Muscle Oxygen Consumption Research Articles

The cost of muscle power production: muscle oxygen consumption per unit work increases at low temperatures inXenopus laevisDaudin

Metabolic energy (ATP) supply to muscle is essential to support activity and behaviour. It is expected, therefore, that there is strong selection to maximise muscle power output for a given rate of ATP use. However, the viscosity and stiffness of muscle increases with a decrease in temperature, which means that more ATP may be required to achieve a given work output. Here, we tested the hypothesis that ATP use increases at lower temperatures for a given power output in Xenopus laevis. To account for temperature variation at different time scales, we considered the interaction between acclimation for 4 weeks (to 15 or 25°C) and acute exposure to these temperatures. Cold-acclimated frogs had greater sprint speed at 15°C than warm-acclimated animals. However, acclimation temperature did not affect isolated gastrocnemius muscle biomechanics. Isolated muscle produced greater tetanus force, and faster isometric force generation and relaxation, and generated more work loop power at 25°C than at 15°C acute test temperature. Oxygen consumption of isolated muscle at rest did not change with test temperature, but oxygen consumption while muscle was performing work was significantly higher at 15°C than at 25°C, regardless of acclimation conditions. Muscle therefore consumed significantly more oxygen at 15°C for a given work output than at 25°C, and plastic responses did not modify this thermodynamic effect. The metabolic cost of muscle performance and activity therefore increased with a decrease in temperature. To maintain activity across a range of temperature, animals must increase ATP production or face an allocation trade-off at lower temperatures. Our data demonstrate the potential energetic benefits of warming up muscle before activity, which is seen in diverse groups of animals such as bees, which warm flight muscle before take-off, and humans performing warm ups before exercise.

Use of NIRS to assess effect of training on peripheral muscle oxygenation changes in elite rugby players performing repeated supramaximal cycling tests.

In most team sports, intermittent high intensity sprint efforts combined with short recovery periods have been identified as a key factor of physical performance; the ability to repeat these efforts at a sustained level is of great importance. Near-infrared spectroscopy (NIRS) has been proposed as a tool to monitor muscle oxygenation changes during such sprint efforts. The purpose of this study was to observe muscle reoxygenation rate (reoxy rate) (% s⁻¹) between sprint efforts in a repeat sprint cycle test. A two wavelength spatially resolved NIR spectrometer (Portamon, Artinis Inc.) was used to assess reoxy rate changes in the vastus lateralis of the dominant leg before and after a training stimulus. Eight UK premiership academy level rugby players were assessed (age 20.6 ± 0.9) years; height 187 ± 0.6 cm; weight 109.5 ± 8.6 kg; quadriceps skin fold 16.6 ± 4.5 mm); the subjects completed ten repeated 10-s cycle sprints interspersed with 40 s recovery, upon a Wattbike Pro cycle. Hemoglobin variables (ΔHHb, ΔtHb, ΔO₂Hb, ΔTSI %) during the sprint and the post-sprint reoxygenation rate (%TSI s⁻¹) were measured. During both cycle tests all subjects experienced a drop in muscle oxygen saturation (Pre-Δ - 12.39 ± 6.01 %), Post-Δ - 14.83 ± 3.88 %). Post-training, there was an increase in the extent of desaturation (drop in TSI %) in the group means, both for the biggest single change and the average of all ten changes. Seven out of eight players showed an increase based on the maximum change and six based on the average of their ten tests. Additionally, seven out of eight players showed a significant increase in ΔHHb (Pre-Δ + 76.80 ± 61.92, Post-Δ + 121.28 ± 69.76) (p < 0.01) (including the one player who did not show a significant effect on the TSI measure). Players who exercised at the highest power tended to decrease their muscle oxygenation to a greater extent. The number of bike training sessions undertaken correlated with improvements in post-exercise recovery of oxygenation (R = 0.63). The simplest explanation for the increase in desaturation following training is an increase in muscle oxygen consumption due to an increase in mitochondrial content. This results in an increased extraction of delivered oxygen as confirmed by the HHb data. In conclusion, NIRS is able to measure positive training effects on muscle oxygen extraction, at the level of the individual elite athlete.

Intrinsic cardiac adrenergic (ICA) cell density and MAO-A activity in failing rat hearts

The efficiency (work/oxygen consumption) of isolated papillary muscles from failing hearts is reduced. We investigated whether this can be due to an increase of intrinsic cardiac adrenergic (ICA) cell density. The number of ICA cells in the septum and both ventricular walls was determined by tyrosine hydroxylase immunohistochemistry in rats with monocrotaline-induced pulmonary hypertension. We found that the number of ICA cells is about 200,000 per rat heart. ICA cell density was significantly lower in right ventricular myocardium of hypertrophied hearts (P < 0.01). MAO-A enzyme histochemistry and inhibition experiments with clorgyline in papillary muscles were performed to localize the enzyme and to determine its oxygen consumption. Upregulation of MAO-A was found in the right ventricular wall and papillary muscles of failing hearts (P = 0.018). A positive correlation between ICA cell density and MAO-A activity was absent. Clorgyline (2 μM) decreased the basal rate of oxygen consumption of right ventricular papillary muscles by 65 μM O(2)/s (P = 0.027). This rate can only be maintained for several seconds judging from the catecholamine content of the preparations reported previously. High ICA cell activity rather than density and/or recycling of oxidized catecholamines are discussed as alternative explanations for the low myocardial efficiency in experimental pulmonary hypertension.

The comparison of dexmedetomidine and morphine on respiratory mechanics in patients with chronic obstructive pulmonary disease during mechanical ventilation

Objective To study the effect of dexmedetomidine(DEX) and morphine hydrochloride on respiratory mechanics in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD) undergoing mechanical ventilation.Methods Forty patients of AECOPD with respiratory failure undergoing mechanically ventilated were randomly divided into two groups (n=20).The control group were treated with morphine for sedation while the experimental group with DEX.APACHE Ⅱ score,bispectral index (BIS) score,ramsay score were recorded.Respiratory mechanical parameters after sedation,and changes in vital signs as well as blood gas were compared before and after sedation.Results Compared with the control group,the mean arterial pressure (MAP) and pulse in the experimental group were decreased after sedation[(80±3) mm Hg vs (75±4) mm Hg(1 mm Hg=0.133 kPa),(90±3) bpm vs (79±3) bpm](P＜0.01).The mean airway pressure(Paw) and plateau pressure(Pplat) were significantly downregulated in experimental group [(7.5±0.7) cm H2O vs (6.2±0.6) cm H2O (1 cm H2O=0.098 kPa),(19.8±1.7) cm H2O vs (18.0±1.1) cm H2O] (P＜0.05).peak esophageal pressure (PPEAK ES) and the peak esophageal manometry reference esophagus pressure difference (dPES) was increased [(-3.4±0.7) cm H2O vs (-5.4±1.0) cm H2O,(-6.9±1.0) cm H2O vs (-9.8±1.3) cm H2O] (P＜0.01).There were no significant difference between the two groups in folding screen the end of the suction gas during transpulmonary pressure (Ptp Plat) and pulmonary static compliance (Cst)[(25.5±2.3) cm H2O vs (26.0±2.6) cm H2O,(20.5±1.9)em H2O vs (20.1±1.2) cm H2O].The airway resistance (Raw)[(20.3±0.9) cm H2O·L-1·s-1 vs (15.6±1.4) cm H2O·L1·s-1](P＜0.01)and mechanical work of breathing (WOBv)[(0.49±0.10) j/L vs (0.43±0.06) j/L](P＜0.05) were increased.The patient work of breathing (WOBp) was significantly increased [(0.11 ±0.02)j/L vs (0.16±0.04)j/L] (P＜0.01).The time of mechanical ventilation and the intensive care unit (ICU)staying time were reduced [(76±5) h vs (64±3) h、(6.0±1.5) d vs (4.6±0.9) d](P＜0.05).Conclusions DEX increased the sedative effect and lung compliance,and decreased Raw in patients undergoing mechanical ventilation compared with morphine.DEX would also unload respiratory muscle oxygen consumption estimated by reducing the inspiratory load and work of breathing. Key words: Dexmedetomidine; Chronic obstructive pulmonary disease; Mechanical ventilation; Respiratory mechanics

Effect of protein-energy wasting (PEW) on muscle protein metabolism and oxygen consumption in patients with end-stage renal disease (ESRD)

Effect of protein-energy wasting (PEW) on muscle protein metabolism and oxygen consumption in patients with end-stage renal disease (ESRD)

Activity-Induced Changes in Skeletal Muscle Metabolism Measured with Optical Spectroscopy

Previous studies have used near-infrared spectroscopy (NIRS) to measure skeletal muscle mitochondrial capacity. This study tested the hypothesis that NIRS-measured mitochondrial capacity would improve with endurance exercise training and decline with detraining. Nine young participants performed 4 wk of progressively increasing endurance exercise training of the wrist flexor muscles followed by approximately 5 wk of inactivity. The rate of recovery of muscle oxygen consumption (mV(˙)O₂) was measured with NIRS every 3-7 d, indicating mitochondrial oxidative capacity. A linear increase in mitochondrial capacity (NIRS rate constant) was found with a group average of 64% ± 37% improvement after 4 wk of exercise training (P < 0.05). Mitochondrial capacity declined exponentially upon cessation of exercise training, with a mean half-time of approximately 7.7 d. Both the magnitude and the time course of mitochondrial adaptations to exercise training and detraining measured with NIRS was consistent with previous studies using both in vitro and in vivo techniques. These findings show that NIRS-based measurements can detect meaningful changes in mitochondrial capacity.

Reproducibility of near-infrared spectroscopy measurements of oxidative function and postexercise recovery kinetics in the medial gastrocnemius muscle.

The purpose of this study was to assess the reproducibility of resting blood flow, resting oxygen consumption, and mitochondrial capacity in skeletal muscle using near-infrared spectroscopy (NIRS). We also determined the influence of 2 exercise modalities (ergometer and rubber exercise bands) on the NIRS measurements. Fifteen young, healthy participants (5 female, 10 male) were tested on 2 nonconsecutive occasions within an 8-day period. The NIRS device was placed on the medial gastrocnemius. Venous and arterial occlusions were performed to obtain blood flow and oxygen consumption. A series of repeated arterial occlusions was used to measure the recovery kinetics of muscle oxygen consumption after ∼7-10 s of voluntary plantar flexion exercise. Resting blood flow had mean coefficients of variation (CV) of 42% and 38% for bands and ergometer, respectively, and resting metabolism had mean CVs of 17% and 12% for bands and ergometer, respectively. The recovery time constant of oxygen consumption (day 1 bands and ergometer: 23.2 ± 3.7 s, 27.6 ± 6.5 s, respectively; day 2 bands and ergometer: 25.5 ± 5.4 s, 25.0 ± 4.9 s, respectively) had mean CVs of 10% and 11% for bands and ergometer, respectively. We conclude that measurements of oxygen consumption and mitochondrial capacity using NIRS can be obtained with good reproducibility.

A cross-validation of near-infrared spectroscopy measurements of skeletal muscle oxidative capacity with phosphorus magnetic resonance spectroscopy

The purpose of this study was to cross-validate measurements of skeletal muscle oxidative capacity made with near-infrared spectroscopy (NIRS) measurements to those made with phosphorus magnetic resonance spectroscopy ((31)P-MRS). Sixteen young (age = 22.5 ± 3.0 yr), healthy individuals were tested with both (31)P-MRS and NIRS during a single testing session. The recovery rate of phosphocreatine was measured inside the bore of a 3-Tesla MRI scanner, after short-duration (∼10 s) plantar flexion exercise as an index of skeletal muscle oxidative capacity. Using NIRS, the recovery rate of muscle oxygen consumption was also measured using repeated, transient arterial occlusions outside the MRI scanner, after short-duration (∼10 s) plantar flexion exercise as another index of skeletal muscle oxidative capacity. The average recovery time constant was 31.5 ± 8.5 s for phosphocreatine and 31.5 ± 8.9 s for muscle oxygen consumption for all participants (P = 0.709). (31)P-MRS time constants correlated well with NIRS time constants for both channel 1 (Pearson's r = 0.88, P < 0.0001) and channel 2 (Pearson's r = 0.95, P < 0.0001). Furthermore, both (31)P-MRS and NIRS exhibit good repeatability between trials (coefficient of variation = 8.1, 6.9, and 7.9% for NIRS channel 1, NIRS channel 2, and (31)P-MRS, respectively). The good agreement between NIRS and (31)P-MRS indexes of skeletal muscle oxidative capacity suggest that NIRS is a valid method for assessing mitochondrial function, and that direct comparisons between NIRS and (31)P-MRS measurements may be possible.

Case Report: Endurance Electrical Stimulation Training Improves Skeletal Muscle Oxidative Capacity in Chronic Spinal Cord Injury

ObjectiveTo describe the use of a novel neuromuscular electrical stimulation (NMES) endurance exercise protocol and its effects on skeletal muscle oxidative capacity. DesignCase report, pre/post intervention. SettingUniversity-based trial. ParticipantA 39-year-old man who suffered a motor complete spinal cord injury (C5-6, ASIA Impairment Scale grade A). InterventionTwenty-four weeks of endurance NMES that consisted of progressive increases in the twitch frequency, duration of sessions, and sessions per week. Main Outcome MeasureMitochondrial capacity was measured, in vivo, as the rate of recovery of muscle oxygen consumption using near-infrared spectroscopy. ResultsThe rate of recovery of muscle oxygen consumption increased approximately 3-fold from 0.52 to 1.43, 1.46, and 1.40/min measured on 3 separate occasions during week 12 of training, and 1.57/min after 24 weeks of NMES endurance training. ConclusionThe findings of this study suggest that NMES endurance training using twitches can increase mitochondrial capacity to comparable levels measured in nonparalyzed muscles of sedentary able-bodied controls.

Slow V̇o2 off-kinetics in skeletal muscle is associated with fast PCr off-kinetics—and inversely

The computer model of the bioenergetic system in skeletal muscle, developed previously, was used to study the effect of the characteristic decay time of the parallel activation of oxidative phosphorylation [τ(OFF)] during muscle recovery on the muscle oxygen consumption rate (Vo2) and phosphocreatine (PCr) work-to-rest transition (off)-kinetics and on the relationship between the Vo2 and PCr rest-to-work transition (on)- and off-kinetics in moderate and heavy exercise. An increase in τ(OFF) slows down the initial phase of the muscle Vo2 off-kinetics and accelerates the PCr off-kinetics. As a result, the relationship between the initial phase of the Vo2 off-kinetics (lasting approximately 3-60 s in computer simulations) and the PCr off-kinetics is inverse: the slower the former, the faster the latter. A faster initial phase of the Vo2 off-kinetics is associated with a slower late phase of the Vo2 off-kinetics, and as a result, the integral of Vo2 above baseline during recovery, representing the oxygen debt, is identical in all cases [values of τ(OFF)] for a given PCr decrease. Depending on τ(OFF), the muscle Vo2 on-kinetics was either equally fast or slower than the Vo2 off-kinetics in moderate exercise and always slower in heavy exercise. PCr on-kinetics was always faster than PCr off-kinetics. This study clearly demonstrates that τ(OFF) has a pronounced impact on the mutual relations between the muscle Vo2 and PCr on- and off-kinetics.

Mitochondrial dysfunction and therapeutic approaches in respiratory and limb muscles of cancer cachectic mice

What is the central question of this study? We explored whether experimental cancer-induced cachexia may alter mitochondrial respiratory chain (MRC) complexes and oxygen uptake in respiratory and peripheral muscles,and whether signalling pathways, proteasome and oxidative stress influence that process. What is the main finding and what is its importance? In cancer cachectic mice, MRC complexes and oxygen consumption were decreased in the diaphragm and gastrocnemius. Blockade of nuclear factor-κB and mitogen-activated protein kinase actions partly restored the muscle mass and force and corrected the MRC dysfunction,while concomitantly reducing tumour burden. Antioxidants improved mitochondrial oxygen consumption without eliciting effects on the loss of muscle mass and force or the tumour size,whereas bortezomib reduced tumour burden without influencing muscle mass and strength or MRC function. Abnormalities in mitochondrial content, morphology and function have been reported in several muscle-wasting conditions. We specifically explored whether experimental cancer-induced cachexia may alter mitochondrial respiratory chain (MRC) complexes and oxygen uptake in respiratory and peripheral muscles, and whether signalling pathways, proteasomes and oxidative stress may influence that process. We evaluated complex I, II and IV enzyme activities (specific activity assays) and MRC oxygen consumption (polarographic measurements) in diaphragm and gastrocnemius of cachectic mice bearing the LP07 lung tumour, with and without treatment with N-acetylcysteine, bortezomib and nuclear factor-κB (sulfasalazine) and mitogen-activated protein kinases (MAPK, U0126) inhibitors (n = 10 per group for all groups). Whole-body and muscle weights and limb muscle force were also assessed in all rodents at baseline and after 1 month. Compared with control animals, cancer cachectic mice showed a significant reduction in body weight gain, smaller sizes of the diaphragm and gastrocnemius, lower muscle strength, decreased activity of complexes I, II and IV and decreased oxygen consumption in both muscles. Blockade of nuclear factor-κB and MAPK actions restored muscle mass and force and corrected the MRC dysfunction in both muscles, while partly reducing tumour burden. Antioxidants improved mitochondrial oxygen uptake without eliciting significant effects on the loss of muscle mass and force or tumour size, whereas the proteasome inhibitor reduced tumour burden without significantly influencing muscle mass and strength or mitochondrial function. In conclusion, nuclear factor-κB and MAPK signalling pathways modulate muscle mass and performance and MRC function of respiratory and limb muscles in this model of experimental cancer cachexia, thus offering targets for therapeutic intervention.

Acute effects of whole body vibration on leg muscle activity, oxygen consumption and heart rate in individuals with chronic stroke

Acute effects of whole body vibration on leg muscle activity, oxygen consumption and heart rate in individuals with chronic stroke

Effects of rapid repetition of a vascular occlusion test on near-infrared spectroscopy-derived variables in healthy subjects and in critically ill patients

Transient ischemia modifies cellular metabolism and microvascular physiology in order to limit damage from future hypoxic episodes, a phenomenon called preconditioning. Near-infrared spectroscopy (NIRS) is a non-invasive technique that, when coupled to a vascular occlusion test (VOT), provides an indirect measurement of muscle oxygen consumption (VO2) and microvascular reactivity. We hypothesized that: rapid repetition of a VOT may alter VOT-induced NIRS-derived variables and these changes could reflect preconditioning; and these alterations would be different in healthy volunteers and critically ill patients.

Muscle oxygen consumption by NIRS and mobility in multiple sclerosis patients

BackgroundThe study of muscle metabolism by near-infrared spectroscopy (NIRS) has been poorly implemented in multiple sclerosis (MS). Aims of the study were to compare resting muscle oxygen consumption (rmVO2) at gastrocnemius in MS patients and in age-matched healthy controls (HC) measured using NIRS, and to evaluate its possible relationship with patients’ mobility.MethodsTwenty-eight consecutively enrolled MS patients (male, n = 16; age = 42.7 ± 14.0 y, Relapsing-Remitting, n = 19; Primary-Progressive, n = 9) and 22 HC (male, n = 13; age = 36.0 ± 8.2 y) were studied during rest applying the NIRS probes at gastrocnemius, producing a venous occlusion at the thigh using a cuff, and analyzing the slope of the total hemoglobin to calculate rmVO2. Mobility was assessed by a 6-Minute Walking Test and 6-Minute Walking Distance (6MWD) was recorded.ResultsrmVO2 was higher in MS compared to HC (0.059 ± 0.038 vs 0.039 ± 0.016 mlO2/min/100 g, P < 0.003), not different in clinical subtypes, not correlated to patients’ characteristics (age, disease duration, Expanded Disability Status Scale, resting heart rate, skinfold thickness), and significantly higher in patients with lower walking ability (6MWD < 450 m, n = 12) compared to those at better performance (respectively, 0.072 ± 0.043 vs 0.049 ± 0.032 mlO2/min/100 g, P = 0.03).ConclusionrmVO2 values, significantly higher in MS patients compared to HC, and in low versus high performing patients, might represent a marker of peripheral adaptations occurred to sustain mobility, as observed in other chronic diseases.

Near-infrared assessments of skeletal muscle oxidative capacity in persons with spinal cord injury.

After spinal cord injury (SCI) skeletal muscle decreases in size, increases in intramuscular fat, and has potential declines in mitochondrial function. Reduced mitochondrial function has been linked to the development of metabolic disease. The aim of this study was to measure mitochondrial function in persons with SCI using near-infrared spectroscopy (NIRS). Oxygen consumption of the vastus lateralis muscle was measured with NIRS during repeated short-duration arterial occlusions in nine able-bodied (AB) and nine persons with motor complete SCI. Skeletal muscle oxidative capacity (V max) was evaluated with two approaches: (1) rate constant of the recovery of oxygen consumption after exercise and (2) extrapolated maximum oxygen consumption from a progressive work test. V max as indicated by the rate constant (k) from the recovery kinetics test was lower in SCI compared with AB participants (k: SCI 0.7 ± 0.3 vs. AB 1.9 ± 0.4 min(-1); p < 0.001). Time constants were SCI 91.9 ± 37.8 vs. AB 33.6 ± 8.3 s. V max from the progressive work test approached a significant difference between groups (SCI 5.1 ± 2.9 vs. AB 9.8 ± 5.5 % Hb-Mb/s; p = 0.06). NIRS measurements of V max suggest a deficit of 50-60 % in participants with SCI compared with AB controls, consistent with previous studies using (31)P-MRS and muscle biopsies. NIRS measurements can assess mitochondrial capacity in people with SCI and potentially other injured/diseased populations.

Electrophysiologic changes with incremental exercise in obstructive sleep apnea

In patients with obstructive sleep apnea (OSA), intermittent apnea and hypopnea might cause different adaptations in inspiratory and peripheral muscles. In this study we aimed to determine the changes that occur in muscle activation characteristics during incremental exercise testing in patients with severe OSA. Surface electromyography of inspiratory muscles and knee extensors was performed. Eleven men with severe OSA and 11 matched controls were recruited. Changes in muscle activity were compared by determining root mean square (RMS) and median power frequency (MPF) values obtained at different exercise intensities. The ratios of RMS to oxygen consumption in inspiratory muscles and vastus lateralis increased significantly at peak workload in the control group (P < 0.05), but not in the OSA group. Patients with severe OSA demonstrated an inability to increase motor unit recruitment of inspiratory muscles and knee extensors during incremental exercise.

Skeletal Muscle Metabolism in Endurance Athletes with Near-Infrared Spectroscopy

To determine whether near-infrared spectroscopy (NIRS) measurements of muscle mitochondrial function could detect the expected differences between endurance-trained athletes (n = 8) and inactive subjects (n = 8). Muscle oxygen consumption (mV˙O2) of the vastus lateralis was measured with continuous-wave NIRS using transient arterial occlusions. The recovery rate of mV˙O2 after electrical stimulation was fit to an exponential curve, with the time constant (Tc) used as an index of mitochondrial capacity. Whole-body peak oxygen uptake was determined by indirect calorimetry during a continuous ramp protocol on a cycle ergometer. Whole-body peak oxygen uptake values for endurance-trained and inactive controls were 73.5 ± 9.1 and 33.7 ± 5.9 mL·kg·min, respectively (P < 0.001). The recovery rates of mV˙O2 after exercise for endurance training were 18.4 ± 3.2 and 18.8 ± 2.5 s, whereas those for inactive controls were 32.4 ± 5.2 and 34.9 ± 5.9 s for the shallow and deep channels, respectively (P < 0.001 for comparison between groups). Resting mV˙O2 was 0.52%·s ± 0.22%·s for endurance athletes and 0.77%·s ± 0.82%·s for inactive controls (P = 0.42). The recovery rates of mV˙O2 after exercise in endurance athletes were almost twofold faster than inactive subjects measured with NIRS, consistent with previous studies using muscle biopsies and magnetic resonance spectroscopy. Our results support the use of NIRS measurements of the recovery of oxygen consumption to assess muscle oxidative capacity.

Effect of postmortem time on the metmyoglobin reductase activity, oxygen consumption, and colour stability of different lamb muscles

The aim of this research was to characterize the lamb M. longissimus dorsi (LD), M. semitendinosus (ST), and M. psoas major (PM) muscles for differences in instrumental colour, tissue oxygen consumption rate (OCR), mitochondrial respiration control ratio (RCR), metmyoglobin reductase activity (MRA), and the relative proportions of myoglobin (Mb) redox forms. LD, ST, and PM muscles were stored for 6 days at 4 °C. Changes in the instrumental colour (CIE L*-value, a*-value, b*-value, Chroma-value, and Hue-value), OCR, RCR, MRA, and relative proportions of Mb redox forms during storage were evaluated. LD revealed the lowest MetMb accumulation and highest colour stability. Muscles with higher colour stability had lower levels of OCR, higher MRA, and less MetMb accumulation. Colour stability and MRA for the lamb muscles were LD > ST > PM. The correlation coefficients among the main parameters were also investigated in this research. The correlation coefficients between a*-value and OxyMb within the same muscle were highly significant (r = 0.951, 0.974, 0.828; P < 0.05). MRA of the muscles was negatively correlated (r = −0.810, −0.942, −0.971, P < 0.05) with the relative percentage of MetMb. The results of the present study suggested that OCR, RCR and MRA contribute to variation in colour stability of different lamb muscles.

On–off asymmetries in oxygen consumption kinetics of single Xenopus laevis skeletal muscle fibres suggest higher‐order control

The mechanisms controlling skeletal muscle oxygen consumption (V(o)₂) during exercise are not well understood. We determined whether first-order control could explain V(o)₂kinetics at contractions onset (V(o)₂(on)) and cessation (V(o)₂off)) in single skeletal muscle fibres differing in oxdidative capacity, and across stimulation intensities up to V(o)₂(max). Xenopus laevis fibres (n = 21) were suspended in a sealed chamber with a fast response P(o)₂ electrode to measure V(o)₂ every second before, during and after stimulated isometric contractions. A first-order model did not well characterize on-transient V(o)₂ kinetics. Including a time delay (TD) in the model provided a significantly improved characterization than a first-order fit without TD (F-ratio; P < 0.05), and revealed separate 'activation' and 'exponential' phases in 15/21 fibres contracting at V(o)₂(max) (mean ± SD TD: 14 ± 3s). On-transient kinetics (τV(o)₂(on)) was weakly and linearly related to V(o)₂(max) (R² = 0.271, P = 0.015). Off-transient kinetics, however, were first-order, and τV(o)₂(off) was greater in low-oxidative (V(o)₂max < 0.05 nmol mm⁻³s⁻¹ than high-oxidative fibres (V(o)₂(max > 0.10 nmol mm ⁻³ s⁻¹; 170 ± 70 vs. 29 ± 6 s, P < 0.001). 1/ τV(o)₂(off) was proportional to V(o)₂(max) (R² = 0.727, P < 0.001), unlike in the on-transient. The calculated oxygen deficit was larger (P < 0.05) than the post-contraction volume of consumed oxygen at all intensities except V(o)₂(max). These data show a clear dissociation between the kinetic control of V(o)₂at the onset and cessation of contractions and across stimulation intensities. More complex models are therefore required to understand the activation of mitochondrial respiration in skeletal muscle at the start of exercise.

Monitoring physiologic change in the bladder in health and disease. A new biomedical application of near-infrared spectroscopy

Biomedical applications of near-infrared spectroscopy (NIRS) utilize non-invasive optical technology to monitor alterations in tissue oxygenation and hemodynamics in real time via changes in concentration of the chromophores oxygenated and deoxygenated hemoglobin. Applications of NIRS to the bladder are novel and recent. Transcutaneous monitoring over the bladder as it fills and empties provides unique physiologic information, as hemodynamic variations in the organ's microcircu- lation and alterations in oxygen supply, demand and consumption in the detrusor muscle can be inferred. Such information, which is not available by other means, enhances investigation of patients with bladder dysfunction, offers new insights into causal pathology and hence potentially impact choice of pharmaceutical agents. Problem voiding is common, but the principal diagnostic test is invasive, and gives limited diagnostic and therapeutic information (pressure/flow). Continuous wave NIRS instruments are used for bladder monitoring. Initially NIR light was laser-generated; now miniaturized self-contained devices using light emitting diodes, spatial configuration of emitters to detector, and wireless capacity enhance research scope and clinical monitoring potential. NIRS bladder chromophore patterns during filling and voiding differ in health and disease. In addition to adding new knowledge re voiding dysfunction causation, data patterns characteristic of specific pathology have allowed construct of algorithms with comparable discriminant ability to current invasive diagnostic measures. Such data are physiologic because NIRS only detects change during events in the voiding cycle, pathologic changes mirror NIRS-derived effects of physiologic events (hypoxia/ischemia/fatigue) observed in other tissues (muscle/brain/spinal cord), and animal data and independent research corroborate the principal findings.