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Medicine & Science in Sports & Exercise:
doi: 10.1249/01.mss.0000433603.54105.af
Abstract

A-28 Thematic Poster - Noninvasive Metabolic Monitoring in Skeletal Muscle

Free Access

May 29, 2013, 9:30 AM - 11:30 AM

Room: 104

103 Chair: Kevin McCully. University of Georgia, Athens, GA.

(No relationships reported)

104 Board #1 May 29, 9:30 AM - 11:30 AM

Reproducibility of Skeletal Muscle Oxidative Function and Postexercise Kinetics Using Near-Infrared Spectroscopy

William M. Southern, Mary Ann Reynolds, Kevin K. McCully, FACSM. University of Georgia, Athens, GA.

(No relationships reported)

Near-infrared spectroscopy (NIRS) is a non-invasive method of measuring muscle oxygenation and hemodynamics in skeletal muscle. PURPOSE: To assess the reproducibility of measuring resting blood flow, resting oxygen consumption, mitochondrial capacity, and physiological heme content in skeletal muscle using NIRS.

METHODS: Seven healthy participants (3 male, 4 female) were tested on two occasions within a 3-day period. The NIRS device was placed on the medial gastrocnemius and venous and arterial occlusions were performed in order to obtain the resting blood flow and oxygen consumption. A series of repeated arterial occlusions was used to measure the recovery kinetics of muscle oxygen consumption after 7 seconds of voluntary plantar flexion exercise.

RESULTS: Resting blood flow and resting oxygen consumption had a mean coefficient of variation (CV) of 43.0% (mean ICC = 0.02) and 13.2% (mean ICC = 0.91) respectively. The recovery time constant of oxygen consumption had a mean CV of 8.9% (mean ICC = 0.92). The physiological heme content had a mean CV of 14.6% (mean ICC = 0.72).

CONCLUSIONS: Measurements of oxygen consumption and mitochondrial capacity using NIRS can be obtained with good reproducibility. However, resting blood flow measures were more variable.

105 Board #2 May 29, 9:30 AM - 11:30 AM

Oxidative Capacity in Trained Cyclists With Near Infrared Spectroscopy

Jared T. Brizendine1, Terence E. Ryan1, Rebecca D. Larson2, Kevin K. McCully, FACSM1. 1University of Georgia, Athens, GA. 2University of Oklahoma, Norman, OK.

(No relationships reported)

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 mVO2 after 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 mVO2 after 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-1 for endurance athletes and 0.77 ± 0.82 %·s-1 for inactive controls (p = 0.42).

CONCLUSION: The recovery rates of mVO2 following 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.

106 Board #3 May 29, 9:30 AM - 11:30 AM

A Comparison of Exercise Type and Intensity on the Noninvasive Assessment of Skeletal Muscle Mitochondrial Function using Near Infrared Spectroscopy

Terence E. Ryan, Jared T. Brizendine, Kevin K. McCully, FACSM. The University of Georgia, Athens, GA.

(No relationships reported)

Near infrared spectroscopy (NIRS) can be used to measure muscle oxygen consumption (mVO2) using arterial occlusions. The recovery rate of mVO2 after exercise can provide an index of skeletal muscle mitochondrial function.

PURPOSE: To test the influence of exercise modality and intensity on NIRS measurements of mitochondrial function. Three experiments were performed.

METHODS: Thirty subjects (age: 18 - 27 years) were. NIRS signals were corrected for blood volume changes. The recovery of mVO2 after exercise was fit to a monoexponential curve, and a rate constant was calculated (directly related to mitochondrial function).

RESULTS: 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).

CONCLUSION: 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.

Supported by NIH Grant RO1 HD039676.

107 Board #4 May 29, 9:30 AM - 11:30 AM

Compression Socks May Enhance Local Oxygen Utilization In Muscle During Exercise

Lara Grobler, Elmarie Terblanche. Stellenbosch University, Stellenbosch, South Africa.

(No relationships reported)

Although the popularity of compression socks (CS) among endurance athletes is on the rise, the mechanism whereby the external compression may enhance performance, or aid recovery, is not clear. In the clinical setting, it seems that CS prevents venous pooling and enhances blood flow to the heart. However, little is known on the effect of CS on the muscle haemodynamics of well-trained athletes.

PURPOSE: To determine the effect of external compression on the local vascular dynamics of endurance athletes during submaximal exercise.

METHODS: 11 endurance trained athletes (Age: 35 ± 4 years; VO2max : 52 ± 7 ml/kg/min) completed, in random order, two 10 km simulated treadmill running protocols at 80% of peak treadmill velocity wearing either CS or flight socks (FS). Systemic blood lactate ([BLa]) was measured at 2 km intervals, while medial gastrocnemius skin temperature (ST) and lateral gastrocnemius muscle oxygenation was measured continuously using near-infrared spectroscopy. A subset of five participants completed a control running session wearing no socks (NS). Analysis of variance (ANOVA) and Fischer’s least square differences (LSD) post hoc tests were applied to establish statistically significant differences in outcome variables between interventions. Cohen’s effect sizes (ES) were calculated to describe practical significant effects. Muscle oxygenation values are expressed relative to baseline.

RESULTS: ST was significantly higher during the CS (Left = 33 ± 0.2 °C; Right = 33 ± 0.2 °C) and FS (Left = 32 ± 0.1 °C; Right = 32 ± 0.1 °C) trials compared to NS (Left = 30 ± 0.4°C; Right = 31 ± 0.2 °C) (p < 0.05). Although there were no statistically significant differences in [BLa], oxy-haemoglobin (O2Hb), deoxy-haemoglobin (HHb), or total haemoglobin index (nTHI) between the three conditions, a large practically significant effect (ES) was found in the HHb measurements between NS (Left = 14 ± 54 ΔμMol; Right = 12 ± 14 ΔμMol) and both the CS (Left = -75 ± 99 ΔμMol; Right = -97 ± 88 ΔμMol) and FS (Left = -74 ± 102 ΔμMol; Right = -58 ± 128 ΔμMol) conditions.

CONCLUSION: The results suggest that CS may possibly decrease venous blood flow velocity in the compressed area, and together with an increased skin temperature, it may cause an increase in oxygen diffusion rate and thus enhanced oxygen utilization in the muscle.

108 Board #5 May 29, 9:30 AM - 11:30 AM

Relationship Between Near Infrared Spectroscopy (NIRS) Signals And Venous Hemoglobin Oxygen Saturation In Skeletal Muscle

Yi Sun, Brian Ferguson, Matthew J. Rogatzki, James R. McDonald, L. Bruce Gladden, FACSM. Auburn University, Auburn, AL.

(No relationships reported)

PURPOSE: The aim of this investigation was to examine the correlation between venous hemoglobin oxygen saturation (O2Hb%) and NIRS signals under a variety of O2 delivery and metabolic rate conditions.

METHODS: Canine gastrocnemius muscles (GS) in six dogs were surgically isolated and pump perfused. NIRS signals were recorded continuously and venous blood was sampled intermittently at various flow rates (Control Flow, High Flow and Low Flow), with inspired gas at three different O2 percentages (12%, 21%, and 100%) as well as during electrically stimulated tetanic muscle contractions at rates of 1 contraction/2 s and 2 contractions/3 s (8V, 50Hz, 0.2ms pulse, 200ms duration).

RESULTS: Venous O2Hb% in resting muscle was 88.1 ± 3.6% - 91.9 ± 1.5% at various flow rates, 76.2 ± 7.3% - 95.7 ± 1.7% with different inspired gases, 24.8 ± 17.6% - 42.0 ± 16.1% during 1 contraction/2 s and 30.3 ± 20.1% - 42.2 ± 11.2% during 2 contractions/3 s. Venous O2Hb% and normalized deoxy-NIRS signals (HHbMb%) were linearly correlated in each of the six dogs (R2 = 0.93 ± 0.05). A high linear correlation was also found between O2Hb% and normalized oxy-NIRS signals (HbMbO2%) (R2 = 0.92 ± 0.03) in five out of the six dogs. The overall relationships between O2Hb% and HHbMb% and HbMbO2% for all animals combined were linear but the correlations (R2 = 0.75 and 0.80, respectively) were limited due to inter-muscle variability.

CONCLUSIONS: In isolated, perfused canine GS muscle, NIRS signals are highly correlated with venous O2Hb% across a wider range of conditions (various flow rates, different inspired O2 fractions, electrically stimulated muscle contractions) than investigated in previous research.

109 Board #6 May 29, 9:30 AM - 11:30 AM

Simultaneously And Continuously Monitoring Ph And Lactate In Human Forearm Muscle After Exercise By 1H-MRS

Jimin Ren, A.Dean Sherry, Craig R. Malloy. University of Texas Southwestern Medical Center, Dallas, TX.

(No relationships reported)

There has been a great interest to measure tissue pH and lactate in sports medicine. Acidification and accumulation of lactate are common metabolic changes occurring in skeletal muscle after high-intensity exercise, affecting muscle performance and recovery. While 31P MRS has proven useful in accessing intracellular pH, this technique suffers from pitfall of overestimating pH in post-exercise muscles. Furthermore, it cannot detect lactate, which is usually done by 1H MRS. To have both measured, interleaved approach, such as alternating 31P and 1H MRS scans, has to be used. But for dynamic studies with short time window, this is often difficult.

PURPOSE: 1) To report a non-invasive localized 1H MRS technique for simultaneous measurement of muscle pH and lactate in vivo. 2) To determine the relationship between pH and lactate in forearm muscle during recovery from short burst of hand-grip exercise.

METHODS: Four healthy human subjects with informed consent underwent proton MR spectroscopy lying prone at 7T. Proton MR spectra were acquired in forearm muscle before and after 2-min of repetitively squeezing a rubber ball. Subjects were instructed to maximally squeeze the ball and then release it, with an on-and-off repetition cycle of 2 sec. Lactate levels were monitored by the intensity of lactate CH resonance at 4.1 ppm, while the pH values were assessed by the frequency shift of carnosine imadazole H4 proton at ∼ 8 ppm. The temporal resolution of the dynamic spectra was 64 sec, using localized STEAM sequence.

RESULTS: After exercise, lactate was markedly increased (30 mmol/kg ww) and decayed rapidly to baseline within ∼10 min. The high-intensity exercise also caused significant acidification in activated muscle (pH6.3)which recovered at a similar rate as pH, with minor difference in time-course pattern. The correlation in lactate and change in pH in relaxing muscle was linear (correlation coefficient R2 = 0.94).

CONCLUSIONS: We demonstrated that 7T 1H MRS enables simultaneously and continuously monitoring of intramyocellular pH and lactate. The linear correlation between lactate level and pH change during post-exercise recovery suggests that the co-transport of lactate and H+ may be the major mechanism responsible for the clear-out of lactate in exercised muscle. Grant support: NIH RR02584.

110 Board #7 May 29, 9:30 AM - 11:30 AM

Temporal Changes in Magnetic Resonance Imaging in the mdx Mouse

Stephen J.P. Pratt, Su Xu, Roger J. Mullins, Richard M. Lovering. University of Maryland School of Medicine, Baltimore, MD. (Sponsor: E.G. McFarland, FACSM)

(No relationships reported)

Duchenne muscular dystrophy (DMD) is characterized clinically by severe, progressive loss of skeletal muscle. The phenotype is much less severe in the mdx mouse model of DMD than that seen in patients with DMD. However, a “critical period” has been described for the mdx mouse, during which there is a peak in muscle weakness and degeneration/regeneration between the 2nd and 5th weeks of life. A number of studies have employed small animal MRI to examine skeletal muscle in various dystrophic models, but such studies represent a snapshot in time rather than a longitudinal view.

PURPOSE: To examine MRI of murine dystrophic hindlimb muscles over time.

METHODS: We monitored a dystrophic (mdx, C57BL10/ScSn) male mouse using MRI every 4 weeks from 5 to 80 weeks of age. Before each imaging session, the mouse was anesthetized with isoflurane using a precision vaporizer. An MR-compatible small-animal monitoring and gating system was used to monitor respiration rate and body temperature. High resolution (120μm in-plane @ 0.5mm slice thickness) T2-weighted spin-echo MR images (TR/TE=5000/32 ms) were acquired on a Bruker Biospec 7T/30 Avance MR system.

RESULTS: The data from the 14 imaging sessions show the unevenly distributed focal hyperintensities throughout the muscles, with a peak in this presentation occurring around 9 and 13 weeks of age. Interestingly, the heterogeneity in mdx muscles appears to change over time. Percent heterogeneity was quantified and shows a peak (10.3%) at 9 weeks of age with a similar peak (8.7%) at week 13. The drop in heterogeneity thereafter remains relatively stable thorough 80 weeks of age. However, there is a stepwise decline in the percent heterogeneity from weeks 5-17 (peak 10.3%), weeks 17-44 (peak 4.7 %), and weeks 48-76 (peak 2.8%).

CONCLUSIONS: The data show localized hyperintense regions in muscles of the mdx mouse, which peak near the critical period. Interestingly, there was little change in the T2 signal heterogeneity from mdx muscles at later ages, at a time when muscle histology deteriorates and muscle necrosis continues despite a slight reduction in regeneration. Our findings suggest that researchers need to consider the age of mdx mice when designing imaging studies or evaluating MRI findings.

Supported by grants to RML from the NIH K01AR053235 and 1R01AR059179.

© 2013 American College of Sports Medicine

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