Publications (14)30.17 Total impact
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Article: Nonuniform Muscle Hypertrophy: Its Relation to Muscle Activation in Training Session.
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ABSTRACT: PURPOSE: Muscle hypertrophy in response to resistance training has been reported to occur nonuniformly along the length of the muscle. The purpose of the present study was to examine whether the regional difference in muscle hypertrophy induced by a training intervention corresponds to the regional difference in muscle activation in the training session. METHODS: Twelve young men participated in a training intervention program for the elbow extensors with a multi-joint resistance exercise for 12 weeks (three days per week). Before and after the intervention, cross-sectional areas (CSAs) of the triceps brachii along its length were measured with magnetic resonance (MR) images. A series of transverse relaxation time (T2)-weighted MR images were recorded before and immediately after the first session of training intervention. The T2 was calculated for each pixel within the triceps brachii. In the images recorded after the session, the number of pixels with a T2 greater than the threshold (mean + 1SD of T2 before the session) was expressed as the ratio to the whole number of pixels within the muscle, and used as an index of muscle activation (%activated area). RESULTS: The %activated area of the triceps brachii in the first session was significantly higher in the middle regions than that in the most proximal region. Similarly, the relative change in CSA induced by the training intervention was also significantly greater in the middle regions than the most proximal region. CONCLUSION: The results suggest that nonuniform muscle hypertrophy after training intervention is due to the region-specific muscle activation during the training session.Medicine and science in sports and exercise 05/2013; · 3.71 Impact Factor -
Article: Relationship between Muscle Architecture and Joint Performance during Concentric Contractions in Humans.
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ABSTRACT: The purpose of this study was to examine the relationship between muscle architecture of the triceps brachii (TB) and joint performance during concentric elbow extensions. Twenty-two men performed maximal isometric and concentric elbow extensions against various loads. Joint torque and angular velocity during concentric contractions were measured, and joint power was calculated. Muscle length, cross-sectional areas and volume of TB were measured from magnetic resonance images. Pennation angle (PA) of TB at rest was determined by ultrasonography. The PA was significantly correlated with the maximal isometric torque (r = 0.471), but not to the torque normalized by muscle volume (r = 0.312). A significant correlation was found between PA and the angular velocity at 0 kg load (r = 0.563), even when the angular velocity was normalized by the muscle length (r = 0.536). The PA was significantly correlated with the maximal joint power (r = 0.519), but not with the power normalized by muscle volume (r = 0.393). These results suggest that PA has a positive influence on the muscle shortening velocity during an unloaded movement, but does not have a significant influence on the maximum power generation in untrained men.Journal of applied biomechanics 08/2012; · 0.76 Impact Factor -
Article: Task-dependent inhomogeneous muscle activities within the bi-articular human rectus femoris muscle.
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ABSTRACT: The motor nerve of the bi-articular rectus femoris muscle is generally split from the femoral nerve trunk into two sub-branches just before it reaches the distal and proximal regions of the muscle. In this study, we examined whether the regional difference in muscle activities exists within the human rectus femoris muscle during maximal voluntary isometric contractions of knee extension and hip flexion. Surface electromyographic signals were recorded from the distal, middle, and proximal regions. In addition, twitch responses were evoked by stimulating the femoral nerve with supramaximal intensity. The root mean square value of electromyographic amplitude during each voluntary task was normalized to the maximal compound muscle action potential amplitude (M-wave) for each region. The electromyographic amplitudes were significantly smaller during hip flexion than during knee extension task for all regions. There was no significant difference in the normalized electromyographic amplitude during knee extension among regions within the rectus femoris muscle, whereas those were significantly smaller in the distal than in the middle and proximal regions during hip flexion task. These results indicate that the bi-articular rectus femoris muscle is differentially controlled along the longitudinal direction and that in particular the distal region of the muscle cannot be fully activated during hip flexion.PLoS ONE 01/2012; 7(3):e34269. · 4.09 Impact Factor -
Article: Association between regional differences in muscle activation in one session of resistance exercise and in muscle hypertrophy after resistance training.
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ABSTRACT: The purpose of this study was to examine if the regional difference in muscle hypertrophy after chronic resistance training is associated with muscle activation after one session of resistance exercise. Twelve men performed one session of resistance exercise of elbow extensors. Before and immediately after the exercise, transverse relaxation time (T2)-weighted magnetic resonance (MR) images of upper arm were recorded to evaluate the muscle activation along its length. In the MR images, T2 for the pixels within the triceps brachii muscle was quantified. The number of pixels with T2 greater than the threshold (mean + 1SD of T2 before the exercise) was expressed as the ratio to the number of pixels occupied by the muscle (%activated area). Another 12 subjects completed 12 weeks of training intervention (3 days per week), which consisted of the same program variables as used in the experiment for the T2 measurement. The cross-sectional areas of the triceps brachii before and after the training intervention were measured from MR images of upper arm. The %activated area of the triceps brachii induced by one session of the exercise was found to be significantly lower in the distal region than the middle and proximal regions. Similarly, the relative increase in muscle cross-sectional area after the 12 weeks of training intervention was significantly less in the distal region than the middle and proximal regions. The results suggest that the regional difference in muscle hypertrophy after chronic resistance training is attributable to the regional difference in muscle activation during the exercise.Arbeitsphysiologie 08/2011; 112(4):1569-76. · 2.15 Impact Factor -
Article: Effect of countermovement on elbow joint extension power-load characteristics.
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ABSTRACT: The aim of the present study was to examine elbow joint extension power-load characteristics with and without a countermovement. Eight male participants performed maximal elbow extensions with and without a countermovement against different loads (0, 2.5, 5.0, 7.5, 10.0, 12.5, and 15.0 kg). Electromyographic activity of the lateral and long heads of the triceps brachii and the biceps brachii muscles was recorded. The average joint power in the concentric phase was significantly enhanced in the countermovement condition at all loads except for 0 kg. The optimal load for the maximal joint power was greater in the countermovement (7.5 kg) than in the no countermovement condition (5.0 kg). Electromyographic activity was unchanged over the intensities and conditions. Our results suggest that the optimal load for the maximal joint power depends on the type of action (i.e. with or without a counter-movement), and that the enhanced joint power in the countermovement condition is due primarily to the storage and utilization of elastic energy.Journal of Sports Sciences 11/2010; 28(14):1535-42. · 1.93 Impact Factor -
Article: Influence of muscle anatomical cross-sectional area on the moment arm length of the triceps brachii muscle at the elbow joint.
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ABSTRACT: The purpose of this study was to test the hypothesis that the musculotendon moment arm length is affected by the muscle anatomical cross-sectional area. The moment arm length of the triceps brachii (TB) muscle at 30°, 50°, 70°, 90°, 110° elbow flexion positions was measured in sagittal magnetic resonance images (MRI) of 18 subjects as the perpendicular distance between the center of the pulley of the humerus to the line through the center of the TB tendon. The moment arm increased as the elbow flexion angle decreased, from 1.74±0.13 cm at 110° to 2.39±0.14 cm at 30°. The maximal anatomical cross-sectional area of the TB muscle was significantly correlated with the moment arms at all joint positions (r=0.545-0.803, p<0.05). Furthermore, the circumference of the upper arm was also significantly correlated with the moment arms at all joint positions, except for 70° (r=0.504-0.702, p<0.05). These results indicate that the moment arm length of the TB muscle is affected by the muscle anatomical cross-sectional area.Journal of biomechanics 10/2010; 43(14):2844-7. · 2.66 Impact Factor -
Article: Development of an equation to predict muscle volume of elbow flexors for men and women with a wide range of age.
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ABSTRACT: The present study examined the age-related changes in muscle thickness (MT) and volume (MV) of elbow flexors and developed a prediction equation of the MV based on the MT applicable to men and women with a wide range of age. The MT and MV were determined from a single ultrasonographic image and multiple magnetic resonance imaging scans, respectively, in 72 men and 75 women aged 19-77 year. As a result of examining the age-MT and age-MV relationships by calculation of partial correlation coefficients with the control variable of gender, MV was decreased with aging whereas the corresponding decline in MT was not significant. The subjects were randomly separated into either a validation (38 men and 42 women) or a cross-validation (34 men and 33 women) group, and a multiple regression equation to estimate MV using not only MT but also upper arm length (L), age and gender as independent variables [MV (cm(3)) = 60.8 x MT (cm) + 6.48 x L (cm) - 0.709 x age (year) + 51.4 x gender (0 women, 1 men) - 187.4] was validated and cross-validated. Thus, the prediction equation for MV of elbow flexors newly developed was shown to be applicable to men and women with a wide range of age.Arbeitsphysiologie 11/2009; 108(4):689-94. · 2.15 Impact Factor -
Article: Effects of knee joint angle on the fascicle behavior of the gastrocnemius muscle during eccentric plantar flexions.
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ABSTRACT: The present study aimed to clarify the effects of knee joint angle on the behavior of the medial gastrocnemius muscle (MG) fascicles during eccentric plantar flexions. Eight male subjects performed maximal eccentric plantar flexions at two knee positions [fully extended (K0) and 90 degrees flexed (K90)]. The eccentric actions were preceded by static plantar flexion at a 30 degrees plantar flexed position and then the ankle joint was forcibly dorsiflexed to 15 degrees of dorsiflexion with an isokinetic dynamometer at 30 degrees /s and 150 degrees /s. Tendon force was calculated by dividing the plantar flexion torque by the estimated moment arm of the Achilles tendon. The MG fascicle length was determined with ultrasonography. The tendon forces during eccentric plantar flexions were influenced by the knee joint angle, but not by the angular velocity. The MG fascicle lengths were elongated as the ankle was dorsiflexed in K0, but in K90 they were almost constant despite the identical range of ankle joint motion. These results suggested that MG fascicle behavior during eccentric actions was markedly affected by the knee joint angle. The difference in the fascicle behavior between K0 and K90 could be attributed to the non-linear force-length relations and/or to the slackness of tendinous tissues.Journal of electromyography and kinesiology: official journal of the International Society of Electrophysiological Kinesiology 10/2009; 19(5):980-7. · 2.00 Impact Factor -
Article: Passive knee movement-induced modulation of the soleus H-reflex and alteration in the fascicle length of the medial gastrocnemius muscle in humans.
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ABSTRACT: In humans, an inhibitory via Ia afferent pathway from the medial gastrocnemius (MG) to the soleus (SOL) motoneuron pool has been suggested. Herein, we examined the relation between MG fascicle length changes and the SOL H-reflex modulation during passive knee movement. Twelve subjects performed static and passive (5 degrees s(-1)) knee movement tasks with the ankle immobilized using an isokinetic dynamometer in sitting posture. The maximal H- and M-waves were measured at four target angles (20 degrees, 40 degrees, 60 degrees, and 80 degrees flexion from full knee extension). The MG fascicles length and velocity were measured using a B-mode ultrasonic apparatus. Results demonstrated that the SOL Hmax/Mmax; i.e., ratio of the maximal H- to M-waves, was attenuated with increasing MG fascicle length in static tasks. The SOL Hmax/Mmax at 20 degrees was significantly attenuated compared with 60 degrees and 80 degrees with increasing MG fascicle length and lengthening velocity in passive knee extension. However, no significant differences in the SOL Hmax/Mmax were found across the target angles in the passive knee flexion task. In conclusion, as muscle spindles increase their discharge with lengthening fascicle velocity, but keep silent when fascicles shorten, our data suggest that lengthening the MG facilitates an inhibitory Ia pathway from MG to SOL, and modulates SOL motoneuron activity during movements.Journal of electromyography and kinesiology: official journal of the International Society of Electrophysiological Kinesiology 10/2009; 20(3):513-22. · 2.00 Impact Factor -
Article: Relationships between muscle strength and indices of muscle cross-sectional area determined during maximal voluntary contraction in middle-aged and elderly individuals.
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ABSTRACT: The present study examined how muscle cross-sectional area (CSA) indices determined at rest and during maximal voluntary contraction (MVC) are related to muscle strength in middle-aged and elderly individuals (22 men and 36 women, 51-77 years). The muscle thickness (MT) of elbow flexors and circumference (C) at the level 60% distal to the upper arm was measured by ultrasonography and a measuring tape, respectively, both at rest and during isometric MVC of elbow flexion. The muscle strength (F) of elbow flexors was calculated by dividing the torque developed during MVC by the forearm length of each subject. The product of MT and C (MTxC) and the square of MT (MT) were defined as the muscle CSA indices. The F was significantly correlated with MTxC during MVC (r = 0.905, p < or = 0.001) and at rest (r = 0.778, p < or = 0.001), with the former relationship significantly stronger than the latter (p < or = 0.001). Similarly, F was significantly correlated with MT both during MVC (r = 0.896, p < or = 0.001) and at rest (r = 0.780, p < or = 0.001), and there was also a significant difference between the correlation coefficients (p < or = 0.01). These findings show that, in middle-aged and elderly individuals, muscle strength is more closely related to muscle CSA indices during MVC than at rest. It is concluded that the present muscle CSA indices taken during MVC enable easy and practical evaluation of the muscle strength per size of elbow flexors in middle-aged and elderly individuals.The Journal of Strength and Conditioning Research 07/2009; 23(4):1258-62. · 1.83 Impact Factor -
Article: Variability of limb muscle size in young men.
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ABSTRACT: The purpose of this study was to determine the interindividual variability of the upper and lower limb muscle size in young men. Subjects were 655 Japanese men aged 18-39 years. They were sedentary and mildly to highly active individuals, including college athletes of various sports. Muscle thicknesses at each of the anterior and posterior portions of the upper arm, thigh, and lower leg were measured using B-mode ultrasonography. Interindividual variability of muscle thickness was evaluated by coefficients of variation (CVs). The CVs of muscle thicknesses were found to be in the order of upper arm posterior (17.7%), thigh anterior (14.8%), thigh posterior (12.6%), upper arm anterior (12.2%), lower leg anterior (9.8%), and lower leg posterior (9.4%). The CVs were significantly different between each pair of measurement sites except for those of upper arm anterior-thigh posterior and lower leg anterior-posterior. These differences remain significant even when the muscle thicknesses were normalized to the segment length. The observed differences in the size variability can be interpreted as muscle-related differences in hypertrophic responsiveness to resistance training. The muscle-dependent size variability may be related to the differences in the fiber-type composition and/or muscle usage in daily life among examined muscle groups.American Journal of Human Biology 07/2009; 22(1):55-9. · 2.27 Impact Factor -
Article: Effects of muscle cooling on the stiffness of the human gastrocnemius muscle in vivo.
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ABSTRACT: The effects of muscle cooling on the stiffness of the human gastrocnemius muscle (GAS) were examined in vivo. The knee joint was passively extended from 90 to 0 degrees (0 degrees = full knee extended position) with a constant ankle angle of 10 degrees dorsiflexed position (0 degrees = the sole of the foot is approximately perpendicular to the anterior margin of the shaft of the tibia) in a control condition (room temperature of 18-23 degrees C) and a cooling condition (muscle temperature decreased by 5.8 +/- 1.7 degrees C after cooling using a cold water bath at a temperature of 5-8 degrees C for 60 min). The change in passive Achilles tendon force, muscle fascicle length of GAS and muscle temperature were measured (n = 6) during the motion. GAS stiffness was significantly greater in the cooling condition (20 +/- 8 N/mm) than the control condition (18 +/- 8 N/mm). There was no cooling effect on the muscle slack length, beyond which passive muscle force arises. The maximum passive Achilles tendon force significantly increased by 19 +/- 20% after cooling. These results suggested that cooling increased the passive muscle force due to the increase in the muscle stiffness rather than the shift of the muscle slack length.Cells Tissues Organs 02/2008; 187(2):152-60. · 2.20 Impact Factor -
Article: Fascicle behavior of medial gastrocnemius muscle in extended and flexed knee positions.
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ABSTRACT: The present study tested the hypotheses that Achilles tendon forces during fast concentric actions do not differ between extended and flexed knee positions, and this phenomenon is attributable to the force-length characteristics and electromyograms (EMGs) of gastrocnemius muscle. Seven healthy men performed static and concentric plantarflexions at fully extended (K0) and 0.785 rad (45 degrees ) flexed (K45) knee positions with the maximal effort. In concentric actions, the angular velocities were set at 0.524 (slow) and 6.109 rad s(-1) (fast). Fascicle length of medial gastrocnemius (MG) was determined with ultrasonography. Surface EMGs of the MG were recorded during each action. Achilles tendon force was calculated from the torque and moment arm of the tendon. Peak tendon forces in fast concentric actions were similar in K0 and in K45, but those in static and slow concentric actions significantly (P<0.05) differed between the two positions. When the tendon force peaked, the fascicle lengths in each action and fascicle velocities in both concentric actions were significantly (P<0.05) greater in K0 than in K45. The EMGs were significantly (P<0.05) higher in K0 than K45 during each action. The results suggest that (1) the difference in the tendon forces between the two positions can be explained by the force-length and -velocity characteristics and the EMGs of the MG, and (2) the contribution of the MG to the tendon force in flexed knee positions is greater in concentric actions than expected from the results in static actions.Journal of Biomechanics 01/2007; 40(10):2291-8. · 2.43 Impact Factor -
Article: Influence of muscle cooling on the passive mechanical properties of the human gastrocnemius muscle.
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ABSTRACT: The purpose of the present study was to examine the influence of muscle cooling on the passive mechanical properties of the human gastrocnemius muscle (GAS) in vivo. In a thermoneutral (a room temperature of 18-23°C) and a local cooling (placing the right lower leg into cold water with a temperature of 5-8°C for 60 min) conditions, the change in passive plantarflexion force (F), which is produced only by the GAS length change, was taken in five subjects during passive knee extension from 90° to 0° with a constant ankle joint angle of 10° dorsiflexion. To evaluate an elastic component of the passive plantarflexion force of GAS, the subject held full knee extended position for 1 min (i.e. relaxation period). Skin and muscle temperature of GAS were also measured using a core temperature thermistor. The peak value of F (Fve) that was measured at the end of the knee extension phase, the decrease of F (ΔF) during the relaxation period, and the F at the end of the relaxation period (Fe) were measured in the two conditions. Muscle cooling decreased the skin and muscle temperature by 6.7 ± 1.1°C and 8.1 ± 2.5°C, respectively. Fve increased by 24% ± 22% by muscle cooling. ΔF in the thermoneutral and local cooling conditions were 11.5 ± 4.9 N and 12.5 ± 2.9 N, respectively. Fe increased by 28% ± 21% by muscle cooling.Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2005; 1:19-21.
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Institutions
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2007–2012
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Waseda University
- Faculty of Sport Sciences
Tokyo, Tokyo-to, Japan
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