Takayuki Sako

CREATINE SUPPLEMENTATION ENHANCES ANAEROBIC ATP SYNTHESIS DURING A SINGLE 10 SEC MAXIMAL HANDGRIP EXERCISE

Forearm muscles of twelve healthy male subjects (age = 22.3 ± 1.1 years (mean ± S.E.)) were examined during a 10 sec maximal dynamic handgrip exercise (Ex10) using 31-phosphorus magnetic resonance spectroscopy before and after ingestion with 30 g creatine (Cr) monohydrate or placebo per day for 14 days. Cr supplementation produced a 11.5 ± 4.6% increase in the resting muscle phosphocreatine (PCr) concentration and a 65.0 ± 4.2% increase in the PCr degradation during Ex10. ATP synthesis rate through PCr hydrolysis and total anaerobic ATP synthesis rate during Ex10 increased from 0.64 ± 0.08 (pre-value) to 0.86 ± 0.14 mmol/kg ww/sec (post-value, p < 0.05) and from 0.97 ± 0.16 (pre-value) to 1.33 ± 0.27 mmol/kg ww/sec (post-value, p < 0.05), respectively. An increase in total anaerobic ATP synthesis during Ex10 after Cr supplementation positively correlated with the increase in ATP synthesis through PCr hydrolysis. Cr supplementation produced a 15.1 ± 3.8% increase in the mean power output during Ex10. There was no significant difference in the mean power output per unit of total anaerobic ATP synthesis during Ex10 between before and after Cr supplementation. ATP synthesis rate through PCr hydrolysis positively correlated with mean power output during Ex10 in all twelve subjects after treatment (r = 0.58, p < 0.05). The results suggest that Cr supplementation enhanced PCr degradation during Ex10. It is strongly indicated that an improvement in performance during Ex10 was associated with the increased PCr availability for the synthesis of ATP.

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.

The Effect of Endurance Training on Resting Oxygen Stores in Muscle Evaluated by Near Infrared Continuous Wave Spectroscopy

The purpose of this study was to examine the effects of endurance training (ET) on resting oxygen store (r-O(2)mus) using near infrared continuous wave spectroscopy (NIR(CWS)), and the validity of using this method for the evaluation of resting muscle oxygen consumption (r-VO(2)mus) in a training study. Ten female subjects were tested in the following study. All subjects were physically active, but did not participate in any regular training besides this study. The subjects were fully informed of the risks and gave their consent before the start of the experiments. For ET subjects cycled for 40 min at 60-70% VO(2)peak, three times a week, for 4 weeks. Before and after the period of ET, VO(2)peak and r-O(2)mus for the vastus lateralis muscle were measured. r-O(2)mus was defined as the amount of O(2) consumed by the muscle, which was determined from r-VO(2)mus measured by NIR(CWS) (HEO200, Omron) during arterial occlusion induced by a pneumatic tourniquet. In order to verify the measurements using NIR(CWS), oxygen consumption for both the whole body (40%-VO(2)) and vastus lateralis muscle (40%-VO(2)mus) were measured at pre and post ET. 40%-VO(2)mus was calculated from the ratio of the declining rates of Hb/MbO(2) immediately post-exercise and during rest (r-VO(2)mus). As a result, VO(2)peak significantly increased after ET. r-O(2)mus also significantly increased (p < 0.05). Neither 40%-VO(2) nor 40%-VO(2)mus changed following ET. Therefore these findings suggest the increase in r-O(2)mus calculated from r-VO(2)mus reflects an increase in resting oxygen stores in the trained muscle. Under the condition when resting muscle oxygen consumption is unchanged, NIR(CWS) can be a useful non-invasive tool for measuring muscle oxygen stores.

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.