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Naoya Tsunoda - One of the best experts on this subject based on the ideXlab platform.
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Active muscle and tendon stiffness of Plantar Flexors in sprinters
Journal of sports sciences, 2016Co-Authors: Keitaro Kubo, Toshihiro Ikebukuro, Hideaki Yata, Daisuke Miyazaki, Masaji Okada, Naoya TsunodaAbstract:The aim of the present study was to investigate and compare muscle and tendon stiffness under active conditions in sprinters and untrained participants. In total, 14 sprinters and 24 untrained men participated in this study. Active muscle stiffness in the medial gastrocnemius muscle was calculated based on changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Tendon stiffness was determined during isometric Plantar flexion using ultrasonography. No significant differences were observed in active muscle stiffness between sprinters and untrained men at any torque levels. Furthermore, no significant difference was noted in tendon stiffness between the two groups. These results suggest that muscle and tendon mechanical properties in the Plantar Flexors under active conditions are similar in sprinters and untrained participants.
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tendon properties and muscle architecture for knee extensors and Plantar Flexors in boys and men
Clinical Biomechanics, 2014Co-Authors: Keitaro Kubo, Takanori Teshima, Toshihiro Ikebukuro, Norikazu Hirose, Naoya TsunodaAbstract:Abstract Background The purpose of this study was to compare the elastic properties and size of tendinous structures and muscle architecture for knee extensors and Plantar Flexors in boys and men. Methods Twenty-two early pubescent boys (9.6–12.7 yrs) and 23 young adult men (19.8–26.2 yrs) participated in this study. The maximal strain and thickness of tendinous structures for knee extensors and Plantar Flexors were measured using ultrasonography. In addition, the fascicle lengths of vastus lateralis and medial gastrocnemius muscles were measured. Findings The maximal strain of tendinous structures for Plantar Flexors was significantly greater in boys than in men, while there was no difference in the maximal strain for knee extensors between the two groups. The relative thickness (to body mass 1/3 ) of Achilles tendon was significantly greater in boys than in men, although there was no difference in that of patellar tendon between the two groups. The relative fascicle length (to limb length) of vastus lateralis muscle was significantly lower in boys than in men, although there was no difference in that of medial gastrocnemius muscle between the two groups. Interpretation These results suggest that the amount of changes in the elastic properties and sizes of tendinous structures and in the fascicle lengths from early pubescence to maturity is different for different muscle groups (in particular, the knee extensors and the Plantar Flexors).
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Effect of gene polymorphisms on the mechanical properties of human tendon structures
SpringerPlus, 2013Co-Authors: Keitaro Kubo, Hideaki Yata, Naoya TsunodaAbstract:Recent studies showed that polymorphisms in alpha 1 chains of types I ( COL1A1 ) and V ( COL5A1 ) collagen, growth and differentiation factor 5 ( GDF5 ), and matrix metalloproteinase 3 ( MMP3 ) genes were associated with injuries in tendons and ligaments (e.g., September et al. (Br J Sports Med 43: 357–365 2009)). In the present study, we aimed to investigate the effects of injury-associated polymorphisms within these four genes on the mechanical properties of human tendon structures in vivo . One hundred Japanese males participated in this experiment. The mechanical properties of tendon structures in knee extensors and Plantar Flexors were measured using ultrasonography. All subjects were genotyped for COL1A1 rs1800012, COL5A1 rs12722, GDF5 rs143383, and MMP3 rs679620 single nucleotide polymorphisms. For COL1A1 , all subjects had a GG genotype. For COL5A1 , maximal tendon elongation and strain of individuals with a CC genotype were significantly greater than individuals with other genotypes (combined TT and CT) for knee extensors, but not for Plantar Flexors. For GDF5 and MMP3 , there were no differences in the mechanical properties of tendon structures in knee extensors and Plantar Flexors among the three genotypes. The present study demonstrated that subjects with a CC genotype of the COL5A1 gene had more extensible tendon structures than those of subjects with other genotypes (combined TT and CT) for knee extensors, but not for Plantar Flexors. The results presented in this study need to be confirmed in a larger cohort of subjects.
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Effects of mechanical properties of muscle and tendon on performance in long distance runners
European Journal of Applied Physiology, 2010Co-Authors: Keitaro Kubo, Toshihiro Ikebukuro, Hideaki Yata, Tomonori Tabata, Katsumi Igarashi, Naoya TsunodaAbstract:The purpose of this study was to investigate the mechanical properties of muscle and tendon in long distance runners and their relations to running performance. Fifteen long distance runners (LDR) and 21 untrained subjects (CON) participated in this study. Muscle strength and activation level of knee extensors and Plantar Flexors were measured. Tendon elongation was determined using ultrasonography, while subjects performed ramp isometric knee extension and Plantar flexion up to the voluntary maximum. Relative MVC (to body mass) of LDR was significantly lower than that of CON for knee extensors, but not for Plantar Flexors. No significant difference in the neural activation levels was found between LDR and CON for both sites. Maximal tendon elongation of LDR was significantly lower than that of CON for knee extensors, but not for Plantar Flexors. Furthermore, faster running time in a 5,000 m race (best official record of LDR) was associated with lower tendon stiffness for both sites. In conclusion, the tendon of long distance runners is less extensible than those of untrained subjects for knee extensors, but not for Plantar Flexors. For both sites, however, the lower tendon stiffness may be in favor of the running performance in long distance runners.
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effects of training on muscle and tendon in knee extensors and Plantar Flexors in vivo
Journal of Applied Biomechanics, 2010Co-Authors: Keitaro Kubo, Toshihiro Ikebukuro, Naoya Tsunoda, Hideaki Yata, Hiroaki KanehisaAbstract:The purpose of this study was to compare the effects of resistance training on muscle and tendon properties between knee extensors and Plantar Flexors in vivo. Twenty healthy young men voluntarily participated in this study. The subjects were randomly divided into two training groups: knee extension group (n = 10) and Plantar flexion group (n = 10). They performed five sets of exercises with a 1-min rest between sets, which consisted of unilateral knee extension for the knee extension group and Plantar flexion for the Plantar flexion group at 80% of 1 repetition maximum with 10 repetitions per set (4 days/wk, 12 wk). Before and after training, muscle strength, neural activation level (by interpolated twitch), muscle volume (by magnetic resonance imaging), and tendon stiffness (by ultrasonography) were measured. There were no differences in the training-induced increases in muscle strength, activation level, muscle volume, and tendon stiffness between knee extensors and Plantar Flexors. These results suggested that if the used protocol of training (i.e., intensity, repetition, etc.) were the same, there were no differences in the training-induced changes in muscle and tendon properties between knee extensors and Plantar Flexors
Keitaro Kubo - One of the best experts on this subject based on the ideXlab platform.
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effects of the strain rate on mechanical properties of tendon structures in knee extensors and Plantar Flexors in vivo
Sports Biomechanics, 2019Co-Authors: Masahiro Kouno, Toshihiro Ikebukuro, Tomonobu Ishigaki, Hideaki Yata, Keitaro KuboAbstract:The purpose of present study was to investigate site differences in the effects of strain rate on tendon properties between knee extensors and Plantar Flexors. Elongation of tendon structures (L) in vastus lateralis and medial gastrocnemius muscles was measured by ultrasonography while participants performed ramp and ballistic contractions to their voluntary maximum, followed by ramp and sudden relaxation. The relationship between muscle force (Fm) and L was fit to linear regression, the slope of which was defined as stiffness of tendon structures. Hysteresis of tendon structures was calculated as ratio of area within Fm-L loop to area beneath loading portion of curve. In knee extensors and Plantar Flexors, L values at all force levels were significantly lower during ballistic than ramp contractions. However, no significant differences were observed in stiffness of tendon structures between two contractions at both measured sites. Hysteresis of tendon structures was significantly higher during ballistic than ramp contractions for knee extensors and Plantar Flexors. In conclusion, elongation of tendon structures was lower and hysteresis was greater during ballistic than ramp contractions. Furthermore, site differences in the effects of strain rate on tendon properties were not found between knee extensors and Plantar Flexors.
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Active muscle and tendon stiffness of Plantar Flexors in sprinters
Journal of sports sciences, 2016Co-Authors: Keitaro Kubo, Toshihiro Ikebukuro, Hideaki Yata, Daisuke Miyazaki, Masaji Okada, Naoya TsunodaAbstract:The aim of the present study was to investigate and compare muscle and tendon stiffness under active conditions in sprinters and untrained participants. In total, 14 sprinters and 24 untrained men participated in this study. Active muscle stiffness in the medial gastrocnemius muscle was calculated based on changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Tendon stiffness was determined during isometric Plantar flexion using ultrasonography. No significant differences were observed in active muscle stiffness between sprinters and untrained men at any torque levels. Furthermore, no significant difference was noted in tendon stiffness between the two groups. These results suggest that muscle and tendon mechanical properties in the Plantar Flexors under active conditions are similar in sprinters and untrained participants.
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tendon properties and muscle architecture for knee extensors and Plantar Flexors in boys and men
Clinical Biomechanics, 2014Co-Authors: Keitaro Kubo, Takanori Teshima, Toshihiro Ikebukuro, Norikazu Hirose, Naoya TsunodaAbstract:Abstract Background The purpose of this study was to compare the elastic properties and size of tendinous structures and muscle architecture for knee extensors and Plantar Flexors in boys and men. Methods Twenty-two early pubescent boys (9.6–12.7 yrs) and 23 young adult men (19.8–26.2 yrs) participated in this study. The maximal strain and thickness of tendinous structures for knee extensors and Plantar Flexors were measured using ultrasonography. In addition, the fascicle lengths of vastus lateralis and medial gastrocnemius muscles were measured. Findings The maximal strain of tendinous structures for Plantar Flexors was significantly greater in boys than in men, while there was no difference in the maximal strain for knee extensors between the two groups. The relative thickness (to body mass 1/3 ) of Achilles tendon was significantly greater in boys than in men, although there was no difference in that of patellar tendon between the two groups. The relative fascicle length (to limb length) of vastus lateralis muscle was significantly lower in boys than in men, although there was no difference in that of medial gastrocnemius muscle between the two groups. Interpretation These results suggest that the amount of changes in the elastic properties and sizes of tendinous structures and in the fascicle lengths from early pubescence to maturity is different for different muscle groups (in particular, the knee extensors and the Plantar Flexors).
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Effect of gene polymorphisms on the mechanical properties of human tendon structures
SpringerPlus, 2013Co-Authors: Keitaro Kubo, Hideaki Yata, Naoya TsunodaAbstract:Recent studies showed that polymorphisms in alpha 1 chains of types I ( COL1A1 ) and V ( COL5A1 ) collagen, growth and differentiation factor 5 ( GDF5 ), and matrix metalloproteinase 3 ( MMP3 ) genes were associated with injuries in tendons and ligaments (e.g., September et al. (Br J Sports Med 43: 357–365 2009)). In the present study, we aimed to investigate the effects of injury-associated polymorphisms within these four genes on the mechanical properties of human tendon structures in vivo . One hundred Japanese males participated in this experiment. The mechanical properties of tendon structures in knee extensors and Plantar Flexors were measured using ultrasonography. All subjects were genotyped for COL1A1 rs1800012, COL5A1 rs12722, GDF5 rs143383, and MMP3 rs679620 single nucleotide polymorphisms. For COL1A1 , all subjects had a GG genotype. For COL5A1 , maximal tendon elongation and strain of individuals with a CC genotype were significantly greater than individuals with other genotypes (combined TT and CT) for knee extensors, but not for Plantar Flexors. For GDF5 and MMP3 , there were no differences in the mechanical properties of tendon structures in knee extensors and Plantar Flexors among the three genotypes. The present study demonstrated that subjects with a CC genotype of the COL5A1 gene had more extensible tendon structures than those of subjects with other genotypes (combined TT and CT) for knee extensors, but not for Plantar Flexors. The results presented in this study need to be confirmed in a larger cohort of subjects.
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Effects of mechanical properties of muscle and tendon on performance in long distance runners
European Journal of Applied Physiology, 2010Co-Authors: Keitaro Kubo, Toshihiro Ikebukuro, Hideaki Yata, Tomonori Tabata, Katsumi Igarashi, Naoya TsunodaAbstract:The purpose of this study was to investigate the mechanical properties of muscle and tendon in long distance runners and their relations to running performance. Fifteen long distance runners (LDR) and 21 untrained subjects (CON) participated in this study. Muscle strength and activation level of knee extensors and Plantar Flexors were measured. Tendon elongation was determined using ultrasonography, while subjects performed ramp isometric knee extension and Plantar flexion up to the voluntary maximum. Relative MVC (to body mass) of LDR was significantly lower than that of CON for knee extensors, but not for Plantar Flexors. No significant difference in the neural activation levels was found between LDR and CON for both sites. Maximal tendon elongation of LDR was significantly lower than that of CON for knee extensors, but not for Plantar Flexors. Furthermore, faster running time in a 5,000 m race (best official record of LDR) was associated with lower tendon stiffness for both sites. In conclusion, the tendon of long distance runners is less extensible than those of untrained subjects for knee extensors, but not for Plantar Flexors. For both sites, however, the lower tendon stiffness may be in favor of the running performance in long distance runners.
Monica A Perez - One of the best experts on this subject based on the ideXlab platform.
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bilateral and asymmetrical contributions of passive and active ankle Plantar Flexors stiffness to spasticity in humans with spinal cord injury
Journal of Neurophysiology, 2020Co-Authors: Jens Nielsen, Bing Chen, Sina Sangari, Jakob Lorentzen, Monica A PerezAbstract:Spasticity is one of the most common symptoms present in humans with spinal cord injury (SCI); however, its clinical assessment remains underdeveloped. The purpose of the study was to examine the contribution of passive muscle stiffness and active spinal reflex mechanisms to clinical outcomes of spasticity after SCI. It is important that passive and active contributions to increased muscle stiffness are distinguished to make appropriate decisions about antispastic treatments and to monitor its effectiveness. To address this question, we combined biomechanical and electrophysiological assessments of ankle Plantarflexor muscles bilaterally in individuals with and without chronic SCI. Spasticity was assessed using the Modified Ashworth Scale (MAS) and a self-reported questionnaire. We performed slow and fast dorsiflexion stretches of the ankle joint to measure passive muscle stiffness and reflex-induced torque using a dynamometer and the soleus H reflex using electrical stimulation over the posterior tibial nerve. All SCI participants reported the presence of spasticity. While 96% of them reported higher spasticity on one side compared with the other, the MAS detected differences across sides in only 25% of the them. Passive muscle stiffness and the reflex-induced torque were larger in SCI compared with controls more on one side compared with the other. The soleus stretch reflex, but not the H reflex, was larger in SCI compared with controls and showed differences across sides, with a larger reflex in the side showing a higher reflex-induced torque. MAS scores were not correlated with biomechanical and electrophysiological outcomes. These findings provide evidence for bilateral and asymmetric contributions of passive and active ankle Plantar Flexors stiffness to spasticity in humans with chronic SCI and highlight a poor agreement between a self-reported questionnaire and the MAS for detecting asymmetries in spasticity across sides.NEW & NOTEWORTHY Spasticity affects a number of people with spinal cord injury (SCI). Using biomechanical, electrophysiological, and clinical assessments, we found that passive muscle properties and active spinal reflex mechanisms contribute bilaterally and asymmetrically to spasticity in ankle Plantarflexor muscles in humans with chronic SCI. A self-reported questionnaire had poor agreement with the Modified Ashworth Scale in detecting asymmetries in spasticity. The nature of these changes might contribute to the poor sensitivity of clinical exams.
Toshihiro Ikebukuro - One of the best experts on this subject based on the ideXlab platform.
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effects of the strain rate on mechanical properties of tendon structures in knee extensors and Plantar Flexors in vivo
Sports Biomechanics, 2019Co-Authors: Masahiro Kouno, Toshihiro Ikebukuro, Tomonobu Ishigaki, Hideaki Yata, Keitaro KuboAbstract:The purpose of present study was to investigate site differences in the effects of strain rate on tendon properties between knee extensors and Plantar Flexors. Elongation of tendon structures (L) in vastus lateralis and medial gastrocnemius muscles was measured by ultrasonography while participants performed ramp and ballistic contractions to their voluntary maximum, followed by ramp and sudden relaxation. The relationship between muscle force (Fm) and L was fit to linear regression, the slope of which was defined as stiffness of tendon structures. Hysteresis of tendon structures was calculated as ratio of area within Fm-L loop to area beneath loading portion of curve. In knee extensors and Plantar Flexors, L values at all force levels were significantly lower during ballistic than ramp contractions. However, no significant differences were observed in stiffness of tendon structures between two contractions at both measured sites. Hysteresis of tendon structures was significantly higher during ballistic than ramp contractions for knee extensors and Plantar Flexors. In conclusion, elongation of tendon structures was lower and hysteresis was greater during ballistic than ramp contractions. Furthermore, site differences in the effects of strain rate on tendon properties were not found between knee extensors and Plantar Flexors.
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Active muscle and tendon stiffness of Plantar Flexors in sprinters
Journal of sports sciences, 2016Co-Authors: Keitaro Kubo, Toshihiro Ikebukuro, Hideaki Yata, Daisuke Miyazaki, Masaji Okada, Naoya TsunodaAbstract:The aim of the present study was to investigate and compare muscle and tendon stiffness under active conditions in sprinters and untrained participants. In total, 14 sprinters and 24 untrained men participated in this study. Active muscle stiffness in the medial gastrocnemius muscle was calculated based on changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Tendon stiffness was determined during isometric Plantar flexion using ultrasonography. No significant differences were observed in active muscle stiffness between sprinters and untrained men at any torque levels. Furthermore, no significant difference was noted in tendon stiffness between the two groups. These results suggest that muscle and tendon mechanical properties in the Plantar Flexors under active conditions are similar in sprinters and untrained participants.
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tendon properties and muscle architecture for knee extensors and Plantar Flexors in boys and men
Clinical Biomechanics, 2014Co-Authors: Keitaro Kubo, Takanori Teshima, Toshihiro Ikebukuro, Norikazu Hirose, Naoya TsunodaAbstract:Abstract Background The purpose of this study was to compare the elastic properties and size of tendinous structures and muscle architecture for knee extensors and Plantar Flexors in boys and men. Methods Twenty-two early pubescent boys (9.6–12.7 yrs) and 23 young adult men (19.8–26.2 yrs) participated in this study. The maximal strain and thickness of tendinous structures for knee extensors and Plantar Flexors were measured using ultrasonography. In addition, the fascicle lengths of vastus lateralis and medial gastrocnemius muscles were measured. Findings The maximal strain of tendinous structures for Plantar Flexors was significantly greater in boys than in men, while there was no difference in the maximal strain for knee extensors between the two groups. The relative thickness (to body mass 1/3 ) of Achilles tendon was significantly greater in boys than in men, although there was no difference in that of patellar tendon between the two groups. The relative fascicle length (to limb length) of vastus lateralis muscle was significantly lower in boys than in men, although there was no difference in that of medial gastrocnemius muscle between the two groups. Interpretation These results suggest that the amount of changes in the elastic properties and sizes of tendinous structures and in the fascicle lengths from early pubescence to maturity is different for different muscle groups (in particular, the knee extensors and the Plantar Flexors).
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Effects of mechanical properties of muscle and tendon on performance in long distance runners
European Journal of Applied Physiology, 2010Co-Authors: Keitaro Kubo, Toshihiro Ikebukuro, Hideaki Yata, Tomonori Tabata, Katsumi Igarashi, Naoya TsunodaAbstract:The purpose of this study was to investigate the mechanical properties of muscle and tendon in long distance runners and their relations to running performance. Fifteen long distance runners (LDR) and 21 untrained subjects (CON) participated in this study. Muscle strength and activation level of knee extensors and Plantar Flexors were measured. Tendon elongation was determined using ultrasonography, while subjects performed ramp isometric knee extension and Plantar flexion up to the voluntary maximum. Relative MVC (to body mass) of LDR was significantly lower than that of CON for knee extensors, but not for Plantar Flexors. No significant difference in the neural activation levels was found between LDR and CON for both sites. Maximal tendon elongation of LDR was significantly lower than that of CON for knee extensors, but not for Plantar Flexors. Furthermore, faster running time in a 5,000 m race (best official record of LDR) was associated with lower tendon stiffness for both sites. In conclusion, the tendon of long distance runners is less extensible than those of untrained subjects for knee extensors, but not for Plantar Flexors. For both sites, however, the lower tendon stiffness may be in favor of the running performance in long distance runners.
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effects of training on muscle and tendon in knee extensors and Plantar Flexors in vivo
Journal of Applied Biomechanics, 2010Co-Authors: Keitaro Kubo, Toshihiro Ikebukuro, Naoya Tsunoda, Hideaki Yata, Hiroaki KanehisaAbstract:The purpose of this study was to compare the effects of resistance training on muscle and tendon properties between knee extensors and Plantar Flexors in vivo. Twenty healthy young men voluntarily participated in this study. The subjects were randomly divided into two training groups: knee extension group (n = 10) and Plantar flexion group (n = 10). They performed five sets of exercises with a 1-min rest between sets, which consisted of unilateral knee extension for the knee extension group and Plantar flexion for the Plantar flexion group at 80% of 1 repetition maximum with 10 repetitions per set (4 days/wk, 12 wk). Before and after training, muscle strength, neural activation level (by interpolated twitch), muscle volume (by magnetic resonance imaging), and tendon stiffness (by ultrasonography) were measured. There were no differences in the training-induced increases in muscle strength, activation level, muscle volume, and tendon stiffness between knee extensors and Plantar Flexors. These results suggested that if the used protocol of training (i.e., intensity, repetition, etc.) were the same, there were no differences in the training-induced changes in muscle and tendon properties between knee extensors and Plantar Flexors
H Takahashi - One of the best experts on this subject based on the ideXlab platform.
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sex difference in strength and size ratios between reciprocal muscle groups in the lower leg
International Journal of Sports Medicine, 2012Co-Authors: Ryota Akagi, Yukihiro Tohdoh, H TakahashiAbstract:This study compared strength and size of reciprocal muscle groups in the lower leg between sexes. 20 young men and 14 young women volunteered as subjects. Joint torques developed during isometric maximal voluntary Plantar flexion (TQPF) and dorsiflexion (TQDF) were measured using a dynamometer. Muscle volumes of Plantar Flexors (MVPF) and dorsiFlexors (MVDF) were determined by magnetic resonance imaging. In each of the muscle groups, joint torque was significantly correlated with muscle volume in young men and women (r=0.610-0.848) and the y-intercept of the regression line between them was not significantly different from zero. Based on these observations, the dependencies of muscle strength ratio on muscle size ratio between the Plantar Flexors and dorsiFlexors were investigated using joint torque and muscle volume. The correlations between the MVPF per MVDF and the TQPF per TQDF were significant both in young men (r=0.608) and women (r=0.773), suggesting that strength ratio is strongly affected by size ratio between the Plantar Flexors and dorsiFlexors in young men and women.
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muscle strength and size balances between reciprocal muscle groups in the thigh and lower leg for young men
International Journal of Sports Medicine, 2012Co-Authors: Ryota Akagi, Yukihiro Tohdoh, H TakahashiAbstract:The present study investigated whether the muscle size balance affects the muscle strength balance between reciprocal muscle groups in the thigh and lower leg. 18 young men volunteered as subjects. The joint torques developed during isometric maximal voluntary knee extension and flexion, Plantar flexion and dorsiflexion were measured using a dynamometer. The muscle volumes of knee extensors and Flexors, Plantar Flexors and dorsiFlexors were determined by magnetic resonance imaging. For each of the muscle groups, the joint torque was significantly correlated with the muscle volume (r=0.644-0.847) and the y-intercept of the regression line between them was not significantly different from zero. Based on these observations, the dependencies of muscle strength balance on muscle size balance between the knee extensors and Flexors and between the Plantar Flexors and dorsiFlexors were investigated using the joint torque and muscle volume. The correlation between muscle volume ratio and joint torque ratio was significant between the Plantar Flexors and dorsiFlexors (r=0.622) but not between the knee extensors and Flexors (r=0.128). Thus, it is suggested that the strength balance is strongly affected by the size balance between the reciprocal muscle groups in the lower leg but not in the thigh.
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comparison of muscle and tendon stiffness jumping ability muscle strength and fatigue in the Plantar Flexors
Scandinavian Journal of Medicine & Science in Sports, 1998Co-Authors: Ulla Svantesson, U Carlsson, H Takahashi, Roland Thomee, Gunnar GrimbyAbstract:Svantesson U, Carlsson U, Takahashi H, Thomee R, Grimby G. Comparison of muscle and tendon stiffness, jumping ability, muscle strength and fatigue in the Plantar Flexors. An isokinetic dynamometer was used to measure Plantar flexion muscle strength at 60°/s and 200°/s in 10 healthy young men (mean age 25 years). Muscle and tendon stiffnesses were determined on the dynamometer by the use of electrical stimulation and passive stretch (200°/s). Differences in jumping heights between squat and counter-movement jumps were calculated from flight times. The number of heel-rises performed until exhaustion, standing on one leg, were counted. Stepwise regression analysis showed that differences in jumping height increased with lower muscle strength and with higher muscle and tendon stiffnesses, indicating that elastic components may be of more importance in persons with lower muscle strength. The number of heel-rises was negatively dependant on tendon stiffness, indicating that increased stiffness may enhance the development of fatigue.