Skeletal Muscle Tissue Oxygenation Research Articles

Short- and long-term effects of transcutaneous spinal cord stimulation on autonomic cardiovascular control and arm-crank exercise capacity in individuals with a spinal cord injury (STIMEX-SCI): study protocol

IntroductionIndividuals with higher neurological levels of spinal cord injury (SCI) at or above the sixth thoracic segment (≥T6), exhibit impaired resting cardiovascular control and responses during upper-body exercise. Over time,...

Contributions to forearm desaturation during transient ischemia in healthy adult males and females across the lifespan.

This study investigated skeletal muscle tissue oxygenation (StO2) desaturation in males and females across the adult lifespan. One hundred-two individuals (51 females) of 41 young, 34 midlife, and 27 older adults completed a vascular occlusion test with near-infrared spectroscopy (NIRS+VOT). This included five minutes of arterial occlusion, inducing transient ischemia in the forearm flexor muscle group while recording StO2. The magnitude of desaturation (StO2mag) was quantified as the difference between baseline StO2 and the minimum StO2 value observed during ischemia. The rate of desaturation was also examined. Forearm adipose tissue thickness (ATT), forearm lean mass, and handgrip muscular strength were measured. A p≤0.05 was considered significant. Two-way between factor Analysis of variance (ANOVAs) indicated that males exhibited significantly (p<0.001) less ATT than females (collapsed across age) and that forearm lean mass (p<0.001) and muscular strength (p<0.001) decreased across the lifespan independent of sex. Bivariate analyses revealed significant (p<0.05) associations for sex, age, ATT, forearm lean mass, and muscular strength with the desaturation metrics. The ATT values demonstrated the strongest relations with StO2mag and desaturation rate (r = -0.620 and 0.618). Using a model comparison approach, ATT plus age offered the best predictive power for StO2mag and desaturation rate (R2=0.456 and 0.438) such that the inclusion of sex did not improve the models. These findings suggested differences in desaturation were primarily explained by variations in ATT and, to a lesser extent, age, but biological sex had no meaningful effect. Future studies must determine what other factors influence desaturation during ischemia.

Age and Handgrip Strength Induce Differences in Micro- and Macro-Vascular Responses

Purpose: Handgrip (HG) strength is a potent predictor of cardiovascular disease (CVD) and all-cause mortality. Advances in technology have provided novel assessments of peripheral microvascular and macrovascular health and function. These advances include measurements of skeletal muscle tissue oxygenation (StO2, %) with near-infrared spectroscopy (NIRS) during vascular occlusion tests (VOT) as well as carotid-femoral pulse-wave velocity (cfPWV), which is the current gold-standard to measure aortic stiffness. Although NIRS-VOT and cfPWV have been shown to change across the lifespan, it is unknown if these variables are sensitive to group differences as defined by HG strength. Therefore, our purpose was to examine mean differences in NIRS-VOT parameters and cfPWV between groups of low and high HG strength. We hypothesized that individuals with lower HG strength would exhibit lower vascular function. Methods: 67 adults were separated into age groups: young (19 – 40 yr), midlife (41 – 64 yr), and older (≥65 yr). Groups were divided into low and high strength at the median for HG strength, and quasi-balanced based on biological sex. This resulted in six participant groups (e.g., midlife low strength). The VOT included 3 min of rest, 5 min of ischemia, and 3 min of reperfusion to determine indices of reactive hyperemia. Indices included the initial (i.e., first 10 s) rate of re-saturation (upslope) and the maximal StO2 (StO2max) percent following ischemia. Aortic stiffness was defined as cfPWV using the time difference between the appearance of the carotid and femoral pulses. Separate 2×3 between factor (HG by Age Group) ANOVAs were conducted for each outcome. A p≤0.05 was considered significant, and data were presented as mean ± SD. Results: For upslope, there was a significant interaction (p=0.042, ηp2=0.078), and follow-up analyses revealed for young and midlife adults the high HG group exhibited greater upslopes than the low strength group (young: 2.24±0.9 vs. 1.64±0.7 and midlife: 2.21±0.9 vs. 1.59±0.7%∙s−1). There was no significant interaction (p=0.360) for StO2max, but there was a significant main effect (p&lt;0.001) of Age such that it progressively decreased across the lifespan (83.9 ± 2.0 &gt; 80.7 ± 2.3 &gt; 77.3 ± 2.8%). Similarly, cfPWV exhibited a significant main effect (p&lt;0.001; ηp2 =0.429) of Age indicating aortic stiffness worsened with age, independent of HG strength. Conclusions: These results indicated that upslope was sensitive to group differences in HG strength, but only in the young and midlife age groups. For StO2max and cfPWV, age differences appeared to elicit a stronger effect than HG strength. The current findings suggested that HG strength may be most reflective of a specific portion of the vascular tree, while the initial rate of re-saturation and StO2max may be influenced by different mechanisms associated with reactive hyperemia. Notably, the participants in this study were relatively healthy based on being free of any chronic disease. Future work is necessary to determine the predictive power of NIRS-VOT parameters for future onset of CVD. We would like to thank the American Physiology Society for support and the University of South Alabama for allowing us to use its facilities. We would also like to thank all of the participants who agreed to adhere to the protocol and procedures of this study. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sex-specific microvascular and hemodynamic responses to passive limb heating in young adults.

We examined sex-specific microvascular reactivity and hemodynamic responses under conditions of augmented resting blood flow induced by passive heating compared to normal blood flow. Thirty-eight adults (19 females) completed a vascular occlusion test (VOT) on two occasions preceded by rest with or without passive heating in a randomized, counterbalanced order. Skeletal muscle tissue oxygenation (StO2, %) was assessed with near-infrared spectroscopy (NIRS), and the rate of desaturation and resaturation as well as maximal StO2 (StO2max) and prolonged hypersaturation (area under the curve, StO2AUC) were quantified. Before the VOT, brachial artery blood flow (BABF), vascular conductance, and relative BABF (BABF normalized to forearm lean mass) were determined. Sex × condition ANOVAs were used. A p-value ≤.05 was considered statistically significant. Twenty minutes of heating increased BABF compared to the control (102.9 ± 28.3 vs. 36.0 ± 20.9 mL min-1; p < .01). Males demonstrated greater BABF than females (91.9 ± 34.0 vs. 47.0 ± 19.1 mL min-1; p < .01). There was no sex difference in normalized BABF. There were no significant interactions for NIRS-VOT outcomes, but heat did increase the rate of desaturation (-0.140 ± 0.02 vs. -0.119 ± 0.03% s-1; p < .01), whereas regardless of condition, males exhibited greater rates of resaturation and StO2max than females. These results suggest that blood flow is not the primary factor causing sex differences in NIRS-VOT outcomes.

Sex differences in NIRS derived values of reactive hyperemia persist after experimentally controlling for the ischemic vasodilatory stimulus.

Men and women exhibit different near-infrared spectroscopy (NIRS) outcomes in response to vascular occlusion tests (VOT), which may be due to phenotypic characteristics or different degrees of desaturation during ischemia. The minimum skeletal muscle tissue oxygenation (StO2min) observed during a VOT may be the primary determinant of reactive hyperemic (RH) responses. Our purpose was to determine the contribution StO2min and participant characteristics including adipose tissue thickness (ATT), lean body mass (LBM), muscular strength, and limb circumference to NIRS-derived indices of RH. Also, we aimed to determine if matching StO2min would eliminate NIRS-VOT sex differences. Thirty-one young adults completed one or two VOTs during which the vastus lateralis was continuously assessed for StO2. The men and women each completed a standard VOT with a 5-min ischemic phase. The men completed a second VOT with a shortened ischemic phase to produce a matching StO2min to the minimum of the women observed during the standard VOT. Mean sex differences were determined with t-tests and relative contributions were assessed with multiple regression and model comparison approaches. During the 5-min ischemic phase, the men exhibited greater upslopes (1.97±0.66 vs. 1.23±0.59%∙s-1) and greater StO2max than the women (80.3±4.17 vs. 76.2±2.86%). Analysis revealed StO2min was a greater contributor to upslope than sex and/or ATT. For StO2max, sex was the only significant predictor (r2=0.26, men ~ 4.09% > women). Experimentally matching StO2min did not eliminate the sex differences in upslope or StO2max, suggesting that characteristics other than the degree of desaturation primarily provoke sex differences in RH.

Polyethylene glycol‐20 ameliorates tissue ischemia and improves renal function following traumatic shock

The “Golden Hour” policy used for US Troops in Iraq and Afghanistan has contributed to the highest survival rates for combat injury in history. Anticipated future combat operations require more options to optimize combat casualty care by extending “the Golden Hour” to “the Golden Day.” Low volume resuscitation with polyethylene glycol‐20K (PEG) has been shown to decrease mortality following hemorrhagic shock, however, the effect of PEG on tissue perfusion and renal function has not been determined. We hypothesized that PEG can ameliorate ischemia and prevent renal injury during prolonged traumatic shock. Anesthetized rats received extremity trauma (soft tissue injury and fracture in one hindlimb) and pressure‐controlled hemorrhage, with mean arterial pressure (MAP) maintained at 55mmHg. MAP, heart rate, renal blood flow (RBF, perivascular ultrasonic transit time flow probe), peripheral skeletal muscle microcirculatory flow and tissue oxygen partial pressure (OxyLite needle probes), blood gases, and electrolytes were monitored throughout the experiment. Glomerular filtration rate (GFR) was recorded using a non‐invasive Fluorescein isothiocyanate‐sinistrin transcutaneous technique. After 45 minutes of shock with MAP at 55mmHg, rats were randomly treated with an intravenous bolus of either 7.5% PEG or saline (1.3 ml/kg, n = 5/group). Measurements were continued from the 45th to the 165th minute without MAP control or any other treatment. Compared with saline, PEG markedly improved MAP recovery (P &lt; 0.001) and survival (P &lt; 0.01) (Figures 1A and 1B). Microcirculatory perfusion and oxygen partial pressure were markedly decreased after hemorrhage and saline treatment elicited no additional effect. However, with PEG, the decreases in capillary flow and tissue oxygen levels were significantly attenuated (P = 0.04 and 0.03, respectively) (Figure 2A). Moreover, blood lactate levels continuously increased in the saline group but returned to levels comparable to baseline within 30 minutes after PEG treatment (P &lt; 0.001) (Figure 2B). In the saline group, RBF markedly decreased concomitantly with a sustained increase in renal vascular resistance (RVR) during the shock period. PEG treatment rapidly restored RBF (P &lt; 0.001) to levels comparable to baseline along with a normalized RVR. GFR was diminished in the saline‐treated rats but was improved in the PEG‐treated group (0.07 ± 0.05 vs. 0.67 ± 0.06 ml/min/100g, respectively; P &lt; 0.001). These results provide strong evidence that PEG rapidly improves macro‐ and microcirculatory hemodynamics ameliorates tissue ischemia, and minimize renal injury and mortality following prolonged traumatic shock.

Test-retest reliability of skeletal muscle oxygenation measurement using near-infrared spectroscopy during exercise in patients with sport-related iliac artery flow limitation.

The ankle‐brachial index is an accurate tool for detecting claudication in atherosclerotic patients. However, this technique fails to identify subtle flow limitations of the iliac arteries (FLIA) in endurance athletes. Near‐infrared spectroscopy (NIRS) is a noninvasive technique that measures skeletal muscle tissue oxygenation status. The aim of the present study is to examine the absolute and relative test–retest reliability of NIRS and evaluate its potential as a diagnostic tool in FLIA. NIRS‐derived exercise variables were analyzed during exercise and recovery in FLIA 17 patients and 19 healthy controls. The relative reliability of absolute variables (such as the maximal value) were slight to yet predominantly substantial (intraclass correlation coefficient [ICC], ICC range: 0.06–0.76) with good to excellent absolute reliability (absolute limits of agreement [ALoA], ALoA range: 0.8 ± 10.2 to 0.7 ± 13.1; coefficient of variation [CV], CV range: 5%–11%). Absolute values encompassing signal amplitudes showed moderate to almost perfect relative reliability (ICC range: 0.51–0.89) and poor to good absolute reliability (ALoA range: −1.3 ± 7.0 to −2.5 ± 15.7; CV range: 15%–32%). Kinetic variables showed moderate to almost perfect relative reliability for most recovery kinetics variables (ICC range: 0.54–0.86) with fair to good absolute reliability (ALoA range: 0.4 ± 12.2 to 3.9 ± 37.9; CV range: 18%–27%). Particularly, kinetic variables showed significant differences between patients and healthy subjects. NIRS is found to be a reliable method for examining muscle tissue oxygenation variables. Given the significant differences in especially recovery kinetics between normal subjects and patients, NIRS may contribute to diagnosing FLIA in endurance athletes.

Men exhibit faster skeletal muscle tissue desaturation than women before and after a fatiguing handgrip.

PurposeThe purpose was to test the hypothesis that sex and fatigue effect of the early phase of skeletal muscle tissue oxygenation (StO2, %) desaturation rate as well as that strength matched adults may exhibit similar responses.MethodsTwenty-four adults visited the laboratory twice to quantify this early phase of desaturation during vascular occlusion tests (VOT) while in a rested state. The second visit included a sustained handgrip task at 25% of maximal muscular strength until task failure. At failure, a post-task VOT was initiated. Muscle desaturation was defined as StO2 and collected by a near-infrared spectroscopy device. The muscle size and adipose thickness were determined via ultrasonography. Linear regression was used to quantify the rates of desaturation during the VOTs as well as during the fatiguing handgrip.ResultsThere were sex differences in the rate of desaturation pre- and post-handgrip, such that independent of fatigue, the men (p < 0.001) desaturated more rapidly than the women (pre: b = − 0.208 vs. − 0.123%∙s−1; post: − 0.079 vs. − 0.070%∙s−1). During the fatiguing handgrip, the transformed StO2 values indicated that the males desaturated more rapidly than the females (b = − 0.070 vs. − 0.015). The matched pairs exhibited the same responses as the total sample.ConclusionOverall, muscle size and strength as well as adipose tissue were likely not the primary cause of the differences in rates of muscle desaturation. We hypothesized that differences in fiber type and mitochondria were the principle mechanisms provoking the differences in muscle oxygenation.

Association between tissue oxygenation and myocardial injury in patients undergoing major spine surgery: a prospective cohort study

ObjectiveTo describe the association between intraoperative tissue oxygenation and postoperative troponin elevation in patients undergoing major spine surgery. We hypothesised that a decrease in intraoperative skeletal muscle tissue oxygenation (SmO2)...

Cerebral and skeletal muscle tissue oxygenation during exercise challenge in children and young adults with sickle cellanaemia.

We used near-infrared spectroscopy to examine tissue oxygenation (StO2) during exercise in 17 children and young adults with sickle cell anaemia (SCA) and 13 controls. Patients had lower cerebral StO2 at all exercise stages and demonstrated significantly greater decreases in cerebral StO2 later during exercise. Quadriceps StO2 increased similarly in patients and controls during early exercise, but decreases from baseline were greater in patients during later exercise. At similar workloads, patients demonstrated lower cerebral StO2 (69·2 ± 6·6 vs. 79·5 ± 5·3%, P < 0·001) and trended towards lower quadriceps StO2 (67·7 ± 9·0 vs. 73·2 ± 7·9%, P = 0·09) Further studies of tissue oxygenation during exercise in SCA are warranted.

Dietary Nitrate Supplementation and Exercise-Related Performance.

Over the last decade, there has been a growing interest in the utility of nitrate (NO3-) supplementation to improve exercise-related performance. After consumption, dietary NO3- can be reduced to nitric oxide, a free radical gas involved in numerous physiological actions including blood vessel vasodilation, mitochondrial respiration, and skeletal muscle contractile function. Emerging evidence indicates that dietary NO3- supplementation has a small but nevertheless significant beneficial effect on endurance performance through the combined effects of enhanced tissue oxygenation and metabolic efficiency in active skeletal muscle. There is further evidence to suggest that dietary NO3- exerts a direct influence on contractile mechanisms within the skeletal muscle through alterations in calcium availability and sensitivity. Response heterogeneity and sizeable variability in the nitrate content of beetroot juice products influence the effectiveness of dietary NO3- for exercise performance, and so dosing and product quality, as well as training history, sex, and individual-specific characteristics, should be considered.

Cerebral and Skeletal Muscle Tissue Oxygenation during Exercise in Children with Sickle Cell Anemia

Introduction: Sickle cell anemia (SCA) causes impaired tissue oxygenation. Children with SCA have lower peak fitness levels compared to controls. The contribution of alterations in skeletal muscle and cerebral tissue oxygenation to exercise limitation in SCA remains unclear. Near infrared spectroscopy (NIRS) is a validated, non-invasive method to measure tissue oxygen saturation. We hypothesize that compared to controls, children with SCA will exhibit greater reductions in regional tissue oxygen saturation (StO2) measured in the quadriceps (vastus lateralis) and pre frontal cortex (PFC) across all workloads during maximal cardiopulmonary exercise testing (CPET). Methods: We used the CASMED ELITE NIRS tissue oximeter to measure tissue oxygen saturation in the PFC and vastus lateralis (VL) muscle during all phases of maximal CPET, including warm up, active exercise and recovery, in 17 subjects with SCA (mean age 13.5 years) and 13 controls (mean age 15.2 years). Maximal CPET was conducted by cycle ergometry using a standard ramp protocol until volitional exhaustion was reached by all participants. Peak oxygen consumption (VO2) was measured from breath-by breath gas exchange data collected during CPET. Results: All subjects and controls completed maximal CPET without adverse events. Peak VO2 was not statistically different in subjects with SCA versus controls (25.3±4.7 vs 29.5±8.9 mL/kg/min, p=0.22). Compared to controls, subjects with SCA had significantly lower PFC StO2 at all time points during exercise, including warm up, 20%, 40%, 60%, 80% and 100% of peak work load (p&lt;0.01) (Figure 1a). Subjects with SCA demonstrated a significant decrease in PFC StO2 from warm up to 80% peak work load (-3.0±2.9% , p=0.002) and from warm up to 100% peak work load (-5.4±3.4 %, p&lt;0.001) (Figure 1b). In contrast, controls did not demonstrate significant decreases in PFC StO2 from warm up to any point during exercise testing. VL StO2 did not significantly differ between subjects and controls during exercise (p=0.149, Figure 1c). Subjects with SCA demonstrated a significant increase in VL StO2 from warm up to 0% (+3.2±2.8%, p&lt;0.001) and 20% peak work load (+2.3±2.5%, p=0.002) and a significant decrease in StO2 from warm up to 60% (-4.8±4.6%, p&lt;0.001), 80% (-8.6±5.9%, p&lt;0.001) and 100% peak work load (-10.5±6.3%, p&lt;0.001) (Figure 1d). Controls had significant increase in VL StO2 from warm up to 0% peak work load (+4.3±4.0%, p=0.02) and a significant decrease only at 80% (-6.5±6.3%, p=0.003). Differences in PFC and VL StO2 between subjects and controls were also examined at the highest VO2 achieved by all participants. At a VO2 of 17.6 mL/kg/min, PFC StO2 was significantly lower in subjects with SCA versus controls (69.2±6.6 vs 79.5±5.3%, p&lt;0.001). There was a trend toward lower VL StO2 in subjects versus controls (67.7±9.0 vs 73.2±7.9%, p=0.09). Conclusion: Unlike VL tissue oxygenation, PFC tissue oxygenation is relatively well preserved in subjects with SCA and controls during maximal CPET. However, compared to controls, subjects with SCA have lower PFC tissue oxygenation at warm up and during exercise as well as demonstrate significantly greater decreases in PFC tissue oxygenation during later stages of exercise. In contrast, VL tissue oxygenation is similar at warm up and during exercise for subjects and controls. VL tissue oxygenation increases during initial stages of exercise in a similar fashion in subjects with SCA and controls but subsequent decreases from warm up are greater in subjects with SCA during later stages of exercise. Future studies may further elucidate how SCA contributes to these observed differences in regional tissue oxygenation during exercise and their potential impact on exercise safety and fitness in this population. Disclosures No relevant conflicts of interest to declare.

Blood flow restricted resistance exercise and reductions in oxygen tension attenuate mitochondrial H2 O2 emission rates in human skeletal muscle.

Blood flow restricted resistance exercise (BFR-RE) is capable of inducing comparable adaptations to traditional resistance exercise (RE), despite a lower total exercise volume. It has been suggested that an increase in reactive oxygen species (ROS) production may be involved in this response; however, oxygen partial pressure ( ) is reduced during BFR-RE, and the influence of on mitochondrial redox balance remains poorly understood. In human skeletal muscle tissue, we demonstrate that both maximal and submaximal mitochondrial ROS emission rates are acutely decreased 2h following BFR-RE, but not RE, occurring along with a reduction in tissue oxygenation during BFR-RE. We further suggest that is involved in this response because an in vitro analysis revealed that reducing dramatically decreased mitochondrial ROS emissions and electron leak to ROS. Altogether, these data indicate that mitochondrial ROS emission rates are attenuated following BFR-RE, and such a response is likely influenced by reductions in . Low-load blood flow restricted resistance exercise (BFR-RE) training has been proposed to induce comparable adaptations to traditional resistance exercise (RE) training, however, the acute signalling events remain unknown. Although a suggested mechanism of BFR-RE is an increase in reactive oxygen species (ROS) production, oxygen partial pressure ( ) is reduced during BFR-RE, and the influence of O2 tension on mitochondrial redox balance remains ambiguous. We therefore aimed to determine whether skeletal muscle mitochondrial bioenergetics were altered following an acute bout of BFR-RE or RE, and to further examine the role of in this response. Accordingly, muscle biopsies were obtained from 10 males at rest and 2h after performing three sets of single-leg squats (RE or BFR-RE) to failure at 30% one-repetition maximum. We determined that mitochondrial respiratory capacity and ADP sensitivity were not altered in response to RE or BFR-RE. Although maximal (succinate) and submaximal (non-saturating ADP) mitochondrial ROS emission rates were unchanged following RE, BFR-RE attenuated these responses by ∼30% compared to pre-exercise, occurring along with a reduction in skeletal muscle tissue oxygenation during BFR-RE (P<0.01 vs. RE). In a separate cohort of participants, evaluation of mitochondrial bioenergetics in vitro revealed that mild O2 restriction (50µm) dramatically attenuated maximal (∼4-fold) and submaximal (∼50-fold) mitochondrial ROS emission rates and the fraction of electron leak to ROS compared to room air (200µm). Combined, these data demonstrate that mitochondrial ROS emissions are attenuated following BFR-RE, a response which may be mediated by a reduction in skeletal muscle .

Prebiotic Effect of Lycopene and Dark Chocolate on Gut Microbiome with Systemic Changes in Liver Metabolism, Skeletal Muscles and Skin in Moderately Obese Persons.

Lycopene rich food and dark chocolate are among the best-documented products with a broad health benefit. This study explored the systemic effect of lycopene and dark chocolate (DC) on gut microbiota, blood, liver metabolism, skeletal muscle tissue oxygenation and skin. 30 volunteers were recruited for this trial, 15 women and 15 men with a mean age of 55 ± 5.7 years and with moderate obesity, 30 < BMI < 35 kg/m2. They were randomized and divided into five equal interventional groups: three received different formulations of lycopene, one of them with a 7 mg daily dose and two with 30 mg; another group was given 10 g of DC with 7 mg lycopene embedded into its matrix, and the last group received 10 g DC. The trial was double-blinded for the three lycopene groups and separately for the 2 DC groups; the trial lasted for 1 month. By the end of the trial there were dose-dependent changes in the gut microbiota profile in all three lycopene groups with an increase of relative abundance of, e.g., Bifidobacterium adolescentis and Bifidobacterium longum. This was also accompanied by dose-dependent changes in the blood, liver metabolism, skeletal muscle and skin parameters. Consumption of DC resulted in increased relative abundance of, e.g., Lactobacillus and a reduction of corneocyte exfoliation. This is the first study which reports the prebiotic potential of lycopene and DC.

Skeletal Muscle Oxidation During an Incremental Exercise Test in Younger and Middle-aged Individuals

Previous research has suggested that age-related decline in mitochondrial enzymes consequently results in reduction of skeletal muscle oxidative function. Limited research exists investigating effects of healthy aging on these observed changes, especially with middle-aged individuals. PURPOSE: The purpose of this study was to investigate the effects of healthy aging on changes in tissue oxygenation in skeletal muscle (SmO2) during a self-paced VO2max (SPV) test in younger and middle-aged subjects. METHODS: This study included seven younger (ages 18-35 years, 4 males, BMI 28.1±3.4 kg/m2) and nine middle-aged (ages 40-55 years, one male, BMI 25.1±3.8 kg/m2) healthy, recreationally active individuals. Subjects visited the lab once to complete the SPV test on a Wattbike cycle ergometer. The Moxy sensor, which uses near-infrared spectroscopy, was used to estimate SmO2. Four Moxy sensors were used and were placed on the right and left quadriceps (vastus lateralis), and right and left gastrocnemius muscles. The SPV test was exactly ten minutes in length, with five 2-minute stages. Each stage was perceptually regulated using the 6-20 rating of perceived exertion (RPE) scale: 11, 13, 15, 17, and 20 (in that order). Repeated-measures ANOVAs were used to compare SmO2 between anatomical sites and stages of the SPV. Age group was used as a between-subjects factor. RESULTS: Measured VO2max was 48.33±7.56 ml/kg/min for the younger and 38.10±7.45 ml/kg/min for the middle-aged subjects. For SmO2, there was no main effect of anatomical site (p=0.170) and no differences between age groups (p=0.906). A main effect was present for SPV stages (p<0.001); values remained steady until the last two stages, where they decreased in both groups (younger: 71.0±3.1, 69.5±3.5, 67.9±3.7, 63.6±4.5, 58.3±5.9 percent; middle-aged 69.4±2.8, 70.4±3.1, 70.4±3.3, 65.4±4.0, 56.1±5.3 percent). CONCLUSION: Since no age-related differences were found in SmO2 during the exercise test, healthy aging (i.e. regular aerobic exercise) can be seen as an effective intervention for maintenance skeletal muscle blood flow and a profound influence for sustaining quantity and quality of mitochondria function. Future research should determine whether the same findings occur with healthy, active elderly subjects.

Blood Flow Restricted Exercise and Reduced Oxygen Tension Decrease Mitochondrial ROS Emission in Human Muscle

Low volume blood flow restricted (BFR) training has been proposed to induce comparable adaptations to traditional resistance training, however the underlying mechanisms remain unknown. Despite the absence of direct support, a suggested mechanism of BFR is an increase in reactive oxygen species (ROS). PURPOSE: We aimed to determine if the rate of mitochondrial ROS emission was altered following an acute bout of occluded (BFR) or non-occluded resistance training (RT), and to mechanistically investigate the role of skeletal muscle O2 partial pressure (pO2) in this response. METHODS: Ten males (25±1yrs) performed 3 sets of single leg squats to failure at 30% 1RM, with either BFR (60-70% occlusion), or without occlusion (RT), while skeletal muscle tissue oxygenation was estimated using near-infrared spectroscopy. Muscle biopsies were obtained at rest and 2-hours post-exercise to determine mitochondrial respiration and ROS emission in permeabilized muscle fibers. In a separate cohort, muscle biopsies were obtained from six males (25±2yrs) to examine the effects of pO2 on in vitro mitochondrial bioenergetics. RESULTS: Resistance exercise, with or without BFR, did not alter maximal respiratory capacity or mitochondrial sensitivity to ADP. While maximal mitochondrial ROS emission was unchanged following RT, BFR decreased this response compared to rest (66.6 vs. 86.2 pmol min-1 mg dry wt-1, p<0.05). Skeletal muscle oxygenation was lower in the BFR compared to RT leg, both during (41.4% vs. 46.1% saturation respectively, p<0.01) and between (50.3% vs. 61.1% saturation respectively, p<0.01) exercise sets. Further evaluation of mitochondrial bioenergetics in vitro revealed that mild O2 restriction (50μM) dramatically attenuated maximal mitochondrial ROS emission (~4-fold), and fraction electron leak to ROS (~3-fold) compared to room air (200μM). This effect was especially evident in the presence of non-saturating ADP, as submaximal ROS emission was almost completely suppressed during O2 restriction, without a reduction in submaximal respiration. CONCLUSIONS: These data indicate that a reduction in skeletal muscle pO2 attenuates the propensity of mitochondria to produce ROS, a mechanism which may contribute to the acute responses to BFR training. This research is supported by NSERC funding.

Tissue Oxygen Recovery Time in Back and Front Squats

Near infrared spectroscopy (NIRS) can be used to measure skeletal muscle tissue oxygen (SmO2) levels, which may be a useful indicator of recovery and fatigue during resistance training. PURPOSE: The purpose of this study was to determine the SmO2 recovery rate in both the Vastus Lateralis (VL) and Biceps Femoris (BF) muscles in traditional back squats and front squats. METHODS: Eleven recreationally resistance trained participants completed the study. The 1-repetition maximum (1-RM) was determined for the front and back squats on two different occasions. In subsequent visits a wireless NIRS device was applied over the VL and BF on each leg. Participants completed 3 sets of 15 repetitions with 2-3 minutes of recovery using 70% of their 1-RM weight. During recovery, participants sat on a bench next to the squat rack. To complete the study, participants would repeat the above procedures for the other squat form (front or back) with at least 48 hours in-between visits. Repeated measures ANOVA was used to determine differences in the recovery rate. RESULTS: The recovery rate of SmO2 (%SmO2/0.5 sec) was calculated as the slope of SmO2 over time between 10-50 seconds of during each recovery period. The mean recovery rate during the third set recovery for VL in back squats was 0.885 ± 0.194 %SmO2/0.5 sec and 0.785 ± 0.129 %SmO2/0.5 sec in front squats. Mean recovery rate for third set recovery for BF in back squats was 0.449 ± 0.083 %SmO2/0.5 sec and 0.290 ± 0.059 %SmO2/0.5 sec in front squats. There were significant differences in the SmO2 recovery rates between the BF and VL in both legs (p<0.05). There were no significant differences between the recovery rates in back vs front squats. Similar differences were found in the first and second set recovery periods. CONCLUSION: During front and back squats the initial rate of recovery of SmO2 is more rapid in the VL than in the BF. Additionally, there are no differences in SmO2 recovery rate between front and back squats.

Targeting skeletal muscle tissue oxygenation (StO2) in adults with severe sepsis and septic shock: a randomised controlled trial (OTO-StS Study)

ObjectiveEvaluation of the ratio of oxyhaemoglobin to total haemoglobin in skeletal muscle (StO2) using near-infrared spectroscopy may aid in the monitoring of patients with sepsis. This study assessed the benefits...

Investigation of microvascular morphological measures for skeletal muscle tissue oxygenation by image-based modelling in three dimensions.

The supply of oxygen in sufficient quantity is vital for the correct functioning of all organs in the human body, especially for skeletal muscle during exercise. Traditionally, microvascular oxygen supply capability is assessed by the analysis of morphological measures on transverse cross-sections of muscle, e.g. capillary density or capillary-to-fibre ratio. In this work, we investigate the relationship between microvascular structure and muscle tissue oxygenation in mice. Phase contrast imaging was performed using synchrotron radiation computed tomography (SR CT) to visualize red blood cells (RBCs) within the microvasculature in mouse soleus muscle. Image-based mathematical modelling of the oxygen diffusion from the RBCs into the muscle tissue was subsequently performed, as well as a morphometric analysis of the microvasculature. The mean tissue oxygenation was then compared with the morphological measures of the microvasculature. RBC volume fraction and spacing (mean distance of any point in tissue to the closest RBC) emerged as the best predictors for muscle tissue oxygenation, followed by length density (summed RBC length over muscle volume). The two-dimensional measures of capillary density and capillary-to-fibre ratio ranked last. We, therefore, conclude that, in order to assess the states of health of muscle tissue, it is advisable to rely on three-dimensional morphological measures rather than on the traditional two-dimensional measures.

LunHab: interactive effects of a 10day sustained exposure to hypoxia and bedrest on aerobic exercise capacity in male lowlanders.

What is the central question of this study? What are the distinct and interactive effects of a 10day exposure to hypoxia and horizontal bedrest on the whole-body peak oxygen uptake and on the regional cerebral and skeletal muscle tissue oxygenation during upright cycle ergometry in male lowlanders? What is the main finding and its importance? A 10day sustained exposure to hypoxia aggravates the bedrest-induced reduction in peak oxygen uptake during dynamic exercise engaging large muscle groups, but mitigates the skeletal muscle oxidative capacity impairment elicited by bedrest. The study examined the interactive effects of a 10day exposure to hypoxia and bedrest on the whole-body peak oxygen uptake (V̇O2 peak ) during maximal exercise and on skeletal muscle and cerebral oxygenation during submaximal exercise. Nine males underwent three 10day confinements, in a Latin-square order, as follows: (i) a normoxic bedrest [NBR; partial pressure of inspired O2 (PI,O2)=134.2±0.7mmHg]; (ii) a hypoxic bedrest (HBR; PI,O2=102.9±0.1mmHg at day1, 91.5±1.2mmHg at days3-10); and (iii) a hypoxic ambulation (HAMB; PI,O2 as in HBR). Before, 1 (R+1) and 3days (R+3) after each confinement, subjects performed exhaustive, incremental-load and moderate-intensity constant-load (CLTs) cycle-ergometry trials, while breathing either room air or a hypoxic gas mixture. During the CLTs, changes in the regional oxygenation of the cerebral frontal cortex and the vastus lateralis and intercostal muscles were monitored with near-infrared spectroscopy. At R+1, the confinement-related impairment in V̇O2 peak was greater after HBR than after NBR or HAMB, regardless of whether the trial was performed in room air or hypoxia (HBR, -16.2%; NBR, -8.3%; HAMB, -4.1%; P=0.001). During the CLTs, bedrest aggravated the exercise-induced reduction in locomotor and respiratory muscle oxygenation (P≤0.05); an effect that was less after HBR than after NBR (P≤0.05). The hypoxic exercise-induced cerebral vasodilatory response was blunted by HBR, probably because of the marked hyperventilation-dependent hypocapnia, attendant to the sustained hypoxic stimulus. Hence, short-term exposure to hypoxia potentiates the reduction in V̇O2 peak , but it mitigates the impairment in skeletal muscle oxidative capacity induced by bedrest.