Biomedical subjects

Hiroshi Akima

Publications and source records attributed to Hiroshi Akima.

15 recordsLinked to original sources

PubMed2006

Oxygen uptake kinetics following 20 days of unilateral lower limb suspension.

The purpose of the present study was to examine the effect of unilateral lower limb suspension (ULLS) deconditioning on oxygen uptake kinetics. Eight healthy males underwent ULLS for 20 days and performed a series of 6-min square-wave transitions from rest to 60-W single-leg cycling exercises just before and after ULLS. To characterize the kinetics of the oxygen uptake response, a single exponential model was applied to the data until the end of the fast component omitted the first 15 s of the on-transit using a nonlinear least-squares fitting procedure. The following results were found: (i) the time constant of oxygen uptake was unchanged before and after ULLS; (ii) although there was no significant difference in the baseline and the asymptotic amplitude of the fast component, the asymptote, i.e., the absolute asymptotic amplitude of the fast component (the sum of the baseline and the asymptotic amplitude), and the end exercise oxygen uptake were decreased after ULLS; (iii) the contribution of the slow component to the total response of oxygen uptake was unchanged at pre- and post-ULLS. In conclusion, the asymptote in the fast component and the end exercise oxygen uptake were decreased after 20-d ULLS, though the response speed and the amplitude of the slow component of oxygen uptake were not changed. It is suggested that deconditioning as a result of limb disuse affects oxygen uptake response.

Adaptation, Physiological↗

PubMed2006

Ventilatory and circulatory responses at the onset of exercise after eccentric exercise.

The purpose of this study was to clarify whether delayed onset muscle soreness (DOMS) and muscle damage after eccentric exercise (ECC) could affect the ventilatory and circulatory responses at the onset of exercise, and whether those effects would continue after the disappearance of DOMS. Ten males participated in this study. We measured ventilatory and circulatory responses at the onset of exercise, for the first 20 s, during knee extension-relaxation voluntary exercise (VOL) and passive movement (PAS), which was achieved by the experimenter alternatively pulling ropes connected to the subjects' ankles for the same period and frequency as during VOL. VOL and PAS were performed before, 2 days after, and 7 days after ECC. The following results were found: (1) the gain of minute ventilation at the onset of VOL at 2 days after ECC was significantly larger than that of before ECC; (2) the gain of minute ventilation at 7 days after ECC during both VOL and PAS was also enhanced significantly as compared to that of before ECC; and (3) heart rate and blood pressure responses were unchanged throughout the experimental period. In conclusion, ventilatory response at the onset of exercise is augmented during DOMS and EIMD after ECC and the enhanced ventilatory response continued after the disappearance of DOMS. It is suggested that enhanced ventilatory response during exercise after ECC is attributed to at least the changes in neural factors and that the mechanisms inducing these augmented ventilatory responses should be different during the period after ECC.

Adult↗

PubMed2006

Ubiquitin ligase gene expression in healthy volunteers with 20-day bedrest.

In animal models, several ubiquitin ligases play an important role in skeletal muscle atrophy caused by unloading. In this study we examined protein ubiquitination and ubiquitin ligase gene expression in quadriceps femoris muscle from healthy volunteers after 20-day bedrest to clarify ubiquitin-dependent proteolysis in human muscles after unloading. During bedrest, thickness and cross-sectional area of the quadriceps femoris muscle decreased significantly by 4.6% and 3.7%, respectively. Ubiquitinated proteins accumulated in these atrophied human muscles. A real-time reverse transcription-polymerase chain reaction system showed that bedrest significantly upregulated expression of two ubiquitin ligase genes, Cbl-b and atrogin-1. We also performed DNA microarray analysis to examine comprehensive gene expression in the atrophied muscle. Bedrest mainly suppressed the expression of muscle genes associated with control of gene expression in skeletal muscle. Our results suggest that, in humans, Cbl-b- or atrogin-1-mediated ubiquitination plays an important role in unloading-induced muscle atrophy, and that unloading stress may preferentially inhibit transcriptional responses in skeletal muscle.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Atrophy of thigh muscles after meniscal lesions and arthroscopic partial menisectomy.

The purpose of this study was to investigate the atrophic pattern of the muscle groups and their individual muscles in the thigh after meniscal lesions and arthroscopic partial menisectomy. A total of 32 individuals (17 men and 15 women) who underwent arthroscopic knee surgery participated in this study. Their operated and non-operated thighs were scanned by magnetic resonance imaging to determine the volume of the quadriceps (QF), hamstring (HM), and adductors (AD). Compared with the non-operated limb, the volume of the QF was significantly lower in the operated limb; however, no significant difference was observed in the HM and AD. The volume of individual muscles of the QF, i.e. the rectus femoris (RF), vastus lateralis (VL), vastus intermedius (VI), and vastus medialis (VM), in the operated limb was significantly lower than the volume of those in the non-operated limb (P<0.01, all). Although the relative change in the VM was significantly higher than that of the RF (P<0.05), specific atrophy was not found among four individual muscles in the QF. We concluded that meniscal lesions and partial menisectomy induce atrophy in the QF only in the thigh, and that no specific atrophy, e.g. VM, seemed to occur within the individual muscles in the QF.

Adult↗

PubMed2005

Neuromuscular activation of triceps surae using muscle functional MRI and EMG.

PURPOSE: The aim of the present study was to clarify the neuromuscular activation patterns among individual triceps surae (TS) muscles during a repetitive plantarflexion using muscle functional magnetic resonance imaging (MRI) (mfMRI) and electromyography (EMG). METHODS: Six healthy men participated in this study, performing 5 sets of 10 repetitions of a calf-raise exercise bilaterally, unilaterally, and unilaterally with an additional 15% of body-weight load. The transverse relaxation times (T2) in the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL) muscles were measured from mfMR images obtained with the subject at rest and immediately after exercise; integrated EMG (iEMG) activity was recorded from the same muscles during exercise using surface electrodes. RESULTS: There was remarkable correspondence between the changes in T2 values and iEMG activity under the three different workloads for individual TS muscles. In addition, changes in T2 value that occurred as a function of increasing exercise loads were linearly correlated with iEMG activity in the MG (r=0.58, P<0.05) and SOL (r=0.63, P<0.01), but not in the LG. CONCLUSIONS: These results suggest that 1) mfMRI signals and iEMG activity correlate with workload in individual TS muscles, 2) mfMRI signals are associated with neuromuscular activity reflected in iEMG in the MG and SOL but not in the LG, and 3) these relationships are associated with neuromuscular and metabolic factors during exercise.

Adult↗

PubMed2005

Intensive cycle training with artificial gravity maintains muscle size during bed rest.

INTRODUCTION: The present study aimed to investigate the effect of intensive cycle training with short-arm centrifuge-induced hypergravity during bed rest on muscle size and function. METHODS: This study involved 10 healthy men who were divided into 2 groups: a countermeasure group, BR-CM (n = 5); and a control group, BR-Cont (n = 5). The BR-CM subjects partook in intensive cycle training (to 90% of maximum HR) with short-arm centrifuge-induced artificial gravity on alternate days during 20-d bed rest. Muscle volume of the thigh and maximum voluntary contraction (MVC) during isometric knee extensions was measured before and after bed rest. Muscle functional magnetic resonance imaging (mfMRI) and electromyogram (EMG) of the quadriceps femoris were obtained during submaximal knee extension exercises at a load of 30% MVC. RESULTS: The volume of the total thigh muscles was maintained in the BR-CM group (-1%), whereas it was not in the BR-Cont group (-9%, p < 0.05). MVC decreased in the BR-CM (7%) and BR-Cont groups (23%). EMG activity in the BR-CM group after bed rest was significantly lower than that of before; however, no significant change was found in the BR-Cont group. There were no significant changes in the resting and exercised mfMRI signals in either the BR-CM or BR-Cont groups. CONCLUSION: These results suggest that intensive cycle training with hypergravity maintained the size of human skeletal muscles during bed rest.

Adult↗

PubMed2004

Human adductor muscles atrophy after short duration of unweighting.

The purpose of this study was to investigate the effect of 20 days of bed rest (BR) on the physiological cross-sectional area (PCSA) of the adductor (AD) muscle group. Five healthy men and five healthy women were kept on a horizontal bed for 20 days. To calculate the PCSA of the AD muscle group, transaxial magnetic resonance imaging of the right thigh was acquired four times for each of the subjects: (1) pre BR, (2) on the tenth day of BR, (3) post BR, and (4) 1 month after BR. Overall, the PCSA measurements of the AD muscle group and its individual muscles were significantly decreased on the tenth day of BR and at post BR; however, they had recovered to the baseline within 1 month of the reambulation period. The amount and pattern of relative change in the PCSA measurements of the AD muscle group were similar to those of the knee extensor (KE) and knee flexor (KF) muscle groups studied previously. These results suggested that the AD muscle group showed an atrophic response that was similar to the KE and KF muscle groups after unweighting; therefore, we should pay much more attention to the AD muscle group when considering countermeasures for future human spaceflight projects.

Adult↗

PubMed2004

Effects of resistance training during bed rest on the viscoelastic properties of tendon structures in the lower limb.

The purpose of this study was to investigate the effects of resistance training on the tendon properties in knee extensors during 20 days of bed rest. Sixteen men were assigned to the resistance training group (BR-Tr) or the non-training, control group (BR-Con). Leg-press exercises were performed as five sets of 10 repetitions at 90% of maximum load daily for 20 days during bed rest. Before and after bed rest, the elongation of the tendon structures of the vastus lateralis muscle during isometric knee extension was determined using ultrasonography, while subjects performed ramp isometric contraction up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force (Fm) and tendon elongation (L) was fitted to a linear regression curve, the slope of which was defined as stiffness. The hysteresis was calculated as the ratio of the area within the Fm-L loop to the area beneath the load portion of the curve. The stiffness decreased significantly after bed rest for BR-Con, but not for BR-Tr. Similarly, the hysteresis increased significantly after bed rest for BR-Con, but not for BR-Tr. These results suggested that the bed rest caused the stiffness of tendon structures to decrease and their hysteresis to increase, and that leg-press training prevents the deconditioning of the tendon structures in knee extensors.

Adult↗

PubMed2004

Ventilatory and cardiovascular responses to hypercapnia after 20 days of head-down bed rest.

INTRODUCTION: Few studies have attempted to investigate the influence of prolonged head-down bed rest (HDBR) on hypercapnic ventilatory chemosensitivity, and there are no data available regarding associated changes in arterial BP and heart rate (HR). The aim of this study was to clarify the influence of prolonged HDBR on ventilatory and cardiovascular responses to hypercapnia. METHODS: There were five healthy men who participated in this study. Resting ventilatory and cardiovascular responses to hypercapnia were measured by means of Read's CO2 rebreathing method 4 d before and on the 19th day of HDBR. Measured variables included systolic and diastolic BP (SBP and DBP, respectively), inspired minute ventilation (VI), and end-tidal partial pressure of CO2 (PETCO2). RESULTS: Ventilatory response to hyperoxic hypercapnia (deltaVI/ deltaPETCO2) decreased significantly on the 19th day of HDBR (1.42 +/- 0.65 to 0.90 +/- 0.41 L x min(-1) x torr(-1), p < 0.05). On the other hand, SBP, DBP, and HR responses (deltaSBP/deltaPETCO2, deltaDBP/deltaPETCO2, and deltaHR/deltaPETCO2) were unchanged. DISCUSSION: The results from this study suggest that prolonged HDBR leads to diminished central hypercapnic ventilatory chemosensitivity.

Adult↗

PubMed2004

Acceleration with exercise during head-down bed rest preserves upright exercise responses.

INTRODUCTION: This study was designed to elucidate the effect of short-arm centrifuge-induced artificial gravity with exercise training during ground-based simulated spaceflight, i.e., prolonged head-down bed rest (HDBR), on respiratory and cardiovascular responses to upright exercise. METHODS: There were 10 healthy men who underwent 20 d of -6 degrees HDBR, and were assigned to either a countermeasure (CM) group (n = 5) or a no countermeasure (No-CM) group (n = 5). The subjects in the CM group performed two sessions (20 min each session, 40 min total) of short-arm centrifuge-induced artificial gravity with exercise training in a supine position on alternate days (10 d total) during HDBR. The first session was set at 0.8-1.4 G load at heart level with a constant exercise intensity (60 W), and the second session began with a 0.3 G load at heart level with an interval exercise protocol (40-80% peak oxygen uptake; VO2peak). The measurements of respiratory and cardiovascular responses to incremental exercise were performed pre- and post-HDBR. RESULTS: The 20 d of HDBR increased minute expired ventilation, heart rate, and respiratory exchange ratio and decreased stroke volume during submaximal exercise in the No-CM group, whereas these parameters were unchanged in the CM group. In the No-CM group, VO2peak decreased significantly (47.0 +/- 8.6 to 34.8 +/- 6.8 ml x kg(-1) x min(-1), p < 0.05), whereas VO2peak in the CM group did not show a significant decrease following 20 d of HDBR (47.7 +/- 10.0 to 43.9 +/- 8.9 ml x kg(-1) x min(-1)). These results suggest that short-arm centrifuge-induced artificial gravity with exercise training is effective in maintaining respiratory and cardiovascular responses to upright exercise.

Adolescent↗

PubMed2004

Effect of centrifuge-induced artificial gravity and ergometric exercise on cardiovascular deconditioning, myatrophy, and osteoporosis induced by a -6 degrees head-down bedrest.

We have reported that centrifuge-induced artificial gravity with ergometric exercise could reduce developing cardiovascular deconditioning in humans. In the present study, we examined this load could prevent the myatrophy and osteoporosis induced by head-down bedrest for 20 days. Subjects were ten healthy male volunteers with informed consent. They were requested to lie down at -6 degrees for 20 days, and evaluation for cardiovascular deconditioning, myatrophy, and osteoporosis. As the result, high G-load with low intensity exercise suppressed the orthostatic intolerance and increase in serum osteoporotic marker, whereas low G-load with high intensity ergometric exercise maintained the maximal oxygen intake, heart dimension, and prevented myatrophy. The combination of high/low G-load with low/high intensity exercise will determine the optimal protocol for prevention of cardiovascular deconditioning, myatrophy, and osteoporosis.

Adult↗

PubMed2003

Short-term creatine supplementation does not improve muscle activation or sprint performance in humans.

The purpose of this study was to examine the influence of short-term creatine (Cr) supplementation on exercise-induced transverse relaxation time (T2) and sprint performance during maximum intermittent cycling exercise using the muscle functional magnetic resonance imaging (mfMRI) technique. Twelve men were divided into a Cr supplementation group [the Cr group, taking 4 x (5 g Cr monohydrate + 2.5 g maltodextrin)/day], or a placebo supplementation group (the P group, taking 4 x 7.5 g maltodextrin/day). The allocation to the groups was based on cycling tests and the subject's physical characteristics, and thus was not randomized. A double-blind research design was employed for a 5-day supplementation period. mfMR images of the right thigh were collected at rest and immediately after two, five, and ten 6-s sprint bouts of maximum intermittent cycling exercise with a 30-s recovery interval between sets. Before and after supplementation, blood was taken to calculate lactate accumulation, and the muscle volume of the thigh was determined by MRI. Following supplementation, there was significant body mass gain in the Cr group ( P<0.05), whereas the P group did not change. The exercise-induced T2, blood lactate levels and sprint performance were not affected by Cr supplementation in any sprint bouts. These results suggest that short-term Cr supplementation does not influence short duration repetitive sprint performance and muscle activation and/or metabolic state during sprint cycling evaluated by mfMRI of the skeletal muscle in humans.

Administration, Oral↗

PubMed2003

Coactivation pattern in human quadriceps during isokinetic knee-extension by muscle functional MRI.

We tested activation patterns of individual muscles and neuromuscular compartments (NMCs) of the quadriceps femoris (QF) during knee-extension exercises (KEE). Eight healthy men performed repetitive isokinetic KEE at 120 degrees s(-1). Before and after KEE, muscle functional magnetic resonance images of the thigh were taken to calculate transverse relaxation times (T2) for the individual muscles of the QF. In terms of exercised T2, a moderate correlation was observed between the rectus femoris (RF) and vastus medialis (VM) ( r=0.493, P<0.001), and between the vastus lateralis (VL) and VM ( r=0.347, P<0.01). Furthermore, a strong correlation was also observed between the vastus intermedius (VI) and VM ( r=0.719, P<0.0001), and between the VL and VI ( r=0.783, P<0.0001). There was a significant difference in T2 between the proximal and distal NMCs of the RF. We conclude that at least two strategies are applied for force production in the human QF: (1) coactivation of specific pairs of individual muscles and (2) regional-specific activation in NMCs in the RF.

Adult↗

PubMed2003

Resistance training during unweighting maintains muscle size and function in human calf.

PURPOSE: A 20-d 6 degrees head-down tilt bed rest project was conducted to evaluate the effect of dynamic leg press and plantar flexion resistance training on muscle size and function in human plantar flexors (PF) throughout the prolonged bed rest. METHODS: Twelve healthy men participated in this study and were divided two groups: resistance training (BR-Tr group: N = 6, age: 23 +/- 2 yr, height: 170 +/- 3 cm, weight: 66 +/- 7 kg) and nontraining (BR-Cont group: N = 6, age: 23 +/- 1 yr, height: 170 +/- 3 cm, weight: 67 +/- 6 kg) during the bed rest. Physiological cross-sectional area (PCSA) and peak torque of the PF muscle group was determined. Spin-spin relaxation times (T2) of the medial (MG) and lateral gastrocnemius (LG) and soleus (Sol) muscle was measured at rest and immediately after unilateral calf-raising exercise (5 sets of 10 reps). RESULTS: PCSA of the PF muscle group did not show any significant change in BR-Tr group; however, for the BR-Cont group, PCSA decreased by 13% after bed rest (P < 0.05). There was no significant change in exercise-induced T2 change of the MG, LG, or Sol muscles between before and after the bed rest in BR-Tr group; however, in the BR-Cont group, significant increases in T2 were found in these three muscles after the bed rest (P < 0.05 to 0.01). CONCLUSION: We conclude that dynamic leg press and plantar flexion resistance training during bed rest maintains muscle size and function (torque and T2), and that this training could be useful for prevention of progressive muscle deconditioning during spaceflight.

Adult↗

PubMed2002

Vastus lateralis fatigue alters recruitment of musculus quadriceps femoris in humans.

This study tested the hypothesis that fatigue of a single member of musculus quadriceps femoris (QF) would alter use of the other three muscles during knee extension exercise (KEE). Six men performed KEE with the left QF at a load equal to 50% of the 4 x 10 repetitions maximum. Subsequently, electromyostimulation (EMS), intended to stimulate and fatigue the left m. vastus lateralis (VL), was applied for 30 min. Immediately after EMS, subjects repeated the KEE. Transverse relaxation time (T2)-weighted magnetic resonance images were taken before and after each bout of KEE and at 3 and 30 min of EMS to assess use and stimulation, respectively, of the QF. T2 of each of the QF muscles was increased 8-13% after the first KEE. During EMS, T2 increased (P < 0.05) even more in VL (10%), whereas it decreased (P < 0.05) to pre-KEE levels in m. vastus medials (VM) and m. rectus femoris (RF). The VL and, to some extent, the m. vastus intermedius were stimulated, whereas the VM and RF were not, thereby recovering from the first bout of KEE. Isometric torque, initially 30% of maximal voluntary, was reduced to 13% at 3 min and 7% at 30 min. T2 was greater (P < 0.05) after the second than the first bout of KEE, especially the increase for the VM and RF. These results suggest that subjects were able to perform the second bout with little contribution of the VL by greater use of the other QF muscles. The simplest explanation is increased central command to the QF such that the intended act could be accomplished despite acute fatigue of one of its synergists.

Adult↗