Hideaki Yata

Time Course of Changes in Muscle and Tendon Properties During Strength Training and Detraining

Kubo, K, Ikebukuro, T, Yata, H, Tsunoda, N, and Kanehisa, H. Time course of changes in muscle and tendon properties during strength training and detraining. J Strength Cond Res 24(2): 322-331, 2010-The purpose of this study was to investigate the time course of changes in mechanical and morphological properties of muscle and tendon during isometric training and detraining. Eight subjects completed 3 months of isometric knee extension training and detraining for another 3 months. At beginning and on every 1 month of training and detraining periods, muscle strength, neural activation level, muscle and tendon cross-sectional areas (CSA), and tendon stiffness were measured. Training increased muscle strength and neural activation level by 29.6 and 7.3% after 2 months and by 40.5 and 8.9% after 3 months (all ps < 0.05). Muscle CSA and tendon stiffness did not change until 2 months of training period, and afterward, the increases in muscle CSA and tendon stiffness reached statistical significance at the end of training period (both ps < 0.05). During detraining period, muscle strength and neural activation level did not change, although muscle CSA and tendon stiffness decreased to pre-training level at 1 and 2 months of detraining, respectively. These results suggest that the adaptations of tendon properties and muscle morphology to resistance training are slower than those of muscle function and inversely that the adaptations of former to detraining are faster than those of latter.

Effects of static and dynamic training on the stiffness and blood volume of tendon in vivo

The purpose of this study was to investigate the effects of static and dynamic training on the stiffness and blood volume of the human tendon in vivo. Ten subjects completed 12 wk (4 days/wk) of a unilateral training program for knee extensors. They performed static training on one side [ST; 70% of maximum voluntary contraction (MVC)] and dynamic training on the other side (DT; 80% of one repetition maximum). Before and after training, MVC, neural activation level (by interpolated twitch), muscle volume (by magnetic resonance imaging), stiffness of tendon-aponeurosis complex and patella tendon (by ultrasonography), and blood volume of patella tendon (by red laser lights) were measured. Both protocols significantly increased MVC (49% for ST, 32% for DT; both P < 0.001), neural activation level (9.5% for ST, 7.6% for DT; both P < 0.01), and muscle volume (4.5% for ST, 5.6% for DT; both P < 0.01). The stiffness of tendon-aponeurosis complex increased significantly after ST (55%; P = 0.003) and DT (30%; P = 0.033), while the stiffness of patella tendon increased significantly after ST (83%; P < 0.001), but not for DT (P = 0.110). The blood volume of patella tendon increased significantly after DT (47%; P = 0.016), but not for ST (P = 0.205). These results implied that the changes in the blood volume of tendon would be related to differences in the effects of resistance training on the tendon properties.

A cross-sectional study of the size and strength of the lower leg muscles during growth.

The influences of age and sex on the cross-sectional area (CSA) and isometric strength of the ankle dorsiflexors and plantarflexors (PF) were investigated in four age groups of 121 boys and 121 girls aged: 7–9, 10–12, 13–15, and 16–18 years. A single anatomical cross-section was determined at 30% of the distance from the articular cleft between the femur and tibiacondyles by using an ultrasonic apparatus. In both sexes, the increase in age was associated with significant increases in the CSA and strength (ST) of these opposing muscle groups. The sex differences became apparent in the 13–15 year group for CSA and in the 16–18 year group for ST but the differences reduced considerably when CSA and ST were expressed per unit of the second power of the lower leg length (CSA·LL−2) and the product of CSA and the lower leg length (ST·CSA−1·LL−1), respectively. However,CSA·LL−2 of both muscles had a tendency to be increased at and over the age of 10–12 years, and was the highest at 16–18 years, andST·CSA−1·LL−1 of PF showed higher values in the older boys than in the younger. Thus, it appeared that, at least in the reciprocal muscle groups of the ankle joint, the sex differences in muscle CSA and ST during growth could be accounted for by differences in LL and muscle mass, respectively. However, other factors must also be involved to explain completely the age differences in these variables.

Relation between grip strength and radial bone mineral density in young athletes

In this study, we evaluated the relationship between bone mineral density (BMD) and muscle strength in young athletes who had not yet experienced age-related bone loss. Radial BMD and grip strength were measured in 10 male college wrestlers, 16 female college basketball players, and 12 female college tennis players. Radial BMD was measured in the distal and middle radius by dual energy x-ray absorptiometry (DEXA). Isometric grip strength was assessed with a hand-held dynamometer. The dominant forearm was examined in the amateur wrestlers and basketball players for grip strength and BMD. Both forearms were examined in the tennis players. A significant positive correlation was found between radial BMD and grip strength in the dominant forearm, and between radial BMD and body weight. Moreover, to eliminate a possible effect of body weight on radial BMD, we compared radial BMD with grip strength in both the dominant and nondominant arm of 12 college tennis players. Grip strength in the dominant forearm was significantly greater than in the nondominant forearm. The midradial BMD of the dominant forearm was also significantly higher than in the nondominant forearm. Based on these findings, we conclude that grip strength is one of the determinant factors of radial BMD in the dominant forearm of young college athletes.

Passive and active muscle stiffness in plantar flexors of long distance runners

The aim of the present study was to compare passive and active muscle stiffness and tendon stiffness between long distance runners and untrained men. Twenty long distance runners and 24 untrained men participated in this study. Active muscle stiffness in the medial gastrocnemius muscle was calculated according to changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Passive muscle stiffness was also calculated from estimated passive muscle force and fascicle length during slow passive stretching. Tendon stiffness was determined during isometric plantar flexion by ultrasonography. Passive muscle stiffness of long distance runners was significantly higher than that of untrained men (p<0.001). Active muscle stiffness at all torque levels of long distance runners was also significantly higher than that of untrained men (p<0.001). No significant difference was observed in tendon stiffness between long distance runners and untrained men (p=0.869). These results suggested that passive and active muscle stiffness were higher in long distance runners than in untrained men, whereas no significant difference was observed in tendon stiffness between the two groups.

Effect of gene polymorphisms on the mechanical properties of human tendon structures

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.

Active muscle and tendon stiffness of plantar flexors in sprinters

ABSTRACT 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.

Effects of Concentric and Eccentric Training on the Stiffness and Blood Circulation of the Patellar Tendon

The aim of the present study was to investigate the effects of concentric (CON) and eccentric (ECC) training on stiffness and blood circulation of the tendon, and clarify whether relative changes in tendon stiffness are related to those in tendon blood circulation. 17 subjects were assigned to training (n=9) and control (n=8) groups. Training group completed 12 weeks of unilateral training program for knee extensors. They performed 5 sets of CON or ECC at 80% of 1RM with 10 repetitions. Before and after training, cross-sectional area, stiffness, hysteresis, blood volume, and oxygen saturation of the patellar tendon were measured. Oxygen saturation significantly increased with CON and ECC. Stiffness significantly increased with CON but not with ECC. Other measured variables did not change after training. Furthermore, the relative change in tendon stiffness did not correlate with that in blood volume or oxygen saturation. In control group, measured variables did not change after training. These results suggest that tendon stiffness increased after CON but not after ECC; however no significant differences in the changes observed in size and blood circulation of the tendon were found between 2 protocols. Furthermore, changes in tendon stiffness were not related to those in tendon blood circulation.