These results indicate that the jump performance gains after plyometric training are attributed to changes in the mechanical properties of muscle-tendon complex, rather than to the muscle activation strategies.

The present study aimed to investigate the effects of low-load resistance training with vascular occlusion on the specific tension and tendon properties by comparing with those of high-load training. Nine participants completed 12 weeks (3 days/week) of a unilateral isotonic training program on knee extensors. One leg was trained using low load (20% of 1 RM) with vascular occlusion (LLO) and other leg using high load (80% of 1 RM) without vascular occlusion (HL). Before and after training, maximal isometric knee extension torque (MVC) and muscle volume were measured. Specific tension of vastus lateralis muscle (VL) was calculated from MVC, muscle volume, and muscle architecture measurements. Stiffness of tendon-aponeurosis complex in VL was measured using ultrasonography during isometric knee extension. Both protocols significantly increased MVC and muscle volume of quadriceps femoris muscle. Specific tension of VL increased significantly 5.5% for HL, but not for LLO. The LLO protocol did not alter the stiffness of tendon-aponeurosis complex in knee extensors, while the HL protocol increased it significantly. The present study demonstrated that the specific tension and tendon properties were found to remain following low-load resistance training with vascular occlusion, whereas they increased significantly after high-load training.

The present study aimed to examine the influences of tendon stiffness, joint stiffness, and electromyographic activity on jump performances consisting of a single-joint movement. Twenty-four men performed three kinds of unilateral maximal jump using only the ankle joint (squat jump: SJ; countermovement jump: CMJ; drop jump: DJ) on the sledge apparatus. The relative differences in the jump height of CMJ and DJ compared to SJ were defined as pre-stretch augmentation. During jumping exercises, electromyographic activities (mEMG) were recorded from the plantar flexors. Ankle joint stiffness was calculated as the change in the joint torque divided by the change in ankle joint angle during the eccentric phase of DJ. Achilles tendon stiffness was measured using ultrasonography during isometric plantar flexion. No significant correlations were found between joint stiffness and pre-stretch augmentation in both CMJ and DJ. On the contrary, tendon stiffness was significantly correlated with pre-stretch augmentation in both CMJ (r = -0.471) and DJ (r = -0.502). The relative mEMG value of CMJ (to that of SJ) during the concentric phase was significantly correlated with pre-stretch augmentation (r = 0.481), although this relationship was not found in DJ. These results suggested that (1) the greater jump height in CMJ could be explained by both the tendon elasticity and the increased activation level of muscle, (2) tendon elasticity played a more significant role in the enhancement of jump height during DJ, and (3) joint stiffness was not related to either pre-stretch augmentation or tendon stiffness.

The purpose of this study was to investigate the effects of 6 months of walking training on muscle strength, muscle thickness and tendon stiffness on various parts of the lower limbs in the elderly. Subjects were assigned to training (n=35) and control (n=10) groups. Maximal isometric torque (MVC) and muscle thickness for knee extensors (KE), knee flexors (KF), dorsi flexors (DF) and plantar flexors (PF) were measured. Tendon stiffness for KE and PF was measured using ultrasonography while subjects performed isometric contraction. No significant changes occurred in any measured variables in the control group. In the training group, muscle thickness increased significantly for KF and DF, but not for PF. For KE, significant increases of muscle thickness at the proximal and medial sides were observed, although mean relative increase of the eight measured sites for KE was not significant. MVC increased significantly for KF, DF, and PF, but not for KE. In addition, tendon stiffness for KE and PF did not change after training. These results indicated that walking training brought about increments of muscle thickness and strength in most of the lower limbs in the elderly, but it did not result in any changes in tendon stiffness.

These results suggest that the processes of age-related changes in the muscle and tendon are different. Furthermore, the differences in age-related changes of muscle and tendon might play a role in the frequency of Achilles tendon ruptures among men in their 30s.

Betaine is an important human nutrient obtained from various foods. In the present study, we assessed the anti-inflammatory effect of betaine on nuclear factor-jB (NF-jB) during aging. Sprague-Dawley (SD) rats, ages 7 and 21 months, were used in this study. The older rats were fed betaine. To elucidate the effect of betaine on oxidative stress-induced NF-jB and its signaling pathway at molecular levels, YPEN-1 cells were used. Results showed that betaine suppressed NF-jB and its related gene expressions of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), vascular cell adhesion molecule-1 (VCAM-1), and intracellular cell adhesion molecule-1 (ICAM-1) in aged kidney. Furthermore, betaine attenuated oxidative stress-induced NF-jB via nuclear factor-inducing kinase/IjB kinase (NIK/IKK) and mitogen-activated protein kinases (MAPKs) in the YPEN-1 cells. On the basis of these results, we concluded that betaine suppressed the age-related NF-jB activities associated with upregulated NIK/IKK and MAPKs that were induced by oxidative stress. Thus, betaine might be useful as a preventive agent against the activation of NF-jB induced during inflammation and aging.

This study aimed to examine and compare the trunk muscularity of track and field throwers and non-athletes, and its predictive value to the physical performance of the athletes. Using a magnetic resonance imaging method, the skeletal muscle volume (SMV) of the trunk (SMV(trunk)) was determined in 19 strength trained athletes and 18 non-athletes. Also, the SMV of upper, middle and lower regions of the trunk was calculated in every 33% of the trunk length. For the athletes, the maximum weight (1RM) of squat, high clean, and deadlift, and shot forward throwing score were measured. The SMV(trunk) in the athletes was 10% greater than that of non-athletes, with a larger difference in the upper region of the trunk. Step-wise multiple regression analysis indicated that the SMV of the lower region was a significant contributor for predicting the 1RM values of the 3 tasks, as well as the shot forward throwing score. The current results indicate that, while the muscularity of the trunk in track and field throwers is characterized by predominant development in the upper region, the muscularity in the lower region is a determinant factor for the 1RM values of the squat, high clean, and deadlift and shot forward throwing score.

No abstract