Aim: Many studies have reported that aerobic exercise is effective in improving psychological well-being. However, there is little knowledge about whether it is effective at a low-frequency of one or two times aweek. The purpose of this study was to examine the effects of low-frequency aerobic exercise training on psychological well-being in young adults using a mental health questionnaire. Methods: University students who did not regularly exercise participated in the present study (training group: n=18, control group: n=16）. The training group performed aerobic exercise training at a lowfrequency (total of 30 times, once a week or more）, while the control group performed no exercise. Estimated V4O2max, body weight and psychological well-being were measured before and after the aerobic exercise training period. Results: V4O2max and body weight did not significantly change after aerobic exercise training. Compared with the control group, however, the training group exhibited a significant improvement in psychological well-being after the aerobic exercise training period.Conclusion: These findings suggest the possibility that even low-frequency aerobic exercise training is effective for improving psychological well-being.

Proper muscle activation is a key feature of survival in different tasks in daily life as well as sports performance, but can be impaired in elderly and in diseases. Therefore it is also clinically important to better understand the phenomenon that can be elucidated in humans non-invasively by positron emission tomography (PET) with measurements of spatial heterogeneity of glucose uptake within and among muscles during exercise. We studied six healthy young men during 35 minutes of cycling at relative intensities of 30% (low), 55% (moderate), and 75% (high) of maximal oxygen consumption on three separate days. Glucose uptake in the quadriceps femoris muscle group (QF), the main force producing muscle group in recreational cycling, and its four individual muscles, was directly measured using PET and 18F-fluoro-deoxyglucose. Within-muscle heterogeneity was determined by calculating the coefficient of variance (CV) of glucose uptake in PET image voxels within the muscle of interest, and among-muscles heterogeneity of glucose uptake in QF was expressed as CV of the mean glucose uptake values of its separate muscles. With increasing intensity, within-muscle heterogeneity decreased in the entire QF as well as within its all four individual parts. Among-muscles glucose uptake heterogeneity also decreased with increasing intensity. However, mean glucose uptake was consistently lower and heterogeneity higher in rectus femoris muscle that is known to consist of the highest percentage of fast twitch type II fibers, compared to the other three QF muscles. In conclusion, these results show that in addition to increased contribution of distinct muscle parts, with increases in exercise intensity there is also an enhanced recruitment of muscle fibers within all of the four heads of QF, despite established differences in muscle-part specific fiber type distributions. Glucose uptake heterogeneity may serve as a useful non-invasive tool to elucidate muscle activation in aging and diseased populations.

This chapter provides an accounting of studies using nuclear medicine techniques, especially positron emission tomography (PET), to measure regional brain activity induced by exercise. We describe the advantages and limitations of PET examinations using [18 F] fl uorodeoxyglucose ([18 F]FDG). PET is an interesting method for the exercise sciences, as studied subjects can move freely during the measurement due to the “metabolic trapping” property of [18 F]FDG. We also describe the molecular mechanisms of cerebral glucose consumption and cerebral blood fl ow regulation.

Many studies have suggested that exercise can improve mental health even in psychiatric patients. However, evidence is still lacking about suitable exercises for patients with psychiatric disorders other than depression. In this study, 3 experiments were performed. In experiment 1, a suitable type of exercise for psychiatric patients was examined; in experiment 2, psychological benefits of exercise were compared between mood disorder patients and schizophrenic patients; and in experiment 3, the effect of long-term exercise as part of a day-care program was examined in a psychiatric clinic. Methods: In experiment 1, acute affective changes of aerobic（ hip-hop dance）, static（ pilates）, and competitive （futsal） exercises were compared with changes induced by a psychological education program. In experiment 2, acute affective changes induced by a hip-hop dance exercise program were compared between mood disorder patients and schizophrenic patients. In experiment 3, self-reported questionnaires about mental health were performed before and after the experimental period（ 6 months）. Changes in scores on the questionnaires were compared between patients who had regularly participated in an exercise program（ exercise group） and patients who had no（t non-exercise group）. Results: In experiment 1, hip-hop dance and pilates improved the affective state better than the psychological education program. Affective states after all types of exercise were better than states after psychological education. In experiment 2, after hip-hop dance exercise, affective states of schizophrenic patients improved more than those of mood disorder patients. At baseline, affective states of schizophrenic patients were worse than mood disorders patients. In experiment 3, the exercise group showed a reduction of psychiatric symptoms（ K10 score） and improvement of self-efficacy（ generalized self-efficacy score） compared with the non-exercise group. Conclusion: 1. All types of exercise（ aerobic, static, and competitive） were effective at improving affective states of psychiatric patients. 2. Improvement of affective states in schizophrenic patients was greater than in mood disorder patients, probably because of the worse affective state of these patients at baseline. 3. Patients who regularly participated in a day-care exercise program showed improved mental health compared with patients who had not.

Gondoh Y, Tashiro M, Itoh M, Masud MM, Sensui H, Watanuki S, Ishii K, Takekura H, Nagatomi R, Fujimoto T. Evaluation of individual skeletal muscle activity by glucose uptake during pedaling exercise at different workloads using positron emission tomography. J Appl Physiol 107: 599-604,2009. First published June 18, 2009; doi:10.1152/japplphysiol.90821.2008.-Skeletal muscle glucose uptake closely reflects muscle activity at exercise intensity levels <55% of maximal oxygen consumption ((V) over dot(O2max)). Our purpose was to evaluate individual skeletal muscle activity from glucose uptake in humans during pedaling exercise at different workloads by using [F-18] fluorodeoxyglucose (FDG) and positron emission tomography (PET). Twenty healthy male subjects were divided into two groups (7 exercise subjects and 13 control subjects). Exercise subjects were studied during 35 min of pedaling exercise at 40 and 55% (V) over dot(O2max) exercise intensities. FDG was injected 10 min after the start of exercise or after 20 min of rest. PET scanning of the whole body was conducted after completion of the exercise or rest period. In exercise subjects, mean FDG uptake [standardized uptake ratio (SUR)] of the iliacus muscle and muscles of the anterior part of the thigh was significantly greater than uptake in muscles of control subjects. At 55% (V) over dot(O2max) exercise, SURs of the iliacus muscle and thigh muscles, except for the rectus femoris, increased significantly compared with SURs at 40% (V) over dot(O2max) exercise. Our results are the first to clarify that the iliacus muscle, as well as the muscles of the anterior thigh, is the prime muscle used during pedaling exercise. In addition, the iliacus muscle and all muscles in the thigh, except for the rectus femoris, contribute when the workload of the pedaling exercise increases from 40 to 55% (V) over dot(O2max).

Corresponding author: Toshihiko Fujimoto

Aim. There is convergent evidence that exercise increases psychological well-being; however, the mechanism of this psychological effect of exercise is not yet completely understood. The purpose of this study was to examine the effects of aerobic exercise training on brain structure and psychological wellbeing in young adults. Methods. University students who had not regularly exercised were divided into training group (N.=15) and control group (N.=15). The training group performed a total 30 periods of aerobic exercise training, while the control group never performed. Whole-brain magnetic resonance imaging scans and mental health questionnaire examinations were performed before and after the exercise training period for all of the participants. A voxel-based morphometry (VBM) analysis was used to compare the changes in gray-matter volumes in the two groups. VBM is an objective whole-brain technique for characterization of regional cerebral volume and tissue concentration differences in structural magnetic resonance images. Results. The results of VBM analysis revealed no change in gray-matter volume in the training group, although the gray-matter volume of the left insula was significantly decreased in the control group after the exercise training period. The training group exhibited significant improvement in some scores on the mental health questionnaire after the exercise training period, compared with the control group. Conclusion. These findings suggest that aerobic exercise training may inhibit gray-matter volume loss in the insula, and that a relationship may exist between preservation of insula gray-matter and improvement of psychological well-being by aerobic exercise training.

CYRIC Annual Report 2009

CYRIC Annual Report 2009

Objective Our aim was to evaluate changes in glucose metabolism of skeletal muscles and viscera induced by different workloads using F-18-2-fluoro-2-deoxyglucose ([F-18]FDG) and three-dimensional positron emission tomography (3-D PET). Methods Five male volunteers performed ergometer bicycle exercise for 40 min at 40% and 70% of the maximal O-2 consumption (V) over dot O-2max). [F-18]FDG was injected 10 min later following the exercise task. Whole-body 3-D PET was performed. Five other male volunteers were studied as a control to compare with the exercise group. The PET image data were analyzed using manually defined regions of interest to quantify the regional metabolic rate of glucose (rMRGlc). Group comparisons were made using analysis of variance, and significant differences (P < 0.05) were determined using Scheffe's test (post hoc analysis). Results Quantitative analysis demonstrated that rMRGlc increased (P < 0.05) in the skeletal muscles of the thigh at mild or moderate workloads when compared with the resting controls. For visceral organs such as the liver and brain, metabolic reduction was significant (P < 0.05) at mild and/or moderate exercise workload. Conclusions The present study demonstrated linear increases or decreases in glucose uptake by skeletal muscles and viscera with mild and moderate exercise workloads, suggesting the presence of homeostatic energy metabolism. This result supports the finding that [F-18]FDG-PET can be used as an index of organ energy metabolism for moderate exercise workloads (70% (V) over dotO(2max)). The results of this investigation may contribute to sports medicine and rehabilitation science.

Our purpose was to evaluate the effects of exercise intensities on free fatty acid (FFA) uptake in skeletal muscles, myocardium and liver among humans using I-123-labeled 15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid (I-123-BMIPP) and single photon emission computed tomography technique (SPECT). Six untrained male subjects were studied after 35 min of ergometer bicycle exercise at 40, 70 and 80% maximal aerobic power (VO2max). One subject was studied as resting control. SPECT scan was done 40 min after I-123-BMIPP injection. Mean fractional uptake (FU) in quadriceps femoris muscle (QF) were 0.029 +/- 0.001, 0.029 +/- 0.002 and 0.025 +/- 0.002% at 40, 70 and 80% VO2max; respectively. FU of QF at 40 and 70% VO2max, were significantly higher than those of 80% VO2max. Mean FU into myocardium were 0.048 +/- 0.002, 0.052 +/- 0.004 and 0.050 +/- 0.003% and those in liver were 0.033 +/- 0.002, 0.032 +/- 0.002 and 0.034 +/- 0.003% at each loads, respectively. Any significant changes were not suggestive in liver and myocardium after exercise. Mean FU (the mean values of all exercise intensity) at exercise is 2.86, 0.96 and 0.71 times higher than those at rest in QF, myocardium and liver. These results suggest: (1) in skeletal muscles, energy requirements at above lactate threshold at high exercise intensity predominantly depend upon other intramuscular energy substrates, (2) there is possibility of energy compensation by other substrates in myocardium at higher exercise intensity, (3) FFA uptake in liver might decrease after exercise; however, the influence of exercise intensities is not suggested.

To investigate exercise-induced regional metabolic and perfusion changes in the human brain, various methods are available, such as positron emission tomography (PET), functional magnetic resonance imaging (fMRI), near-infrared spectroscopy (NIRS) and electroencephalography (EEG). In this paper, details of methods of metabolic measurement using PET, [F-18]fluorodeoxyglucose (F-18]FDG) and [O-15]radio-labelled water ([O-15]H2O) will be explained. Functional neuroimaging in the field of neuroscience was started in the 1970s using an autoradiography technique on experimental animals. The first human functional neuroimaging exercise study was conducted in 1987 using a rough measurement system known as Xe-133 inhalation. Although the data was useful, more detailed and exact functional neuroimaging, especially with respect to spatial resolution, was achieved by positron emission tomography. Early studies measured the cerebral blood flow changes during exercise. Recently, PET was made more applicable to exercise physiology and psychology by the use of the tracer [18F]FDG. This technique allowed subjects to be scanned after an exercise task is completed but still obtain data from the exercise itself, which is similar to autoradiography studies. In this report, methodological information is provided with respect to the recommended protocol design, the selection of the scanning mode, how to evaluate the cerebral glucose metabolism and how to interpret the regional brain activity using voxel-by-voxel analysis and regions of interest techniques (ROI). Considering the important role of exercise in health promotion, further efforts in this line of research should be encouraged in order to better understand health behavior. Although the number of research papers is still limited, recent work has indicated that the [F-18]FDG-PET technique is a useful tool to understand brain activity during exercise. (C) 2008 Elsevier Inc. All rights reserved.

CYRIC Annual Report 2008

It is well known that acute bouts of aerobic exercise are sufficient to improve the psychological state. One possible mechanism of its effect is the mastery hypothesis which suggests that command of a challenging pursuit inculcates a sense of independence and success. To evaluate mastery hypothesis, we compared the change of mood following two types of acute aerobic exercise, learning some movements of hip-hop dance and simple walking. Experiments were conducted in both normal subjects and schizophrenic patients. Nine sedentary male university students（normal group）and 7 schizophrenic patients（4 men and 3 women）, under day-care treatmen（t patient group）, participated in this study. Each subject performed 30 min of hip-hop dance, walking or waiting control on separate days. Mood was measured before（pre）, 10 min after （post 10′） and 30 min after （post 30′）each trial by self-reported questionnaire（MCL-S.2）. Mean % maximal heart rate during the two exercises was almost the same in both groups. In the normal group, both hip-hop dance and walking increased pleasure compared with the control condition; however, there were no statistical differences in mood alterations between the two exercises. In the patient group, hip-hop dance increased pleasure compared with the control condition. Although there were no statistical differences in mood alteration between hip-hop dance and walking, walking did not significantly increase pleasure compared with the control condition. This study could not support the mastery hypothesis; however, acute aerobic exercise improved the mood, not only of normal subjects but also schizophrenic patients.

Eds. ESASHI Masayoshi, ISHII Keizo, OHUCHI Noriaki, OSUMI Noriko, SATO Masaaki, YAMAGUCHI Takami. Imperial College Press.

Eds. ESASHI Masayoshi, ISHII Keizo, OHUCHI Noriaki, OSUMI Noriko, SATO Masaaki, YAMAGUCHI Takami. Imperial College Press.

Eds. ESASHI Masayoshi, ISHII Keizo, OHUCHI Noriaki, OSUMI Noriko, SATO Masaaki, YAMAGUCHI Takami. Imperial College Press.

CYRIC Annual Report 2007

CYRIC Annual Report 2007

CYRIC Annual Report 2007

CYRIC Annual Report 2007

CYRIC Annual Report 2006

Muscular contraction and loading of adjacent tendons has been demonstrated to cause increased blood flow and metabolic activity in the peritendinous region. However, it is poorly known to what extent the human tendon itself takes up glucose during exercise. Thus, the purpose of this study was to measure tendon glucose uptake with increasing exercise intensity and to compare it to muscle glucose uptake at the same intensities. Eight young men were examined on three separate days during which they performed 35 min of cycling at 30, 55 and 75% of VO2max, respectively. Glucose uptake was measured directly by positron emission tomography (PET) with 2-[F-18]fluoro-2-deoxyglucose ([F-18]FDG). [F-18]FDG was injected after 10 min of exercise that was continued for a further 25 min after the injection. PET scanning of the thigh and Achilles region was performed after the exercise. Glucose uptake of the Achilles tendon (AT) remained unchanged (7.1 +/- 1.5, 6.6 +/- 1.1, and 6.0 +/- 1.1 mu mol (.) kg(-1) (.) min(-1)) with the increasing workload, although the glucose uptake in m. quadriceps femoris simultaneously clearly increased (48 +/- 35, 120 +/- 35, and 152 +/- 74 mu mol (.) kg(-1) (.) min(-1), p < 0.05). In conclusion, the AT takes up glucose during exercise but in significantly smaller amounts than the skeletal muscle does. Furthermore, glucose uptake in the AT is not increased with the increasing exercise intensity. This may be partly explained by the cycle ergometry exercise used in the present study, which probably causes only a little increase in strain to the AT with increasing exercise intensity.

Physiological activation increases glucose uptake locally in the brain. However, it is not known how high intensity exercise affects regional and global brain glucose uptake. The effect of exercise intensity and exercise capacity on brain glucose uptake was directly measured using positron emission tomography (PET) and [F-18]fluoro-deoxy-glucose ([F-18]FDG). Fourteen healthy, right-handed men were studied after 35 min of bicycle exercise at exercise intensities corresponding to 30, 55 and 75% of V-O2max on three separate days. [F-18]FDG was injected 10 min after the start of the exercise. Thereafter exercise was continued for another 25 min. PET scanning of the brain was conducted after completion of the exercise. Regional glucose metabolic rate (rGMR) decreased in all measured cortical regions as exercise intensity increased. The mean decrease between the highest and lowest exercise intensity was 32% globally in the brain (38.6 +/- 4.6 versus 26.1 +/- 5.0 mu mol (100 g)(-1) min(-1), P < 0.001). Lactate availability during exercise tended to correlate negatively with the observed brain glucose uptake. In addition, the decrease in glucose uptake in the dorsal part of the anterior cingulate cortex (37% versus 20%, P < 0.05 between 30% and 75% of V-O2max) was significantly more pronounced in subjects with higher exercise capacity. These results demonstrate that brain glucose uptake decreases with increase in exercise intensity. Therefore substrates other than glucose, most likely lactate, are utilized by the brain in order to compensate the increased energy needed to maintain neuronal activity during high intensity exercise. Moreover, it seems that exercise training could be related to adaptive metabolic changes locally in the frontal cortical regions.

CYRIC Annual Report 2005

Purpose: Endurance training enhances skeletal muscle glucose uptake at rest, but the responses to different exercise intensities are unknown. In the present study, we tested whether glucose uptake is enhanced in trained men during low-, moderate-, and high-intensity exercise as compared with untrained men. Methods: Seven trained and untrained men were studied without any dietary manipulation during bicycle exercise at relative intensities of 30%, 55%, and 75% of maximal oxygen consumption ((V) over dot O-2max) on three separate days. Glucose uptake in the quadriceps femoris muscle was directly measured using positron emission tomography (PET) and F-18-fluoro-deoxy-glucose ([F-18]FDG). [F-18]FDG was injected 10 min after the start of the exercise. Thereafter exercise was continued for another 25 min. PET scanning was conducted immediately after completion of the exercise. The measured glucose uptake values reflect the situation during exercise due to chemical characteristics of the [F-18]FDG. Results: Muscle glucose uptake increased from 30% to 55% (V) over dot O-2max intensity exercise similarly in both groups (P < 0.05). However, from 55% to 75% (V) over dot O-2max intensity exercise, only athletes were able to further enhance glucose uptake. Furthermore, at highest intensity, glucose uptake was significantly higher in trained than in untrained men (236.6 +/- 29.6 vs 176.3 +/- 22.4 mumol.kg(-1).min(-1), P < 0.05). There were no differences in plasma glucose, insulin, or lactate in any time point at 75% (V) over dot O-2max intensity between groups. Conclusions: These results show that skeletal muscle glucose uptake is higher in trained than in untrained men at high relative exercise intensity, although at lower relative exercise intensities no differences are observed. Thus, endurance training improves the capacity of contraction-induced glucose uptake in skeletal muscle.

The purpose of this study was to investigate the effect of moderate intensity exercise on gastric emptying and absorption using positron emission tomography（PET）with oral 18F-fluoro-deoxy-glucose（18FFDG） intake. Seven healthy subjects aged 20～28 years volunteered to participate in this study. Each subject exercised on a bicycle ergometer for 30 minutes at 60％ maximal oxygen uptake（Exercise trial）. A control trial（without exercise）was also performed by the subjects. Immediately before starting exercise， 300ml of water containing 18F-FDG was orally administered. 18F-FDG accumulation in the alimentary tract was measured with 3D PET after the end of exercise. Regions of interest were drawn on visually defined stomach and small intestine. To measure blood glucose, plasma radioactivity, and plasma CCK, blood was sampled 4 times every 10 minutes throughout the exercise. Percent contents of remaining radioactivity in stomach in exercise trial was higher than that in control. Significant change in blood glucose level due to exercise was showed. Plasma CCK level in exercise trial was higher than that in control at the end of exercise. The effect of exercise on ％contents of remaining radioactivity in the total alimentary tract or change in plasma radioactivity level was not significant.These findings suggest that cycling exercise for 30 minutes at moderate intensity has a depressive effect on gastric emptying of fluid intake partially influenced by CCK, but no marked effect on absorption of 18F-FDG from the intestine in normal human subjects.

We analyzed muscular activity of the lower extremities during level walking using positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG). We examined 17 healthy male subjects 11 were assigned to a walking group and 6 to a resting group. After 18F-FDG injection, the walking group subjects walked at a free speed for 15 min. A whole-body image was then obtained by a PET camera, and the standardized uptake ratio (SUR) was computed for each muscle. The SUR for each muscle of the walking group was compared with that for the corresponding muscles in the resting group. The level of muscular activity of all the muscles we examined were higher during level walking than when resting. The activity of the lower leg muscles was higher than that of the thigh muscles during level walking. The muscular activity of the soleus was highest among all the muscles examined. Among the gluteal muscles, the muscular activity of the gluteus minimus was higher than that of the gluteus maximus and gluteus medius. The concurrent validity of measuring muscular activity of the lower extremity during level walking by the PET method using 18F-FDG was demonstrated.

The purpose of this study was to investigate the effects of exercise on myocardial glucose uptake and Whether the pattern of glucose uptake is the same as in skeletal muscle. Glucose uptake was measured using positron emission tomography (PET) and 2-[F-18]fluoro-2-deoxy-D-glucose ([F-18]FDG). Twelve healthy men were studied during rest, while 14 subjects were studied after 35 min of bicycle exercise corresponding to 30,55 and 75% of maximal oxygen consumption ((V)over dot(O2,max)) on three separate days. [F-18]FDG was injected 10 min after the start of exercise and exercise continued for a further 25 min. Myocardial and skeletal muscle PET scanning was commenced directly after the completion of the exercise bout. As compared to the resting state, exercise doubled myocardial glucose uptake at the 30% (P = 0.056) and 55% intensity levels (P < 0.05), while at the 75% intensity level glucose uptake was reduced significantly compared to the lower exercise intensities. There was no significant difference between the highest intensity level and the resting state (P = 0.18). At rest and during low-intensity exercise, myocardial glucose uptake was inversely associated with circulating levels of free fatty acids. However, during higher exercise intensities when plasma lactate concentrations increased significantly, this association disappeared. In contrast to, myocardial responses, skeletal muscle glucose uptake rose in parallel with exercise intensity from rest to 30% and then 55% (V)over dot(O2,max) (P < 0.001) and tended to increase further at the intensity of 75% (P = 0.065). In conclusion, these results demonstrate that myocardial glucose uptake is increased during mild- and moderate-intensity exercise, but is decreased during high-intensity exercise. This finding suggests that the increased myocardial energy that is needed during high-intensity exercise is supplied by substrates other than glucose.

Background. To examine regional metabolic changes in the human brain induced by free running in upright posture. Methods. Experimental design: regional brain changes in glucose uptake induced by running were examined by comparing brain images obtained by positron emission tomography (PET) and F-18-fluorodeoxyglucose (FDG), Setting: the study was conducted at a research institute and involved participation of healthy young volunteers. Data sampling and analysis required special imaging device and special computer hardware/software. Participants: subjects were 17 healthy male volunteers. They were divided at random into two equal groups, those who ran 4-5 km and the others sat in the room. Measures: differences in regional cerebral glucose uptake between runners and control groups were assessed statistically. Plasma glucose Level was also measured and global cerebral uptake was estimated. Results, Running was associated with a relative increase of glucose uptake in the temporoparietal association cortex, occipital cortex, premotor cortex and the cerebellar vermis, The highest activity was noted in the temporoparietal association cortex. Activity of the primary sensorimotor cortex was higher in the superomedial part (leg motor area) than the lateral part (thorax and arm). Conclusions. Running augmented energy consumption in the parieto-occipital region relative to the motor area, probably to the higher energy consumption necessary for integration of multimodal sensory information than for generation of motor output. Our results indicate that FDG PET is a useful tool for brain mapping under various physiological conditions.

We attempted to visualize dynamic adjustment of glucose utilization in humans in the whole-body organs during physical exercise by using three-dimensional positron emission tomography (3D-PET) and [F-18]-2-fluoro-deoxy-glucose (FDG). Twelve healthy male volunteers collaborated on the study; six subjects were assigned to the resting control group (C) and the other six to the running group (E). Group E subjects performed running on a flat road for 35 min. After 15 min of running. subjects injected FDG and kept on running thereafter for another 20 min. Group C subjects sat on a comfortable chair in a quiet room for 35 min after the injection of FDG. After scanning by PET, the regions of interest (ROIs) were manually set on brain, heart, thorax, abdomen, lower extremities, and the rest of the body on the corresponding transaxial images. The uptake of FDG in each region was evaluated as the % fraction of FDG accumulation relative to the total amount of whole-body accumulation. The results revealed increase of FDG uptake after running in the lower leg muscles from 24.6+/-95% to 43.1+/-4.7% and in the heart from 2.3+/-0.4% to 2.8+/-0.6%. The differences were significant (P < 0.05). These increases reflect the rise in energy consumption in leg and heart muscles and were balanced by the reduction of energy consumption in the other part of the body. FDG uptake in the abdominal region reduced from 37.3+/-7.2% to 19.7+/-4.9%. However, FDG uptake in the brain remained stable, i.e., 11.9+/-2.8% at rest and 10.3+/-2.5% after exercise. Thus, 3D-PET is a tool to visualize the dynamic adjustment of energy consumption during physical exercise in humans.

The purpose of this study was to examine, by positron emission tomography (PET), the distribution of [18F]fluoro-deoxy-glucose ([18F]FDG) uptake by human muscles during 35 min of running. Thirteen healthy male subjects were studied, seven of whom participated in the exercise study. Running intensity was kept constant such that the subjects' heart rates were maintained at between 140 and 150 beats per minute. [18F]FDG [62.9 (14.8) MBq, mean (SD)] was injected after 15 min of running. PET imaging was started immediately after the running ended. The ratio of [18F]FDG uptake by muscles in runners to that in control subjects (r-c ratio) varied from three to six for the muscles of the foot and leg below the knee joint. The r-c ratio of the medial head of the gastrocnemius (MG) was higher than that of its lateral head (LG). The r-c ratio of the rectus femoris (RF) was lower than that of the other three muscles of the quadriceps femoris (QF). The r-c ratio of inactive muscles located above the waist was approximately 0.7. These results suggest that, during the moderate running of this study: (1) glucose uptake by muscles of the foot and leg below the knee joint clearly increases, (2) the r-c ratio differs significantly among the skeletal muscles, which act synergistically, and (3) glucose uptake by inactive skeletal muscles decreases.

CYRIC Annual Report 1996

CYRIC Annual Report 1996

CYRIC Annual Report 1996

The contractile properties and conduction velocity of motor units are estimated by using surface array electrodes during voluntary isometric contractions of the human vastus lateralis muscle. The subjects develop and maintain sufficient force to steadily discharge a given motor unit, assisted by visual feedback from an oscilloscope. The torque curve developed around the knee joint is triggered by an individual motor unit and averaged. 31 motor units in five subects are studied. The twitch tension detected ranges from 3 to 27 m Nm with a mean of 12.3 m Nm. The threshold force ranges from 1.88 to 10.12 Nm with a mean of 5.48 Nm, which is 3% of the maximal voluntary contraction. The rise time ranges from 56 to 106 ms with a mean of 83 ms. The mean value of conduction velocity is 4.64 m s(-1). The twitch tension is positively correlated to the threshold force (r = 0.839, p < 0.01), but has no relation to the other parameters. It is concluded that the use of non-invasive surface array electrodes provides the contractile properties of motor units and muscle fibre conduction velocity during weak contractions.

The factors involving muscle fatigue of the first dorsal interosseous (FDI) muscle were studied during 5-min isometric maximal voluntary contractions (MVC). Measurement of the MVC force, integrated electromyogram (IEMG) and the force induced by tetanic electrical stimulation (50 Hz, 2 s in duration) , recording of M wave from two subjects, and measurement of whole blood K^+ concentration were performed during the fatiguing exercise and recovery period of 1O min. k^+ concentration in the draining vein increased significantly from 3.4 ± 0.5 m Eq/l to 5.0 ± 1.1 m Eq/l and the area of the M wave obtained from two subjects decreased by 5-10% of the control value. These facts suggest that the resting membrane potential declined, leading to the loss of contraction force. The declining rate of the MVC force was bigger than that of the IEMG during the fatiguing exercise and at the early stage of the recovery period. While whole blood K^+ concentration recovered to its normal level quickly, there was a marked delay in the recovery of MVC force. These results suggest that the electrical excitation was not efficiently converted to muscle contraction. The MVC force declined in parallel to the 50Hz stimulation force, indicating that the central nervous system (CNS) failure was not involved in this experiments. Thus, we conclude that the failure in muscle membrane excitation and in excitation/contraction coupling are involved in the deteriorating force generating capacity of the FDI during the 5-min MVC.

We measured the contractile properties of the first dorsal interosseous muscle by surface electrodes and needle electrodes during submaximal voluntary contraction. Twenty-seven single motor units were recorded from 5 volunteers by surface electrodes, which were confirmed by subsequent needle electrode recordings. Twitch tension ranged from 0.6 to 10.0 g with a mean of 3.7 g based on an averaging method triggered by surface myoelectric signals, and the tension calculated from the needle myoelectric signals ranged from 0.8 to 11.7 g with a mean of 3.6 g. Rise time ranged from 33.9 to 81.6 msec with a mean of 49.4 msec for the surface electrode recordings, and from 33.0 to 73.2 msec with a mean of 50.8 msec for the needle electrode recordings. The obtained data of surface electrode recordings indicated a high correlation with that of the needle electrode recordings, r = 0.92 (P < 0.001) for twitch tension and r = 0.91 (P < 0.001) for rise time. We also found a positive correlation between threshold force and twitch tension (by surface electrodes: r = 0.71, P < 0.05; by needle electrodes: r = 0.77, P < 0.05). Our studies indicate that it is possible to record single motor units by non-invasive surface electrodes provided that the unit has a threshold force of less than 2 kg.

Factors involving muscle fatigue were studied at intermittent isometric contraction of the first dorsal interosseous muscle (FDI). Subjects made repeated contraction of 6 s, 40% of maximal voluntary contraction (40% MVC) (= target force) followed by 4 s rest until the target force could no longer be maintained. Measurement of MVC, recording of M wave evoked from the relaxed muscle, force measurement during tetanic electrical stimulation and measurement of serum K+ concentration were performed every 2 min during the fatiguing exercise and after 10 min of recovery. The declining rate of MVC force was always smaller than that of the force generated by 50 Hz stimulation, suggesting that no central nervous system (CNS) failure was involved. The amplitude and the area of the M wave declined while the duration of the wave increased, accompanied by the rise in serum K+ concentration. After 10 min of recovery, all parameters except the MVC force were restored. Thus we concluded that the failure in muscle membrane excitation, as well as the failure in excitation/contraction coupling, is involved in the deteriorating force generating capacity of FDI during intermittent isometric contraction.