Effects of occlusion pressure on hemodynamic responses recorded by near-infrared spectroscopy across two visits

Ischemic Preconditioning (IPC) has emerged as a promising approach to mitigate the impact of hypoxia on physiological functions. However, the heterogeneity of occlusion pressures for inducing arterial occlusion has led to inconsistent hemodynamic outcomes across studies. This study aims to evaluate the peripheral hemodynamic responses to partial and total blood-flow occlusions on the left arm at rest, using absolute or individualized pressures, on two occasions. Thirty-five young males volunteered to participate in this study. IPC procedure (3 × 7-min) was performed on the left upper arm with cuff pressures at 50 mmHg (G1), 50 mmHg over the systolic blood pressure (SBP + 50 mmHg) (G2) or 250 mmHg (G3). NIRS-derived parameters were assessed for each occlusion and reperfusion phase in the brachioradialis. Results showed a significantly lower magnitude of deoxygenation (TSIAUC) for G1 compared to G2 (-1959.2 ± 1417.4 vs. -10908.1 ± 1607.5, P < 0.001) and G3 -1959.2 ± 1417.4 vs. -11079.3 ± 1828.1, P < 0.001), without differences between G2 and G3. However, G3 showed a significantly faster reoxygenation only for tissue saturation index (TSIslope) compared to G2 (1.3 ± 0.1 vs. 1.0 ± 0.2, P = 0.010), but without differences in the speed of recovery of deoxyhemoglobin [(HHb) slope], or in the magnitude of post-occlusive hyperemia (PORH). Besides TSI reoxygenation speed, G2 and G3 elicit comparable resting hemodynamic responses measured by NIRS. Thus, this study highlights the practicality and effectiveness of using relative occlusion pressures based on systolic blood pressure (SBP) rather than relying on excessively high absolute pressures.

Daily Physical Activity Does Not Contribute to Differences in Muscle Oxidative Capacity Between Overweight and Obesity

BACKGROUND

The interaction between physical activity, skeletal muscle health, and adiposity has been explored in normal weight and overweight/obesity grouped together; however, the overall risks associated with being overweight are less than those observed with obesity and can be confounded by disparities in both sex and race. Thus, the present study sought to investigate the intricate interplay of daily physical activity and skeletal muscle oxidative capacity (SMOC) in overweight and obesity, while exploring how sex and race impact this dynamic relationship.

METHODS

One hundred and forty participants were grouped by body mass index (BMI) as overweight (n = 73; BMI >25-<30 kg/m2) or obese (n = 67; BMI ≥30 kg/m2). SMOC was assessed using near-infrared spectroscopy and daily physical activity was assessed for 7 days using accelerometry.

RESULTS

Overweight individuals exhibited a higher (p = 0.004) SMOC and engaged in more (p = 0.007) vigorous physical activity compared to obese individuals. In addition, SMOC was lower (p = 0.005) in obese non-Hispanic Black (NHB) men compared to overweight NHB men. No relationships between physical activity and SMOC were observed.

CONCLUSION

Physical activity is not associated with differences in SMOC in overweight and obesity. Obese individuals engage in less vigorous physical activity and exhibit lower SMOC compared to overweight individuals and these differences are emphasised in NHB men.

Methodological considerations on near-infrared spectroscopy derived muscle oxidative capacity

PURPOSE

Different strategies for near-infrared spectroscopy (NIRS)-derived muscle oxidative capacity assessment have been reported. This study compared and evaluated (I) approaches for averaging trials; (II) NIRS signals and blood volume correction equations; (III) the assessment of vastus lateralis (VL) and tibialis anterior (TA) muscles in two fitness levels groups.

METHODS

Thirty-six participants [18 chronically trained (CT: 14 males, 4 females) and 18 untrained (UT: 10 males, 8 females)] participated in this study. Two trials of twenty transient arterial occlusions were performed for NIRS-derived muscle oxidative capacity assessment. Muscle oxygen consumption ( V ˙ O2m) was estimated from deoxygenated hemoglobin (HHb), corrected for blood volume changes following Ryan (HHbR) and Beever (HHbB) equations, and from oxygen saturation (StO2) in VL and TA.

RESULTS

Superimposing or averaging V ˙ O2m or averaging the rate constants (k) from the two trials resulted in equivalent k values [two one-sided tests (TOST) procedure with 5% equivalence margin-P < 0.001]. Whereas HHbR (2.35 ± 0.61 min-1) and HHbB (2.34 ± 0.58 min-1) derived k were equivalent (P < 0.001), StO2 derived k (2.81 ± 0.92 min-1) was greater (P < 0.001) than both. k values were greater in CT vs UT in both muscles (VL: + 0.68 min-1, P = 0.002; TA: + 0.43 min-1, P = 0.01).

CONCLUSION

Different approaches for averaging trials lead to similar k. HHb and StO2 signals provided different k, although different blood volume corrections did not impact k. Group differences in k were detected in both muscles.

Association of skeletal muscle oxidative capacity with muscle function, sarcopenia-related exercise performance, and intramuscular adipose tissue in older adults

Muscle function and exercise performance measures, such as muscle endurance capacity, maximal strength, chair stand score, gait speed, and Timed Up and Go score, are evaluated to diagnose sarcopenia and frailty in older individuals. Furthermore, intramuscular adipose tissue (IntraMAT) content increases with age. Skeletal muscle oxidative capacity determines muscle metabolism and maintains muscle performance. This study aimed to investigate the association of skeletal muscle oxidative capacity with muscle function, exercise performance, and IntraMAT content in older individuals. Thirteen older men and women participated in this study. Skeletal muscle oxidative capacity was assessed by the recovery speed of muscle oxygen saturation after exercise using near-infrared spectroscopy from the medial gastrocnemius. We assessed two muscle functions, peak torque and time to task failure, and four sarcopenia-related exercise performances: handgrip strength, gait speed, 30-s chair stand, and Timed Up and Go. The IntraMAT content was measured using axial magnetic resonance imaging. The results showed a relationship between skeletal muscle oxidative capacity and gait speed but not with muscle functions and other exercise performance measures. Skeletal muscle oxidative capacity was not related to IntraMAT content. Skeletal muscle oxidative capacity, which may be indicative of the capacity of muscle energy production in the mitochondria, is related to locomotive functions but not to other functional parameters or skeletal fat infiltration.

Muscle Oximetry in Sports Science: An Updated Systematic Review

BACKGROUND

In the last 5 years since our last systematic review, a significant number of articles have been published on the technical aspects of muscle near-infrared spectroscopy (NIRS), the interpretation of the signals and the benefits of using the NIRS technique to measure the physiological status of muscles and to determine the workload of working muscles.

OBJECTIVES

Considering the consistent number of studies on the application of muscle oximetry in sports science published over the last 5 years, the objectives of this updated systematic review were to highlight the applications of muscle oximetry in the assessment of skeletal muscle oxidative performance in sports activities and to emphasize how this technology has been applied to exercise and training over the last 5 years. In addition, some recent instrumental developments will be briefly summarized.

METHODS

Preferred Reporting Items for Systematic Reviews guidelines were followed in a systematic fashion to search, appraise and synthesize existing literature on this topic. Electronic databases such as Scopus, MEDLINE/PubMed and SPORTDiscus were searched from March 2017 up to March 2023. Potential inclusions were screened against eligibility criteria relating to recreationally trained to elite athletes, with or without training programmes, who must have assessed physiological variables monitored by commercial oximeters or NIRS instrumentation.

RESULTS

Of the identified records, 191 studies regrouping 3435 participants, met the eligibility criteria. This systematic review highlighted a number of key findings in 37 domains of sport activities. Overall, NIRS information can be used as a meaningful marker of skeletal muscle oxidative capacity and can become one of the primary monitoring tools in practice in conjunction with, or in comparison with, heart rate or mechanical power indices in diverse exercise contexts and across different types of training and interventions.

CONCLUSIONS

Although the feasibility and success of the use of muscle oximetry in sports science is well documented, there is still a need for further instrumental development to overcome current instrumental limitations. Longitudinal studies are urgently needed to strengthen the benefits of using muscle oximetry in sports science.

Muscle Oxidative Capacity in Vivo Is Associated With Physiological Parameters in Trained Rowers

Purpose: The muscle oxygen uptake (m V ˙ O 2 ) kinetics following exercise, measured by near-infrared spectroscopy, has been used as a functional evaluation of muscle oxidative metabolism. This study aimed to determine the m V ˙ O 2 off-kinetics and verify the relationship of the recovery rate of m V ˙ O 2 (k) with time-trial performance and different aerobic parameters in trained rowers. Methods: Eleven male rowers (age: 20 ± 3 years; V ˙ O 2 m a x : 4.28 ± 0.35 L·min-1) used a rowing ergometer to perform (I) an incremental test to determine the maximal oxygen uptake (V ˙ O 2 m a x ) and peak power output (Ppeak); (II) several visits to determine maximal lactate steady state (MLSS); and (III) a 2000-m rowing ergometer performance test. Also, one test to determine m V ˙ O 2 off-kinetics of the vastus lateralis muscle using a repeated arterial occlusions protocol. Results: The m V ˙ O 2 generated a good monoexponential fit (R2 = 0.960 ± 0.030; SEE = 0.041 ± 0.018%.s-1). The k of m V ˙ O 2 (2.06 ± 0.58 min-1) was associated with relative V ˙ O 2 m a x (r = 0.79), power output at MLSS (r = 0.76), and Ppeak (r = 0.83); however, it was not related with 2000-m rowing performance (r = -0.38 to 0.52; p > .152). Conclusion: These findings suggest that although not associated with rowing performance, the m V ˙ O 2 off-kinetics determined after a submaximal isometric knee extension may be a practical and less-exhaustive approach than invasive responses and incremental tests to assess the muscle oxidative metabolism during a training program.

Monitoring Muscle Oxygen Asymmetry as a Strategy to Prevent Injuries in Footballers

Purpose: It has been hypothesized that sports injury risk is explained by muscle metabolism. The objective was to evaluate the muscle oxygen saturation slopes (ΔSmO2 slopes) and muscle oxygenation asymmetry (MO2Asy) at rest and to study their associations with injuries during the pre-season. Methods: A total of 16 male and 10 female footballers participated in this study. Injuries were diagnosed and classified by level of severity during the pre-season. The workload was also evaluated using the rate of perceived exertion × training time, from which the accumulated loads. The SmO2 was measured at rest in the gastrocnemius muscle using the arterial occlusion method in the dominant and non-dominant legs. The repeated measures ANOVA, relative risk, and binary logistic regression were applied to assess the probability of injury with SmO2 and workload. Results: Higher MO2Asy and ΔSmO2 Slope 2 were found among footballer who suffered high-severity injuries and those who presented no injuries. In addition, an MO2Asy greater than 15% and an increase in accumulated load were variables that explained a greater probability of injury. Conclusion: This study presents the new concept of muscle oxygenation asymmetry in sports science and its possible application in injury prevention through the measurement of SmO2 at rest.

Exercise responses to heart rate clamped cycling with graded blood flow restriction

OBJECTIVES

To quantify the acute effects of graded blood flow restriction on the interaction between changes in mechanical output, muscle oxygenation trends and perceptual responses to heart rate clamped cycling.

DESIGN

Repeated measures.

METHODS

Twenty-five adults (21 men) performed six, 6-min cycling bouts (24 min of recovery) at a clamped heart rate corresponding to their first ventilatory threshold at 0 % (unrestricted), 15 %, 30 %, 45 %, 60 % and 75 % of arterial occlusion pressure with the cuffs inflated bilaterally from the fourth to the sixth minute. Power output, arterial oxygen saturation (pulse oximetry) and vastus lateralis muscle oxygenation (near-infrared spectroscopy) were monitored during the final 3 min of pedalling, whilst perceptual responses (modified Borg CR10 scales) were obtained immediately after exercise.

RESULTS

Compared to unrestricted cycling, average power output for minutes 4-6 decreased exponentially for cuff pressures ranging 45-75 % of arterial occlusion pressure (P < 0.001). Peripheral oxygen saturation averaged ∼96 % across all cuff pressures (P = 0.318). Deoxyhemoglobin changes were larger at 45-75 % versus 0 % of arterial occlusion pressure (P < 0.05), whereas higher total haemoglobin values occurred at 60-75 % of arterial occlusion pressure (P < 0.05). Sense of effort, ratings of perceived exertion, pain from cuff pressure, and limb discomfort were exaggerated at 60-75 % versus 0 % of arterial occlusion pressure (P < 0.001).

CONCLUSIONS

Blood flow restriction of at least 45 % of arterial occlusion pressure is required to reduce mechanical output during heart rate clamped cycling at the first ventilatory threshold. Whilst power decreases non-linearly above this pressure threshold, higher occlusion levels ranging 60-75 % of arterial occlusion pressure also accentuate muscle deoxygenation and exercise-related sensations.

Evaluation of inter-rater and test-retest reliability for near-infrared spectroscopy reactive hyperemia measures

BACKGROUND

Near-infrared spectroscopy (NIRS) is a non-invasive tool used to measure blood flow in peripheral tissues. More information on inter-rater agreement and test-retest reliability of NIRS-based reperfusion assessments is needed.

PURPOSE

To assess inter-rater agreement for NIRS based data analysis, and evaluate the measurement's reliability across days.

METHODS

On three separate days (average days between visits 1 and 3: 19.4 ± 6.9 days), participants' (N = 15 males, 22 ± 2 yr.) post-occlusion reactive hyperemia (PORH) was measured in the left gastrocnemius muscle using Continuous-Wave NIRS (CW-NIRS). A blood pressure cuff was placed proximal to the knee and inflated to occlude lower leg blood flow for 5 min. The following CW-NIRS parameters were selected: (1) percent saturation in HbO₂ (StO₂%) at baseline; (2) the O₂Hb range used to normalize the NIRS signal; (3) the time for the O₂Hb signal to reach 50 % peak post-occlusion hyperemia (T_1/2), and (4) the post peak hyperemic O₂Hb recovery slope (O₂REC-SLP). Absolute agreement between the two analysts was calculated using two-way random effects Intraclass Correlation Coefficients (ICC_2,1). Consistency between analysts and across days was calculated using two-way mixed models (ICC_3,1). Mean and 95 % confidence intervals (CI) of ICCs are reported. Coefficient of variation (CV) and standard error of the measurement (SEM) are reported.

RESULTS

The ICC_2,1 data indicated "adequate" to "excellent" absolute agreement between the two NIRS analysts. ICC_2,3 data indicated "adequate" to "good" reliability across visits. The CV and SEM for rater 1 and rater 2 across visit were StO₂ (CV: 3.79 % ± 2.71 % and 4.50 % ± 2.37 %; SEM: 3.42 and 3.82), O₂Hb range (CV: 10.50 ± 5.93 and 12.79 ± 12.41; SEM: 3.26 and 4.71), T_1/2 (CV: 11.15 % ± 5.52 % and 10.96 % ± 4.50; SEM: 1.22 and 1.11), and O₂REC-SLP (CV: 19.49 % ± 9.99 % and 18.45 % ± 9.48 %; SEM: 0.04 and 0.04).

CONCLUSION

It is concluded that NIRS parameters assessed show adequate reliability between analysts and across three visits. It is recommended, when feasible and because of the absence of 100 % reliability, that investigators employ more than one rater for scoring at least a portion of the data across each trial in a study's control condition in order to have the ability to estimate the magnitude of error attributable to imperfect reliability.

Evaluation of transcutaneous near-infrared spectroscopy for early detection of cardiac arrest in an animal model

Sudden cardiac arrest (SCA) is a leading cause of mortality worldwide. The SCA-to-resuscitation interval is a key determinant of patient outcomes, highlighting the clinical need for reliable and timely detection of SCA. Near-infrared spectroscopy (NIRS), a non-invasive optical technique, may have utility for this application. We investigated transcutaneous NIRS as a method to detect pentobarbital-induced changes during cardiac arrest in eight Yucatan miniature pigs. NIRS measurements during cardiac arrest were compared to invasively acquired carotid blood pressure and partial oxygen pressure (PO₂) of spinal cord tissues. We observed statistically significant decreases in mean arterial pressure (MAP) 64.68 mmHg ± 13.08, p < 0.0001), spinal cord PO₂ (38.16 mmHg ± 20.04, p = 0.0028), and NIRS-derived tissue oxygen saturation (TSI%) (14.50% ± 3.80, p < 0.0001) from baseline to 5 min after pentobarbital administration. Euthanasia-to-first change in hemodynamics for MAP and TSI (%) were similar [MAP (10.43 ± 4.73 s) vs TSI (%) (12.04 ± 1.85 s), p = 0.3714]. No significant difference was detected between NIRS and blood pressure-derived pulse rates during baseline periods (p > 0.99) and following pentobarbital administration (p = 0.97). Transcutaneous NIRS demonstrated the potential to identify rapid hemodynamic changes due to cardiac arrest in periods similar to invasive indices. We conclude that transcutaneous NIRS monitoring may present a novel, non-invasive approach for SCA detection, which warrants further investigation.

Intra- and Inter-Day Reliability of the NIRS Portamon Device after Three Induced Muscle Ischemias

(1) Background: Near-infrared spectroscopy (NIRS) is an innovative and non-invasive technology used to investigate muscular oxygenation. The aim of this study is to assess the within- and between-session reliability of the NIRS Portamon (Artinis, Elst, Netherlands) device following three sets of induced muscle ischemia. (2) Methods: Depending on the experimental group (G1, G2 or G3), a cuff was inflated three times on the left upper arm to 50 mmHg (G1), systolic blood pressure (SBP) + 50 mmHg (G2) or 250 mmHg (G3). Maximum, minimum and reoxygenation rate values were assessed after each occlusion phase, using a Portamon device placed on the left brachioradialis. Reliability was assessed with intraclass correlation coefficient (ICC) value and ICC 95% confidence interval (CI-95%), coefficient of variation (CV) and standard error of measurement (SEM) (3) Results: Our results showed a good to excellent reliability for maximums and minimums within-session. However, the reoxygenation rate within sessions as well as measurements between sessions cannot predominantly show good reliability. (4) Conclusions: Multiple measurements of maximums and minimums within a single session appeared to be reliable which shows that only one measurement is necessary to assess these parameters. However, it is necessary to be cautious with a comparison of maximum, minimum and reoxygenation rate values between sessions.

Assessment of mitochondrial respiratory capacity using minimally invasive and noninvasive techniques in persons with spinal cord injury

Purpose

Muscle biopsies are the gold standard to assess mitochondrial respiration; however, biopsies are not always a feasible approach in persons with spinal cord injury (SCI). Peripheral blood mononuclear cells (PBMCs) and near-infrared spectroscopy (NIRS) may alternatively be predictive of mitochondrial respiration. The purpose of the study was to evaluate whether mitochondrial respiration of PBMCs and NIRS are predictive of respiration of permeabilized muscle fibers after SCI.

Methods

Twenty-two individuals with chronic complete and incomplete motor SCI between 18–65 years old were recruited to participate in the current trial. Using high-resolution respirometry, mitochondrial respiratory capacity was measured for PBMCs and muscle fibers of the vastus lateralis oxidizing complex I, II, and IV substrates. NIRS was used to assess mitochondrial capacity of the vastus lateralis with serial cuff occlusions and electrical stimulation.

Results

Positive relationships were observed between PBMC and permeabilized muscle fibers for mitochondrial complex IV (r = 0.86, P < 0.0001). Bland-Altman displayed agreement for complex IV (MD = 0.18, LOA = -0.86 to 1.21), between PBMCs and permeabilized muscles fibers. No significant relationships were observed between NIRS mitochondrial capacity and respiration in permeabilized muscle fibers.

Conclusions

This is the first study to explore and support the agreement of less invasive clinical techniques for assessing mitochondrial respiratory capacity in individuals with SCI. The findings will assist in the application of PBMCs as a viable alternative for assessing mitochondrial health in persons with SCI in future clinical studies.

Evidence that large vessels do affect near infrared spectroscopy

The influence of large vessels on near infrared spectroscopy (NIRS) measurement is generally considered negligible. Aim of this study is to test the hypothesis that changes in the vessel size, by varying the amount of absorbed NIR light, could profoundly affect NIRS blood volume indexes. Changes in haemoglobin concentration (tHb) and in tissue haemoglobin index (THI) were monitored over the basilic vein (BV) and over the biceps muscle belly, in 11 subjects (7 M - 4 F; age 31 ± 8 year) with simultaneous ultrasound monitoring of BV size. The arm was subjected to venous occlusion, according to two pressure profiles: slow (from 0 to 60 mmHg in 135 s) and rapid (0 to 40 mmHg maintained for 30 s). Both tHb and THI detected a larger blood volume increase (1.7 to 4 fold; p < 0.01) and exhibited a faster increase and a greater convexity on the BV than on the muscle. In addition, NIRS signals from BV exhibited higher correlation with changes in BV size than from muscle (r = 0.91 vs 0.55, p < 0.001 for THI). A collection of individual relevant recordings is also included. These results challenge the long-standing belief that the NIRS measurement is unaffected by large vessels and support the concept that large veins may be a major determinant of blood volume changes in multiple experimental conditions.

Muscle Oxygenation of the Paretic and Nonparetic Legs During and After Arterial Occlusion in Chronic Stroke

Oxygen delivery and demand are reduced in the paretic leg post-stroke, reflecting decreased vascular function and reduced muscle quantity and quality. However, it is unknown how muscle oxygenation, the balance between muscle oxygen delivery and utilization, is altered in chronic stroke during and after occlusion-induced ischemia.

OBJECTIVES

The objective was to determine muscle oxygen consumption rate, microvascular responsiveness and reactive hyperemia in the paretic and nonparetic legs during and after arterial occlusion post-stroke.

MATERIALS AND METHODS

Muscle oxygen saturation was measured with near-infrared spectroscopy on the vastus lateralis of each leg during 3-minute arterial occlusion and recovery (3 min). Muscle oxygen consumption was derived from the desaturation slope during ischemia, microvascular responsiveness was derived from the resaturation slope after ischemia and reactive hyperemia was derived from the area under the curve above baseline after ischemia.

RESULTS

Eleven subjects (91% male; 32.2±6.1 months post-stroke; age 62.9±13.6 years) with a hemiparetic gait pattern participated. There was no significant between-leg muscle oxygenation difference at rest (paretic: 64.9±16.6%; nonparetic: 70.6±15.6%, p = 0.13). Muscle oxygen consumption in the paretic leg (-0.53±0.24%/s) was significantly reduced compared to the nonparetic leg (-0.70±0.36%/s; p = 0.03). Microvascular responsiveness was significantly reduced in the paretic leg compared to the nonparetic leg (paretic: 4.6±1.8%/s; nonparetic: 5.7±1.6%/s, p = 0.04). Reactive hyperemia was not significantly different between legs (paretic:4384±2341%·s; nonparetic: 3040±2216%·s, p = 0.07).

CONCLUSION

Muscle oxygen consumption and microvascular responsiveness are impaired in the paretic compared to the nonparetic leg, suggesting both reduced skeletal muscle aerobic function and reduced ability to maximally perfuse muscle tissue.

Effect of heat pre-conditioning on recovery following exercise-induced muscle damage

This study investigated the influence of heat pre-conditioning on the recovery of muscle torque, microvascular function, movement economy and stride mechanics following exercise-induced muscle damage (EIMD). Twenty male participants were equally assigned to a control (CON) and an experimental group (HEAT), and performed a 30-min downhill run (DHR) to elicit EIMD. HEAT group received three consecutive days of heat exposure (45.1 ​± ​3.2 ​min of hot water immersion at 42 ​°C) prior to DHR. Microvascular function (near-infrared spectroscopy), maximal voluntary contraction (MVC) torque of the knee extensors, as well as two treadmill-based steady-state runs performed below (SSR-1) and above (SSR-2) the first ventilatory threshold were assessed prior to DHR and repeated for four consecutive days post-DHR (D1-POST to D4-POST). The decline in MVC torque following EIMD was attenuated in HEAT compared with CON at D1-POST (p ​= ​0.037), D3-POST (p ​= ​0.002) and D4-POST (p ​= ​0.022). Muscle soreness increased in both CON and HEAT, but was significantly attenuated in HEAT compared with CON at D2-POST (p ​= ​0.024) and D3-POST (p ​= ​0.013). Microvascular function decreased in CON from D1-POST to D3-POST (p ​= ​0.009 to 0.018), and was lower compared with HEAT throughout D1-POST to D3-POST (p ​= ​0.003 to 0.017). Pre-heat treatment decreased the magnitude of strength loss and muscle soreness, as well as attenuated the decline in microvascular function following EIMD. Heat treatment appears a promising pre-conditioning strategy when embarking on intensified training periods or competition.

•

Three days of heat pre-conditioning decreases the extent of strength loss, soreness and microvascular function after EIMD.

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Pre heat treatment might be a promising preconditioning tool prior to intensified training periods or competition.

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Heat tretament may positively impact activities of daily living, training quality and adherence to training programs.

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

Purpose

The 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.

Methods

Twenty-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.

Results

There 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.

Conclusion

Overall, 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.

Thoracic Spinal Manipulation Effect on Neuroendocrine Response in People With Achilles Tendinopathy: A Randomized Crossover Trial

OBJECTIVE

The purpose of the present study was to determine the neuroendocrine response after a thoracic spinal manipulation in people with Achilles tendinopathy.

METHODS

This was a randomized 2-sequence, 2-period crossover trial. A total of 24 participants, mean (standard deviation) age of 48 (7) years, with a diagnosis of Achilles tendinopathy (>3 mo) were randomly assigned into sequence 1 (sham intervention and then thoracic spinal manipulation) or sequence 2 (thoracic spinal manipulation and then sham intervention). The trial was conducted at a university laboratory with a washout period of 1 week. The primary outcome measure was the testosterone/cortisol (T/C) ratio (salivary samples). The secondary outcome measures included heart rate variability (measured with electrocardiography) and total oxygenation index (nmol/L) of calf muscle and Achilles tendon (measured with near-infrared spectroscopy). A 2-way mixed-model analysis of variance was performed. The statistic of interest was the condition by time interaction.

RESULTS

A statistically significant condition by time interaction was found for the T/C ratio (mean difference: -0.16; confidence interval: -0.33 to 0.006; interaction: P < .05) and the total oxygenation index (mean difference: 1.35; confidence interval: -1.3 to 4.1; interaction: P < .05) of calf muscle but not for Achilles tendon (P = .6); however, no difference was found for heart rate variability (P = .5).

CONCLUSION

In people with Achilles tendinopathy, thoracic spinal manipulation resulted in immediate increase in the total oxygenation index in the calf muscle followed by an increase in the T/C ratio 6 hours post-intervention.

Measuring tibial hemodynamics and metabolism at rest and after exercise using near-infrared spectroscopy

The bone vascular system is important, yet evaluation of bone hemodynamics is difficult and expensive. This study evaluated the utility and reliability of near-infrared spectroscopy (NIRS), a portable and relatively inexpensive device, in measuring tibial hemodynamics and metabolic rate. Eleven participants were tested twice using post-occlusive reactive hyperemia technique with the NIRS probes placed on the tibia and the medial gastrocnemius (MG) muscle. Measurements were made at rest and after 2 levels of plantarflexion exercise. The difference between oxygenated and deoxygenated hemoglobin signal could be reliably measured with small coefficients of variation (CV; range 5.7-9.8%) and high intraclass correlation coefficients (ICC; range 0.73-0.91). Deoxygenated hemoglobin rate of change, a potential marker for bone metabolism, also showed good reliability (CV range 7.5-9.8%, ICC range 0.90-0.93). The tibia was characterized with a much slower metabolic rate compared with MG (p < 0.001). While exercise significantly increased MG metabolic rate in a dose-dependent manner (all p < 0.05), no changes were observed for the tibia after exercise compared with rest (all p > 0.05). NIRS is a suitable tool for monitoring hemodynamics and metabolism in the tibia. However, the local muscle exercise protocol utilized in the current study did not influence bone hemodynamics or metabolic rate. Novelty: NIRS can be used to monitor tibial hemodynamics and metabolism with good reliability. Short-duration local muscle exercise increased metabolic rate in muscle but not in bone. High level of loading and exercise volume may be needed to elicit measurable metabolic changes in bone.

Muscle mitochondrial capacity in high- and low-fitness females using near-infrared spectroscopy

The recovery of muscle oxygen consumption (m V ˙ O₂ ) after exercise measured using near-infrared spectroscopy (NIRS) provides a measure of skeletal muscle mitochondrial capacity. Nevertheless, due to sex differences in factors that can influence scattering and thus penetration depth of the NIRS signal in the tissue, e.g., subcutaneous adipose tissue thickness and intramuscular myoglobin and hemoglobin, it is unknown whether results in males can be extrapolated to a female population. Therefore, the aim of this study was to measure skeletal muscle mitochondrial capacity in females at different levels of aerobic fitness to test whether NIRS can measure relevant differences in mitochondrial capacity. Mitochondrial capacity was analyzed in the gastrocnemius muscle and the wrist flexors of 32 young female adults, equally divided in relatively high ( V ˙ O₂ peak ≥ 47 ml/kg/min) and relatively low aerobic fitness group ( V ˙ O₂ peak ≤ 37 ml/kg/min). m V ˙ O₂ recovery was significantly faster in the high- compared to the low-fitness group in the gastrocnemius, but not in the wrist flexors (p = 0.009 and p = 0.0528, respectively). Furthermore, V ˙ O₂ peak was significantly correlated to m V ˙ O₂ recovery in both gastrocnemius (R²  = 0.27, p = 0.0051) and wrist flexors (R²  = 0.13, p = 0.0393). In conclusion, NIRS measurements can be used to assess differences in mitochondrial capacity within a female population and is correlated to V ˙ O₂ peak. This further supports NIRS assessment of muscle mitochondrial capacity providing additional evidence for NIRS as a promising approach to monitor mitochondrial capacity, also in an exclusively female population.

Bilateral NIRS measurements of muscle mitochondrial capacity: Feasibility and repeatability

Background

Non‐invasive determination of mitochondrial capacity via near infrared spectroscopy (NIRS) typically involves voluntary exercise of a single muscle group followed by as many as 26 brief ischemic cuff occlusions to determine a single recovery rate constant (k).

Purpose

To determine the within‐ and between‐visit repeatability of a shortened bilateral NIRS protocol, and to establish the feasibility of hamstring k measurements.

Methods

Sixteen young (eight women, eight men; 22 ± 3 years) active adults underwent a bilateral electrical stimulation protocol in which multiple (n = 4) measurements of k for the vastus lateralis (VL) and medial hamstring (MH) muscles were determined on two visits. Repeatability (CV% and intraclass correlations, ICC) and equivalency across visits were assessed for both muscles.

Results

Mean k values in the VL were consistent with published values and within‐visit ICCs were moderately high for both muscles in both sexes. In men, average k values on visit 2 were within 1% (VL muscle) and 5% (MH muscle) of the values on visit 1 (all p > 0.78). In women, average k values were 10%–15% lower on visit 2 (p = 0.01 and p = 0.15 for MH and VL) with the largest between‐visit differences in a subset of participants with the most days between visits.

Conclusions

This bilateral NIRS protocol is time efficient and provides valid estimates of k in both sexes and muscle groups with acceptable within‐visit repeatability. Lower than expected between‐visit repeatability in some participants reinforces the need for further investigation of this newly developed protocol to identify and control for experimental and behavioral sources of variation.

Sex differences in the contribution of different physiological systems to physical function in older adults

Having the physical function to undertake activities of daily living (ADLs) is essential in order to maintain independence. The aim of this study is to investigate factors associated with physical function in older adults and determine if these associations differ in men versus women. In total, 726 participants (57% men; 73±7 years old) from a population-based cohort, the Southall and Brent Revisited (SABRE) study, completed questionnaires permitting a physical function score (PFS) to be calculated. Detailed phenotyping was performed including cardiovascular (echocardiography and macrovascular and microvascular functions), skeletal muscle (grip strength and oxidative capacity) and lung (pulmonary) function measurements. In a sub-group, maximal aerobic capacity was estimated from a sub-maximal exercise test. In women versus men, the association between grip strength and PFS was nearly 3 times stronger, and the association between microvascular dysfunction and PFS was over 5 times stronger (standardized β-coefficient (95% CI) 0.34 (0.22, 0.45) versus 0.11 (0.01,0.22) and -0.27 (-0.37, -0.17) versus -0.05 (-0.14, 0.04), respectively). In men, the association between cardiorespiratory fitness and PFS was 3 times greater than that in women (standardized β-coefficient (95% CI) 0.33 (0.22, 0.45) versus 0.10 (-0.04, 0.25). Cardiovascular, skeletal muscle and pulmonary factors all contribute to self-reported physical function, but the relative pattern of contribution differs by sex. Grip strength and microvascular function are most strongly associated with physical function in women while cardiorespiratory fitness is most strongly associated with physical function in men. This is relevant to the design of effective interventions that target maintenance of physical function in old age.

Measurement of muscle blood flow and O2 uptake via near-infrared spectroscopy using a novel occlusion protocol

We describe here a novel protocol that sequentially combines venous followed by arterial occlusions to determine muscle blood flow and O₂ uptake from a single measurement point using near-infrared spectroscopy (NIRS) during handgrip exercise. NIRS data were obtained from the flexor digitorum superficialis (FDS) muscle on the dominant arm of 15 young, healthy adults (3 women; 26 ± 7 years; 78.6 ± 9.1 kg). Participants completed a series of 15-s static handgrip contractions at 20, 40 and 60% of maximal voluntary contraction (MVC) immediately followed by either a: (i) venous occlusion (VO); (ii); arterial occlusion (AO); or venous then arterial occlusion (COMBO). Each condition was repeated 3 times for each exercise-intensity. The concordance correlation coefficient (CCC) and robust linear mixed effects modeling were used to determine measurement agreement between vascular occlusion conditions. FDS muscle blood flow ([Formula: see text]) and conductance ([Formula: see text]) demonstrated strong absolute agreement between VO and COMBO trials from rest up to 60%MVC, as evidenced by high values for CCC (> 0.82) and a linear relationship between conditions that closely approximated the line-of-identity (perfect agreement). Conversely, although FDS muscle O₂ uptake ([Formula: see text]) displayed "substantial" to "near perfect" agreement between methods across exercise intensities (i.e., CCC > 0.80), there was a tendency for COMBO trials to underestimate [Formula: see text] by up to 7%. These findings indicate that the COMBO method provides valid estimates of [Formula: see text] and, to a slightly lesser extent, [Formula: see text] at rest and during static handgrip exercise up to 60%MVC. Practical implications and suggested improvements of the method are discussed.

The Case for Measuring Long Bone Hemodynamics With Near-Infrared Spectroscopy

Diseases and associated fragility of bone is an important medical issue. There is increasing evidence that bone health is related to blood flow and oxygen delivery. The development of non-invasive methods to evaluate bone blood flow and oxygen delivery promise to improve the detection and treatment of bone health in human. Near-infrared spectroscopy (NIRS) has been used to evaluate oxygen levels, blood flow, and metabolism in skeletal muscle and brain. While the limited penetration depth of NIRS restricts its application, NIRS studies have been performed on the medial aspect of the tibia and some other prominent bone sites. Two approaches using NIRS to evaluate bone health are discussed: (1) the rate of re-oxygenation of bone after a short bout of ischemia, and (2) the dynamics of oxygen levels during an intervention such as resistance exercise. Early studies have shown these approaches to have the potential to evaluate bone vascular health as well as the predicted efficacy of an intervention before changes in bone composition are detectable. Future studies are needed to fully develop and exploit the use of NIRS technology for the study of bone health.

NIRS-derived skeletal muscle oxidative capacity is correlated with aerobic fitness and independent of sex

Near-infrared spectroscopy (NIRS) provides a simple and reliable measure of skeletal muscle oxidative capacity; however, its relationship to aerobic fitness and sex are unclear. We hypothesized that NIRS-derived oxidative capacity in the vastus lateralis (VL) and medial gastrocnemius (MG) would be correlated with indices of aerobic fitness and independent of sex. Twenty-six participants (13 males, 13 females) performed ramp- and step-incremental tests to volitional exhaustion on separate days to establish maximal oxygen uptake (V̇o2max), peak power output (PPO), lactate threshold (LT), gas exchange threshold (GET), respiratory compensation point (RCP), and maximal fat oxidation (MFO). Data were normalized to lean body mass to account for sex-based differences in body composition. Exercise tests were preceded by duplicate measurements of NIRS-derived oxidative capacity on the VL and MG muscles (i.e., repeated arterial occlusions following a brief set of muscle contractions). Skeletal muscle oxidative capacity for the VL (means ± SD: 21.9 ± 4.6 s) and MG (22.5 ± 6.1 s) were similar but unrelated (r2 = 0.03, P = 0.39). Skeletal muscle oxidative capacity for the VL, but not the MG (P > 0.05 for all variables), was significantly correlated with V̇o2max (r2 = 0.24; P = 0.01), PPO (r2 = 0.23; P = 0.01), LT (r2 = 0.23; P = 0.01), GET (r2 = 0.23; P = 0.01), and RCP (r2 = 0.27; P = 0.006). MFO was not correlated with VL or MG skeletal muscle oxidative capacity (P > 0.05). Females (54.9 ± 4.5 mL·kg LBM-1·min-1) and males (56.0 ± 6.2 mL·kg LBM-1·min-1), matched for V̇o2max (P = 0.62), had similar NIRS-derived oxidative capacities for VL (20.7 ± 4.4 vs. 23.2 ± 4.6 s; P = 0.18) and MG (24.4 ± 6.8 vs. 20.5 ± 4.8 s; P = 0.10). Overall, NIRS-derived skeletal muscle oxidative capacity in VL is indicative of aerobic fitness and independent of sex in humans.NEW & NOTEWORTHY Near-infrared spectroscopy (NIRS) can be used to measure skeletal muscle oxidative capacity. Here, we demonstrated that NIRS-derived skeletal muscle oxidative capacity of the vastus lateralis was independent of sex, reliable across and within days, and correlated with maximal and submaximal indices of aerobic fitness, including maximal oxygen uptake, lactate threshold, and respiratory compensation point. These findings highlight the utility of NIRS for investigating skeletal muscle oxidative capacity in females and males.

Reliability and reproducibility of a four arterial occlusions protocol for assessing muscle oxidative metabolism at rest and after exercise using near-infrared spectroscopy

OBJECTIVE

To assess the reliability and reproducibility of using a four arterial occlusions protocol and near-infrared spectroscopy (NIRS) to measure resting and post-exercise muscle oxidative metabolism (mVO₂).

APPROACH

mVO₂ was measured on the forearm muscles on two different days (day1 and day2) within one week in 11 healthy young adults (24.2 ± 2.7 years; 5 males). mVO₂ was measured using NIRS during four repeated arterial occlusions at rest, and 5 min after exercise consisting of 90 s of rapid concentric contractions (5 minEPOC).

MAIN RESULTS

Resting mVO₂ with four measurements was 17.88 ± 3.04% min^-1 on day 1 and 19.42 ± 3.03% min^-1 on day 2 (p = 0.171) with a coefficient of variation (CV) of 10.1%. When using only the first measurement, the CV increased to 18.5% (p = 0.039). 5minEPOC was 212.4 ± 142.5% and 177.1 ± 125.8% higher than resting and was not different between days one and two (53.83 ± 21.17% min^-1 and 52.22 ± 22.10% min^-1, respectively, p= 0.199). The CV and intraclass correlation (ICC) for 5minEPOC between days one and two were, 6.5% and 0.98, respectively. Using only the first value for 5minEPOC resulted in slightly higher CV but similar ICC (7.6% and 0.98, respectively; both p > 0.05).

SIGNIFICANCE

Our results suggest that within a single testing session, one arterial occlusion can provide reproducible measurements for both resting and post-exercise mVO₂ similar to that of a four arterial occlusions protocol. While a four arterial occlusion protocol provides similar reliability for post-exercise mVO₂ with one arterial occlusion, it reduces the day-to-day variance for resting mVO₂ and therefore should be employed for longitudinal studies.

Type 2 diabetes does not account for ethnic differences in exercise capacity or skeletal muscle function in older adults

AIMS/HYPOTHESIS

The aim of this study was to compare exercise capacity, strength and skeletal muscle perfusion during exercise, and oxidative capacity between South Asians, African Caribbeans and Europeans, and determine what effect ethnic differences in the prevalence of type 2 diabetes has on these functional outcomes.

METHODS

In total, 708 participants (aged [mean±SD] 73 ± 7 years, 56% male) were recruited from the Southall and Brent Revisited (SABRE) study, a UK population-based cohort comprised of Europeans (n = 311) and South Asian (n = 232) and African Caribbean (n = 165) migrants. Measurements of exercise capacity using a 6 min stepper test (6MST), including measurement of oxygen consumption ([Formula: see text]) and grip strength, were performed. Skeletal muscle was assessed using near infrared spectroscopy (NIRS); measures included changes in tissue saturation index (∆TSI%) with exercise and oxidative capacity (muscle oxygen consumption recovery, represented by a time constant [τ]). Analysis was by multiple linear regression.

RESULTS

When adjusted for age and sex, in South Asians and African Caribbeans, exercise capacity was reduced compared with Europeans ([Formula: see text] [ml min-1 kg-1]: β = -1.2 [95% CI -1.9, -0.4], p = 0.002, and β -1.7 [95% CI -2.5, -0.8], p < 0.001, respectively). South Asians had lower and African Caribbeans had higher strength compared with Europeans (strength [kPa]: β = -9 [95% CI -12, -6), p < 0.001, and β = 6 [95% CI 3, 9], p < 0.001, respectively). South Asians had greater decreases in TSI% and longer τ compared with Europeans (∆TSI% [%]: β = -0.9 [95% CI -1.7, -0.1), p = 0.024; τ [s]: β = 11 [95% CI 3, 18], p = 0.006). Ethnic differences in [Formula: see text] and grip strength remained despite adjustment for type 2 diabetes or HbA1c (and fat-free mass for grip strength). However, the differences between Europeans and South Asians were no longer statistically significant after adjustment for other possible mediators or confounders (including physical activity, waist-to-hip ratio, cardiovascular disease or hypertension, smoking, haemoglobin levels or β-blocker use). The difference in ∆TSI% between Europeans and South Asians was marginally attenuated after adjustment for type 2 diabetes or HbA1c and was also no longer statistically significant after adjusting for other confounders; however, τ remained significantly longer in South Asians vs Europeans despite adjustment for all confounders.

CONCLUSIONS/INTERPRETATION

Reduced exercise capacity in South Asians and African Caribbeans is unexplained by higher rates of type 2 diabetes. Poorer exercise tolerance in these populations, and impaired muscle function and perfusion in South Asians, may contribute to the higher morbidity burden of UK ethnic minority groups in older age.

Near Infrared Spectroscopy Measurements of Mitochondrial Capacity Using Partial Recovery Curves

Background

Near-infrared spectroscopy (NIRS) has been used to measure muscle mitochondrial capacity (mVO₂max) as the recovery rate constant of muscle metabolism after exercise. The current method requires as many as 50 short ischemic occlusions to generate two recovery rate constants.

Purpose

To determine the validity and repeatability of using a 6-occlusion protocol versus one with 22 occlusions to measure muscle mitochondrial capacity. The order effect of performing multiple Mito6 test was also evaluated.

Method

In two independent data sets (bicep n = 7, forearm A n = 23), recovery curves were analyzed independently using both the 6 and 22 occlusion methods. A third data set (forearm B n = 16) was generated on the forearm muscles of healthy subjects using four 6-occlusion tests performed in succession. Recovery rate constants were generated using a MATLAB routine.

Results

When calculated from the same data set, the recovery rate constants were not significantly different between the 22 occlusion and 6 occlusion methods for the bicep (1.43 ± 0.33 min^–1, 1.43 ± 0.35 min^–1, p = 0.81) and the forearm A (1.97 ± 0.40 min^–1, 1.97 ± 0.43 min^–1, p = 0.90). Equivalence testing showed that the mean difference was not different than zero and the 90% confidence intervals were within 5% of the average rate constant. This was true for the Mito6 and the Mito5^∗ approaches. Bland–Altman analysis showed a slope of 0.21 min^–1 and an r of 0.045 for the bicep dataset and a slope of −0.01 min^–1 and an r of 0.045 for the forearm A dataset. When performing the four 6-occlusion tests; recovery rate constants showed no order effects (1.50 ± 0.51 min^–1, 1.42 ± 0.54 min^–1, 1.26 ± 0.41 min^–1, 1.29 ± 0.47 min^–1, P > 0.05).

Conclusion

The Mito6 analysis is a valid and repeatable approach to measure mitochondrial capacity. The Mito6 protocol used fewer ischemic occlusion periods and multiple tests could be performed in succession in less time, increasing the practicality of the NIRS mitochondrial capacity test. There were no order effects for the rate constants of four repeated 6-occlusion tests of mitochondrial capacity, supporting the use of multiple tests to improve accuracy.

MUSCLE MITOCHONDRIAL CAPACITY AND ENDURANCE IN ADULTS WITH TYPE 1 DIABETES

The impact of type 1 diabetes (T1D) on muscle endurance and oxidative capacity is currently unknown.

Purpose

Measure muscle endurance and oxidative capacity of adults with T1D compared to controls.

Methods

A cross-sectional study design with a control group was used. Subjects (19-37 years old) with T1D (n=17) and controls (n=17) were assessed with hemoglobin A1c (HbA1c) and casual glucose. Muscle endurance was measured with an accelerometer at stimulation frequencies of 2, 4, and 6 Hz for a total of nine minutes. Mitochondrial capacity was measured using near-infrared spectroscopy after exercise as the rate constant of the rate of recovery of oxygen consumption.

Results

T1D and control groups were similar in age, sex, height, and race. The T1D group had slightly higher BMI values and adipose tissue thickness over the forearm muscles. Casual glucose was 150±70 mg/dL for T1D and 98±16 mg/dL for controls (P=0.006). HbA1c of T1D subjects was 7.1±0.9% and 5.0±0.4% for controls (P<0.01). Endurance indexes at 2, 4, and 6 Hz were 94.5±5.2%, 81.8±8.4%, and 68.6±13.5% for T1D and 94.6±4.1%, 85.9±6.3%, and 68.7±15.4% for controls (p = 0.97, 0.12, 0.99, respectively). There were no differences between groups in mitochondrial capacity (T1D= 1.9±0.5 min^-1 and control=1.8±0.4 min^-1, P=0.29) or reperfusion rate (T1D= 8.8±2.8s and control=10.3±3.0s, P=0.88). There were no significant correlations between HbA1c and either muscle endurance, mitochondrial capacity or reperfusion rate.

Conclusions

Adults with T1D did not have reduced oxidative capacity, muscle endurance or muscle reperfusion rates compared to controls. HbA1c also did not correlate with muscle endurance, mitochondrial capacity or reperfusion rates. Future studies should extend these measurements to older people or people with poorly-controlled T1D.

Evaluating the NIRS-derived microvascular O2 extraction "reserve" in groups varying in sex and training status using leg blood flow occlusions

It has been demonstrated that the plateau in the near-infrared spectroscopy (NIRS) derived deoxygenated hemoglobin and myoglobin (deoxy[Hb+Mb]) signal (i.e., deoxy[Hb+Mb]PLATEAU) towards the end of a ramp-incremental (RI) test does not represent the upper-limit in O2 extraction of the vastus lateralis (VL) muscle, given that an O2 extraction reserve has been recently observed. This study aimed to investigate whether this O2 extraction reserve was present in various populations and whether it exhibited sex- and/or training- related differences.Sixteen men- 8 untrained (27±5 years; 83±11 kg; 179±9 cm), 8 trained (27±4 years; 82±10 kg; 182±8 cm) and 9 trained women (27±2 years; 66±10 kg; 172±6 cm) performed a RI cycling test to exhaustion. The NIRS-derived deoxy[Hb+Mb] signal was measured continuously on the VL as a proxy for O2 extraction. A leg blood flow occlusion (i.e., ischemia) was performed at rest (LBFOCC 1) and immediately post the RI test (LBFOCC 2).No significant difference was found between the deoxy[Hb+Mb] amplitude during LBFOCC 1 and the deoxy[Hb+Mb]PLATEAU (p>0.05) nor between baseline (bsln) deoxy[Hb+Mb] values. deoxy[Hb+Mb] amplitude during LBFOCC 2 was significantly greater than LBFOCC 1 and at deoxy[Hb+Mb]PLATEAU (p<0.05) with group means ~30-45% higher than the deoxy[Hb+Mb]PLATEAU and LBFOCC 1 (p<0.05). No significant differences were found between groups in O2 extraction reserve, regardless of sex- or training-statusThe results of this study demonstrated the existence of an O2 extraction reserve in different populations, and that neither sex- nor training-related differences affect the amplitude of the reserve.

Development of a near-infrared spectroscopy interface able to assess oxygen recovery kinetics in the right and left sides of the pelvic floor

Near-infrared spectroscopy (NIRS) muscle oxygenation data are relied on in sports medicine. Many women with urinary incontinence (UI) have dysfunctional pelvic floor muscles (PFMs) but their evaluation lacks such measures; a transvaginal NIRS interface would enable the PFM to be interrogated. Paired miniature fiber-optic cables were configured on a rigid foam insert so their emitter detector arrays with an interoptode distance of 20 mm apposed the right and left inner sides of a disposable clear plastic vaginal speculum, and linked to a standard commercial NIRS instrument. Measurement capability was assessed through conduct of three maximum voluntary contractions (MVCs) and one sustained maximum voluntary contraction of the PFM with calculation of HbDiff (½RT), a validated muscle reoxygenation kinetic parameter. In all four asymptomatic controls, mean age 40, mean BMI 21.4, MVCs were associated with changes in PFM oxyhemoglobin (O2Hb), deoxyhemoglobin (HHb) concentration, and their difference (HbDiff) comparable to those in voluntary muscle sports medicine studies. NIRS data during recovery (reoxygenation) allowed calculation of HbDiff (½RT). New techniques are called for to evaluate UI. This NIRS interface warrants further development as the provision of quantitative reoxygenation kinetics offers more comprehensive evaluation of patients with PFM dysfunction.

Interpretation of Near-Infrared Spectroscopy (NIRS) Signals in Skeletal Muscle

Near-infrared spectroscopy (NIRS) uses the relative absorption of light at 850 and 760 nm to determine skeletal muscle oxygen saturation. Previous studies have used the ratio of both signals to report muscle oxygen saturation.

PURPOSE

The purpose of this pilot study is to assess the different approaches used to represent muscle oxygen saturation and to evaluate the pulsations of oxygenated hemoglobin/myoglobin (O₂heme) and deoxygenated hemoglobin/myoglobin (Heme) signals.

METHOD

Twelve participants, aged 20-29 years, were tested on the forearm flexor muscles using continuous-wave NIRS at rest. Measurements were taken during 2-3 min rest, physiological calibration (5 min ischemia), and reperfusion. Ten participants were included in the study analysis.

RESULTS

There was a significant difference in pulse size between O₂heme and Heme signals at the three locations (p < 0.05). Resting oxygen saturation was 58.8% + 9.2%, 69.6% + 3.9%, and 89.2% + 6.9% when calibrated using O₂heme, the tissue oxygenation/saturation index (TSI), and Heme, respectively.

CONCLUSION

The difference in magnitude of O₂heme and Heme pulses with each heartbeat might suggest different anatomical locations of these signals, for which calibrating with just one of the signals instead of the ratio of both is proposed. Calculations of physiological calibration must account for increased blood volume in the tissue because of the changes in blood volume, which appear to be primarily from the O₂heme signal. Resting oxygen levels calibrated with Heme agree with theoretical oxygen saturation.

Understanding near infrared spectroscopy and its application to skeletal muscle research

Near infrared spectroscopy (NIRS) is a powerful noninvasive tool with which to study the matching of oxygen delivery to oxygen utilization and the number of new publications utilizing this technique has increased exponentially in the last 20 yr. By measuring the state of oxygenation of the primary heme compounds in skeletal muscle (hemoglobin and myoglobin), greater understanding of the underlying control mechanisms that couple perfusive and diffusive oxygen delivery to oxidative metabolism can be gained from the laboratory to the athletic field to the intensive care unit or emergency room. However, the field of NIRS has been complicated by the diversity of instrumentation, the inherent limitations of some of these technologies, the associated diversity of terminology, and a general lack of standardization of protocols. This Cores of Reproducibility in Physiology (CORP) will describe in basic but important detail the most common methodologies of NIRS, their strengths and limitations, and discuss some of the potential confounding factors that can affect the quality and reproducibility of NIRS data. Recommendations are provided to reduce the variability and errors in data collection, analysis, and interpretation. The goal of this CORP is to provide readers with a greater understanding of the methodology, limitations, and best practices so as to improve the reproducibility of NIRS research in skeletal muscle.

Muscle-Specific Endurance of the Lower Back Erectors Using Electrical Twitch Mechanomyography

Lower back pain is a common symptom potentially associated with skeletal muscle dysfunction. The purpose of this study was to evaluate endurance in the lower back muscles of healthy participants using accelerometer-based mechanomyography. Methods: Young healthy subjects (N = 7) were tested. Surface electrodes and a tri-axial accelerometer were placed over the erector spinae muscle along the T11-L1 Vertebrae. Stimulation was for 3 min each at 2, 4, and 6 Hz, and changes in acceleration were used to calculate an endurance index (EI). Reproducibility of the endurance index measurements was tested on two separate days. Wrist flexor and vastus lateralis muscles were tested for comparison. Near Infrared Spectroscopy (NIRS) was used to measure muscle oxygen levels (O₂Hb) (N = 5). EI was 70.3 + 13.4, 32.6 + 8.4, and 19.2 + 6.2% for 2, 4, 6 Hz, respectively. The coefficients of variation were 9.8, 13.9, and 20.3% for 2, 4, 6 Hz, respectively. EI values were lower in the erector spinae muscles compared to the arm and the leg (p < 0.05). O₂Hb values were 86.4 + 10.9% at rest and were 77.2 + 15.5, 84.3 + 14.1, and 84.1 + 18.9% for 2, 4, 6 Hz, respectively (p > 0.05, all comparisons). An endurance index can be obtained from the lower back erectors muscles that is reproducible and not influenced by voluntary effort or muscle oxygen levels.

Muscle Oximetry in Sports Science: A Systematic Review

BACKGROUND

Since the introduction (in 2006) of commercially available portable wireless muscle oximeters, the use of muscle near-infrared spectroscopy (NIRS) technology is gaining in popularity as an application to observe changes in muscle metabolism and muscle oxygenation during and after exercise or training interventions in both laboratory and applied sports settings.

OBJECTIVES

The objectives of this systematic review were to highlight the application of muscle oximetry in evaluating oxidative skeletal muscle performance to sport activities and emphasize how this technology has been applied to exercise and training.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed in a systematic fashion to search, assess and synthesize existing literature on this topic. The Scopus and MEDLINE/PubMed electronic databases were searched to 1 March 2017. Potential inclusions were screened against eligibility criteria relating to recreationally trained to elite athletes, with or without training programs, who must have assessed physiological variables monitored by commercial oximeters or NIRS instrumentation.

RESULTS

Of the 14,609 identified records, only 57 studies met the eligibility criteria. This systematic review highlighted a number of key findings in 16 sporting activities. Overall, NIRS information can be used as a marker of skeletal muscle oxidative capacity and for analyzing muscle performance factors.

CONCLUSIONS

Although NIRS instrumentation is promising in evaluating oxidative skeletal muscle performance when used in sport settings, there is still the need for further instrumental development and randomized/longitudinal trials to support the detailed advantages of muscle oximetry utilization in sports science.

Near infrared spectroscopy-guided exercise training for claudication in peripheral arterial disease

Rationale

Supervised treadmill exercise for claudication in peripheral arterial disease is effective but poorly tolerated because of ischemic leg pain. Near infrared spectroscopy allows non-invasive detection of muscle ischemia during exercise, allowing for characterization of tissue perfusion and oxygen utilization during training.

Objective

We evaluated walking time, muscle blood flow, and muscle mitochondrial capacity in patients with peripheral artery disease after a traditional pain-based walking program and after a muscle oxygen-guided walking program.

Method and results

Patients with peripheral artery disease trained thrice weekly in 40-minute-long sessions for 12 weeks, randomized to oxygen-guided training ( n = 8, age 72 ± 9.7 years, 25% female) versus traditional pain-based training ( n = 10, age 71.6 ± 8.8 years, 20% female). Oxygen-guided training intensity was determined by maintaining a 15% reduction in skeletal muscle oxygenation by near infrared spectroscopy rather than relying on symptoms of pain to determine exercise effort. Pain free and maximal walking times were measured with a 12-minute Gardner treadmill test. Gastrocnemius mitochondrial capacity and blood flow were measured using near infrared spectroscopy. Baseline pain-free walking time was similar on a Gardner treadmill test (2.5 ± 0.9 vs. 3.6 ± 1.0 min, p = 0.5). After training, oxygen-guided cohorts improved similar to pain-guided cohorts (pain-free walking time 6.7 ± 0.9 vs. 6.9 ± 1.1 min, p < 0.01 for change from baseline and p = 0.97 between cohorts). Mitochondrial capacity improved in both groups but more so in the pain-guided cohort than in the oxygen-guided cohort (38.8 ± 8.3 vs. 14.0 ± 9.3, p = 0.018). Resting muscle blood flow did not improve significantly in either group with training.

Conclusions

Oxygen-guided exercise training improves claudication comparable to pain-based training regimens. Adaptations in mitochondrial function rather than increases in limb perfusion may account for functional improvement. Increases in mitochondrial oxidative capacity may be proportional to the degree of tissue hypoxia during exercise.

Skeletal Muscle Neurovascular Coupling, Oxidative Capacity, and Microvascular Function with 'One Stop Shop' Near-infrared Spectroscopy

Exercise represents a major hemodynamic stress that demands a highly coordinated neurovascular response in order to match oxygen delivery to metabolic demand. Reactive hyperemia (in response to a brief period of tissue ischemia) is an independent predictor of cardiovascular events and provides important insight into vascular health and vasodilatory capacity. Skeletal muscle oxidative capacity is equally important in health and disease, as it determines the energy supply for myocellular processes. Here, we describe a simple, non-invasive approach using near-infrared spectroscopy to assess each of these major clinical endpoints (reactive hyperemia, neurovascular coupling, and muscle oxidative capacity) during a single clinic or laboratory visit. Unlike Doppler ultrasound, magnetic resonance images/spectroscopy, or invasive catheter-based flow measurements or muscle biopsies, our approach is less operator-dependent, low-cost, and completely non-invasive. Representative data from our lab taken together with summary data from previously published literature illustrate the utility of each of these end-points. Once this technique is mastered, application to clinical populations will provide important mechanistic insight into exercise intolerance and cardiovascular dysfunction.

Near-infrared spectroscopy detects age-related differences in skeletal muscle oxidative function: promising implications for geroscience

Age is the greatest risk factor for chronic disease and is associated with a marked decline in functional capacity and quality of life. A key factor contributing to loss of function in older adults is the decline in skeletal muscle function. While the exact mechanism(s) remains incompletely understood, age-related mitochondrial dysfunction is thought to play a major role. To explore this question further, we studied 15 independently living seniors (age: 72 ± 5 years; m/f: 4/11; BMI: 27.6 ± 5.9) and 17 young volunteers (age: 25 ± 4 years; m/f: 8/9; BMI: 24.0 ± 3.3). Skeletal muscle oxidative function was measured in forearm muscle from the recovery kinetics of muscle oxygen consumption using near-infrared spectroscopy (NIRS). Muscle oxygen consumption was calculated as the slope of change in hemoglobin saturation during a series of rapid, supra-systolic arterial cuff occlusions following a brief bout of exercise. Aging was associated with a significant prolongation of the time constant of oxidative recovery following exercise (51.8 ± 5.4 sec vs. 37.1 ± 2.1 sec, P = 0.04, old vs. young, respectively). This finding suggests an overall reduction in mitochondrial function with age in nonlocomotor skeletal muscle. That these data were obtained using NIRS holds great promise in gerontology for quantitative assessment of skeletal muscle oxidative function at the bed side or clinic.

Improved Exercise-Related Skeletal Muscle Oxygen Consumption Following Uptake of Endurance Training Measured Using Near-Infrared Spectroscopy

Skeletal muscle metabolic function is known to respond positively to exercise interventions. Developing non-invasive techniques that quantify metabolic adaptations and identifying interventions that impart successful response are ongoing challenges for research. Healthy non-athletic adults (18–35 years old) were enrolled in a study investigating physiological adaptations to a minimum of 16 weeks endurance training prior to undertaking their first marathon. Before beginning training, participants underwent measurements of skeletal muscle oxygen consumption using near-infrared spectroscopy (NIRS) at rest (resting muscleV˙O₂) and immediately following a maximal exercise test (post-exercise muscleV˙O₂). Exercise-related increase in muscleV˙O₂ (ΔmV˙O₂) was derived from these measurements and cardio-pulmonary peakV˙O₂ measured by analysis of expired gases. All measurements were repeated within 3 weeks of participants completing following the marathon and marathon completion time recorded. MuscleV˙O₂ was positively correlated with cardio-pulmonary peakV˙O₂ (r = 0.63, p < 0.001). MuscleV˙O₂ increased at follow-up (48% increase; p = 0.004) despite no change in cardio-pulmonary peakV˙O₂ (0% change; p = 0.97). Faster marathon completion time correlated with higher cardio-pulmonary peakV˙O₂ (r_partial = −0.58, p = 0.002) but not muscleV˙O₂ (r_partial = 0.16, p = 0.44) after adjustment for age and sex [and adipose tissue thickness (ATT) for muscleV˙O₂ measurements]. Skeletal muscle metabolic adaptions occur following training and completion of a first-time marathon; these can be identified non-invasively using NIRS. Although the cardio-pulmonary system is limiting for running performance, skeletal muscle changes can be detected despite minimal improvement in cardio-pulmonary function.

Age-related microvascular dysfunction: novel insight from near-infrared spectroscopy

NEW FINDINGS

What is the central question of this study? Can near-infrared spectroscopy (NIRS)-derived post-occlusion tissue oxygen saturation recovery kinetics be used to study age-related impairments in microvascular function? What is the main finding and its importance? Using a previously established 5 min cuff occlusion protocol, we found that NIRS-derived indices of microvascular function were markedly reduced in elderly compared with young participants. However, when we controlled for the absolute level of vasodilatory stimulus and matched the tissue desaturation level between groups, we found similar responses in young and elderly participants. Overall, these data highlight the important role NIRS can serve in clinical vascular biology, but also establish the need for assessing tissue ischaemia during cuff occlusion protocols. Near-infrared spectroscopy (NIRS) has emerged as a promising tool to evaluate vascular reactivity in vivo. Whether this approach can be used to assess age-related impairments in microvascular function has not been tested. Tissue oxygen saturation (StO2) post-occlusion recovery kinetics were measured in two distinct age groups (<35 and >65 years of age) using NIRS placed over the flexor digitorum profundus. Key end-points included the following: (i) the desaturation rate during cuff occlusion; (ii) the lowest StO2 value obtained during ischaemia (StO2min); (iii) StO2 reperfusion rate; (iv) the highest StO2 value reached after cuff release (StO2max); and (v) the reactive hyperaemia area under the curve (AUC). At first, using a conventional 5 min cuff occlusion protocol, the elderly participants achieved a much slower rate of oxygen recovery (1.5 ± 0.2 versus 2.5 ± 0.2% s^-1 ), lower StO2max (85.2 ± 2.9 versus 92.3 ± 1.5%) and lower reactive hyperaemia AUC (2651.8 ± 307.0 versus 4940.0 ± 375.8% s^-1 ). However, owing to a lower skeletal muscle resting metabolic rate, StO2min was also significantly attenuated in the elderly participants compared with the young control subjects (55.7 ± 3.5 versus 41.0 ± 3.4%), resulting in a much lower ischaemic stimulus. To account for this important difference between groups, we then matched the level of tissue ischaemia in a subset of young healthy participants by reducing the cuff occlusion protocol to 3 min. Remarkably, when we controlled for tissue ischaemia, we observed no differences in any of the hyperaemic end-points between the young and elderly participants. These data highlight the important role NIRS can serve in vascular biology, but also establish the need for assessing tissue ischaemia during cuff occlusion protocols.

In Vivo Assessment of Mitochondrial Dysfunction in Clinical Populations Using Near-Infrared Spectroscopy

The ability to sustain submaximal exercise is largely dependent on the oxidative capacity of mitochondria within skeletal muscle, and impairments in oxidative metabolism have been implicated in many neurologic and cardiovascular pathologies. Here we review studies which have demonstrated the utility of Near-infrared spectroscopy (NIRS) as a method of evaluating of skeletal muscle mitochondrial dysfunction in clinical human populations. NIRS has been previously used to noninvasively measure tissue oxygen saturation, but recent studies have demonstrated the utility of NIRS as a method of evaluating skeletal muscle oxidative capacity using post-exercise recovery kinetics of oxygen metabolism. In comparison to historical methods of measuring muscle metabolic dysfunction in vivo, NIRS provides a more versatile and economical method of evaluating mitochondrial oxidative capacity in humans. These advantages generate great potential for the clinical applicability of NIRS as a means of evaluating muscle dysfunction in clinical populations.

Neuroendocrine Response Following a Thoracic Spinal Manipulation in Healthy Men

Study Design Controlled laboratory study. Background Spinal manipulation (SM) can trigger a cascade of responses involving multiple systems, including the sympathetic nervous system and the endocrine system, specifically, the hypothalamic-pituitary axis. However, no manual therapy study has investigated the neuroendocrine response to SM (ie, sympathetic nervous system-hypothalamic-pituitary axis) in the same trial. Objective To determine short-term changes in sympathetic nervous system activity, heart rate variability, and endocrine activity (cortisol, testosterone, and testosterone-cortisol [T/C] ratio) following a thoracic SM. Methods Twenty-four healthy men aged between 18 and 45 years were randomized into 2 groups: thoracic SM (n = 12) and sham (n = 12). Outcome measures were salivary cortisol (micrograms per deciliter), salivary testosterone (picograms per milliliter), T/C ratio, heart rate variability, and changes in oxyhemoglobin concentration of the right calf muscle (micromoles per liter). Measurements were done before and at 5 minutes, 30 minutes, and approximately 6 hours after intervention. Results A statistically significant group-by-time interaction was noted for T/C ratio (P<.05) and salivary cortisol (P<.01) concentrations. Significant between-group differences were noted for salivary cortisol concentration at 5 minutes (mean difference, 0.35; 95% confidence interval: 0.12, 0.6; interaction: P<.01) and for T/C ratio at 6 hours postintervention (mean difference, -0.09; 95% confidence interval: -0.16, -0.04; P = .02). However, SM did not differentially alter oxyhemoglobin, testosterone, or heart rate variability relative to responses in the sham group. Conclusion Thoracic SM resulted in an immediate decrease in salivary cortisol concentration and reduced T/C ratio 6 hours after intervention. A pattern of immediate sympathetic excitation was also observed in the SM group. J Orthop Sports Phys Ther 2017;47(9):617-627. Epub 13 Jul 2017. doi:10.2519/jospt.2017.7348.

Skeletal muscle mitochondrial capacity in people with multiple sclerosis

Background

People with multiple sclerosis (MS) have functional disability and may have reduced muscle mitochondrial capacity.

Objective

The objective of this paper is to measure muscle mitochondrial capacity of leg muscles using near-infrared spectroscopy (NIRS) and compare to functional status.

Materials and methods

People with MS (n = 16) and a control (CON) group (n = 9) were evaluated for 25-ft walk time. Mitochondrial capacity of both gastrocnemius muscles were measured with NIRS as the rate of recovery of oxygen consumption in after exercise.

Results

Mitochondrial capacity was lower in the MS group compared to the CON group (rate constants: 1.13 ± 0.29 vs. 1.68 ± 0.37 min⁻¹, p < 0.05). There was a tendency for people with MS who used assistive devices to have lower mitochondrial capacity in the weaker leg (p = 0.07).

Conclusion

NIRS measurements of mitochondrial capacity suggest a 40% deficit in people with MS compared to CONs and this may contribute to walking disability.

Reproducibility of NIRS assessment of muscle oxidative capacity in smokers with and without COPD

Low muscle oxidative capacity contributes to exercise intolerance in chronic obstructive pulmonary disease (COPD). Near-infrared spectroscopy (NIRS) allows non-invasive determination of the muscle oxygen consumption (mV̇O₂) recovery rate constant (k), which is proportional to oxidative capacity assuming two conditions are met: 1) exercise intensity is sufficient to fully-activate mitochondrial oxidative enzymes; 2) sufficient O₂ availability. We aimed to determine reproducibility (coefficient of variation, CV; intraclass correlation coefficient, ICC) of NIRS k assessment in the gastrocnemius of 64 participants with (FEV₁ 64±23%predicted) or without COPD (FEV₁ 98±14%predicted). 10-15s dynamic contractions preceded 6min of intermittent arterial occlusions (5-10s each, ∼250mmHg) for k measurement. k was lower (P<0.05) in COPD (1.43±0.4min^-1; CV=9.8±5.9%, ICC=0.88) than controls (1.74±0.69min^-1; CV=9.9±8.4%; ICC=0.93). Poor k reproducibility was more common when post-contraction mV̇O₂ and deoxygenation were low, suggesting insufficient exercise intensity for mitochondrial activation and/or the NIRS signal contained little light reflected from active muscle. The NIRS assessment was well tolerated and reproducible for muscle dysfunction evaluation in COPD.

Oxygenation Threshold Derived from Near-Infrared Spectroscopy: Reliability and Its Relationship with the First Ventilatory Threshold

BACKGROUND

Near-infrared spectroscopy (NIRS) measurements of oxygenation reflect O2 delivery and utilization in exercising muscle and may improve detection of a critical exercise threshold.

PURPOSE

First, to detect an oxygenation breakpoint (Δ[O2HbMb-HHbMb]-BP) and compare this breakpoint to ventilatory thresholds during a maximal incremental test across sexes and training status. Second, to assess reproducibility of NIRS signals and exercise thresholds and investigate confounding effects of adipose tissue thickness on NIRS measurements.

METHODS

Forty subjects (10 trained male cyclists, 10 trained female cyclists, 11 endurance trained males and 9 recreationally trained males) performed maximal incremental cycling exercise to determine Δ[O2HbMb-HHbMb]-BP and ventilatory thresholds (VT1 and VT2). Muscle haemoglobin and myoglobin O2 oxygenation ([HHbMb], [O2HbMb], SmO2) was determined in m. vastus lateralis. Δ[O2HbMb-HHbMb]-BP was determined by double linear regression. Trained cyclists performed the maximal incremental test twice to assess reproducibility. Adipose tissue thickness (ATT) was determined by skinfold measurements.

RESULTS

Δ[O2HbMb-HHbMb]-BP was not different from VT1, but only moderately related (r = 0.58-0.63, p<0.001). VT1 was different across sexes and training status, whereas Δ[O2HbMb-HHbMb]-BP differed only across sexes. Reproducibility was high for SmO2 (ICC = 0.69-0.97), Δ[O2HbMb-HHbMb]-BP (ICC = 0.80-0.88) and ventilatory thresholds (ICC = 0.96-0.99). SmO2 at peak exercise and at occlusion were strongly related to adipose tissue thickness (r2 = 0.81, p<0.001; r2 = 0.79, p<0.001). Moreover, ATT was related to asymmetric changes in Δ[HHbMb] and Δ[O2HbMb] during incremental exercise (r = -0.64, p<0.001) and during occlusion (r = -0.50, p<0.05).

CONCLUSION

Although the oxygenation threshold is reproducible and potentially a suitable exercise threshold, VT1 discriminates better across sexes and training status during maximal stepwise incremental exercise. Continuous-wave NIRS measurements are reproducible, but strongly affected by adipose tissue thickness.

Measuring reactive hyperemia in the lower limb using near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) has been used to measure reactive hyperemia following a vascular occlusion. However, the procedures and methods of analysis used have varied. The purpose of the present study is to identify reproducible methods for measuring reactive hyperemia using HbO2 NIRS signals in the calf and foot. Healthy participants (10 male, 10 female) aged 19 to 28 years performed one of two tests: reproducibility trials or elevation protocol (30 and 60 cm limb elevation above the heart). The time to 50% reperfusion (T1/2) and the second (R2q) quartile rates of reperfusion were found to be the most reproducible parameters (coefficient of variation= 7.12 to 14.1%). The time to 95% reperfusion (T95) was 12.7% more reproducible on average than the previously reported parameter of time to peak hyperemia. Measures of reperfusion time and rate slowed with increasing limb elevation. Correlations were identified between the calf and foot in the measurements of R2q (R2 = 0.713, p = 0.021), T1/2 (R2 = 0.673, p = 0.033), and T95 (R2 = 0.792, p = 0.006). Half and 95% recovery times and second and third quartile rates expressed good reproducibility and sensitivity to change with reduced perfusion pressure. NIRS measures of reactive hyperemia have the potential to evaluate microvascular perfusion in clinical populations.

High oxygen extraction and slow recovery of muscle deoxygenation kinetics after neuromuscular electrical stimulation in COPD patients

PURPOSE

It was hypothesized that patients with chronic obstructive pulmonary disease (COPD) would exhibit a slow muscle deoxygenation (HHb) recovery time when compared with sedentary controls.

METHODS

Neuromuscular electrical stimulation (NMES 40 and 50 mA, 50 Hz, 400 µs) was employed to induce isometric contraction of the quadriceps. Microvascular oxygen extraction (µO2EF) and HHb were estimated by near-infrared spectroscopy (NIRS). Recovery kinetic was characterized by measuring the time constant Tau (HHb-τ). Torque and work were measured by isokinetic dynamometry in 13 non-hypoxaemic patients with moderate-to-severe COPD [SpO2 = 94.1 ± 1.6 %; FEV1 (% predict) 48.0 ± 9.6; GOLD II-III] and 13 age- and sex-matched sedentary controls.

RESULTS

There was no desaturation in either group during NMES. Torque and work were reduced in COPD versus control for 40 and 50 mA [torque (Nm) 50 mA = 28.9 ± 6.9 vs 46.1 ± 14.2; work (J) 50 mA = 437.2 ± 130.0 vs. 608.3 ± 136.8; P < 0.05 for all]. High µO2EF values were observed in the COPD group at both NMES intensities (corrected by muscle mass 50 mA = 6.18 ± 1.1 vs. 4.68 ± 1.0 %/kg; corrected by work 50 mA = 0.12 ± 0.05 vs. 0.07 ± 0.02 %/J; P < 0.05 for all). Absolute values of HHb-τ (50 mA = 31.11 ± 9.27 vs. 18.08 ± 10.70 s), corrected for muscle mass (50 mA 3.80 ± 1.28 vs. 2.05 ± 1.45 s/kg) and corrected for work (50 mA = 0.08 ± 0.04 vs. 0.03 ± 0.02 s/J) were reduced in COPD (P < 0.05 for all). The variables behaviour for 40 mA was similar to those of 50 mA.

CONCLUSIONS

COPD patients exhibited a slower muscle deoxygenation recovery time after NMES. The absence of desaturation, low torque and work, high µO2EF and high values for recovery time corrected by muscle mass and work suggest that intrinsic muscle dysfunction has an impact on muscle recovery capacity.

Recent developments in near-infrared spectroscopy (NIRS) for the assessment of local skeletal muscle microvascular function and capacity to utilise oxygen

Purpose of review

Continuous wave near infrared spectroscopy (CW NIRS) provides non-invasive technology to measure relative changes in oxy- and deoxy-haemoglobin in a dynamic environment. This allows determination of local skeletal muscle O₂ saturation, muscle oxygen consumption (V˙O2) and blood flow. This article provides a brief overview of the use of CW NIRS to measure exercise-limiting factors in skeletal muscle.

Recent findings

NIRS parameters that measure O₂ delivery and capacity to utilise O₂ in the muscle have been developed based on response to physiological interventions and exercise. NIRS has good reproducibility and agreement with gold standard techniques and can be used in clinical populations where muscle oxidative capacity or oxygen delivery (or both) are impaired. CW NIRS has limitations including: the unknown contribution of myoglobin to the overall signals, the impact of adipose tissue thickness, skin perfusion during exercise, and variations in skin pigmentation. These, in the main, can be circumvented through appropriate study design or measurement of absolute tissue saturation.

Summary

CW NIRS can assess skeletal muscle O₂ delivery and utilisation without the use of expensive or invasive procedures and is useable in large population-based samples, including older adults.

•

An overview of CW NIRS to measure O₂ utilisation and delivery is presented.

•

CW NIRS is cheap, non-invasive, portable and useable in population-based samples.

•

It is useful for understanding underlying mechanisms of deterioration in capacity.

The impact of venous occlusion per se on forearm muscle blood flow: implications for the near-infrared spectroscopy venous occlusion technique

The purpose of this study was to examine the effect of venous occlusion per se on forearm muscle blood flow, as determined by the near-infrared spectroscopy (NIRS) venous occlusion technique (NIRS-VOT). NIRS data were obtained from the flexor digitorum superficialis (FDS) muscle on the dominant arm of 16 young, ostensibly healthy participants (14 men and two women; 30 ± 6 year; 73 ± 7 kg). Participants completed a series of five venous occlusion trials while seated at rest, and a series of 12 venous occlusion trials during a reactive hyperaemia induced by 5 min of forearm arterial occlusion. The NIRS-VOT was used to assess FDS muscle blood flow (Q˙mus), beat-by-beat, over the first four cardiac beats during venous occlusions. Q˙mus was also reported as a cumulative value, wherein the first two, first three and first four cardiac beats were used to calculate muscle blood flow. We observed that Q˙mus was highest when calculated over the first cardiac beat during venous occlusions performed at rest and throughout reactive hyperaemia (P<0·05). Moreover, the inclusion of more than one cardiac beat in the calculation of Q˙mus underestimated muscle blood flows, irrespective of the prevailing level of arterial inflow. These findings support the idea that venous occlusion per se affects the measurement of Q˙mus via the NIRS-VOT. Accordingly, it is recommended that Q˙mus is determined over the first cardiac beat when using the NIRS-VOT to assess microvascular blood flow of human forearm muscles.