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Rationale: Supervised treadmill exercise for claudication in peripheral arterial disease is effective but poorly tolerated because of ischemic leg pain. Near infrared spectroscopy allows non-invasive detection of muscle ischemia during exercise, allowing for characterization of tissue perfusion and oxygen utilization during training., Objective: We evaluated walking time, muscle blood flow, and muscle mitochondrial capacity in patients with peripheral artery disease after a traditional pain-based walking program and after a muscle oxygen-guided walking program., Method and Results: Patients with peripheral artery disease trained thrice weekly in 40-minute-long sessions for 12 weeks, randomized to oxygen-guided training ( n = 8, age 72 ± 9.7 years, 25% female) versus traditional pain-based training ( n = 10, age 71.6 ± 8.8 years, 20% female). Oxygen-guided training intensity was determined by maintaining a 15% reduction in skeletal muscle oxygenation by near infrared spectroscopy rather than relying on symptoms of pain to determine exercise effort. Pain free and maximal walking times were measured with a 12-minute Gardner treadmill test. Gastrocnemius mitochondrial capacity and blood flow were measured using near infrared spectroscopy. Baseline pain-free walking time was similar on a Gardner treadmill test (2.5 ± 0.9 vs. 3.6 ± 1.0 min, p = 0.5). After training, oxygen-guided cohorts improved similar to pain-guided cohorts (pain-free walking time 6.7 ± 0.9 vs. 6.9 ± 1.1 min, p < 0.01 for change from baseline and p = 0.97 between cohorts). Mitochondrial capacity improved in both groups but more so in the pain-guided cohort than in the oxygen-guided cohort (38.8 ± 8.3 vs. 14.0 ± 9.3, p = 0.018). Resting muscle blood flow did not improve significantly in either group with training., Conclusions: Oxygen-guided exercise training improves claudication comparable to pain-based training regimens. Adaptations in mitochondrial function rather than increases in limb perfusion may account for functional improvement. Increases in mitochondrial oxidative capacity may be proportional to the degree of tissue hypoxia during exercise.

Introduction: We examined ultrasound-estimated intramuscular fat of 4 muscles: rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and medial gastrocnemius (MG), and compared the results with other health measures., Methods: Forty-two participants were tested. Muscle echo intensity was quantified into percent intramuscular fat using previously published equations., Results: Strong correlations were found in percent intramuscular fat in the 4 muscles (r ≥ 0.8). Weak to moderate correlations were found between intramuscular fat and body mass index (r ≥ 0.2), waist/hip ratio (r ≥ 0.2), muscle thickness (r = -0.5 in RF, r = -0.4 in TA, r = -0.7 in MG), and muscle strength (leg extension: r = 0.4; leg flexion: r = -0.5). A relationship between intramuscular fat in RF and MG and physical activity was also observed (P < 0.05)., Conclusion: Ultrasound-estimated intramuscular fat was associated with other health measures and may provide physiological insight into the health consequences of obesity. Muscle Nerve 54: 743-749, 2016., (© 2016 Wiley Periodicals, Inc.)

Introduction: The aim of this study was to compare ultrasound echo intensity (EI) with high-resolution T1 -weighted MRI and to establish calibration equations to estimate percent intramuscular fat from EI., Methods: Thirty-one participants underwent both ultrasound and MRI testing of 4 muscles: rectus femoris (RF); biceps femoris (BF); tibialis anterior (TA); and medial gastrocnemius (MG)., Results: Strong correlations were found between MRI percent fat and muscle EI after correcting for subcutaneous fat thickness (r = 0.91 in RF, r = 0.80 in BF, r = 0.80 in TA, r = 0.76 in MG). Three types of calibration equations were established., Conclusions: Muscle ultrasound is a practical and reproducible method that can be used as an imaging technique for examination of percent intramuscular fat. Future ultrasound studies are needed to establish equations for other muscle groups to enhance its use in both research and clinical settings., (© 2015 Wiley Periodicals, Inc.)

Objective: To describe the use of a novel neuromuscular electrical stimulation (NMES) endurance exercise protocol and its effects on skeletal muscle oxidative capacity., Design: Case report, pre/post intervention., Setting: University-based trial., Participant: A 39-year-old man who suffered a motor complete spinal cord injury (C5-6, ASIA Impairment Scale grade A)., Intervention: Twenty-four weeks of endurance NMES that consisted of progressive increases in the twitch frequency, duration of sessions, and sessions per week., Main Outcome Measure: Mitochondrial capacity was measured, in vivo, as the rate of recovery of muscle oxygen consumption using near-infrared spectroscopy., Results: The rate of recovery of muscle oxygen consumption increased approximately 3-fold from 0.52 to 1.43, 1.46, and 1.40/min measured on 3 separate occasions during week 12 of training, and 1.57/min after 24 weeks of NMES endurance training., Conclusion: The findings of this study suggest that NMES endurance training using twitches can increase mitochondrial capacity to comparable levels measured in nonparalyzed muscles of sedentary able-bodied controls., (Copyright © 2013 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.)

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.

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.