Age-associated alteration of muscle oxygenation measured by near infrared spectroscopy during exercise

The influence of ageing on the capacity to increase muscle oxygen delivery during exercise is unclear. This was investigated by comparing the evolution of Near InfraRed Spectroscopy (NIRS) in 10 old (67 +/- 5 years, Old group) and 13 young subjects (27 +/- 4 years, Young group), during a progressive maximal exercise. The NIRS probe was placed on the vastus lateralis; muscle oxygen saturation - IR-SmO(2) - values were expressed on a scale using an arterial occlusion as the lower reference point and the subsequent reactive hyperaemia as the upper reference point. Resting IR-SmO( 2) was found to be significantly lower in the Old as co mpared to the Young group. During exercise, VO(2) increased similarly as a function of the workload whereas IR-SmO(2) decreased faster in old subjects than in young ones. Conversely, when expressed at the same percentage of VO( 2max), IR-SmO(2) followed a similar evolution in both groups from rest to maximal exercise (27.3 +/- 16.7 vs 24.3 +/- 12.9% decrease, in Old and Young group, respectively, NS). Thus, the initial difference remained constant between the two groups. During recovery, the time to recover the signal variation was not different between the two groups. We concluded that Old subjects demonstrate a systematic lower muscle oxygen saturation than Young ones. This difference could be explained by an age related decrease in muscle blood flow limiting O(2) supply.     

Effects of acute hypoxia on cerebral and muscle oxygenation during incremental exercise.

To determine if fatigue at maximal aerobic power output was associated with a critical decrease in cerebral oxygenation, 13 male cyclists performed incremental maximal exercise tests (25 W/min ramp) under normoxic (Norm: 21% Fi(O2)) and acute hypoxic (Hypox: 12% Fi(O2)) conditions. Near-infrared spectroscopy (NIRS) was used to monitor concentration (microM) changes of oxy- and deoxyhemoglobin (Delta[O2Hb], Delta[HHb]) in the left vastus lateralis muscle and frontal cerebral cortex. Changes in total Hb were calculated (Delta[THb] = Delta[O2Hb] + Delta[HHb]) and used as an index of change in regional blood volume. Repeated-measures ANOVA were performed across treatments and work rates (alpha = 0.05). During Norm, cerebral oxygenation rose between 25 and 75% peak power output {Power(peak); increased (inc) Delta[O2Hb], inc. Delta[HHb], inc. Delta[THb]}, but fell from 75 to 100% Power(peak) {decreased (dec) Delta[O2Hb], inc. Delta[HHb], no change Delta[THb]}. In contrast, during Hypox, cerebral oxygenation dropped progressively across all work rates (dec. Delta[O2Hb], inc. Delta[HHb]), whereas Delta[THb] again rose up to 75% Power(peak) and remained constant thereafter. Changes in cerebral oxygenation during Hypox were larger than Norm. In muscle, oxygenation decreased progressively throughout exercise in both Norm and Hypox (dec. Delta[O2Hb], inc. Delta [HHb], inc. Delta[THb]), although Delta[O2Hb] was unchanged between 75 and 100% Power peak. Changes in muscle oxygenation were also greater in Hypox compared with Norm. On the basis of these findings, it is unlikely that changes in cerebral oxygenation limit incremental exercise performance in normoxia, yet it is possible that such changes play a more pivotal role in hypoxia.     

Skeletal muscle oxygenation during incremental exercise

The purpose of this study was to investigate the relationship between muscle oxygenation level at exhaustion and maximal oxygen uptake (VO2max) in an incremental cycling exercise. Nine male subjects took part in an incremental exhaustive cycling exercise, and then cuff occlusion was performed. Changes in oxy-(deltaHbO2) and deoxy-(deltaHb) hemoglobin concentrations in the vastus lateralis muscle were measured with a near infrared spectroscopy (NIRS). Muscle oxygenation during incremental exercise was expressed as a percentage (%Moxy) of the maximal range observed during an arterial occlusion as the lower reference point. A systematic decrease was observed in %Moxy with increasing intensity. A significant relationship was observed between %Moxy at exhaustion and VO2max (p < 0.01). We concluded that the one of the limiting factor of VO2max is the muscle oxygen diffusion capacity, and %Moxy during exercise could be one of the indexes of muscle oxygen diffusion capacity.     

Changes in skeletal muscle oxygenation during incremental exercise measured with near infrared spectroscopy

To determine the change in muscle oxygenation in response to progressively increasing work rate exercise, muscle oxyhemoglobin + oxymyoglobin saturation was measured transcutaneously with near infrared spectroscopy in the vastus lateralis muscle during cycle ergometry. Studies were done in 11 subjects while gas exchange was measured breath-by-breath. As work rate was increased, tissue oxygenation initially either remained constant near resting levels or, more usually, decreased. Near the work rate and metabolic rate where significant lactic acidosis was detected by excess CO₂ production (lactic acidosis threshold, LAT), muscle oxygenation decreased more steeply. As maximum oxygen uptake ( ) was approached, the rate of desaturation slowed. In 8 of the 11 subjects, tissue O₂ saturation reached a minimum which was sustained for 1–3 min before was reached. The LAT correlated with both the (r = 0.95,P < 0.0001) and the work rate (r = 0.94,P < 0.0001) at which the rate of tissue O₂ desaturation accelerated. These results describe a consistent pattern in the rate of decrease in muscle oxygenation, slowly decreasing over the lower work rate range, decreasing more rapidly in the work rate range of the LAT and then slowing at about 80% of , approaching or reaching a minimum saturation at .     

Changes in muscle oxygenation during weight-lifting exercise

The quantitative analysis of haemoglobin oxygenation of contracting human muscle during weight-lifting exercise was studied noninvasively and directly using near-infrared spectroscopy. This method was developed as a three-wavelength method which confirmed the volume changes in oxygenated haemoglobin (oxy-Hb), deoxygenated haemoglobin (deoxy-Hb) and blood volume (total-Hb; Oxy-Hb + deoxy-Hb). Nine healthy adult men with various levels of training experience took part in the study. Ten repetition maximum (10 RM) one-arm curl exercise was performed by all the subjects. Results showed that at the beginning of the 10-RM exercise, rapid increases of deoxy-Hb and decreases of oxy-Hb were observed. In addition, total-Hb gradually increased during exercise. These results corresponded to the condition of arm blood flow experimentally restricted using a tourniquet in contact with the shoulder joint, and they showed the restriction of venous blood flow and an anoxic state occurring in the dynamically contracted muscle. In three sets of lifting exercise with short rest periods, these tendencies were accelerated in each set, while total-Hb volume did not return to the resting state after the third set for more than 90 s. These results would suggest that a training regimen emphasizing a moderately high load and a high number of repetitions, and a serial set with short rest periods such as usually performed by bodybuilders, caused a relatively long-term anoxic state in the muscle.     

Skin blood flow influences near-infrared spectroscopy-derived measurements of tissue oxygenation during heat stress.

Near-infrared (NIR) spectroscopy is a noninvasive optical technique that is increasingly used to assess muscle oxygenation during exercise with the assumption that the contribution of skin blood flow to the NIR signal is minor or nonexistent. We tested this assumption in humans by monitoring forearm tissue oxygenation during selective cutaneous vasodilation induced by locally applied heat (n = 6) or indirect whole body heating (i.e., heating subject but not area surrounding NIR probes; n = 8). Neither perturbation has been shown to cause a measurable change in muscle blood flow or metabolism. Local heating (approximately 41 degrees C) caused large increases in the NIR-derived tissue oxygenation signal [before heating = 0.82 +/- 0.89 optical density (OD), after heating = 18.21 +/- 2.44 OD; P < 0.001]. Similarly, whole body heating (increase internal temperature 0.9 degrees C) also caused large increases in the tissue oxygenation signal (before heating = -0.31 +/- 1.47 OD, after heating = 12.48 +/- 1.82 OD; P < 0.001). These increases in the tissue oxygenation signal were closely correlated with increases in skin blood flow during both local heating (mean r = 0.95 +/- 0.02) and whole body heating (mean r = 0.89 +/- 0.04). These data suggest that the contribution of skin blood flow to NIR measurements of tissue oxygenation can be significant, potentially confounding interpretation of the NIR-derived signal during conditions where both skin and muscle blood flows are elevated concomitantly (e.g., high-intensity and/or prolonged exercise).     

Skeletal muscle oxygenation monitoring by near infrared spectroscopy.

The oxygenation of human forearm muscle tissue was studied using an optic fiber fast scanning spectrophotometer. We investigated near infrared (700-1100 nm) hemoglobin (Hb) and myoglobin (Mb) spectral changes in flow and/or oxygen-limited conditions. The superimposition of deoxy Hb and deoxy Mb spectra was confirmed "in vivo" on perfluorocarbon-blood exchanged transfused rats. Oxygenation changes were evaluated in 15 volunteers during 10 min forearm arterial occlusion. Rapid desaturation occurred until a plateau was reached after about 4 min, suggesting rapid anaerobic glycolytic activation.     

Regional blood flow during exercise in humans measured by near-infrared spectroscopy and indocyanine green.

Using near-infrared spectroscopy (NIRS) and the tracer indocyanine green (ICG), we quantified blood flow in calf muscle and around the Achilles tendon during plantar flexion (1-9 W). For comparison, blood flow in calf muscle was determined by dye dilution in combination with magnetic resonance imaging measures of muscle volume, and, for the peritendon region, blood flow was measured by (133)Xe washout. From rest to a peak load of 9 W, NIRS-ICG blood flow in calf muscle increased from 2.4+/-0.2 to 74+/-5 ml x 100 ml tissue(-1) x min(-1), similar to that measured by reverse dye (77+/-6 ml x 100 ml tissue(-1) x min(-1)). Achilles peritendon blood flow measured by NIRS-ICG rose with exercise from 2.2+/-0.5 to 15.1+/-0.2 ml x 100 ml(-1) x min(-1), which was similar to that determined by (133)Xe washout (2.0+/-0.6 to 14.6+/-0.3 ml x 100 ml tissue(-1) x min(-1)). This is the first study using NIRS and ICG to quantify regional tissue blood flow during exercise in humans. Due to its high spatial and temporal resolution, the technique may be useful for determining regional blood flow distribution and regulation during exercise in humans.     

Effect of arterial oxygenation on quadriceps fatigability during isolated muscle exercise

The effect of various levels of oxygenation on quadriceps muscle fatigability during isolated muscle exercise was assessed in six male subjects. Twitch force (Q(tw)) was assessed using supramaximal magnetic femoral nerve stimulation. In experiment 1, maximal voluntary contraction (MVC) and Q(tw) of resting quadriceps muscle were measured in normoxia [inspired O(2) fraction (Fi(O(2))) = 0.21, percent arterial O(2) saturation (Sp(O(2))) = 98.4%, estimated arterial O(2) content (Ca(O(2))) = 20.8 ml/dl], acute hypoxia (Fi(O(2)) = 0.11, Sp(O(2)) = 74.6%, Ca(O(2)) = 15.7 ml/dl), and acute hyperoxia (Fi(O(2)) = 1.0, Sp(O(2)) = 100%, Ca(O(2)) = 22.6 ml/dl). No significant differences were found for MVC and Q(tw) among the three Fi(O(2)) levels. In experiment 2, the subjects performed three sets of nine, intermittent, isometric, unilateral, submaximal quadriceps contractions (62% MVC followed by 1 MVC in each set) while breathing each Fi(O(2)). Q(tw) was assessed before and after exercise, and myoelectrical activity of the vastus lateralis was obtained during exercise. The percent reduction of twitch force (potentiated Q(tw)) in hypoxia (-27.0%) was significantly (P < 0.05) greater than in normoxia (-21.4%) and hyperoxia (-19.9%), as were the changes in intratwitch measures of contractile properties. The increase in integrated electromyogram over the course of the nine contractions in hypoxia (15.4%) was higher (P < 0.05) than in normoxia (7.2%) or hyperoxia (6.7%). These results demonstrate that quadriceps muscle fatigability during isolated muscle exercise is exacerbated in acute hypoxia, and these effects are independent of the relative exercise intensity.     

Reliability of telemetric electromyography and near-infrared spectroscopy during high-intensity resistance exercise

This study quantified the inter- and intra-test reliability of telemetric surface electromyography (EMG) and near infrared spectroscopy (NIRS) during resistance exercise. Twelve well-trained young men performed high-intensity back squat exercise (12 sets at 70–90% 1-repetition maximum) on two occasions, during which EMG and NIRS continuously monitored muscle activation and oxygenation of the thigh muscles. Intra-test reliability for EMG and NIRS variables was generally higher than inter-test reliability. EMG median frequency variables were generally more reliable than amplitude-based variables. The reliability of EMG measures was not related to the intensity or number of repetitions performed during the set. No notable differences were evident in the reliability of EMG between different agonist muscles. NIRS-derived measures of oxyhaemoglobin, deoxyhaemoglobin and tissue saturation index were generally more reliable during single-repetition sets than multiple-repetition sets at the same intensity. Tissue saturation index was the most reliable NIRS variable. Although the reliability of the EMG and NIRS measures varied across the exercise protocol, the precise causes of this variability are not yet understood. However, it is likely that biological variation during multi-joint isotonic resistance exercise may account for some of the variation in the observed results.     

Effects of respiratory muscle unloading on leg muscle oxygenation and blood volume during high-intensity exercise in chronic heart failure

Blood flow requirements of the respiratory muscles (RM) increase markedly during exercise in chronic heart failure (CHF). We reasoned that if the RM could subtract a fraction of the limited cardiac output (QT) from the peripheral muscles, RM unloading would improve locomotor muscle perfusion. Nine patients with CHF (left ventricle ejection fraction = 26 +/- 7%) undertook constant-work rate tests (70-80% peak) receiving proportional assisted ventilation (PAV) or sham ventilation. Relative changes (Delta%) in deoxy-hemoglobyn, oxi-Hb ([O2Hb]), tissue oxygenation index, and total Hb ([HbTOT], an index of local blood volume) in the vastus lateralis were measured by near infrared spectroscopy. In addition, QT was monitored by impedance cardiography and arterial O2 saturation by pulse oximetry (SpO2). There were significant improvements in exercise tolerance (Tlim) with PAV. Blood lactate, leg effort/Tlim and dyspnea/Tlim were lower with PAV compared with sham ventilation (P < 0.05). There were no significant effects of RM unloading on systemic O2 delivery as QT and SpO2 at submaximal exercise and at Tlim did not differ between PAV and sham ventilation (P > 0.05). Unloaded breathing, however, was related to enhanced leg muscle oxygenation and local blood volume compared with sham, i.e., higher Delta[O2Hb]% and Delta[HbTOT]%, respectively (P < 0.05). We conclude that RM unloading had beneficial effects on the oxygenation status and blood volume of the exercising muscles at similar systemic O2 delivery in patients with advanced CHF. These data suggest that blood flow was redistributed from respiratory to locomotor muscles during unloaded breathing.     

Effects of compression on muscle tissue oxygenation at the onset of exercise

The effects of compression on gastrocnemius medialis muscle oxygenation and hemodynamics during a short-term dynamic exercise was investigated in a sample of 15 male subjects (mean ± SD; age 25.8 ± 4.9 years; mass 70.6 ± 4.3 kg). Elastic compression sleeves were used to apply multiple levels of compression to the calf muscles during exercise, and noncompressive garments were used for the control condition. Tissue hemoglobin oxygen saturation was measured as the relative "tissue oxygen index" (TOI) with a near-infrared spectrometer. The recovery of TOI during exercise was determined from the slope of oxygenation recovery in a nonoccluded situation. The TOI recovery rate during the first 2 minutes of the exercise was 24% higher (p = 0.042) for the compression condition than for the control condition. A significant correlation (r = 0.61, p = 0.012) between the level of compression and the tissue oxygenation recovery during exercise was observed. Muscle energy use was determined from the rate of decline of TOI immediately upon arterial occlusion during early exercise. Muscle energy use measured during the occluded situation was not significantly influenced by compression. Based on these results, it was concluded that compression induced changes in tissue blood flow and perfusion appear to result in improved oxygenation during short-term exercise. Assuming that increased muscle oxygen availability positively influences performance, compression of muscles may enhance performance especially in sports that require repeated short bouts of exercise.     

Effects of L-carnitine L-tartrate supplementation on muscle oxygenation responses to resistance exercise

Previous research has shown that L-carnitine L-tartrate (LCLT) supplementation beneficially affects markers of hypoxic stress following resistance exercise. However, the mechanism of this response is unclear. Therefore, the primary purpose of this study was to determine the effects of LCLT supplementation on muscle tissue oxygenation during and after multiple sets of squat exercise. Nine healthy, previously resistance-trained men (25.2 +/- 6.years, 91.2 +/- 10.2 kg, 180.2 +/- 6.3 cm) ingested 2 g.d of LCLT or an identical placebo for 23 days in a randomized, balanced, crossover, double-blind, placebo-controlled, repeated-measures study design. On day 21, forearm muscle oxygenation was measured during and after an upper arm occlusion protocol using near infrared spectroscopy (NIRS), which measures the balance of oxygen delivery in relation to oxygen consumption. On day 22, subjects performed 5 sets of 15 to 20 repetitions of squat exercise with corresponding measures of thigh muscle oxygenation, via NIRS, and serial blood draws. Compared to the placebo trial, muscle oxygenation was reduced in the LCLT trial during upper arm occlusion and following each set of resistance exercise. Despite reduced oxygenation, plasma malondealdehyde, a marker of membrane damage, was attenuated during the LCLT trial. There were no differences between trials in the vasoactive substance prostacyclin. In conclusion, because oxygen delivery was occluded during the forearm protocol, it is proposed that enhanced oxygen consumption mediated the reduced muscle oxygenation during the LCLT trial. Enhanced oxygen consumption would explain why hypoxic stress was attenuated with LCLT supplementation.     

Effects of prior exercise on muscle metabolism during sprint exercise in horses.

The effect of warm-up exercise on energy metabolism and muscle glycogenolysis during sprint exercise (Spr) was examined in six fit Standardbred horses exercised at 115% of maximal O(2) consumption (VO(2 max)) until fatigued, 5 min after each of three protocols: 1) no warm-up (NWU); 2) 10 min at 50% of VO(2 max) [low-intensity warm-up (LWU)]; and 3) 7 min at 50% VO(2 max) followed by 45-s intervals at 80, 90, and 100% VO(2 max) [high-intensity warm-up (HWU)]. Warm-up increased (P < 0.0001) muscle temperature (T(m)) at the onset of Spr in LWU (38.3 +/- 0.2 degrees C) and HWU (40.0 +/- 0. 3 degrees C) compared with NWU (36.6 +/- 0.2 degrees C), and the rate of rise in T(m) during Spr was greater in NWU than in LWU and HWU (P < 0.01). Peak VO(2) was higher and O(2) deficit lower (P < 0. 05) when Spr was preceded by warm-up. Rates of muscle glycogenolysis were lower (P < 0.05) in LWU, and rates of blood and muscle lactate accumulation and anaerobic ATP provision during Spr were lower in LWU and HWU compared with NWU. Mean runtime (s) in LWU (173 +/- 10 s) was greater than HWU (142 +/- 11 s) and NWU (124 +/- 4 s) (P < 0. 01). Warm-up was associated with augmentation of aerobic energy contribution to total energy expenditure, decreased glycogenolysis, and longer run time to fatigue during subsequent sprint exercise, with no additional benefit from HWU vs. LWU.     

Quantification of cerebral oxygenation by full-spectrum near-infrared spectroscopy using a two-point method

The aim of this study was to quantify the relative concentrations of oxyhemoglobin and deoxyhemoglobin within the light path of the brain and to estimate cerebral hemoglobin (Hb) oxygen saturation using full-spectrum near-infrared spectroscopy (fsNIRS). For this purpose, we developed a novel exponential correction equation as well as a two-point spectroscopy method to estimate the relative concentrations of Hb and Hb oxygen saturation in biological tissues. The results of evaluation of measurements using an in vitro model indicated that our fsNIRS method enables accurate and non-invasive measurements of Hb content and saturation in a highly scattered medium such as the human brain. According to the results of analysis using a hypoxic piglet model, the mean cerebral Hb oxygen saturation (SbO(2)) of newborn piglets at an inspired oxygen gas concentration of 0.21 was estimated to be 63+/-4% (mean+/-S.D.). Umbilical arterial and left internal jugular venous Hb oxygen saturation were simultaneously estimated to be 96+/-2% and 52+/-11%, respectively. SbO(2) and arterial Hb oxygen saturation values had a linear relationship. The average oxygenation state of cerebral tissue is comparable with that of the cerebral vein. The results of this study showed that our method can be used to monitor Hb oxygen saturation in the neonatal brain at the bedside in an intensive care unit.     

Comparison of femoral blood gases and muscle near-infrared spectroscopy at exercise onset in humans

We hypothesized that near-infrared spectroscopy(NIRS) measures of hemoglobin and/or myoglobinO₂ saturation(IR-SO₂)in the vascular bed of exercising muscle would parallel changes infemoral venous O₂ saturation(Sfv_O2)at the onset of leg-kicking exercise in humans. Six healthy subjectsperformed transitions from rest to 48 ± 3 (SE)-W two-legged kickingexercise while breathing 14, 21, or 70% inspiredO₂.IR-SO₂ wasmeasured over the vastus lateralis muscle continuouslyduring all tests, and femoral venous and radial artery blood sampleswere drawn simultaneously during rest and during 5 min of exercise. Inall gas-breathing conditions, there was a rapid decrease in bothIR-SO₂ andSfv_O2 at the onset of moderate-intensityleg-kicking exercise. Although Sfv_O2 remained atlow levels throughout exercise,IR-SO₂increased significantly after the first minute of exercise in bothnormoxia and hyperoxia. Contrary to the hypothesis, these data showthat NIRS does not provide a reliable estimate of hemoglobinand/or O₂ saturation asreflected by direct femoral vein sampling.     

13C-NMR measurements of muscle glycogen during low-intensity exercise

Glycogen metabolism in exercising gastrocnemius muscles was examined by natural abundance 13C nuclear magnetic resonance (NMR) spectroscopy. Five-minute 13C-NMR measurement of muscle glycogen had a reproducibility of +/- 6.5% (+/- 4.8 mM). Experiments were performed on healthy fed male and female subjects. Two protocols were followed. 1) Subjects performed plantar flexion from rest at 15, 20, or 25% of maximum voluntary contraction for up to 9 h. 2) Subjects predepleted gastrocnemius glycogen with heavy exercise and then either performed low-intensity exercise as before or rested. Gastrocnemius glycogen was measured by NMR at rest and after each hour of exercise. In some sessions, both the exercised leg and the nonexercised leg were monitored with 13C-NMR. In protocol 1, blood velocity in the femoral artery was similarly assessed with ultrasonography. During low-intensity exercise from rest (protocol 1) muscle glycogen fell to a new steady-state value after several hours and then remained constant despite continued exercise. Mean blood velocity increased ninefold within 2 min of onset of exercise and remained constant thereafter. After predepletion (protocol 2), muscle glycogen was repleted both during low-intensity exercise and at rest. After 1 h the amount of glycogen repletion was greater when coupled with light exercise [48.5 +/- 2.8 mM after 1 h of exercise, 39.7 +/- 1.1 mM after 1 h of rest (P less than 0.05)]. During subsequent light exercise, glycogen reached a steady-state value similar to that obtained in protocol 1, while in resting, recovery glycogen levels continued to increase (+2.7 mM/h) over a 7-h period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Human respiratory muscle blood flow measured by near-infrared spectroscopy and indocyanine green.

Measurement of respiratory muscle blood flow (RMBF) in humans has important implications for understanding patterns of blood flow distribution during exercise in healthy individuals and those with chronic disease. Previous studies examining RMBF in humans have required invasive methods on anesthetized subjects. To assess RMBF in awake subjects, we applied an indicator-dilution method using near-infrared spectroscopy (NIRS) and the light-absorbing tracer indocyanine green dye (ICG). NIRS optodes were placed on the left seventh intercostal space at the apposition of the costal diaphragm and on an inactive control muscle (vastus lateralis). The primary respiratory muscles within view of the NIRS optodes include the internal and external intercostals. Intravenous bolus injection of ICG allowed for cardiac output (by the conventional dye-dilution method with arterial sampling), RMBF, and vastus lateralis blood flow to be quantified simultaneously. Esophageal and gastric pressures were also measured to calculate the work of breathing and transdiaphragmatic pressure. Measurements were obtained in five conscious humans during both resting breathing and three separate 5-min bouts of constant isocapnic hyperpnea at 27.1 +/- 3.2, 56.0 +/- 6.1, and 75.9 +/- 5.7% of maximum minute ventilation as determined on a previous maximal exercise test. RMBF progressively increased (9.9 +/- 0.6, 14.8 +/- 2.7, 29.9 +/- 5.8, and 50.1 +/- 12.5 ml 100 ml(-1) min(-1), respectively) with increasing levels of ventilation while blood flow to the inactive control muscle remained constant (10.4 +/- 1.4, 8.7 +/- 0.7, 12.9 +/- 1.7, and 12.2 +/- 1.8 ml 100 ml(-1) min(-1), respectively). As ventilation rose, RMBF was closely and significantly correlated with 1) cardiac output (r = 0.994, P = 0.006), 2) the work of breathing (r = 0.995, P = 0.005), and 3) transdiaphragmatic pressure (r = 0.998, P = 0.002). These data suggest that the NIRS-ICG technique provides a feasible and sensitive index of RMBF at different levels of ventilation in humans.     

Regional muscle oxygenation differences in vastus lateralis during different modes of incremental exercise

Background

Near infrared spectroscopy (NIRS) is used to assess muscle oxygenation (MO) within skeletal muscle at rest and during aerobic exercise. Previous investigations have used a single probe placement to measure MO during various forms of exercise. However, regional MO differences have been shown to exist within the same muscle which suggests that different areas of the same muscle may have divergent MO. Thus, the aim of this study was to examine whether regional differences in MO exist within the same muscle during different types of incremental (rest, 25, 50, 75, 100 % of maximum) exercise (1 leg knee extension (KE), 2 leg KE, or cycling).

Methods

Nineteen healthy active males (Mean ± SD: Age 27 ± 4 yrs; VO_2max: 55 ± 11 mL/kg/min) performed incremental exercise to fatigue using each mode of exercise. NIRS probes were placed on the distal and proximal portion of right leg vastus lateralis (VL). Results were analyzed with a 3-way mixed model ANOVA (probe × intensity × mode).

Results

Differences in MO exist within the VL for each mode of exercise, however these differences were not consistent for each level of intensity. Comparison of MO revealed that the distal region of VL was significantly lower throughout KE exercise (1 leg KE proximal MO – distal MO = 9.9 %; 2 leg KE proximal MO – distal MO = 13 %). In contrast, the difference in MO between proximal and distal regions of VL was smaller in cycling and was not significantly different at heavy workloads (75 and 100 % of maximum).

Conclusion

MO is different within the same muscle and the pattern of the difference will change depending on the mode and intensity of exercise. Future investigations should limit conclusions on MO to the area under assessment as well as the type and intensity of exercise employed.