The aim of this study was to clarify exercise-induced vasodilation by comparing the changes in muscle oxygenation during constant-work exercise (CWE) between untrained and endurance-trained individuals using time-resolved near-infrared spectroscopy (TR-NIRS). Ten healthy young untrained and 9 endurance-trained individuals performed CWE at moderate and high intensities each for 6 minutes. Muscle oxy/deoxygenation in the vastus lateralis was continuously monitored by TR-NIRS. Our results have demonstrated that endurance-trained individuals with high aerobic capacities showed increased muscle oxygenation during CWE, leading to higher exercise tolerance function. Thus, TR-NIRS can provide an optimal exercise training intensity for athletes to improve aerobic capacity.
We examined the seasonal variation of brown adipose tissue vascular density (BAT-d), which was estimated using total hemoglobin concentration in the supraclavicular region, in healthy subjects (9 men and 10 women) from November 2016 to November 2017. Generally, BAT-d was significantly higher in winter than in summer for all subjects. Although monthly BAT-d was significantly different for a year, no statistically significant difference was found from November to April. In conclusion, there was a seasonal variation of BAT-d from summer to winter and a lack of variation during late fall to the middle of spring among healthy subjects.
The aims of this study were to clarify the influences of fat layer thickness (FLT) and aerobic capacity on optical property dynamics during exercise by using near-infrared time-resolved spectroscopy (NIRTRS) in humans. Endurance-trained men and healthy control men with various FLT performed a ramp incremental cycling exercise test until exhaustion. Absorption coefficient, reduced scattering coefficient, and mean optical pathlength in the vastus lateralis were continuously monitored by three-wavelength (763, 801 and 836 nm) NIRTRS. Our results have demonstrated that FLT and aerobic capacity affect the optical property dynamics during exercise and that the effects may differ depending on the wavelength.
Mitochondrial oxidative phosphorylation, which modulates resynthesis of PCr, depends in part on the availability of O2 for the mitochondria in working muscle. Particularly during intense exercise, the induced lower O2 availability due to hypoxic condition by inadequate blood flow affects mitochondrial oxidative phosphorylation. However, there are few studies which have reported the relationship between mitochondrial stimuli and oxygen diffusion rate from capillary to mitochondria in skeletal muscle (muscle rDO2) during varying-workload exercise including under severe acidosis conditions in humans. The purpose of this study was to investigate the relationship between muscle PCr, rDO2, and muscle deoxygenation in humans during incremental dynamic exercise. Twelve healthy, nonsmoking male subjects participated in this study. The subjects performed incremental dynamic handgrip exercise until exhaustion. Muscle PCr during exercise was evaluated using 31-phosphorus magnetic resonance spectroscopy. Muscle deoxygenation level was monitored using near-infrared spectroscopy, and muscle rDO2 was determined by the rate of muscle deoxygenation during temporary arterial occlusion immediately after the end of each exercise stage. Muscle PCr level subsequently decreased with higher workloads, and muscle rDO2 above 10%MVC significantly increased from the resting, and was constant with higher workloads. Muscle deoxygenation level was also significantly greater above 10%MVC, and gradually increased with higher workloads. These results suggest that muscle rDO2 is limited at higher workloads, although mitochondrial stimuli are increased. The constant muscle rDO2 with higher workloads may be caused by reduced O2 gradient from capillary to mitochondria.
Brown/beige adipose tissue (BAT) is expected to contribute to protecting lifestyle-related diseases. The purpose of this study was to examine if near-infrared time-resolved spectroscopy (NIRTRS) is capable of distinguishing BAT from muscle and white adipose tissue (WAT). We analyzed the optical characteristics of tissues in the supraclavicular region, where BAT deposits can be located, and deltoid and abdominal regions in 36 participants (16 men and 20 women) who were apparently healthy individuals, with a median age of 44.5 years, in winter and summer. They also had a median body fat percentage of 28.3% and a deltoid and abdominal adipose tissue thickness of 0.85 cm and 1.71 cm, respectively. The total hemoglobin concentration [total-Hb] and the reduced scattering coefficient (μs′) were determined using nearinfrared time-resolved spectroscopy (NIRTRS) with a 3 cm optode separation for supraclavicular and deltoid regions and a 2 cm optode separation for abdominal region. The results regarding data collected in winter were the following: deltoid (μs' = 9.6 [9.1, 10.4] cm-1 , [total-Hb] = 114.9 [107.0, 127.7] μM); abdominal (μs' = 9.0 [7.9, 10.1] cm-1 , [total-Hb] = 11.2 [8.0, 16.0] μM); and supraclavicular (μs' = 7.9 [7.2, 8.7] cm-1 , [total-Hb] = 60.7 [48.9, 74.7] μM)) in winter. Some data are overlapped between groups of muscle and BAT. These results indicated that [total-Hb] and μs′ show region-specific characteristics. We conclude that using [total-Hb] - μs′ relationship determined by NIRTRS is a useful strategy to distinguish BAT from other tissues in a simple, rapid, and non-invasive manner.
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