Muscle microvascular hemoglobin concentration and oxygenation within the contraction-relaxation cycle

Inability to directly measure microvascular oxygen distribution and extraction in striated muscle during a contraction/relaxation cycle limits our understanding of oxygen transport to and utilization by contracting muscle. We examined muscle microvascular hemoglobin concentration (total [Hb/Mb]) and oxygenation within the contraction-relaxation cycle to determine if microvascular RBC volume would be preserved and if oxygen extraction continued during the actual contraction phase. Eight subjects performed dynamic knee extension exercise (40 contractions/min) at moderate ( approximately 30% of peak work rate) and heavy ( approximately 80% of peak) work rates. Total hemoglobin/myoglobin (total [Hb/Mb]) and deoxy-hemoglobin/myoglobin (deoxy-[Hb/Mb]) were measured in the rectus femoris using NIRS to determine if microvascular total [Hb/Mb] would be preserved during the contraction, and to estimate microvascular oxygen extraction, respectively. Mean values during the relaxation (RP) and contractile phases and the peak values during the contractile phase for both moderate and heavy exercise were calculated. Total [Hb/Mb] increased from rest to steady-state exercise (6.36+/-5.08 microM moderate; 5.72+/-4.46 microM heavy exercise, both P<0.05), but did not change significantly within the contraction/relaxation cycle. Muscle contractions were associated with a significant (1.29+/-0.98 microM moderate; 2.16+/-2.12 microM heavy exercise, P<0.05) increase in deoxy-[Hb/Mb] relative to RP. We conclude that (a) microvascular RBC volume is preserved during muscle contractions (i.e., RBCs are present in the capillaries), and (b) the cyclical pattern of deoxygenation/oxygenation during the respective contraction/relaxation phases of the contraction cycle suggests that oxygen extraction is not restricted to the relaxation phase but continues to occur during muscle contractions.     

Influence of priming exercise on muscle deoxy[Hb?+?Mb] during ramp cycle exercise

The aim of the present study was to gain better insight into the mechanisms underpinning the sigmoid pattern of deoxy[Hb + Mb] during incremental exercise by assessing the changes in the profile following prior high-intensity exercise. Ten physically active students performed two incremental ramp (25 W min⁻¹) exercises (AL and LL, respectively) preceded on one occasion by incremental arm (10 W min⁻¹) and on another occasion by incremental leg exercise (25 W min⁻¹), which served as the reference test (RT). Deoxy[Hb + Mb] was measured by means of near-infrared spectroscopy and surface EMG was recorded at the Vastus Lateralis throughout the exercises. Deoxy[Hb + Mb], integrated EMG and Median Power Frequency (MdPF) were expressed as a function of work rate (W) and compared between the exercises. During RT and AL deoxy[Hb + Mb] followed a sigmoid increase as a function of work rate. However, during LL deoxy[Hb + Mb] increased immediately from the onset of the ramp exercise and thus no longer followed a sigmoid pattern. This different pattern in deoxy[Hb + Mb] was accompanied by a steeper slope of the iEMG/W-relationship below the GET (LL: 0.89 ± 0.11% W⁻¹; RT: 0.74 ± 0.08% W⁻¹; AL: 0.72 ± 0.10% W⁻¹) and a more pronounced decrease in MdPF in LL (17.2 ± 4.5%) compared to RT (5.0 ± 2.1%) and AL (3.9 ± 3.2%). It was observed that the sigmoid pattern of deoxy[Hb + Mb] was disturbed when the ramp exercise was preceded by priming leg exercise. Since the differences in deoxy[Hb + Mb] were accompanied by differences in EMG it can be suggested that muscle fibre recruitment is an important underlying mechanism for the pattern of deoxy[Hb + Mb] during ramp exercise.     

Pattern of deoxy[Hb + Mb] during ramp cycle exercise: influence of aerobic fitness status

During ramp exercise the deoxy[Hb + Mb] pattern follows a sigmoid model [f(x) = f ₀ + A/(1 + exp^{−(−c  + dx)})], indicating a non-linear muscle blood flow -relationship. We hypothesised that in trained cyclists the sigmoid would display a rightward shift, due to an increased oxidative capacity and/or higher percentage of slow-twitch fibres. A total of 10 cyclists and 11 physically active students (PA students) performed a relative ramp exercise (±12 min) and a ramp25-exercise (25 W min⁻¹). Deoxy[Hb + Mb] was measured at the M. Vastus Lateralis by NIRS, normalized to the total amplitude of the response and expressed as a function of absolute and relative (%peakP) work rate. The work rate corresponding to c/d (i.e.50% of the amplitude of the deoxy[Hb + Mb] response) was the only parameter of the sigmoid that differed significantly between cyclists (57.9 ± 4.4% and 60.1 ± 4.1%peakP in the relative and ramp25, respectively) and PAstudents (49.6 ± 4.2% and 48.2 ± 5.1%peakP, respectively), indicating a rightward shift of the sigmoid in the cyclists. These results suggest a change in the time course of C_(a–v)O₂ as a function of aerobic fitness status.     

Characterizing near-infrared spectroscopy responses to forearm post-occlusive reactive hyperemia in healthy subjects

During post-occlusive reactive hyperemia (PORH) there is a temporary increase in the total hemoglobin + myoglobin (T[Hb+Mb]) signal as measured by near-infrared spectroscopy (NIRS). This transient increase predicts differences in the kinetic responses of deoxy[Hb+Mb] and oxy[Hb+Mb] during PORH. The purpose of this study was to determine whether sigmoidal (Gompertz or logistic) or exponential functions better describe these response curves during PORH. The fit of the three functions (exponential, Gompertz and logistic) to the NIRS responses, as determined from residual sum of squares, was compared using repeated measures ANOVA on Ranks. The Gompertz function provided a better fit to the oxy[Hb+Mb] response curve than did either the exponential or logistic function (χ ² = 21.7, df = 2, p < 0.001). The logistic function provided a better fit for the deoxy[Hb+Mb] response (χ ² = 22.9, df = 2, p < 0.001) than did either the Gompertz or exponential functions. For both NIRS signals, the better fitting sigmoidal functions fit the data well, with an average r value of 0.99 or greater. Adipose tissue thickness was correlated with parameters related to signal strength (amplitude, r = 0.86–0.89; baseline, r = 0.67–0.75; all p < 0.001) but was not related to kinetic parameters (time constant and inflection point; p > 0.05 for all comparisons). These results suggest that during PORH distinct sigmoidal mathematical functions best describe the responses of the oxy[Hb+Mb] (Gompertz) and deoxy[Hb+Mb] (logistic) as measured by NIRS. Further, differences in both the kinetic and amplitude aspects for the responses of oxy[Hb+Mb] and deoxy[Hb+Mb] predict the observed transient change in T[Hb+Mb]. Our methods provide a technique to evaluate and quantify NIRS responses during PORH, which may have clinical utility.     

Matching of blood flow to metabolic rate during recovery from moderate exercise in humans

It is unclear whether measurement of limb or conduit artery blood flow during recovery from exercise provides an accurate representation of flow to the muscle capillaries where gas exchange occurs. To investigate this, we: (a) examined the kinetic responses of femoral artery blood flow (QFA), estimated muscle capillary blood flow (Qcap) and estimated muscle oxygen uptake (VO2m) following cessation of exercise; and (b) compared these responses to verify the adequacy of O2 delivery during recovery. Pulmonary VO2 (VO2p) was measured breath by breath, QFA was measured using Doppler ultrasonography, and deoxy-haemoglobin/myoglobin (deoxy-[Hb/Mb]) was estimated by near-infrared spectroscopy over the rectus femoris in nine healthy subjects during a series of transitions from moderate knee-extension exercise to rest. The time course of Qcap was estimated by rearranging the Fick equation [i.e. Qcap(t) alpha VO2m(t)/deoxy-[Hb/Mb](t)], using the primary component of Vo2p to represent VO2m and deoxy-[Hb/Mb] as a surrogate for arteriovenous O2 difference. There were no significant differences among the overall kinetics of VO2m (tau, 31.4+/-8.2 s), QFA [mean response time (MRT), 34.5+/-20.4 s] and Qcap (MRT, 31.7+/-14.7 s). The VO2m kinetics were also significantly correlated (P<0.05) with those of both QFA and Qcap. Both QFA and Qcap appear to be coupled with VO2m during recovery from moderate knee-extension exercise, such that extraction falls (thus cellular energetic state is not further compromised) throughout recovery.     

Near-infrared spectroscopy provides an index of blood flow and vasoconstriction in calf skeletal muscle during lower body negative pressure

Aim: Near‐infrared spectroscopy (NIRS) has been used previously for forearm blood flow estimation at rest and during exercise. In this study we applied NIRS to selectively monitor deep calf oxygenated haemoglobin (Hb) responses in order to estimate blood flow changes in the calf muscle during lower body negative pressure (LBNP). The purpose of this study was to test the hypothesis that changes in calf skeletal muscle oxygenated‐Hb, after the removal of superficial tissue responses, were related to blood flow changes during orthostatic stress, and to determine the efficacy of using NIRS measurements as an index of vasoconstriction. Methods: Twenty‐nine subjects participated in this study. All attempted a graded LBNP trial from baseline (0 mmHg) to ?60 mmHg LBNP in 10 mmHg steps at 5‐min intervals. Calf blood flow changes were estimated by oxygenated‐Hb responses in relation to changes in mercury strain gauge plethysmography and muscle sympathetic nerve activity (MSNA). Results: Calf selective deep oxygenated‐Hb decreased continuously from ?10 mmHg LBNP. Regression analysis showed that oxygenated‐Hb was significantly related to declines in plethysmography evaluations of blood flow [oxygenated‐Hb = (?1.57 ± 0.26) + (1.86 ± 0.49) plethysmography, r² = 0.87 ± 0.09]. Changes in MSNA (total activity) were also inversely related to oxygenated‐Hb (slope < 0, P = 0.037; r² = 0.52 ± 0.15). Conclusion: These results suggest that changes in selective deep calf oxygenated‐Hb can be utilized to estimate calf muscle blood flow changes that are most likely caused by vasoconstriction during graded LBNP.     

Insights into central and peripheral factors affecting the “oxidative performance” of skeletal muscle in aging

During exercises with relatively small muscle masses, limitations to exercise performance by the cardiovascular system should be significantly reduced, allowing one to fully-test the “oxidative potential” of the investigated muscles. Ten elderly males (E, 77.8 ± 2.9 years [ ]) and eight young controls (Y, 26.6 ± 3.0) underwent incremental exercises to voluntary exhaustion on a dynamic leg-extension (dominant limb) machine (knee-extension, KE) and on a cycloergometer (CYCLO). During KE the load was increased every 3 min to loads corresponding to 20, 40 and 60% of the force of one-repetition maximum (1RM). The following variables were determined (vastus lateralis muscle): concentration changes of deoxygenated haemoglobin and myoglobin (Δ[deoxy(Hb + Mb)]) by near-infrared spectroscopy (NIRS), expressed as percentage of the maximal value obtained during transient limb ischemia, and taken as an index of O₂ extraction; root mean square (RMS) and median power frequency (MDF) by electromyography. The total lifted load during KE and peak workload during CYCLO were lower in E versus Y (620.4 ± 321.9 kg vs. 1347.4 ± 458.7; 113.5 ± 23.9 W vs. 224.3 ± 41.0, respectively). During CYCLO Δ[deoxy(Hb + Mb)] peak (i.e. the value determined at exhaustion) was lower in E (44.5 ± 17.7%) versus Y (67.1 ± 22.9), whereas during KE Δ[deoxy(Hb + Mb)] peak was higher in E (56.8 ± 20.9%) versus Y (38.6 ± 15.8). “Thresholds”, that is abrupt increases in RMS slopes, were detected in Y but not in E, suggesting less recruitment or a preferential atrophy of type 2 fibers in the elderly. These findings, associated with the preserved capacity of O₂ extraction, suggest a shift towards oxidative metabolism in skeletal muscles of 78 year-old subjects, which could preserve, at least in part, their capacity to carry out exercise.     

Exercise with hypoventilation induces lower muscle oxygenation and higher blood lactate concentration: role of hypoxia and hypercapnia

Eight men performed three series of 5-min exercise on a cycle ergometer at 65% of normoxic maximal O₂ consumption in four conditions: (1) voluntary hypoventilation (VH) in normoxia (VH_0.21), (2) VH in hyperoxia (inducing hypercapnia) (inspired oxygen fraction [F_IO₂] = 0.29; VH_0.29), (3) normal breathing (NB) in hypoxia (F_IO₂ = 0.157; NB_0.157), (4) NB in normoxia (NB_0.21). Using near-infrared spectroscopy, changes in concentration of oxy-(Δ[O₂Hb]) and deoxyhemoglobin (Δ[HHb]) were measured in the vastus lateralis muscle. Δ[O₂Hb − HHb] and Δ[O₂Hb + HHb] were calculated and used as oxygenation index and change in regional blood volume, respectively. Earlobe blood samples were taken throughout the exercise. Both VH_0.21 and NB_0.157 induced a severe and similar hypoxemia (arterial oxygen saturation [SaO₂] < 88%) whereas SaO₂ remained above 94% and was not different between VH_0.29 and NB_0.21. Arterialized O₂ and CO₂ pressures as well as P50 were higher and pH lower in VH_0.21 than in NB_0.157, and in VH_0.29 than in NB_0.21. Δ[O₂Hb] and Δ[O₂Hb − HHb] were lower and Δ[HHb] higher at the end of each series in both VH_0.21 and NB_0.157 than in NB_0.21 and VH_0.29. There was no difference in Δ[O₂Hb + HHb] between testing conditions. [La] in VH_0.21 was greater than both in NB_0.21 and VH_0.29 but not different from NB_0.157. This study demonstrated that exercise with VH induced a lower tissue oxygenation and a higher [La] than exercise with NB. This was caused by a severe arterial O₂ desaturation induced by both hypoxic and hypercapnic effects.     

Effects of endurance training on hyperammonaemia during a 45-min constant exercise intensity

Summary Eleven laboratory-pretrained subjects (initial =54 ml·kg⁻¹·min⁻¹) took part in a study to evaluate the effect of a short endurance training programme [8–12 sessions, 1 h per session, with an intensity varying from 60% to 90% maximal oxygen consumption ] on the responses of blood ammonia (b[NH ₄ ⁺ ]) and lactate (b[la]) concentrations during progressive and constant exercise intensities. After training, during which did not increase, significant decreases in b[NH ₄ ⁺ ], b[la] and muscle proton concentration were observed at the end of the 80% constant exercise intensity, although b[NH ₄ ⁺ ] and b[la] during progressive exercise were unchanged. On the other hand, no correlations were found between muscle fibre composition and b[NH ₄ ⁺ ] in any of the exercise procedures. This study demonstrated that a constant exercise intensity was necessary to reveal the effect of training on muscle metabolic changes inducing the decrease in b[NH ₄ ⁺ ] and b[la]. At a relative power of exercise of 80% , there was no effect of muscle fibre composition on b[NH ₄ ⁺ ] accumulation.     

Determinants of performance in 1,500-m runners

Our aim was to investigate the relationship between physiological variables (not previously studied) and performance in elite 1,500-m runners. We assessed eight male athletes with an average personal best time of 233.3 ± 6.9 s (110% of the world record) for the 1,500-m race. Ventilatory measurements, maximal oxygen consumption $ (\dot{V}{\text{O}}_{{2{\max }}} ), Our aim was to investigate the relationship between physiological variables (not previously studied) and performance in elite 1,500-m runners. We assessed eight male athletes with an average personal best time of 233.3 ± 6.9 s (110% of the world record) for the 1,500-m race. Ventilatory measurements, maximal oxygen consumption VO2max maximal vastus lateralis muscle deoxygenation (?[deoxy(Hb+Mb)])max via near-infrared spectroscopy (NIRS), and maximal velocity (V (max)) were obtained during an incremental treadmill test. During subsequent constant-speed exercise at Vmax, we determined the time to exhaustion (Tlim), end-exercise blood lactate concentration ([La]b(max)), VO2 and ?[deoxy(Hb+Mb)] kinetics parameters. The mean VO2max, [La]b(max) and Vmax were 70.2 ± 3.9 mL kg(-1) min(-1), 12.7 ± 2.4 mmol L(-1), 21.5 ± 0.5 km h(-1), respectively. VO2 at Vmax showed a significant negative correlation with Tlim, whereas [La]b(max) was positively correlated with Tlim. Race speed was found to significantly correlate with ?[deoxy(Hb+Mb)](max) (79% of maximal value obtained during a transient limb ischemia), ?[deoxy(Hb+Mb)] slow component (22.9 ± 9.3% of total amplitude) and [La]b(max) at Vmax. [La]b(max) at Vmax was also significantly correlated with ?[deoxy(Hb+Mb)] slow component, suggesting a greater release of oxygen from the hemoglobin due to the Bohr effect. We conclude that both the maximal capacity of muscle to extract O2 from the blood and the end-exercise blood lactate accumulation are important predictors of best performance in 1,500-m runners.     

Reliability of near infrared spectroscopy (NIRS) for measuring forearm oxygenation during incremental handgrip exercise

The purpose of this study was to test the reliability of a new handgrip exercise protocol measuring forearm oxygenation in 20 healthy subjects on two occasions. The retest took place 48 h later and at the same time of the day. The incremental exercise consisted of 2 min steps of cyclic handgrip contraction (1/2 Hz) separated by 1 min of recovery. The exercise started at 20% MVC, was increased with 10% MVC each step and was performed until exhaustion (69.5 and 73% MVC). Near infrared spectroscopy (NIRS) was used to measure deoxygenation (deoxy[Hb + Mb]) and oxygen saturation (SmO(2)) in the forearm muscles. Prior to the exercise protocol an arterial occlusion of the forearm was performed until deoxy(Hb + Mb) did no longer increase. Maximal increase in deoxy[Hb + Mb] during 10 s of each exercise bout was expressed relative to the occlusion amplitude. ICC was used to examine the test-retest reliability. Significant ICC's were reported at 50% (r = 0.466, p = 0.017) and 60% MVC (r = 0.553, p = 0.005). The group mean of the maximum increase in oxygen extraction was 45.6 ± 16.7% and at the retest 44.9 ± 17.0% with an ICC of r = 0.867 (p < 0.001) which could be classified (Landis and Koch 1979) as almost perfect. The absolute SmO(2) values showed reliable ICC's for every submaximal intensity except at 60% MVC. An ICC of r = 0.774 (p < 0.001) was found at maximal intensity. The results of the present study show that deoxy[Hb + Mb] and SmO(2) responses during this protocol are highly reliable and indicate that this protocol could be used to get insight into deoxygenation and oxygen saturation in a population with low exercise tolerance.     

Deactivation and activation of left frontal lobe during and after low-frequency repetitive transcranial magnetic stimulation over right prefrontal cortex: A near-infrared spectroscopy study

The effects of low-frequency repetitive transcranial magnetic stimulation (rTMS) over the right frontal lobe on the function of the left frontal lobe were examined by near-infrared spectroscopy (NIRS) in eleven healthy subjects. rTMS applied 5 cm anterior to the motor cortex at 1 Hz and approximately 50% of the motor threshold intensity (MT) for 60 s resulted in a significantly larger decrease in the concentration of oxygenated hemoglobin ([oxy-Hb]) during the stimulation period followed by a significantly larger increase in [oxy-Hb] and a smaller decrease in the concentration of deoxygenated hemoglobin ([deoxy-Hb]) during the poststimulation baseline period than sham stimulation. These findings are interpreted as demonstrating the deactivation and activation of the left frontal cortex during and after rTMS of the right frontal cortex, respectively. If replicated in depressed patients, NIRS can be employed for monitoring rTMS effects as brain [Hb] changes in vivo, and may be helpful for determining therapeutic parameters of rTMS for individual patients.     

Near-infrared monitoring of tissue oxygenation during application of lower body pressure at rest and during dynamical exercise in humans

During the application of a wide range of graded lower body pressures (LBP) (–50 to 50 mmHg), we examined how (1) the tissue oxygenation in the lower and upper parts of the body changes at rest, and (2) how tissue oxygenation changes in the lower extremities during dynamical leg exercise. We used near-infrared spectroscopy (NIRS) to measure the changes induced by LBP in total Hb content and Hb oxygenation in seven subjects. At rest, total Hb increased and Hb oxygenation decreased in the thigh muscles during –25 and –50 mmHg LBP, while both decreased during +25 and +50 mmHg LBP. However, in the forearm muscles during graded LBP, the pattern of change in total Hb was the reverse of that in the thigh. Measurements from the forehead showed changes only during +50 mmHg LBP. These results demonstrated that the pattern of change in total Hb and Hb oxygenation differed between upper and lower parts with graded LBP at rest. During dynamical leg exercise, total Hb and Hb oxygenation in the thigh muscles decreased during stepwise increases in LBP above –25 mmHg, Hb oxygenation decreasing markedly during +50 mmHg LBP. These results suggest that during dynamical exercise (i) LBP at +25 mmHg or more causes a graded decline in blood volume and/or flow in the thigh muscles, and (ii) especially at +50 mmHg LBP, the O₂ content may decrease markedly in active muscles. Our results suggest that NIRS can be used to monitor in a non-invasive and continuous fashion the changes in oxygenation occurring in human skeletal muscles and head during the graded changes in blood flow and/or volume caused by changes in external pressure and secondary reflexes both at rest and during dynamical exercise.     

Noninvasive optical quantification of absolute blood flow, blood oxygenation, and oxygen consumption rate in exercising skeletal muscle

This study investigates a method using novel hybrid diffuse optical spectroscopies [near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS)] to obtain continuous, noninvasive measurement of absolute blood flow (BF), blood oxygenation, and oxygen consumption rate (V?O(2)) in exercising skeletal muscle. Healthy subjects (n=9) performed a handgrip exercise to increase BF and V?O(2) in forearm flexor muscles, while a hybrid optical probe on the skin surface directly monitored oxy-, deoxy-, and total hemoglobin concentrations ([HbO(2)], [Hb], and THC), tissue oxygen saturation (S(t)O(2)), relative BF (rBF), and relative oxygen consumption rate (rV?O(2)). The rBF and rV?O(2) signals were calibrated with absolute baseline BF and V?O(2) obtained through venous and arterial occlusions, respectively. Known problems with muscle-fiber motion artifacts in optical measurements during exercise were mitigated using a novel gating algorithm that determined muscle contraction status based on control signals from a dynamometer. Results were consistent with previous findings in the literature. This study supports the application of NIRS/DCS technology to quantitatively evaluate hemodynamic and metabolic parameters in exercising skeletal muscle and holds promise for improving diagnosis and treatment evaluation for patients suffering from diseases affecting skeletal muscle and advancing fundamental understanding of muscle and exercise physiology.     

Exercise training associated with estrogen therapy induced cardiovascular benefits after ovarian hormones deprivation

Menopause is recognized as a period of increased risk for coronary heart disease. Although the benefits of exercise training in lowering cardiovascular risk factors are well established, the risks and benefits of hormone therapy have been questioned. The purpose of the present study was to investigate the effects of estrogen therapy (HT) associated or not with exercise training (ET) in autonomic cardiovascular control in ovariectomized (OVX) rats. Female rats were divided into: control, OVX, OVX + HT, OVX + ET and OVX + HT + ET. HT was performed using a 0.25 mg 8-weeks sustained release pellet. Trained groups were submitted to an 8-week exercise training protocol on treadmill. Baroreflex sensitivity (BRS) was evaluated by heart rate responses to arterial pressure (AP) changes, and vagal and sympathetic tonus by pharmacological blockade. Ovariectomy induced an AP increase (123 ± 2 mmHg vs. 108 ± 2 mmHg), BRS impairment (∼69%), sympathetic activation (∼100%) and vagal tonus reduction (∼77%) compared to controls. HT or ET normalized the changes in parasympathetic tonus. However, only the association HT + ET was able to promote normalization of AP, BRS and sympathetic tonus, as compared to controls. These results indicate that ET induces cardiovascular and autonomic benefits in OVX rats under HT, suggesting a positive role of this association in the management of cardiovascular risk factor in postmenopausal women.     

Near-infrared monitoring of tissue oxygenation during application of lower body pressure at rest and during dynamical exercise in humans.

During the application of a wide range of graded lower body pressures (LBP) (-50 to 50 mmHg), we examined how (1) the tissue oxygenation in the lower and upper parts of the body changes at rest, and (2) how tissue oxygenation changes in the lower extremities during dynamical leg exercise. We used near-infrared spectroscopy (NIRS) to measure the changes induced by LBP in total Hb content and Hb oxygenation in seven subjects. At rest, total Hb increased and Hb oxygenation decreased in the thigh muscles during -25 and -50 mmHg LBP, while both decreased during +25 and +50 mmHg LBP. However, in the forearm muscles during graded LBP, the pattern of change in total Hb was the reverse of that in the thigh. Measurements from the forehead showed changes only during +50 mmHg LBP. These results demonstrated that the pattern of change in total Hb and Hb oxygenation differed between upper and lower parts with graded LBP at rest. During dynamical leg exercise, total Hb and Hb oxygenation in the thigh muscles decreased during stepwise increases in LBP above -25 mmHg, Hb oxygenation decreasing markedly during +50 mmHg LBP. These results suggest that during dynamical exercise (i) LBP at +25 mmHg or more causes a graded decline in blood volume and/or flow in the thigh muscles, and (ii) especially at +50 mmHg LBP, the O2 content may decrease markedly in active muscles. Our results suggest that NIRS can be used to monitor in a non-invasive and continuous fashion the changes in oxygenation occurring in human skeletal muscles and head during the graded changes in blood flow and/or volume caused by changes in external pressure and secondary reflexes both at rest and during dynamical exercise.     

Effects and post-effects of two-hour exhausting exercise on composition and gas transport functions of blood

Summary Eleven male sport students (age 23.3±1.7 years) exercised for 2 h on a bicycle ergometer (60 rpm), the braking force of which was regulated to yield a constant pulse rate (156±3 min^–1). Before, at end of, and 3 and 6 h after exercise blood was sampled from a cubital vein and an earlobe for measurement of hemoglobin (Hb) concentration, hematocrit (Hct) value, osmolality (Osm), plasma protein (Prot), sodium (Na⁺), potassium (K⁺), inorganic phosphate (P_i), and lactate (Lac) concentrations, red cell 2,3-diphosphoglycerate (DPG) and adenosin triphosphate (ATP) concentrations, acid base status and half saturation pressure (P₅₀) of the oxygen dissociation curve. At end of exercise [Hb], Hct, [Prot], Osm, [K⁺], [P_i] and [Lac] were significantly elevated, pH in ear lobe (+0.04) and venous blood (+0.08) was also increased by both respiratory and nonrespiratory effects (BE + 1.4 mmol/l). The oxygen dissociation curve showed an unexplained slight right shift (standard P₅₀+0.19 kPa). During the post-exercise period most parameters approximated to control values after only 3 h. [Prot] and especially [P_i], however, remained elevated while [DPG] slightly rose during the post-exercise period. It is suggested that these changes are first signs of adaptation to exercise, perhaps caused by endocrine stimulation.     

Mitochondrial function in physically active elders with sarcopenia

Physical activity is reported to protect against sarcopenia and preserve mitochondrial function. Healthy normal lean (NL: n = 15) and sarcopenic (SS: n = 9) participants were recruited based on body composition (DXA, Lunar DPX™), age, and physical activity. Gastrocnemius mitochondrial function was assessed by ³¹P MRS using steady-state exercise in a 4 T Bruker Biospin. Total work (429.3 ± 160.2 J vs. 851.0 ± 211.7 J, p < 0.001) and muscle volume (p = 0.006) were lower in SS, although these variables were not correlated (NL r = −0.31, p = 0.33, SS r = (0.03, p = 0.93). In the SS resting ATP/ADP was lower (p = 0.03) and ATP hydrolysis higher (p = 0.02) at rest. Free energy ATP hydrolysis was greater at the end of exercise (p = 0.02) and [ADP] relative to total work output was higher in SS (ANCOVA, p = 0.005). [PCr] recovery kinetics were not different between the groups. Adjusting these parameters for differences in total work output and muscle volume did not explain these findings. These data suggest that aerobic metabolism in physically active older adults with sarcopenia is mildly impaired at rest and during modest levels of exercise where acidosis was avoided. Muscle energetics is coordinated at multiple cellular levels and further studies are needed to determine the loci/locus of energy instability in sarcopenia.     

SSVEP and ERP measurement of cognitive fatigue caused by stereoscopic 3D

Characteristically within the resting brain there are slow fluctuations (around 0.1 Hz) of EEG and NIRS-(de)oxyhemoglobin ([deoxy-Hb], [oxy-Hb]) signals. An interesting question is whether such slow oscillations can be related to the intention to perform a motor act. To obtain an answer we analyzed continuous blood pressure (BP), heart rate (HR), prefrontal [oxy-Hb], [deoxy-Hb] and EEG signals over sensorimotor areas in 10 healthy subjects during 5 min of rest and during 10 min of voluntary finger movements. Analyses of prefrontal [oxy-Hb]/[deoxy-Hb] oscillations around 0.1 Hz and central EEG band power changes in the beta (alpha) band revealed that the positive [oxy-Hb] peaks preceded the central EEG beta (alpha) power peak by 3.6 ± 0.9 s in the majority of subjects. A similar relationship between prefrontal [oxy-Hb] and central EEG beta power was found during voluntary movements whereby the post movement beta power increase (beta rebound) is known to coexist with a decreased excitability of cortico-spinal neurons. Therefore, we speculate that the beta power increase ∼3 s after slow fluctuating [oxy-Hb] peaks during rest is indicative for a slow excitability change of central motor cortex neurons. This work provides the first evidence that initiation of finger movements at free will in relatively constant intervals around 10 s could be temporally related to slow oscillations of prefrontal [oxy-Hb] and autonomic blood pressure in the resting brain.     

Influence of prior exercise on muscle [phosphorylcreatine] and deoxygenation kinetics during high-intensity exercise in men

(31)Phosphate-magnetic resonance spectroscopy and near infrared spectroscopy (NIRS) were used for the simultaneous assessment of changes in quadriceps muscle metabolism and oxygenation during consecutive bouts of high-intensity exercise. Six male subjects completed two 6 min bouts of single-legged knee-extension exercise at 80% of the peak work rate separated by 6 min of rest while positioned inside the bore of a 1.5 T superconducting magnet. The total haemoglobin and oxyhaemoglobin concentrations in the area of the quadriceps muscle interrogated with NIRS were significantly higher in the baseline period prior to the second compared with the first exercise bout, consistent with an enhanced muscle oxygenation. Intramuscular phosphorylcreatine concentration ([PCr]) dynamics were not different over the fundamental region of the response (time constant for bout 1, 51 +/- 15 s versus bout 2, 52 +/- 17 s). However, the [PCr] dynamics over the entire response were faster in the second bout (mean response time for bout 1, 72 +/- 16 s versus bout 2, 57 +/- 8 s; P < 0.05), as a consequence of a greater fall in [PCr] in the fundamental phase and a reduction in the magnitude of the 'slow component' in [PCr] beyond 3 min of exercise (bout 1, 10 +/- 6% versus bout 2, 5 +/- 3%; P < 0.05). These data suggest that the increased muscle O(2) availability afforded by the performance of a prior bout of high-intensity exercise does not significantly alter the kinetics of [PCr] hydrolysis at the onset of a subsequent bout of high-intensity exercise. The greater fall in [PCr] over the fundamental phase of the response following prior high-intensity exercise indicates that residual fatigue acutely reduces muscle efficiency.