Differences in oxidative metabolism modulation induced by ischemia/reperfusion between trained and untrained individuals assessed by NIRS

Skeletal Muscle Resaturation Relates to Aerobic Fitness in Adults Participating in Strength and Aerobic Exercises

Purpose: This study examined differences in metrics of skeletal muscle re-saturation between strength and aerobically oriented individuals and potential relations between re-saturation and aerobic fitness. Methods: Forty-nine healthy young adult men and women completed body composition analysis, a maximal lower-body strength assessment, a maximal aerobic fitness (V . O 2 max ) test, and a near-infrared spectroscopy vascular occlusion test (NIRS+VOT). Skeletal muscle tissue oxygenation (StO2), oxygenated hemoglobin (O2Hb), and deoxygenated (HHb) hemoglobin were collected from a NIRS device attached to the vastus lateralis. Re-saturation measures (e.g. upslope, re-saturation max, and hypersaturation area under the curve (AUC)) were derived from the reperfusion phase of the NIRS+VOT. Results: All O2Hb and StO2 re-saturation metrics, particularly upslope (r = 0.622 and r = -.613, respectively), were significantly (p < .05) related to V . O 2 max . In the strength group, O2Hb and HHb upslope (r = 0.584; p < .001; r = -.550; p = .001, respectively) and re-saturation max (r = 0.372; p = .036; r = .562, p < .001, respectively) were significantly related to V . O 2 max . For the aerobic group, O2Hb upslope (r = .486; p = .048), re-saturation max (r = 0.535; p = .027), and hypersaturation AUC (r = 0.564; p = .018) were significantly related to V . O 2 max . The aerobic group had significantly (p = .011; BF10 = 8.043) greater O2Hb upslope (1.6 ± .789 vs. 1.1 ± .474 A.U.s-1) and (p = .027; BF10 = 2.929) hypersaturation AUC (1158.3 ± 545.02 vs. 860.4 ± 365.35 A.U.s-1) than the strength group. Conclusion: Upslope was the most related to V . O 2 max in strength and aerobically oriented adults. Interestingly, O2Hb re-saturation max may not be sensitive to differences between routine strength and aerobic exercise and may reflect shared underlying physiological mechanisms of the predominant fitness orientation.

Exercise responses to perceptually regulated high intensity interval exercise with continuous and intermittent hypoxia in inactive overweight individuals

To investigate the acute effects of hypoxia applied during discrete work and recovery phases of a perceptually regulated, high-intensity interval exercise (HIIE) on external and internal loads in inactive overweight individuals. On separate days, 18 inactive overweight (28.7 ± 3.3 kg m-2; 31 ± 8 years) men and women completed a cycling HIIE protocol (6 × 1 min intervals with 4 min active recovery, maintaining a perceived rating of exertion of 16 and 10 during work and recovery, respectively, on the 6-20 Borg scale) in randomized conditions: normoxia (NN), normobaric hypoxia (inspired O2 fraction ∼0.14) during both work and recovery (HH), hypoxia during recovery (NH) and hypoxia during work only (HN). Markers of external (relative mean power output, MPO) and internal load (blood lactate concentration, heart rate and tissue saturation index (TSI)) were measured. MPO was lower in HH compared to NN, NH and HN (all P < 0.001), with HN also being lower than NN (P < 0.001) and NH (P < 0.023). Heart rate was higher in HN than NN, HH and NH (all P < 0.001). Blood lactate response was higher in NN than HH (P = 0.003) and NH (P = 0.008). Changes in the TSI area above the curve were greater in HN relative to NN, HH and NH (all P < 0.001). Hypoxia applied intermittently during the work or recovery phases may mitigate the declines in mechanical output observed when exercise is performed in continuous hypoxia, although hypoxia implemented during the work phase resulted in elevated heart rate and lactate response. Specifically, exercise performance largely comparable to that in normoxia can be achieved when hypoxia is implemented exclusively during recovery.

Near-Infrared Spectroscopy (NIRS) to Assess Infection Complications During the Acute Phase of Acute Pancreatitis

BACKGROUND

Acute pancreatitis (AP) severity is correlated with systemic infection incidence in the acute phase, and it is important to assess inflammation during the disease course and to recognize infection at an early stage. As in sepsis, inflammation in AP impairs tissue oxygen metabolism and disrupts microcirculation. We performed a vascular occlusion test (VOT) via near-infrared spectroscopy (NIRS), which noninvasively monitors local oxygen in peripheral tissues, to evaluate tissue oxygen metabolism and blood circulation during the acute AP phase.

METHODS

Tissue oxygen metabolism was measured via an NIRS probe attached to the thenar eminence at admission and 7 days after admission. The upper arm was wrapped with a sphygmomanometer cuff while avoiding brachial artery compression for 3 min. The minimum desaturation value was defined as the minimum tissue oxygen index (TOI), the maximum reactive hyperemia value after release was defined as the maximum TOI, and the difference was defined as the ∆TOI. The time from the minimum TOI to maximum TOI was defined as the TOI interval.

RESULTS

Fifteen healthy volunteers, 13 patients with AP, and 12 patients with sepsis were included. The TOI at baseline and ∆TOI (parameter describing tissue oxygen metabolism) decreased in a stepwise manner, and the TOI interval (measure of peripheral vasodilatory capacity) was protracted in a stepwise manner among the three groups. In a subgroup analysis, no significant differences in the NIRS-derived variables between patients with AP complicated by infection and those without infection were observed at admission; however, after 7 days, the groups significantly differed. Additionally, blood lactate concentrations were significantly correlated with the ∆TOI and TOI.

CONCLUSIONS

Mild tissue oxygen metabolism impairment and tissue perfusion occurred in AP compared with sepsis, and changes similar to those in sepsis occur in AP complicated by infection. Further research is needed to evaluate whether these values can be applied to treating this group of patients.

Muscle Oxygen Extraction during Vascular Occlusion Test in Physically Very Active versus Inactive Healthy Men: A Comparative Study

An increase in the delivery and use of oxygen to the musculature in physically active subjects are determinants of improving health-related aerobic capacity. Additional health benefits, such as an increase in the muscle mass and a decrease in fat mass, principally in the legs, could be achieved with weekly global physical activity levels of more than 300 min. The objective was to compare the muscle vascular and metabolic profiles of physically very active and inactive subjects. Twenty healthy men participated in the study; ten were assigned to the physically very active group (25.5 ± 4.2 years; 72.7 ± 8.1 kg; 173.7 ± 7.6 cm) and ten to the physically inactive group (30.0 ± 7.4 years; 74.9 ± 11.8 kg; 173.0 ± 6.4 cm). The level of physical activity was determined by the Global Physical Activity Questionnaire (GPAQ). A resting vascular occlusion test (5 min of an ischemic phase and 3 min of a reperfusion phase) was used, whereas a near-field infrared spectroscopy (NIRS) device was used to evaluate the muscle oxygenation in the right vastus lateralis of the quadriceps muscle. The area under the curve of the deoxyhemoglobin (HHb) during the ischemic phase and above the curve of the tissue saturation index (TSI) during the reperfusion phase were obtained to determine muscle metabolic and vascular responses, respectively. Physically very active group showed a higher absolute HHb (3331.9 ± 995.7 vs. 6182.7 ± 1632.5 mmol/s) and lower TSI (7615.0 ± 1111.9 vs. 5420.0 ± 781.4 %/s) and relative to body weight (46.3 ± 14.6 vs. 84.4 ± 27.1 mmol/s/kg and 106.0 ± 20.6 vs. 73.6 ± 13.8 %/s/kg, respectively), muscle mass (369.9 ± 122.2 vs. 707.5 ± 225.8 mmol/kg and 829.7 ± 163.4 vs. 611.9 ± 154.2 %/s/kg) and fat mass (1760.8 ± 522.9 vs. 2981.0 ± 1239.9 mmol/s/kg and 4160.0 ± 1257.3 vs. ±2638.4 ± 994.3 %/s/kg, respectively) than physically inactive subjects. A negative correlation was observed between HHb levels and TSI (r = -0.6; p < 0.05). Physically very active men (>300 min/week) present better muscle oxidative metabolism and perfusion and perform significantly more physical activity than physically inactive subjects. Extra benefits for vascular health and muscle oxidative metabolism are achieved when a subject becomes physically very active, as recommended by the World Health Organization. In addition, a higher level of physical activity determined by GPAQ is related to better vascular function and oxidative metabolism of the main locomotor musculature, i.e., the quadriceps.

Association between Fractional Oxygen Extraction from Resting Quadriceps Muscle and Body Composition in Healthy Men

This study aimed to associate body composition with fractional oxygen extraction at rest in healthy adult men. Fourteen healthy adults (26.93 ± 2.49 years) from Chile participated. Body composition was assessed with octopole bioimpedance, and resting muscle oxygenation was evaluated in the vastus lateralis quadriceps with near-infrared spectroscopy (NIRS) during a vascular occlusion test, analyzing the muscleVO2, resaturation velocity during reactive hyperemia via the muscle saturation index (%TSI), and the area above the curve of HHb (AACrep). It was observed that the total and segmented fat mass are associated with lower reoxygenation velocities during hyperemia (p = 0.008; β = 0.678: p = 0.002; β = 0.751), and that the total and segmented skeletal muscle mass are associated with higher reoxygenation velocities during hyperemia (p = 0.020; β = -0.614: p = 0.027; β = -0.587). It was also observed that the total and segmented fat mass were associated with a higher area above the curve of HHb (AACrep) during hyperemia (p = 0.007; β = 0.692: p = 0.037; β = 0.564), and that total and segmented skeletal muscle mass was associated with a lower area above the curve of HHb (AACrep) during hyperemia (p = 0.007; β = -0.703: p = 0.017; β = -0.632). We concluded that fat mass is associated with lower resaturation rates and lower resting fractional O2 extraction levels. In contrast, skeletal muscle mass is associated with higher resaturation rates and fractional O2 extraction during reactive hyperemia. The AACrep may be relevant in the evaluation of vascular adaptations to exercise and metabolic health.

Microvascular and oxidative stress responses to acute high-altitude exposure in prematurely born adults

Premature birth is associated with endothelial and mitochondrial dysfunction, and chronic oxidative stress, which might impair the physiological responses to acute altitude exposure. We assessed peripheral and oxidative stress responses to acute high-altitude exposure in preterm adults compared to term born controls. Post-occlusive skeletal muscle microvascular reactivity and oxidative capacity from the muscle oxygen consumption recovery rate constant (k) were determined by Near-Infrared Spectroscopy in the vastus lateralis of seventeen preterm and seventeen term born adults. Measurements were performed at sea-level and within 1 h of arrival at high-altitude (3375 m). Plasma markers of pro/antioxidant balance were assessed in both conditions. Upon acute altitude exposure, compared to sea-level, preterm participants exhibited a lower reperfusion rate (7 ± 31% vs. 30 ± 30%, p = 0.046) at microvascular level, but higher k (6 ± 32% vs. -15 ± 21%, p = 0.039), than their term born peers. The altitude-induced increases in plasma advanced oxidation protein products and catalase were higher (35 ± 61% vs. -13 ± 48% and 67 ± 64% vs. 15 ± 61%, p = 0.034 and p = 0.010, respectively) and in xanthine oxidase were lower (29 ± 82% vs. 159 ± 162%, p = 0.030) in preterm compared to term born adults. In conclusion, the blunted microvascular responsiveness, larger increases in oxidative stress and skeletal muscle oxidative capacity may compromise altitude acclimatization in healthy adults born preterm.

The effect of severe intensity bouts on muscle oxygen saturation responses in trained cyclists

Near-infrared spectroscopy (NIRS) quantifies muscle oxygenation (SmO₂) during exercise. Muscle oxygenation response to self-paced, severe-intensity cycling remains unclear. Observing SmO₂ can provide cycling professionals with the ability to assess muscular response, helping optimize decision-making. We aimed to describe the effect of self-paced severe intensity bouts on SmO₂, measured noninvasively by a wearable NIRS sensor on the vastus lateralis (VL) muscle, and examine its reliability. We hypothesized a greater desaturation response with each bout, whereas, between trials, good reliability would be observed. Fourteen recreationally trained, and trained cyclists completed a ramp test to determine the power output (PO) at the respiratory compensation point (RCP). Athletes completed two subsequent visits of 50-minute sessions that included four severe-intensity bouts done at 5% above RCP PO. Muscle oxygenation in the VL was monitored using a wearable NIRS device. Measures included mean PO, heart-rate (HR), cadence, and SmO₂ at bout onset, during work (work SmO₂), and ΔSmO₂. The bouts were compared using a one-way repeated measures ANOVA. For significant differences, a Fisher's least square difference post-hoc analysis was used. A two-way repeated measures ANOVA was used using trial and bout as main factors. Intraclass correlations (ICC) were used to quantify relative reliability for mean work, and standard error of the measurement (SEM) was used to quantify absolute agreement of mean work SmO₂. Both PO and cadence showed no effect of bout or trial. Heart-rate at bout 2 (168 ± 8 bpm) and 4 (170 ± 7 bpm) were higher than bout 1 (160 ± 6 bpm). Onset SmO₂ (%) response significantly increased in the final two bouts of the session. Mean work SmO₂ increased across bouts, with the highest value displayed in bout 4 (36 ± 22%). ΔSmO₂ showed a smaller desaturation response during bout 4 (27 ± 10%) compared to bout 3 (31 ± 10%). Mean work SmO₂ ICC showed good reliability (ICC = 0.87), and SEM was 12% (CI 9-15%). We concluded that a non-invasive, affordable, wearable NIRS sensor demonstrated the heterogeneous muscle oxygenation response during severe intensity cycling bouts with good reliability in trained cyclists.

Effects of Inspiratory Muscle Training on Muscle Oxygenation during Vascular Occlusion Testing in Trained Healthy Adult Males

Inspiratory muscle training (IMT) may have an additional effect on cardiovascular autonomic modulation, which could improve the metabolism and vascular function of the muscles.

AIM

To determine the effects of IMT on vascular and metabolic muscle changes and their relationship to changes in physical performance.

METHODS

Physically active men were randomly placed into an experimental (IMTG; n = 8) or IMT placebo group (IMTPG; n = 6). For IMT, resistance load was set at 50% and 15% of the maximum dynamic inspiratory strength (S-Index), respectively. Only the IMTG's weekly load was increased by 5%. In addition, both groups carried out the same concurrent training. Besides the S-Index, a 1.5-mile running test, spirometry, and deoxyhemoglobin (HHb_AUC during occlusion) and reperfusion tissue saturation index (TSI_MB and TSI_MP: time from minimum to baseline and to peak, respectively) in a vascular occlusion test were measured before and after the 4-week training program. In addition, resting heart rate and blood pressure were registered.

RESULTS

IMTG improved compared to IMTPG in the S-Index (Δ = 28.23 ± 26.6 cmH₂O), maximal inspiratory flow (MIF: Δ = 0.91 ± 0.6 L/s), maximum oxygen uptake (Δ = 4.48 ± 1.1 mL/kg/min), 1.5-mile run time (Δ = -0.81 ± 0.2 s), TSI_MB (Δ = -3.38 ± 3.1 s) and TSI_MP (Δ = -5.88 ± 3.7 s) with p < 0.05. ΔVO_2max correlated with S-Index (r = 0.619) and MIF (r = 0.583) with p < 0.05. Both ΔTSI_MB and TSI_MP correlated with ΔHHb_AUC (r = 0.516 and 0.596, respectively) and with Δ1.5-mile run time (r = 0.669 and 0.686, respectively) with p < 0.05.

CONCLUSION

IMT improves vascular function, which is related to additional improvements in physical performance.

Mild obesity does not affect the forearm muscle microvascular responses to hyperglycemia

INTRODUCTION

Mild obesity has been associated with postprandial brachial artery vascular dysfunction. However, direct assessment of these effects within the forearm skeletal muscle microcirculation remains unclear. Thus, this study aimed to investigate the effects of mild obesity on the arm micro- and macrovascular responses to glucose ingestion.

METHODS

This cross-sectional study combined NIRS assessments of forearm skeletal muscle (FDS) reactivity (reperfusion slope) with %FMD of conduit artery function (brachial artery) before (Pre), as well as 60 and 120 min after glucose ingestion in 10 lean (BMI 23.9 ± 1.8) and 10 obese (BMI 32.9 ± 1.9) individuals.

RESULTS

Both groups showed a significant increase in the reperfusion slope at 60 and 120 min after glucose ingestion compared with the pre-glucose ingestion measurements. Obese individuals showed a significant (p < .05) reduction in %FMD at 60 min after glucose ingestion, while no significant changes in postprandial %FMD were observed in lean participants.

CONCLUSION

Even though obese individuals showed impaired postprandial brachial artery function, the current findings suggest that mild obesity does not affect the forearm skeletal muscle responses to glucose ingestion.

Circumferential tissue compression at the lower limb during walking, and its effect on discomfort, pain and tissue oxygenation: Application to soft exoskeleton design

Soft exoskeletons apply compressive forces at the limbs via connection cuffs to actuate movement or stabilise joints. To avoid excessive mechanical loading, the interface with the wearer's body needs to be carefully designed. The purpose of this study was to establish the magnitude of circumferential compression at the lower limb during walking that causes discomfort/pain. It was hypothesized that the thresholds differ from those during standing. A cohort of 21 healthy participants were tested using two sizes of pneumatic cuffs, inflated at the thigh and calf in a tonic or phasic manner. The results showed lower inflation pressures triggering discomfort/pain at the thigh, with tonic compression, and wider pneumatic cuffs. The thresholds were lower during walking than standing still. Deep tissue oxygenation increased during phasic compression and decreased during tonic compression. According to the findings, circumferential compression by soft exoskeletons is preferably applied at anatomical sites with smaller volumes of soft tissue, using narrow connection cuffs and inflation pressures below 14 kPa.

Noninvasive and in vivo assessment of upper and lower limb skeletal muscle oxidative metabolism activity and microvascular responses to glucose ingestion in humans

This study investigated changes in muscle oxidative metabolism and microvascular responsiveness induced by glucose ingestion in the upper and lower limbs using near-infrared spectroscopy (NIRS). Fourteen individuals (aged 27 ± 1.4 years) underwent 5 vascular occlusion tests (VOT) (pre-intervention (Pre), 30 min, 60 min, 90 min, and 120 min after glucose challenge). NIRS-derived oxygen saturation (StO2) was measured on the forearm and leg muscle at each VOT. Muscle oxidative metabolism was determined by the StO2 downslope during cuff inflation (deoxygenation slope); microvascular responsiveness was estimated by the StO2 upslope (reperfusion slope) following cuff deflation. There was a significant increase in arm (p < 0.05; 1-β = 0.860) and leg (p < 0.05; 1-β = 1.000) oxidative metabolism activity as represented by the faster deoxygenation slope at 60, 90, and 120 min (0.08 ± 0.03, 0.08 ± 0.03, 0.08 ± 0.02%·s–1, respectively) (leg) and at 90 min (0.16 ± 0.08%·s−1) (arm) observed after glucose ingestion when compared with their respective Pre values (leg = 0.06 ± 0.02; arm = 0.11 ± 0.04%·s−1). There was a significant increase in arm (p < 0.05; 1-β = 0.880) and leg (p < 0.05; 1-β = 0.983) reperfusion slope at 60 min (arm = 3.63 ± 2.1%·s−1; leg = 1.56 ± 0.6%·s−1), 90 min (arm = 3.91 ± 2.1%·s−1; leg = 1.60 ± 0.6%·s−1), and 120 min (arm = 3.91 ± 1.6%·s−1; leg = 1.54 ± 0.6%·s−1) when compared with their Pre values (arm = 2.79 ± 1.7%·s−1; leg = 1.26 ± 0.5%·s−1). Our findings showed that NIRS–VOT technique is capable of detecting postprandial changes in muscle oxidative metabolism activity and microvascular reactivity in the upper and lower limb.

Novelty NIRS-VOT is a promising noninvasive clinical approach that may help in the early, limb-specific detection of impairments in glucose oxidation and microvascular function.

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.

Tissue Oxygenation in Response to Different Relative Levels of Blood-Flow Restricted Exercise

Blood flow restrictive (BFR) exercise elicits a localized hypoxic environment compatible with greater metabolic stress. We intended to compare the acute changes in muscle microvascular oxygenation following low-intensity knee extension exercise, combined with different levels of BFR. Thirteen active young men (age: 23.8 ± 5.4 years) were tested for unilateral knee extension exercise (30 + 15 + 15 + 15 reps at 20% one repetition maximum) on four different conditions: no-BFR (NOBFR), 40, 60, and 80% of arterial occlusion pressure (AOP). Deoxyhemoglobin+myoglobin concentration Deoxy[Hb+Mb], total hemoglobin [T(H+Mb)] and tissue oxygen saturation [TOI] were measured on the vastus lateralis muscle using near-infrared spectroscopy (NIMO, Nirox srl, Brescia, Italy). The magnitude of change in Deoxy[Hb+Mb]during exercise was similar between 60 and 80% AOP. Overall, compared to that seen during 60 and 80% AOP, NOBFR as well as 40% AOP resulted in a lower magnitude of change in Deoxy[Hb+Mb] (p < 0.05). While the oxygen extraction decreased during each inter-set resting interval in NOBFR and 40% AOP, this was not the case for 60 or 80% AOP. Additionally, TOI values obtained during recovery from each set of exercise were similarly affected by all conditions. Finally, our data also show that, when performed at higher restrictive values (60 and 80%), BFR exercise increases total Deoxy[Hb+Mb] extraction (p < 0.05). Taken together, we provide evidence that BFR is effective for increasing deoxygenation and reducing tissue oxygenation during low-intensity exercise. We also showed that when using low loads, a relative pressure above 40% of the AOP at rest is required to elicit changes in microvascular oxygenation compared with the same exercise with unrestricted conditions.

Differences in vascular function between trained and untrained limbs assessed by near-infrared spectroscopy

PURPOSE

The aim of this study was to examine whether differences in vascular responsiveness associated with training status would be more prominent in the trained limb (leg) than in the untrained limb (arm) microvasculature.

METHODS

Thirteen untrained (26 ± 5 year) and twelve trained (29 ± 4 year) healthy men were submitted to a vascular occlusion test (VOT) (2 min baseline, 5 min occlusion, and 8 min re-oxygenation). The oxygen saturation signal (StO₂) was assessed using near-infrared spectroscopy (NIRS) throughout the VOT. Vascular responsiveness within the microvasculature was evaluated by the re-oxygenation Slope 2 (Slope 2 StO₂) and the area under the curve (StO_2AUC) of (StO₂) signal during re-oxygenation in the leg and arm.

RESULTS

There was a significant interaction between training status and limb for the slope 2 StO₂ (P < 0.01). The leg of the trained group showed a steeper slope 2 StO₂ (1.35 ± 0.12% s^-1) when compared to the slope 2 StO₂ of the leg in their untrained counterparts (0.86 ± 0.09% s^-1) (P < 0.05). There was a medium effect size of 0.58 for slope 2 StO₂ on the arm and a large effect size of 1.21 for slope 2 StO₂ on the leg. In addition, there was a small effect size of 0.24 for StO_2AUC on the arm and a medium effect size of 0.64 for StO_2AUC on the leg.

CONCLUSION

The present study suggests that the vascular adaptations induced by lower limb endurance exercise training are more prominent in the trained limb than in the untrained limb microvasculature.

Differences in oxidative metabolism modulation induced by ischemia/reperfusion between trained and untrained individuals assessed by NIRS

Endurance training is associated with skeletal muscle adaptations that regulate the oxidative metabolism during ischemia/reperfusion. The aim of this study was to noninvasively assess in vivo differences in the oxidative metabolism activity during ischemia/reperfusion between trained and untrained individuals, using near infrared spectroscopy (NIRS) combined with a vascular occlusion test (VOT) technique (NIRS-VOT). Sixteen untrained (26.3 ± 5.1 year) and seventeen trained (29.4 ± 4.9 year) healthy young adult men were submitted to a VOT (2 min baseline, 5 min occlusion, and 8 min reperfusion). Oxygen utilization was estimated from the area under the curve of the NIRS-derived deoxyhemoglobin [HHb] signal during occlusion (AUCocc). Muscle reperfusion was derived from the area above the curve (AACrep) of the [HHb] signal after cuff release. The AUCocc of the untrained participants (21010 ± 9553 % · s) was significantly larger than the AUCocc of their trained counterparts (12320 ± 3283 % · s); P = 0.001). The AACrep of the untrained participants (5928 ± 3769 % · s) was significantly larger than the AACrep of the trained participants (3745 ± 1900 % · s; P = 0.042). There was a significant correlation between AUCocc and AACrep (r = 0.840; P = 0.001). NIRS assessment of oxidative metabolism showed that trained individuals are more efficient in shifting between oxidative and anaerobic metabolism in response to ischemia and reperfusion.