Publications

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    ABSTRACT: The purpose of this study was to assess the reproducibility of resting blood flow, resting oxygen consumption, and mitochondrial capacity in skeletal muscle using near-infrared spectroscopy (NIRS). We also determined the influence of 2 exercise modalities (ergometer and rubber exercise bands) on the NIRS measurements. Fifteen young, healthy participants (5 female, 10 male) were tested on 2 nonconsecutive occasions within an 8-day period. The NIRS device was placed on the medial gastrocnemius. Venous and arterial occlusions were performed to obtain blood flow and oxygen consumption. A series of repeated arterial occlusions was used to measure the recovery kinetics of muscle oxygen consumption after ∼7-10 s of voluntary plantar flexion exercise. Resting blood flow had mean coefficients of variation (CV) of 42% and 38% for bands and ergometer, respectively, and resting metabolism had mean CVs of 17% and 12% for bands and ergometer, respectively. The recovery time constant of oxygen consumption (day 1 bands and ergometer: 23.2 ± 3.7 s, 27.6 ± 6.5 s, respectively; day 2 bands and ergometer: 25.5 ± 5.4 s, 25.0 ± 4.9 s, respectively) had mean CVs of 10% and 11% for bands and ergometer, respectively. We conclude that measurements of oxygen consumption and mitochondrial capacity using NIRS can be obtained with good reproducibility.
    Applied Physiology Nutrition and Metabolism 05/2014; 39(5):521-9. · 2.01 Impact Factor
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    ABSTRACT: Introduction: Mitochondrial dysfunction in the motor neuron has been suspected in amyotrophic lateral sclerosis (ALS). If mitochondrial abnormalities are also found in skeletal muscle, assessing skeletal muscle could be an important biomarker of disease progression. Methods: Using (31) P magnetic resonance ((31) P-MRS) and near infrared spectroscopy (NIRS), we compared the absolute values and reproducibility of skeletal muscle oxidative capacity in people with ALS (n = 6) and healthy adults (young, n = 7 and age-matched, n = 4). Results: ALS patients had slower time constants for phosphocreatine (PCr) and mVO2 compared with young, but not age-matched controls. The coefficient of variation (CV) for the time constant was 10% (SD = 2.8%) and 17% (SD = 6.2%) for PCr and mVO2 , respectively. Discussion: People with ALS had, on average, a small but not statistically significant, impairment in skeletal muscle mitochondrial function measured by both (31) P-MRS and NIRS. Both methods demonstrated good reproducibility. © 2014 Wiley Periodicals, Inc.
    Muscle & Nerve 02/2014; · 2.31 Impact Factor
  • Applied Physiology Nutrition and Metabolism 11/2013; · 2.01 Impact Factor
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    ABSTRACT: The purpose of this study was to cross-validate measurements of skeletal muscle oxidative capacity made with near infrared spectroscopy (NIRS) measurements to those made with phosphorus magnetic resonance spectroscopy ((31)P-MRS). Sixteen young (age = 22.5 ± 3.0 years), healthy individuals were tested with both (31)P-MRS and NIRS during a single testing session. The recovery rate of phosphocreatine was measured inside the bore of a 3 tesla MRI scanner, after short duration (~10 seconds) plantarflexion exercise as an index of skeletal muscle oxidative capacity. Using NIRS, the recovery rate of muscle oxygen consumption (mVO2) was also measured using repeated, transient arterial occlusions outside the MRI scanner, after short duration (10 seconds) plantarflexion exercise as another index of skeletal muscle oxidative capacity. The average recovery time constant was 31.5 ± 8.5 s for PCr and 31.5 ± 8.9 s for mVO2 for all participants (p = 0.709). (31)P-MRS time constants correlated well with NIRS time constants for both Channel 1 (Pearson's r = 0.88, p < 0.0001) and Channel 2 (Pearson's r = 0.95, p < 0.0001). Furthermore, both (31)P-MRS and NIRS exhibit good repeatability between trials (CV = 8.1%, 6.9%, and 7.9% for NIRS Channel 1, NIRS Channel 2, and 31P-MRS respectively). The good agreement between NIRS and (31)P-MRS indices of skeletal muscle oxidative capacity suggest that NIRS is a valid method for assessing mitochondrial function, and that direct comparisons between NIRS and (31)P-MRS measurements may be possible.
    Journal of Applied Physiology 10/2013; · 3.48 Impact Factor
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    ABSTRACT: Cytokine receptor subunits are released from cells in a regulated manner and circulate in soluble forms at concentrations that are orders of magnitude greater than the concentrations of the cytokines themselves. The purpose of this study was to determine if the circulating concentrations of soluble receptor subunits for interleukin-1 beta (IL-1β), tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) might serve as early indicators of vascular dysfunction independent of the traditional cardiovascular disease (CVD) risk factors in women. Healthy women, aged 20-50 years (n = 36), were assessed for circulating concentrations of the cytokines IL-1β, IL-6 and TNFα and the soluble cytokine receptor subunits interleukin-1 receptor type I (sIL-1RI), sIL-1RII, sIL-6Rα, glycoprotein 130 (s-gp130), soluble TNF receptor type 1 (sTNFR1), and sTNFR2, along with traditional CVD risk factors. Cytokine receptor subunit expression on mononuclear cells and the release of these subunits in vitro were also determined. Brachial artery flow-mediated dilation (FMD), carotid intima-media thickness (cIMT) and carotid-femoral pulse wave velocity (cfPWV) were assessed by ultrasonography and Doppler probes. Circulating sIL-6Rα correlated negatively with FMD (r = -0.56, p = 0.007) independent of age and other CVD risk factors. Circulating sTNFR1 correlated positively with cfPWV (r = 0.60, p = 0.002). TNFR1 receptor expression on monocytes correlated positively with cIMT (r = 0.51, p = 0.004). Plasma concentrations of IL-1β, IL-6 and TNFα were not significantly associated with FMD, cIMT or cfPWV. These data suggest that the receptors for IL-6 and TNFα, rather than the cytokines themselves, may be better indicators of early vascular changes that are associated with CVD.
    Vascular Medicine 10/2013; 18(5):282-9. · 1.62 Impact Factor
  • Wm Potter, L Wang, Kk McCully, Q Zhao
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    ABSTRACT: We introduce a new dual-tuned Hydrogen/Phosphorus ((1)H/(31)P) birdcage coil, referred to as split birdcage coil, and evaluate its performance using both simulations and magnetic resonance (MR) experiments on a 3 T MR scanner. The proposed coil simplifies the practical matters of tuning and matching, which makes the coil easily reproducible. Simulations were run with the Finite Difference in Time Domain (FDTD) method to evaluate the sensitivity and homogeneity of the magnetic field generated by the proposed (1)H coils. Following simulations, MR experiments were conducted using both a phantom and human thigh to compare the proposed design with a currently available commercial dual-tuned flexible surface coil, referred to as flex surface coil, for signal to noise ratio (SNR) as well as homogeneity for the (31)P coil. At regions deep within the human thigh, the split birdcage coil was able to acquire spectroscopic signal with a higher average SNR than the flex surface coil. For all regions except those close to the flex surface coil, the split birdcage coil matched or exceeded the performance of the flex surface coil.
    Concepts in Magnetic Resonance Part B Magnetic Resonance Engineering 08/2013; 43(3):90-99. · 0.71 Impact Factor
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    ABSTRACT: To examine the effects of sixteen weeks of electrically-induced resistance training on insulin resistance and glucose tolerance, along with changes in muscle size, composition, and metabolism in paralyzed muscle. Pre-Post Intervention. University based trial. Fourteen participants (11 males and 3 females) with chronic, (greater than two years post-SCI), motor-complete spinal cord injury (SCI). Home-based electrically-induced resistance exercise training twice weekly for sixteen weeks. Plasma glucose and insulin throughout a standard clinical oral glucose tolerance test, thigh muscle and fat mass via dual-energy x-ray absorptiometry, quadriceps and hamstrings muscle size and composition via magnetic resonance imaging, muscle oxidative metabolism using phosphorus magnetic resonance spectroscopy. Muscle mass increased in all participants (39 ± 27%; Range = 5 - 84%). The change in intramuscular fat was 3 ± 22%. PCr recovery time constants were 102 ± 24 and 77 ± 18 seconds before and after electrical stimulation-induced resistance training, respectively (P > 0.05). There was no improvement in fasting blood glucose levels, HOMA-IR, 2-hour insulin, or 2-hour glucose. Sixteen weeks of electrical stimulation-induced resistance training increased muscle mass, but did not reduce intramuscular fat. Similarly, factors associated with insulin resistance or glucose tolerance did not improve with training. We did find a 25% improvement in mitochondrial function as measured by PCr recovery rates. Larger improvements in mitochondrial function may translate into improved glucose tolerance and insulin resistance.
    Archives of physical medicine and rehabilitation 06/2013; · 2.18 Impact Factor
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    ABSTRACT: To describe the use of a novel neuromuscular electrical stimulation (NMES) endurance exercise protocol and its effects on skeletal muscle oxidative capacity. Case report, pre/post intervention. University based trial. A 39-year old male who suffered a motor complete SCI (C5-C6, AIS-A). Twenty-four weeks of endurance NMES that consisted of progressive increases in the twitch frequency, duration of sessions, and sessions per week. Mitochondrial capacity was measured, in vivo, as the rate of recovery of muscle oxygen consumption (mVO2) using near infrared spectroscopy (NIRS). The rate of recovery of mVO2 increased approximately three fold from 0.52 min(-1) to 1.43, 1.46, and 1.40 min(-1) measured on three separate occasions during the twelve week of training, and 1.57 min(-1) after twenty-four weeks of NMES endurance training. The findings of this study suggest that NMES endurance training using twitches can increase mitochondrial capacity to comparable levels measured in non-paralyzed muscles of sedentary able-bodied controls.
    Archives of physical medicine and rehabilitation 06/2013; · 2.18 Impact Factor
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    ABSTRACT: After spinal cord injury (SCI) skeletal muscle decreases in size, increases in intramuscular fat, and has potential declines in mitochondrial function. Reduced mitochondrial function has been linked to the development of metabolic disease. The aim of this study was to measure mitochondrial function in persons with SCI using near-infrared spectroscopy (NIRS). Oxygen consumption of the vastus lateralis muscle was measured with NIRS during repeated short-duration arterial occlusions in nine able-bodied (AB) and nine persons with motor complete SCI. Skeletal muscle oxidative capacity (V max) was evaluated with two approaches: (1) rate constant of the recovery of oxygen consumption after exercise and (2) extrapolated maximum oxygen consumption from a progressive work test. V max as indicated by the rate constant (k) from the recovery kinetics test was lower in SCI compared with AB participants (k: SCI 0.7 ± 0.3 vs. AB 1.9 ± 0.4 min(-1); p < 0.001). Time constants were SCI 91.9 ± 37.8 vs. AB 33.6 ± 8.3 s. V max from the progressive work test approached a significant difference between groups (SCI 5.1 ± 2.9 vs. AB 9.8 ± 5.5 % Hb-Mb/s; p = 0.06). NIRS measurements of V max suggest a deficit of 50-60 % in participants with SCI compared with AB controls, consistent with previous studies using (31)P-MRS and muscle biopsies. NIRS measurements can assess mitochondrial capacity in people with SCI and potentially other injured/diseased populations.
    Arbeitsphysiologie 05/2013; · 2.66 Impact Factor
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    ABSTRACT: PURPOSE: Previous studies have used near-infrared spectroscopy (NIRS) to measure skeletal muscle mitochondrial capacity. This study tested the hypothesis that NIRS measured mitochondrial capacity would improve with endurance exercise training and decline with detraining. METHODS: Nine, young, participants performed four weeks of progressively increasing endurance exercise training of the wrist flexor muscles followed by approximately five weeks of inactivity. The rate of recovery of muscle oxygen consumption (mVO2) was measured with NIRS every 3-7 days, indicating mitochondrial oxidative capacity. RESULTS: A linear increase in mitochondrial capacity (NIRS rate constant) was found with a group average of 64 ± 37% improvement after four weeks of exercise training (p < 0.05). Mitochondrial capacity declined exponentially upon cessation of exercise training, with a mean half-time of ~7.7 days. CONCLUSION: Both the magnitude and time course of mitochondrial adaptations to exercise training and detraining measured with NIRS was consistent with previous studies using both in vitro and in vivo techniques. These findings show that NIRS based measurements can detect meaningful changes in mitochondrial capacity.
    Medicine and science in sports and exercise 05/2013; · 4.48 Impact Factor
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    ABSTRACT: Near infrared spectroscopy (NIRS) can be used to measure muscle oxygen consumption (mVO(2)) using arterial occlusions. The recovery rate of mVO(2) after exercise can provide an index of skeletal muscle mitochondrial function. The purpose of this study was to test the influence of exercise modality and intensity on NIRS measurements of mitochondrial function. Three experiments were performed. Thirty subjects (age: 18 - 27 years) were. NIRS signals were corrected for blood volume changes. The recovery of mVO(2) after exercise was fit to a monoexponential curve, and a rate constant was calculated (directly related to mitochondrial function). No differences were found in NIRS rate constants for VOL and ES exercises (2.04 ± 0.57 vs. 2.01 ± 0.59 min(-1) for VOL and ES respectively; p = 0.317). NIRS rate constants were independent of the contraction frequency for both VOL and ES (VOL : p = 0.166; and ES: p = 0.780). ES current intensity resulted in significant changes to the normalized time-tension integral (54 ± 11, 82 ± 7, and 100 ± 0% for low, medium, and high currents respectively; p < 0.001), but did not influence NIRS rate constants (2.02 ± 0.54, 1.95 ± 0.44, 2.02 ± 0.46 min-1 for low, medium, and high currents respectively; p = 0.771). In summary, NIRS measurements of skeletal muscle mitochondrial function can be compared between VOL and ES exercises, and were independent of the intensity of exercise. NIRS represents an important new technique that is practical for testing in research and clinical settings.
    Journal of Applied Physiology 04/2013; 114(2):230-237. · 3.48 Impact Factor
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    ABSTRACT: PURPOSE: To determine if near-infrared spectroscopy (NIRS) measurements of muscle mitochondrial function could detect the expected differences between endurance trained athletes (N=8) and inactive subjects (N=8). METHODS: Muscle oxygen consumption (mVO2) of the vastus lateralis was measured with continuous-wave NIRS using transient arterial occlusions. The recovery rate of mVO2after electrical stimulation was fit to an exponential curve, with the time constant (Tc) used as an index of mitochondrial capacity. Whole-body peak oxygen uptake was determined by indirect calorimetry during a continuous ramp protocol on a cycle ergometer. RESULTS: Whole body peak oxygen uptake values for endurance trained and inactive controls were 73.5 ± 9.1 and 33.7 ± 5.9 ml/kg/min, respectively (p< 0.001). The recovery rates of mVO2after exercise for endurance trained were 18.4 ± 3.2 and 18.8 ± 2.5 seconds, whereas inactive controls were 32.4 ± 5.2 and 34.9 ± 5.9 seconds, for the shallow and deep channels respectively (p< 0.001 for comparison between groups). Resting mVO2 was 0.52 ± 0.22 %·s for endurance athletes and 0.77 ± 0.82 %·s for inactive controls (p = 0.42). CONCLUSIONS: The recovery rates of mVO2following exercise in endurance athletes were almost two-fold faster than inactive subjects measured with NIRS, consistent with previous studies using muscle biopsies and magnetic resonance spectroscopy. Our results support the use of NIRS measurements of the recovery of oxygen consumption to assess muscle oxidative capacity.
    Medicine and science in sports and exercise 04/2013; 45(5):869-875. · 4.48 Impact Factor
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    ABSTRACT: Bilateral differences in lower-limb strength in people with multiple sclerosis (MS) have been clinically observed. The objectives of this study were to quantify bilateral differences in lower-limb performance and metabolism during exercise. Eight ambulatory individuals with mild MS with an Expanded Disability Status Scale score of 2.6 +/- 1.6 and seven non-MS controls completed bilateral assessments of muscle strength and incremental cycling. Individuals with MS had significant (p < 0.05) between-leg differences in leg strength (strong leg: 43.3 +/- 12.7 kg vs weak leg: 37.7 +/- 15.2 kg), peak oxygen uptake (strong leg: 13.7 +/- 3.2 mL/kg/min vs weak leg: 10.6 +/- 3.0 mL/kg/min), and peak workload (strong leg: 73.4 +/- 22.3 W vs weak leg: 56.3 +/- 26.2 W). No between-leg differences were found in controls (p > 0.05). As anticipated, individuals with MS exhibited significantly greater asymmetry for strength, oxygen uptake, and workload than controls (p < 0.05). The differences between legs varied from 2% to 30% for maximal strength and 4% to 66% for cycling workload in the MS group and 4% to 24% and 0% to 8% for the control group, respectively. Preliminary evidence suggests that the magnitude of differences may be related to limitations in aerobic function.
    The Journal of Rehabilitation Research and Development 04/2013; 50(2):215-22. · 1.78 Impact Factor
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    Annual Meeting of the Southeast Chapter of the American College of Sports Medicine; 02/2013
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    Annual Meeting of the Southeast Chapter of the American College of Sports Medicine; 02/2013
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    Annual Meeting of the Southeast Chapter of the American College of Sports Medicine; 02/2013
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    Annual Meeting of the American College of Sports Medicine; 05/2012
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    ABSTRACT: Near-infrared spectroscopy (NIRS) is a well-known method used to measure muscle oxygenation and hemodynamics in vivo. The application of arterial occlusions allows for the assessment of muscle oxygen consumption (mVo(2)) using NIRS. The aim of this study was to measure skeletal muscle mitochondrial capacity using blood volume-corrected NIRS signals that represent oxygenated hemoglobin/myoglobin (O(2)Hb) and deoxygenated hemoglobin/myoglobin (HHb). We also assessed the reliability and reproducibility of NIRS measurements of resting oxygen consumption and mitochondrial capacity. Twenty-four subjects, including four with chronic spinal cord injury, were tested using either the vastus lateralis or gastrocnemius muscles. Ten healthy, able-bodied subjects were tested on two occasions within a period of 7 days to assess the reliability and reproducibility. NIRS signals were corrected for blood volume changes using three different methods. Resting oxygen consumption had a mean coefficient of variation (CV) of 2.4% (range 1-32%). The recovery of oxygen consumption (mVo(2)) after electrical stimulation at 4 Hz was fit to an exponential curve, which represents mitochondrial capacity. The time constant for the recovery of mVo(2) was reproducible with a mean CV of 10% (range 1-22%) only when correcting for blood volume changes. We also examined the effects of adipose tissue thickness on measurements of mVo(2). We found the mVo(2) measurements using absolute units to be influenced by adipose tissue thickness (ATT), and this relationship was removed when an ischemic calibration was performed, supporting its use to compare mVo(2) between individuals of varying ATT. In conclusion, in vivo oxidative capacity can be assessed using blood volume-corrected NIRS signals with a high degree of reliability and reproducibility.
    Journal of Applied Physiology 05/2012; 113(2):175-83. · 3.48 Impact Factor
  • Kevin K McCully
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    ABSTRACT: no abstract.
    Journal of Applied Physiology 04/2012; 112(12):1957-8. · 3.48 Impact Factor

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