p < 0.05). At matched VO2, stroke volume and tidal volume were reduced and maintained with LN and LH vs. U, respectively (p < 0.05). Increases in cardiac output and minute ventilation at matched VO2 (with LH) and speed (with LN and LH), were primarily accomplished via increases in heart rate and breathing frequency (p < 0.05). Cerebral oxygenated hemoglobin (O2HHb) was increased at all intensities with LN, but deoxygenated hemoglobin and total hemoglobin were increased with LH (p < 0.05). Muscle oxygen kinetics and substrate utilization were similar between LN and U, but LH increased CHO dependence and reduced muscle O2HHb at matched speed (p < 0.05).ConclusionLoad carriage reduces cardiorespiratory efficiency and increases physiological strain, particularly in hypoxic environments. Potential load carriage-induced alterations in cerebral blood flow may increase the risk for altitude illnesses and requires further study.

PD24-04 DETECTION OF PELVIC FLOOR MUSCLE ACTIVITY AND QUANTIFICATION OF OXYGEN KINETICS IN WOMEN WITH SPINAL CORD INJURY AND NEUROGENIC LOWER URINARY TRACT DYSFUNCTION

You have accessJournal of UrologyCME1 May 2022PD24-04 DETECTION OF PELVIC FLOOR MUSCLE ACTIVITY AND QUANTIFICATION OF OXYGEN KINETICS IN WOMEN WITH SPINAL CORD INJURY AND NEUROGENIC LOWER URINARY TRACT DYSFUNCTION Lynn Stothers, and Andrew Macnab Lynn Stothers Lynn Stothers More articles by this author , and Andrew MacnabAndrew Macnab More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000002566.04AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Paralysis and changes in sensation following spinal cord injury (SCI) are a significant barrier to the performance and quantification of pelvic floor muscle (PFM) exercise in women, although international guidelines recommend PFM therapy. Aims: (1) to translate for use in PFM evaluation, a validated optical measure of oxygen kinetics used in sports medicine which uses near infrared (NIR) spectroscopy to quantify the half recovery time of reoxygenation (HbDiff(½RT)) following sustained maximal voluntary muscle contraction (SMVC), and (2) design and test a vaginal interface incorporating NIRS technology specific to the needs of women with compromised PFM function due to SCI. METHODS: The vaginal interface (fig left) incorporates 4 NIRS emitter detector arrays; photons of NIR light (wavelengths 825, 950, 1000 nm) monitor changes in oxygenated and deoxygenated hemoglobin (O2Hb/HHb) at capture rates of 10 Hz during PFM muscle contractions. The study protocol included clinical assessment, bladder diary and Qualiveen symptom scores and perineometry, plus changes in O2Hb/HHb at rest and during PFM rehabilitation exercises. The absolute measure HbDiff(½RT) is derived from the slope of reoxygenation following release of each SMVC. RESULTS: N=15 women aged 25-59 yrs (5 controls, 10 SCI ASIA B, C, D) completed 4 weeks of PFMT; HbDiff(½RT) data sets were compared within individuals and between clinical groups. Repeatability of patterns of recovery were demonstrable within individuals (fig right). CONCLUSIONS: HbDiff(½RT) is a quantifiable absolute measure of skeletal muscle oxygen kinetics; use of the vaginal interface allows individual elements of the PFM to be evaluated; the ability to quantify right and left sided function independently is particularly relevant in women with PFM dysfunction due to partial SCI. Translation of measurement of HbDiff(½RT) to the PFM now allows a validated muscle reoxygenation parameter to be applied in evaluation of PFM dysfunction following SCI in women, and offers a means to quantify clinical training effects from rehabilitation exercise in NLUTD. Source of Funding: Craig Neilsen Foundation © 2022 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 207Issue Supplement 5May 2022Page: e416 Advertisement Copyright & Permissions© 2022 by American Urological Association Education and Research, Inc.MetricsAuthor Information Lynn Stothers More articles by this author Andrew Macnab More articles by this author Expand All Advertisement PDF DownloadLoading ...

Sex-specific muscle activation and oxygenation kinetics during a repetitive forward pointing task.

We compared the minute-by-minute muscle activity and oxygenation responses to a repetitive arm motion-induced fatiguing task between the sexes in order to address the literature gap on these time-dependent fatigue responses. Twenty-six (13 females) healthy adults performed a repetitive pointing task (RPT) with the arm moving forward/backward at shoulder height until reaching 8/10 (Borg CR10) for neck/shoulder perceived exertion (RPE). Neck/shoulder RPE, oxygenation and electromyography were recorded every minute and compared between first and second half of the task and between the sexes. Greater changes in oxygen supply and activation amplitude occurred during the second half of the task. Despite similar time to fatigue-terminal (p > 0.05), females showed greater anterior deltoid activation amplitude at all time points than males, and only the males showed increases in anterior and posterior deltoid activation amplitudes. In females, middle (ρ = -0.34, p = 0.04) and posterior (ρ = -0.44, p = 0.01) deltoid amplitudes were negatively correlated with perceived exertion during the first half of the task. Results suggest that reduced modulation of anterior deltoid activation amplitude in females may reflect a sub-optimal fatigue-mitigation mechanism compared with males and may help explain their greater susceptibility to neck/shoulder musculoskeletal disorders. Novelty: Despite similar fatigability and trapezius oxygenation, females showed greater deltoid activation throughout the task. Deltoid activation increased in males but not in females. The results support the important role of the deltoid in sex-specific neck/shoulder injury mechanisms.

Comparison of cardiopulmonary function and local skeletal muscle oxygenation kinetics in female medium- or long-distance runners and nonathletes

Comparison of cardiopulmonary function and local skeletal muscle oxygenation kinetics in female medium- or long-distance runners and nonathletes

Heart Rate and Muscle Oxygenation Kinetics During Dynamic Constant Load Intermittent Breath-Holds.

Introduction: Acute apnea evokes bradycardia and peripheral vasoconstriction in order to conserve oxygen, which is more pronounced with face immersion. This response is contrary to the tachycardia and increased blood flow to muscle tissue related to the higher oxygen consumption during exercise. The aim of this study was to investigate cardiovascular and metabolic responses of dynamic dry apnea (DRA) and face immersed apnea (FIA).Methods: Ten female volunteers (17.1 ± 0.6 years old) naive to breath-hold-related sports, performed a series of seven dynamic 30 s breath-holds while cycling at 25% of their peak power output. This was performed in two separate conditions in a randomized order: FIA (15°C) and DRA. Heart rate and muscle tissue oxygenation through near-infrared spectroscopy were continuously measured to determine oxygenated (m[O2Hb]) and deoxygenated hemoglobin concentration (m[HHb]) and tissue oxygenation index (mTOI). Capillary blood lactate was measured 1 min after the first, third, fifth, and seventh breath-hold.Results: Average duration of the seven breath-holds did not differ between conditions (25.3 s ± 1.4 s, p = 0.231). The apnea-induced bradycardia was stronger with FIA (from 134 ± 4 to 85 ± 3 bpm) than DRA (from 134 ± 4 to 100 ± 5 bpm, p < 0.001). mTOI decreased significantly from 69.9 ± 0.9% to 63.0 ± 1.3% (p < 0.001) which is reflected in a steady decrease in m[O2Hb] (p < 0.001) and concomitant increase in m[HHb] (p = 0.001). However, this was similar in both conditions (0.121 < p < 0.542). Lactate was lower after the first apnea with FIA compared to DRA (p = 0.038), while no differences were observed in the other breath-holds.Conclusion: Our data show strong decreases in heart rate and muscle tissue oxygenation during dynamic apneas. A stronger bradycardia was observed in FIA, while muscle oxygenation was not different, suggesting that FIA did not influence muscle oxygenation. An order of mechanisms was observed in which, after an initial tachycardia, heart rate starts to decrease after muscle tissue deoxygenation occurs, suggesting a role of peripheral vasoconstriction in the apnea-induced bradycardia. The apnea-induced increase in lactate was lower in FIA during the first apnea, probably caused by the stronger bradycardia.

Oxyhemoglobin Concentration and Oxygen Uptake Signal During Recovery From Exhaustive Exercise in Healthy Subjects-Relationship With Aerobic Capacity.

This proof of concept study is dedicated to the quantification of the short-term recovery phase of the muscle oxygenation and whole-body oxygen uptake kinetics following an exhaustive cycling protocol. Data of 15 healthy young participants (age 26.1 ± 2.8 years, peak oxygen uptake 54.1 ± 5.1 mL∗min-1∗kg-1) were recorded during 5 min cool down-cycling with a power output of 50 W on an electro-magnetically braked cycle ergometer. The oxygen uptake (VO2) signal during recovery was modeled by exponential function. Using the model parameters, the time (T1/2) needed to return VO2 to 50% of VO2peak was determined. The Hill’s model was used to analyze the kinetics of oxyhemoglobin concentration (Sm, %), non-invasively recorded by near-infrared spectroscopy (NIRS) over the M. vastus lateralis. Analysis of the Pearson correlation results in statistically significant negative relationships between T1/2 and relative VO2peak (r = −0.7). Relevant significant correlations were determined between constant defining the slope of VO2 decrease (parameter B) and the duration of the anaerobic phase (r = −0.59), as well as between Hill’s coefficient and average median Smmax for the final 2 min of recovery. The high correlation between traditional variables commonly used to represent the cardio-metabolic capacity and the parameters of fits from exponential and Hill models attests the validity of our approach. Thus, proposed descriptors, derived from non-invasive NIRS monitoring during recovery, seem to reflect aerobic capacity. However, the practical usefulness of such modeling for clinical or other vulnerable populations has to be explored in studies using alternative testing protocols.

Patients with complex congenital heart disease have slower calf muscle oxygenation during exercise

BackgroundPeripheral muscle factors are presumed to be contributors to the reduced exercise capacity in congenital heart disease (CHD), but the underlying mechanisms are poorly understood. The aim was to investigate if muscle oxygenation, at rest and during exercise, and the resting blood flow in the calf muscle is impaired in adults with complex CHD in comparison to controls. MethodSeventy-four adults with complex CHD (35.6 ± 14.3 years, females n = 22 [30%], males n = 52 [70%]) and seventy-four age and sex matched subjects were recruited. Muscle oxygenation was successfully determined using near-infrared spectroscopy on the medial portion of m. gastrocnemius in 63 patients and 67 controls. Measurements were made at rest, during venous occlusion to estimate blood flow (indicated by slope increase of total haemoglobin, HbT), and post arterial occlusion. Additionally, measurements were made at the onset of isotonic unilateral heel-lifts to exhaustion and during recovery post exercise. ResultsAdults with CHD had a slower desaturation rate at exercise onset (−7.7 ± 4.3%StO2x3.5sec−1vs. −11.7 ± 5.8%StO2x3.5sec−1, p < 0.001) a slower half recovery time (28.6 ± 21.2s vs. 16.8 ± 11.1s, p < 0.001) and a slower resaturation rate post exercise in comparison to the control subjects (3.9 ± 3.7%StO2x3.5sec−1vs. 6.1 ± 3.8%StO2x3.5sec−1, p = 0.002). In contrast, there were no differences in muscle oxygen kinetics at rest. ConclusionSlower muscle oxygenation kinetics during muscle exercise found in adults with complex CHD may give insight to the mechanisms for the reduced exercise capacity commonly found in this population. This finding may also provide implications for design of exercise training programs targeting muscle function for these patients.

Isolated finger flexor vs. exhaustive whole-body climbing tests? How to assess endurance in sport climbers?

Sport climbing requires high-intensity finger flexor contractions, along with a substantial whole-body systemic oxygen uptake ([Formula: see text]O2) contribution. Although fatigue is often localised to the finger flexors, the role of systemic ̇[Formula: see text]O2 and local aerobic mechanisms in climbing performance remains unclear. As such, the primary purpose of this study was to determine systemic and local muscle oxygen responses during both isolated finger flexion and incremental exhaustive whole-body climbing tests. The secondary aim was to determine the relationship of isolated and whole-body climbing endurance tests to climbing ability. Twenty-two male sport climbers completed a series of isometric sustained and intermittent forearm flexor contractions, and an exhaustive climbing test with progressive steepening of the wall angle on a motorised climbing ergometer. Systemic [Formula: see text]O2 and flexor digitorum profundus oxygen saturation (StO2) were recorded using portable metabolic analyser and near-infra red spectroscopy, respectively. Muscle oxygenation breakpoint (MOB) was identifiable during an incremental exhaustive climbing test with progressive increases in angle (82 ± 8% and 88 ± 8% [Formula: see text]O2 and heart rate climbing peak). The peak angle from whole-body treadwall test and impulse from isolated hangboard endurance tests were interrelated (R2 = 0.58-0.64). Peak climbing angle together with mean [Formula: see text]O2 and StO2 from submaximal climbing explained 83% of variance in self-reported climbing ability. Both systemic and muscle oxygen kinetics determine climbing-specific endurance. Exhaustive climbing and isolated finger flexion endurance tests are interrelated and suitable to assess climbing-specific endurance. An exhaustive climbing test with progressive wall angle allows determination of the MOB.

Effect of Blood Flow on Hemoglobin and Myoglobin Oxygenation in Contracting Muscle Using Near-Infrared Spectroscopy.

Insufficient O2 delivery to, and uptake by skeletal muscle can produce mobility limitations for patients with chronic diseases. Near-infrared spectroscopy (NIRS) can be used to noninvasively quantify the balance between skeletal muscle O2 delivery and utilization during contraction. However, it is not clear how the oxygenated or deoxygenated NIRS signal should be used to assess muscle O2 changes. This issue is related to the fact that the contributions of hemoglobin (Hb) and myoglobin (Mb) cannot be distinguished. This conundrum can be resolved by quantitative analysis of experimental data by computer simulations with a mechanistic, mathematical model. Model simulations distinguish dynamic responses of the oxygenated (HbO2, MbO2) and deoxygenated (HHb, HMb) contributions to the NIRS signal components (HbMbO2, HHbMb). Simulations of muscle O2 uptake and NIRS kinetics correspond closely to published experimental data (Hernández et al.,J Appl Physiol 108: 1169-1176, 2010). Simulated muscle O2 uptake and oxygenation kinetics with different blood flows indicate (1) faster O2 delivery is responsible for slower muscle oxygenation kinetics; (2) Hb and Mb contributions to the HbMbO2 are similar (40-60%); and (3) Hb and Mb contributions to the HHbMb are significantly different, 80% and 20%, respectively. The effect of slow blood flow kinetics on oxygenated Hb and Mb contributions is minimal. However, the effect on the imbalance between O2 delivery and utilization rates causes significant overshoots and undershoots of deoxygenated Hb and Mb contributions. Model analysis in combination with NIRS measurements and information on hemodynamic and microvascular distribution can help to determine the use of NIRS signal in evaluating the factors limiting exercise tolerance in health and disease states.

Efficiency of Pneumatic Tourniquet Cuff With Asymmetric Pressure Distribution at Rest and During Isometric Muscle Action

Ipavec, M, Grapar Žargi, T, Jelenc, J, and Kacin, A. Efficiency of pneumatic tourniquet cuff with asymmetric pressure distribution at rest and during isometric muscle action. J Strength Cond Res 33(9): 2570-2578, 2019-The aim of this study was to compare effects of newly designed double-chamber cuff with asymmetric pressure (APC) distribution and standard single-chamber cuff with symmetric pressure (SPC) distribution on muscle perfusion and volitional activation. First, the 2 cuffs were compared bilaterally on resting thigh muscles of 17 healthy volunteers at 4 cuff pressures (120, 160, 200, and 240 mm Hg). Then, the subjects performed the isometric endurance test of knee extensor muscles to volitional failure at 40% of maximal volitional isometric action in both free-flow and blood flow restricted condition. Changes in hemoglobin kinetics in vastus lateralis muscle (near-infrared spectroscopy), surface electromyography of vastus medialis muscle, and pain intensity (visual analogue scale [VAS]) were continuously recorded. At rest, a significant difference (p = 0.009) in velocity of change in total hemoglobin concentration was noted between the cuffs at 160 mm Hg (APC = 0.028 μM·s and SPC = 0.056 μM·s). The VAS scores significantly increased (p = 0.031) at pressures ≥200 mm Hg, with no difference between the cuffs. Duration of isometric action with blood flow restriction was 12% shorter (p = 0.003) than in free-flow condition, with no difference between the cuffs. There were no significant differences in muscle activation or hemoglobin kinetics between the exercise conditions or cuff types. The results show that APC reduces blood flow in quadriceps femoris muscle at rest at lower pressure than SPC, which suggests its enhanced efficiency for blood flow restriction. Given that application of either type of cuff during sustained isometric action had only minor impact on muscle endurance and oxygen kinetics, future research must focus primarily on dynamic muscle actions.

Comparing Physiological Responses to Single and Double Leg Submaximal Cycling in Normoxia and Hypoxia

INTRODUCTION:It has been well established that exercise intensity as well as exercise performance declines at altitude. However, it has yet to be determined how femoral blood flow and muscle oxygenation kinetics (total tissue saturation, oxy- and deoxygenated hemoglobin, as well as total hemoglobin) are influenced by altitude during submaximal and maximal performances. Furthermore, it has yet to be determined if the utilization of small muscle mass exercise, which allows for greater blood flow to the active muscle, will allow an individual to generate the same muscle oxygenation kinetics in hypoxic conditions that is achieved during larger muscle mass activities in normoxia. PURPOSE: Thus, the purpose of this study was to determine if tissue oxygenation was compromised at altitude during submaximal bouts of exercise and whether reducing the active muscle mass exercise could be used to offset any observed decrement due to increases in blood flow. METHODS: 10 individuals performed double leg cycling for four minutes at 50%, 60%, 70% and 80% of their maximal oxygen consumption, rested for 15 minutes and then performed single leg cycling utilizing the same protocol but at half the double leg work rate in both normoxic and hypoxic conditions (oxygen concentration of 15% which simulated an altitude of 2,740 meters). RESULTS: The amount of blood flow during the single leg trial in hypoxia was significantly higher compared to blood flow during double leg cycling in hypoxia (p = 0.02). There was no significant difference between the single leg trial in hypoxia and the double leg trial in normoxia (p = 0.36) nor between the two double leg trials in normoxia and hypoxia (p = 0.87). No difference was found in the amount of oxygenated hemoglobin when comparing the single leg trial in hypoxia to the double leg trials in normoxia (p = 0.36) and hypoxia (p = 0.13). CONCLUSIONS: The results suggest that elevated hemoglobin saturation and femoral blood flow during the single leg condition in hypoxia are similar to that observed during double leg cycling in normoxia and may prove to be a viable training modality that would offset the main disadvantage of living at altitude by enabling an individual to exercise at the same level of intensity achieved at normoxia.

Skeletal Muscle Oxygen Kinetics During Exercise In Adults With Obstructive Sleep Apnea.

Obstructive sleep apnea (OSA) is associated with persistent and progressive nighttime sympathetic nervous system (SNS) arousal strain in response to both hypopnea and apnea events. This repetitive strain of nighttime activation of the SNS may promote daytime hyperactivity, possibly limiting microvascular reactivity. PURPOSE: The purpose of this study was to examine the on-kinetic profile of muscle deoxygenation during sub-maximal walking in adults with OSA. METHODS: Twelve adults with OSA (age=48±10years, BMI=29±5kg/m2, Apnea–hypopnea index (AHI)=50±24) and 12 healthy non-OSA (NO) adults (42±8years, BMI=24±3kg/m2) completed two 6-minute bouts of submaximal exercise on a motorized treadmill, corresponding to 85% of anaerobic threshold. Using near-infrared spectroscopy (NIRS), concentration changes in deoxygenated hemoglobin-myoglobin (∆[HHb]) was measured continuously from the left lateral gastrocnemius muscle. The two bouts were averaged to form a single ∆[HHb] response profile per subject. Indices of ∆[HHb] on-kinetics include the time constant (τ), ∆[HHb] amplitude (∆[HHb]amp), and mean response time (MRT=time delay+τ). In addition, the transition constant (Kt=∆[HHb]amp/MRT) reflects the overall normalized rate of ∆[HHb] on-kinetics. Data were compared using age, BMI, gender, race, total physical activity and sleep duration as covariates for ANCOVA. RESULTS: Both τ and MRT did not differ between the groups (OSA:19.8±8.2s, NO:19.4±4.4s, p=0.835; and OSA:28.9±7.2s, NO:24.4±5.9s, p=0.515 respectively). However, ∆[HHb]amp and Kt were lower in OSA compared to NO (OSA:2.8 ±2a.u., NO:8.7±5.3a.u., p=0.011; and OSA:0.101±0.07a.u/s, NO:0.354±0.17a.u./s, p=0.002, respectively). Further, the multivariate regression analysis showed that AHI was a strong predictor of and was negatively associated with ∆[HHb]amp as well as Kt (p=0.015 and p=0.019 respectively). CONCLUSION: The lower normalized response rate of muscle deoxygenation may be reflective of impaired capability of the muscle to extract/utilize oxygen, which may contribute towards a decreased ability to sustain physical activity. Disease severity was also directly related to the normalized ∆[HHb] response rate, which has implications for physical activity participation in persons with OSA.

Slower Skeletal Muscle Oxygenation Kinetics in Adults With Complex Congenital Heart Disease

BackgroundAdults with complex congenital heart disease (CHD) show reduced aerobic exercise capacity and impaired skeletal muscle function compared with healthy peers. Peripheral muscle factors are presumed to be important contributors to the aerobic capacity, but the mechanisms are poorly understood. The aim of the present study was to investigate differences between adults with CHD and controls in muscle oxygenation kinetics at rest, and during and after exercise. MethodsSeventy-four patients with complex CHD (mean age 35.6 ± 14.3 years, female n = 22) were recruited. Seventy-four age- and sex-matched subjects were recruited as controls. Muscle oxygenation was successfully determined on the anterior portion of the deltoid muscle using near-infrared spectroscopy in 65 patients and 71 controls. Measurements were made at rest, during isotonic shoulder flexions (0-90°) to exhaustion, and during recovery. ResultsThe patients with CHD performed fewer shoulder flexions (40 ± 17 vs 69 ± 40; P < 0.001), had lower muscle oxygen saturation (StO2) at rest (58 ± 18% vs 69 ± 18%; P < 0.001), slower desaturation rate at exercise onset (−9.7 ± 5.9 vs −15.1 ± 6.5% StO2 × 3.5 s−1, P <0.001), and slower resaturation rate post exercise (4.0 ± 2.7 vs 5.4 ± 3.6% StO2 × 3.5 s−1; P = 0.009) compared with the controls. ConclusionsIn comparison with age- and sex-matched controls, adults with complex CHD had slower oxygenation kinetics. This altered skeletal muscle metabolism might contribute to the impaired skeletal muscle endurance capacity shown and thereby also to the reduced aerobic capacity in this population.

Lower limb ischemic preconditioning combined with dietary nitrate supplementation does not influence time-trial performance in well-trained cyclists

ObjectivesDietary nitrate (NO3−) supplementation and ischaemic preconditioning (IPC) can independently improve exercise performance. The purpose of this study was to explore whether NO3− supplementation, ingested prior to an IPC protocol, could synergistically enhance parameters of exercise. DesignDouble-blind randomized crossover trial. MethodsTen competitive male cyclists (age 34±6years, body mass 78.9±4.9kg, V⋅O2peak 55±4 mLkgmin−1) completed an incremental exercise test followed by three cycling trials comprising a square-wave submaximal component and a 16.1km time-trial. Oxygen uptake (V⋅O2) and muscle oxygenation kinetics were measured throughout. The baseline (BASE) trial was conducted without any dietary intervention or IPC. In the remaining two trials, participants received 3×5min bouts of lower limb bilateral IPC prior to exercise. Participants ingested NO3−-rich gel (NIT+IPC) 90min prior to testing in one trial and a low NO3− placebo in the other (PLA+IPC). Plasma NO3− and nitrite (NO2−) were measured immediately before and after application of IPC. ResultsPlasma [NO3−] and [NO2−] were higher before and after IPC in NIT+IPC compared to BASE (P<0.001) but did not differ between BASE and PLA+IPC. There were no differences in V⋅O2 kinetics or muscle oxygenation parameters between trials (all P>0.4). Performance in the time-trial was similar between trials (BASE 1343±72s, PLA+IPC 1350±75s, NIT+IPC 1346±83s, P=0.98). ConclusionsPre-exercise IPC did not improve sub-maximal exercise or performance measures, either alone or in combination with dietary NO3− supplementation.

Muscle Oxygenation &amp; Systemic Metabolic Responses during Maximal Sprint Exercise in Hypoxia among Athletes

The influence of maximal sprint exercise in moderate hypoxia on muscle oxygenation and systemic metabolic responses has not been fully elucidated. PURPOSE: The purpose of the present study was to determine the effects of maximal sprint exercise in moderate hypoxia on muscle oxygenation, systemic oxygen uptake and power output among competitive athletes. METHODS: Seven sprinters (height; 176.1 ± 2.2 cm, body weight; 67.8 ± 3.4 kg, BMI; 22.6 ± 0.7 kg/m2) participated. They performed two trials under either hypoxic (HYP, FiO2: 14.5%, a simulated altitude of 3000m) or normoxic (NOR, FiO2: 20.9%) conditions in a randomized, with a single-blind and crossover design. The exercise in each trial consisted of three consecutive sets of 20-s maximal sprints with a 5 min rest period between sets. Time-course changes in percutaneous oxygen saturation (SpO2), power output during exercise, blood lactate, glucose concentrations, and muscle oxygenation [oxy-hemoglobin (Hb), deoxy-Hb, total-Hb], and respiratory variables were evaluated. RESULTS: A significant main effect of number of set was observed for mean power output during exercise (P<0.01). However, no significant interaction (trial × number of set, P=0.76) or main effect of trial (P=0.66) for mean power output was observed. There were significant main effects of trial (P<0.01) and time (P<0.01) for blood lactate concentration, and post-exercise blood lactate concentrations were significantly higher in the HYP (22.8 ± 0.6 mmol/L) than in the NOR (20.0 ± 0.7 mmol/L, P<0.05). Both trials showed significant increases in deoxy-Hb and total-Hb during the exercise (main effect of time, P<0.01). However, deoxy-Hb and total-Hb tended to be higher in the HYP during the latter sets of sprint. Accumulated VO2 during exercise was significantly lower in the HYP (1419 ± 76 ml) than in the NOR (1973 ± 120 ml, P<0.01), whereas accumulated VCO2 was not significantly different between the trials (main effect of trial, P=0.65). CONCLUSION: No apparent difference in muscle oxygenation kinetics during maximal sprint exercise was found between hypoxic and normoxic conditions. However, exercise-induced elevations of muscle deoxygenation (deoxy-Hb) tended to be augmented under hypoxic condition.