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.

No abstract

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 p's < 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 p's < 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.

H. Effects of static and dynamic training on the stiffness and blood volume of tendon in vivo. J Appl Physiol 106: 412-417, 2009. First published December 26, 2008 doi:10.1152/japplphysiol.91381.2008.-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 Ͻ 0.001), neural activation level (9.5% for ST, 7.6% for DT; both P Ͻ 0.01), and muscle volume (4.5% for ST, 5.6% for DT; both P Ͻ 0.01). The stiffness of tendon-aponeurosis complex increased significantly after ST (55%; P ϭ 0.003) and DT (30%; P ϭ 0.033), while the stiffness of patella tendon increased significantly after ST (83%; P Ͻ 0.001), but not for DT (P ϭ 0.110). The blood volume of patella tendon increased significantly after DT (47%; P ϭ 0.016), but not for ST (P ϭ 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. knee extensor; tendon stiffness; cross-sectional area; activation level RECENT STUDIES USING ULTRASONOGRAPHY demonstrated that the stiffness of human tendon increased after resistance training in vivo (2,17,21,25,35). According to these previous findings, there is much larger variability in the previously reported increase in tendon stiffness, ranging between 17 and 65%. In particular, the increases of tendon stiffness after the static training (ϩ58% Recent studies demonstrated that the blood flow and type I collagen synthesis of the human tendons changed during the physical activities (7, 8, 28 -32). For example, Boushel et al. (8) reported that the blood flow in the Achilles tendon rose up to sevenfold during intense plantar flexion exercise compared with values obtained at rest. Langberg et al. (32) showed that the acute exercise (3 h of running) caused the increased formation of type I collagen in the recovery period (72 h after exercise). In addition, Kjaer et al. (15) suggested that the blood circulation within the tendons would contribute to "repair of the tendon" after all sorts of physical activities. Indeed, some previous researchers showed that the blood supply of the human Achilles tendon was lower in the midsection compared with other regions of the tendon (e.g., Ref. 10), and thus the rupture of Achilles tendon occurred most commonly in this region (e.g., Ref. 9). Therefore, we should consider the eff...

The purpose of this study was to investigate the time course of changes in human tendon properties and metabolism during resistance training and detraining. Nine men (21-27 years) completed 3 months of isometric plantar flexion training and another 3 months of detraining. At the beginning and on every 1 month of training and detraining periods, the stiffness, blood circulation (blood volume and oxygen saturation), serum procollagen type 1 C-peptide (P1P; reflects synthesis of type 1 collagen), echointensity (reflects collagen content), and MRI signal intensity (reflects collagen structure) of the Achilles tendon were measured. Tendon stiffness did not change until 2 months of training, and the increase (50.3%) reached statistical significance at the end of the training period. After 1 month of detraining, tendon stiffness had already decreased to pre-training level. Blood circulation in the tendon did not change during the experimental period. P1P increased significantly after 2 months of training. Echointensity increased significantly by 9.1% after 2 months of training, and remained high throughout the experiment. MRI signal intensity increased by 24.2% after 2 months and by 21.4% after 3 months of training, but decreased to the pre-training level during the detraining period. These results suggested that the collagen synthesis, content, and structure of human tendons changed at the 2-month point of training period. During detraining, the sudden decrease in tendon stiffness might be related to changes in the structure of collagen fibers within the tendon.