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Near-infrared spectroscopy (NIRS) has become an increasingly valuable tool to monitor tissue oxygenation (Toxy) in vivo. Observations of changes in the absorption of light with Toxy have been recognized as early as 1876, leading to a milestone NIRS paper by Jobsis in 1977. Changes in the absorption and scatting of light in the 700–850-nm range has been successfully used to evaluate Toxy. The most practical devices use continuous-wave light providing relative values of Toxy. Phase-modulated or pulsed light can monitor both absorption and scattering providing more accurate signals. NIRS provides excellent time resolution (~ 10 Hz), and multiple source–detector pairs can be used to provide low-resolution imaging. NIRS has been applied to a wide range of populations. Continued development of NIRS devices in terms of lower cost, better detection of both absorption and scattering, and smaller size will lead to a promising future for NIRS studies.

Longitudinal. The purpose of this study was to evaluate the effect of lower extremity resistance training on quadriceps fatigability, femoral artery diameter, and femoral artery blood flow. Academic Institution. Five male chronic spinal cord injury (SCI) individuals (American Spinal Injury Association (ASIA): A complete; C5–T10; 36±5 years old) completed 18 weeks of home-based neuromuscular electrical stimulation (NMES) resistance training. Subjects trained the quadriceps muscle group twice a week with four sets of 10 dynamic knee extensions against resistance while in a seated position. All measurements were made before training and after 8, 12, and 18 weeks of training. Ultrasound was used to measure femoral artery diameter and blood flow. Blood flow was measured before and after 5 and 10 min of distal cuff occlusion, and during a 4-min isometric electrical stimulation fatigue protocol. Training resulted in significant increases in weight lifted and muscle mass, as well as a 60% reduction in muscle fatigue (P=0.001). However, femoral arterial diameter did not increase. The range was 0.44±0.03 to 0.46±0.05 cm over the four time points (P=0.70). Resting, reactive hyperemic, and exercise blood flow did not appear to change with training. NMES resistance training improved muscle size and fatigue despite an absence of response in the supplying vasculature. These results suggest that the decreases in arterial caliber and blood flow seen with SCI are not tightly linked to muscle mass and fatigue resistance. In addition, muscle fatigue in SCI patients can be improved without increases in arterial diameter or blood flow capacity. Grants HL65179, HD39676, and HD39676S2.

This study tested whether regional differences in oxygenation status could result from differences in muscle fiber architecture. Architectural properties, oxygen supply, and consumption in the medial head of the gastrocnemius muscle (GM) were determined in vivo in six men using B-mode ultrasound and functional near infrared (NIR) imaging devices. Fascicle length, fascicle angle, NIR-O(2) saturation (deoxygenated Hb or oxygenated Hb), and NIR-blood volume (sum of deoxygenated and oxygenated Hb) were obtained in the distal and proximal portions of the GM at rest and during contraction. Exercise consisted of 2 min of standing plantar flexion at 1 Hz with an additional load of 50% of each subject's weight. Plantar flexion produced larger decreases (Delta: difference between rest and exercise values) in NIR-O(2) saturation [mean saturation (SD) of 0.14 (0.05) vs 0.07 (0.04) optical density units] and NIR-blood volume [mean saturation (SD) of -0.23 (0.08) vs -0.13 (0.04) optical density units] in the distal compared with the proximal portion ( P0.05 for all comparisons). It also produced larger changes (Delta) in fascicle length [mean length (SD) of -16.5 (4.7) vs -8.2 (4.2) mm] and fascicle angle (mean angle (SD) of 10.8 (1.4) degrees vs 3.9 (2.1) degrees ] in the distal compared with the proximal portion ( P0.05 for all comparisons). There were significant correlations between DeltaNIR-O(2 )saturation and Deltafascicle length ( r=-0.84, P0.05), and between DeltaNIR-O(2) saturation and Deltafascicle angle ( r=-0.90, P0.05), between DeltaNIR-blood volume and Deltafascicle length ( r=0.91, P0.05), between DeltaNIR-blood volume and Deltafascicle angle ( r=-0.85, P0.05). In conclusion, the plantar flexion exercise produced regional differences in oxygenation status consistent with regional differences in muscle architecture.

Individuals with chronic fatigue syndrome (CFS) have been shown to have reduced activity levels associated with heightened feelings of fatigue. Previous research has demonstrated that exercise training has beneficial effects on fatigue-related symptoms in individuals with CFS. The aim of this study was to sustain an increase in daily physical activity in CFS patients for 4 weeks and assess the effects on fatigue, muscle pain and overall mood. Six CFS and seven sedentary controls were studied. Daily activity was assessed by a CSA accelerometer. Following a two week baseline period, CFS subjects were asked to increase their daily physical activity by 30% over baseline by walking a prescribed amount each day for a period of four weeks. Fatigue, muscle pain and overall mood were reported daily using a 0 to 100 visual analog scale and weekly using the Profile of Mood States (Bipolar) questionnaire. CFS patients had significantly lower daily activity counts than controls (162.5 ± 51.7 × 103 counts/day vs. 267.2 ± 79.5 × 103 counts/day) during a 2-week baseline period. At baseline, the CFS patients reported significantly (P < 0.01) higher fatigue and muscle pain intensity compared to controls but the groups did not differ in overall mood. CFS subjects increased their daily activity by 28 ± 19.7% over a 4 week period. Overall mood and muscle pain worsened in the CFS patients with increased activity. CFS patients were able to increase their daily physical activity for a period of four weeks. In contrast to previous studies fatigue, muscle pain, and overall mood did not improve with increased activity. Increased activity was not presented as a treatment which may account for the differential findings between this and previous studies. The results suggest that a daily "activity limit" may exist in this population. Future studies on the impact of physical activity on the symptoms of CFS patients are needed.

Background: The purpose of this study was to measure blood flow in the carotid and femoral arteries, heart rate and blood pressure in response to postural challenge in older adults. A second purpose was to determine if older men and women have different cardiovascular responses to a postural challenge such as tilt. Methods: Thirty-seven healthy elderly men and women participated in this study (69–82 years old). All subjects had similar physical activity levels. Postural challenge was induced by a 60° tilt at the level of the waist. Continuous carotid blood flow and femoral blood flow was measured with Doppler ultrasound. Results: Carotid blood flow was significantly reduced 17% in both men and women immediately after tilt (p < 0.001), and by 3.2% two minutes after tilt (p < 0.001). Femoral blood flow decreased 59.4% in men and 61% in women immediately after tilt (p < 0.001), and remained significantly decreased two minutes after tilt by 21% (p

Flow-mediated dilation (FMD) measures the ability of an artery to relax in response to increases in blood velocity. FMD, primarily of the brachial artery, has been used as a noninvasive method of assessing vascular health. The purpose of this study was to assess FMD in the lower legs of humans. Six healthy subjects (27 ± 6 yrs) were tested. Doppler ultrasound images of the posterior tibial artery were taken before, during, and after 5 minutes of proximal cuff occlusion. FMD was measured as the percent increase in diameter after cuff release. Vascular tone was calculated using the resting diameter as a percentage of the vessel's vasoactive range. Minimum diameter occurred during ischemia and maximal diameter occurred following reactive hyperemia with local heating. The lower leg was heated with 10 minutes of immersion in 44°C water. Mean diameters at rest, cuff, and during release were 0.267 ± 0.062, 0.162 ± 0.036, 0.302 ± 0.058 cm, respectively. FMD was 13.5 ± 6.6 % and vascular tone was 29 ± 16.3%. We also found that retesting on a second day produced mean diameter values within 8% of the first day. Larger resting diameter (decreased tone) correlated with decreased FMD (r2 = 0.73). These results suggest that FMD and vascular tone can be measured in the posterior tibial artery. This is a potentially powerful tool to non-invasively measure vascular health in the lower legs of people at risk for vascular disease.

Correction After publication of our paper [1], we discovered that our normalized blood velocity and compliance numbers were 60 times higher than they should have been. The revised Figure 1 and Figure 2, along with Table 1 are shown here with the correct values. Heart rate, blood pressure, and half time to recovery of blood flow and oxygen saturation from the original article are all correct. The statistical analysis and interpretation of the data remain unchanged. We apologize for the error. Published: 08 July 2003

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Our purpose was to determine if aging had an influence on muscle blood flow independent of habitual physical activity levels. Blood flow was measured in the femoral artery by Doppler ultrasound after cuff occlusion of 10 minutes. Active and inactive older subjects (73 ± 7 years) were compared to active and inactive young subjects (26 ± 6 years). Peak blood flow capacity when normalized to lean muscle mass was related to activity level (p < 0.001), but not to age. Specifically, the young active group had higher peak blood flows than the young inactive (p = 0.031) or older inactive (p = 0.005) groups. Resting blood flow and conductance were not significantly different between groups. Mean arterial pressure was significantly higher in the older compared to young group (p = 0.002). Conductance was related to both activity (p = 0.002) and age (p = 0.003). A prolonged time for blood flow to recover was found in the older compared to the young group (p = 0.038) independent of activity status. The prolonged recovery time in the older subjects may suggest a reduced vascular reactivity associated with increased cardiovascular disease risk. Peak blood flow capacity is maintained in older subjects by physical activity. In summary, maximal flow capacity and prolonged recovery of blood flow are influenced by different mechanisms in young and older active and inactive subjects.

Magnetic resonance spectroscopy is a non-invasive and repeatable method of studying muscle metabolism. Magnetic resonance spectroscopy uses specific radiofrequency pulses in a strong magnetic field to determine the relative concentrations of chemical compounds in the sample. 31P Magnetic resonance spectroscopy provides indirect measures of phosphate compounds such as adenosine triphosphate (ATP), phosphocreatine and inorganic phosphate. Muscle intracellular pH can also be determined. Exercise tests can be performed in the magnet such that the metabolic response to steady-state exercise can be measured. The ratio of inorganic phosphate to phosphocreatine reflects the relative metabolic rate of mitochondrial respiration (V) and the extrapolated maximum capacity of oxidative metabolism (Vm). Normal humans vary considerably in their metabolic response to exercise. These differences are reflected in their Vms and the degree of acidosis during exercise. Active muscles in endurance trained athletes have higher Vms and faster recovery rates than normal controls. Preliminary studies have been done to assess muscle glycolytic capacity by measuring the degree of acidosis during ischaemic exercise. Exercise-induced muscle injury can be detected as an increased inorganic phosphate to phosphocreatine ratio in resting muscle. The increase in the inorganic phosphate to phosphocreatine ratio with injury reaches a peak 1 to 2 days after the injury and lasts for up to a week. Similar increases in the inorganic phosphate to phosphocreatine ratio occur in patients with destructive neuromuscular diseases. Thus changes in the resting inorganic phosphate to phosphocreatine ratio may be used to detect the degree of muscle injury following exercise. Levels of H2PO4- in muscle are thought to be important in causing muscle fatigue during exercise. As 31P magnetic resonance spectroscopy can measure H2PO4-, magnetic resonance spectroscopy has become a useful technique in the study of the metabolic causes of muscle fatigue. It may also be possible to identify the relative populations of fast twitch and slow twitch fibres in a skeletal muscle using pH changes measured with 31P magnetic resonance spectroscopy. Magnetic resonance spectroscopy using other nuclei, such as 1H, 13C and 23Na, have the potential to provide information on other metabolic changes which occur with exercise. Magnetic resonance spectroscopy has shown promise as a technique to monitor the effects of training, including overtraining, in specific muscle groups in athletes.