Toshiyuki Homma

Noninvasive monitoring of deterioration in skeletal muscle function with forearm cast immobilization and the prevention of deterioration

BackgroundIn this research inactivity was simulated by immobilizing the forearm region in a plaster cast. Changes in skeletal muscle oxidative function were measured using near-infrared spectroscopy (NIRS), and the preventative effect of the training protocol on deterioration of skeletal muscle and the clinical utility of NIRS were examined.MethodsFourteen healthy adult men underwent immobilization of the forearm of the non-dominant arm by plaster cast for 21 days. Eight healthy adult subjects were designated as the immobilization group (IMM) and six were designated as the immobilization + training group (IMM+TRN). Grip strength, forearm circumference and dynamic handgrip exercise endurance were measured before and after the 21-day immobilization period. Using NIRS, changes in oxidative function of skeletal muscles were also evaluated. Muscle oxygen consumption recovery was recorded after the completion of 60 seconds of 40% maximum voluntary contraction (MVC) dynamic handgrip exercise 1 repetition per 4 seconds and the recovery time constant (TcVO2mus) was calculated.ResultsTcVO2mus for the IMM was 59.7 ± 5.5 seconds (average ± standard error) before immobilization and lengthened significantly to 70.4 ± 5.4 seconds after immobilization (p < 0.05). For the IMM+TRN, TcVO2mus was 78.3 ± 6.2 seconds before immobilization and training and shortened significantly to 63.1 ± 5.6 seconds after immobilization and training (p < 0.05).ConclusionsThe training program used in this experiment was effective in preventing declines in muscle oxidative function and endurance due to immobilization. The experimental results suggest that non-invasive monitoring of skeletal muscle function by NIRS would be possible in a clinical setting.

Delayed reoxygenation after maximal isometric handgrip exercise in high oxidative capacity muscle.

We hypothesized that after maximal short-term isometric exercise, when O2 demand is still high and O2 supply is not fully activated, higher oxidative capacity muscle may exhibit slower muscle reoxygenation after the exercise than low oxidative capacity muscle. Seven healthy male subjects performed a maximal voluntary isometric handgrip exercise for 10xa0s. The reoxygenation rate after the exercise (Reoxy-rate) in the finger flexor muscle was determined by near infrared continuous wave spectroscopy (NIRcws) while phosphocreatine (PCr) was measured simultaneously by 31P magnetic resonance spectroscopy. Muscle oxygen consumption (muscle V̇O2) and muscle oxidative capacity were evaluated using the rate of PCr resynthesis post-exercise. The forearm blood flow (FBF) index at the end of exercise was measured using NIRcws. There was a significant positive correlation between the Reoxy-rate, which ranged between 0.53%xa0s−1 and 12.47%xa0s−1, and the time constant for PCr resynthesis, which ranged between 17.8xa0s and 38.3xa0s (r2=0.939, P<0.001). At the end of the exercise, muscle V̇O2 exceeded the resting level by approximately 25-fold, while the FBF index exceeded the resting level by only 3-fold on average. The Reoxy-rate closely correlated with muscle V̇O2 (r2=0.727, P<0.05), but not with the FBF index. Also, the estimated O2 balance (muscle V̇O2 index/FBF index) was negatively correlated with the Reoxy-rate (r2=0.820, P<0.001). These results support our hypothesis that higher oxidative capacity muscle shows slower muscle reoxygenation after maximal short-term isometric exercise because the Reoxy-rate after this type of exercise may be influenced more by muscle V̇O2 than by O2 supply.

Muscle Oxygen Consumption at Onset of Exercise by Near Infrared Spectroscopy in Humans

In this study, we tried to continuously measure muscle oxygen consumption (m-VO2) by near infrared spectroscopy (NIRS) without arterial occlusions. We used an intermittent isometric exercise at high intensity, which elicits a spontaneous occlusion of the blood flow to the muscle due to an increase in intramuscular pressure. Changes in muscle oxygenation and phosphocreatine (PCr) concentration were monitored in 5 subjects during an intermittent isometric exercise (5 sec. contraction/5 sec. relaxation) at 50% of maximum voluntary contraction for 3 minutes. The rate of deoxygenation was measured from the 2nd sec. to the 3rd sec. of each muscle contraction. The rate of deoxygenation at the onset of exercise followed an exponential time course with a time constant of 42.0 +/- 12.5 sec. (mean +/- SD). This value agreed with the time constant of the decrease in PCr (48.2 +/- 10.2 sec.). This result suggests that m-VO2 was successfully monitored with a time resolution of 10 sec. by NIRS during exercise without arterial occlusion.

A practical indicator of muscle oxidative capacity determined by recovery of muscle O 2 consumption using NIR spectroscopy

We examined the relationship between the time constant (Tc) for muscle oxygen consumption (VO 2mus) recovery after exercise, as measured by near-infrared continuous wave spectroscopy (NIRcws), and the Tc for phosphocreatine (PCr) recovery as an index of muscle oxidative capacity. Eight healthy male subjects performed a dynamic handgrip exercise, and the VO2mus recovery after exercise was measured with NIRcws by repeated arterial occlusion. VO2mus was determined from the rate of deoxygenation during arterial occlusion, and muscle oxidative capacity was calculated from the Tc for PCr recovery using 31 phosphorus-magnetic resonance spectroscopy. VO2mus increased 8.9 ± 4.9 (mean ± SD) fold of resting after exercise and thereafter decreased exponentially. The Tc for VO2mus recovery and the Tc for PCr recovery were 33.1 ± 9.0 and 35.0 ± 8.5 s, respectively. The Tc for VO2mus recovery was significantly correlated to the Tc for PCr recovery (r = 0.92, p < .01).

Muscle oxidative metabolism accelerates with mild acidosis during incremental intermittent isometric plantar flexion exercise.

BackgroundIt has been thought that intramuscular ADP and phosphocreatine (PCr) concentrations are important regulators of mitochondorial respiration. There is a threshold work rate or metabolic rate for cellular acidosis, and the decrease in muscle PCr is accelerated with drop in pH during incremental exercise. We tested the hypothesis that increase in muscle oxygen consumption (o2mus) is accelerated with rapid decrease in PCr (concomitant increase in ADP) in muscles with drop in pH occurs during incremental plantar flexion exercise.MethodsFive male subjects performed a repetitive intermittent isometric plantar flexion exercise (6-s contraction/4-s relaxation). Exercise intensity was raised every 1 min by 10% maximal voluntary contraction (MVC), starting at 10% MVC until exhaustion. The measurement site was at the medial head of the gastrocnemius muscle. Changes in muscle PCr, inorganic phosphate (Pi), ADP, and pH were measured by 31P-magnetic resonance spectroscopy. o2mus was determined from the rate of decrease in oxygenated hemoglobin and/or myoglobin using near-infrared continuous wave spectroscopy under transient arterial occlusion. Electromyogram (EMG) was also recorded. Pulmonary oxygen uptake (o2pul ) was measured by the breath-by-breath gas analysis.ResultsEMG amplitude increased as exercise intensity progressed. In contrast, muscle PCr, ADP, o2mus, and o2pul did not change appreciably below 40% MVC, whereas above 40% MVC muscle PCr decreased, and ADP, o2mus, and o2pul increased as exercise intensity progressed, and above 70% MVC, changes in muscle PCr, ADP, o2mus, and o2pul accelerated with the decrease in muscle pH (~6.78). The kinetics of muscle PCr, ADP, o2mus, and o2pul were similar, and there was a close correlation between each pair of parameters (r = 0.969~0.983, p < 0.001).ConclusionWith decrease in pH muscle oxidative metabolism accelerated and changes in intramuscular PCr and ADP accelerated during incremental intermittent isometric plantar flexion exercise. These results suggest that rapid changes in muscle PCr and/or ADP with mild acidosis stimulate accelerative muscle oxidative metabolism.

Low-volume muscle endurance training prevents decrease in muscle oxidative and endurance function during 21-day forearm immobilization

Aim:u2002 To examine the effects of low‐volume muscle endurance training on muscle oxidative capacity, endurance and strength of the forearm muscle during 21‐day forearm immobilization (IMM‐21d).

The Effects of Food Intake on Muscle Oxygen Consumption

Diet-induced thermogenesis (DIT) is the energy expended in excess of resting metabolic rate for digestion, absorption, transport, metabolism, and storage of foods. Despite a large number of studies on human DIT (Bahr et al., 1991; Burkhard-Jagodzinska et al., 1999; Pittet et al., 1974; Segal et al., 1990; Sekhar et al., 1998; Van Zant et al., 1992; Westerterp et al., 1999), it is not clear in which tissues DIT mainly takes place. Although Astrup et al. (1985, 1986) have shown the possible involvement of skeletal muscle with DIT in humans, rather than brown adipose tissue, there have been few studies examining DIT in skeletal muscle. Furthermore, the effects of various kinds of food, especially sympathetic nervous system (SNS) stimulating agents such as cayenne pepper, on human skeletal muscle metabolism are not fully understood.

Food Intake Increases Resting Muscle Oxygen Consumption As Measured By Near-infrared Spectroscopy

The purpose of this study was to quantitatively examine the changes in muscle oxygen consumption (VO2mus) after food intake as measured by near-infrared continuous wave spectroscopy (NIRcws). Six healthy male subjects were given a meal with a calculated total energy content of 10 kcal/kg body. VO2mus was measured from 15 min to 150 min after they finished eating. VO2mus in the finger flexor muscles was estimated by the rate of deoxygenation during arterial occlusion using NIRcws. The absolute value of VO2mus was calculated using each subjects resting metabolic rate measured by 31Phosphorus-magnetic resonance spectroscopy (31P-MRS). Deep tissue temperature (TD) was also monitored in the forearm same area. The control experiment followed the same protocol but without meal. There was a significant increase in VO2mus: pre-meal value was 1.47 ± 0.17 μM O2/s, post-meal peak value (post 120 min) was 2.31 ± 0.38 μM O2/s (p < .05 vs. pre). In contrast, the control experiment did not show any increase. There was no significant difference in TD between the two experiments. The results indicate that food intake induced a significant increase in VO2mus. NIRcws can be used to provide specific information about changes in localized muscle metabolism elicited by food intake.