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 present study aimed to investigate changes in elasticity, blood volume, and oxygen saturation of tendon caused by repeat contractions of different durations. Eight male subjects performed endurance tests, which consisted of isometric plantar flexion with two different durations: a shorter contraction (SC) and a longer contraction (LC). During endurance tests and a recovery period, we measured the total hemoglobin (THb) and oxygen saturation (StO(2)) of the medial gastrocnemius muscle and Achilles tendon using near infrared spectroscopy and red laser lights. In addition, elongation of the Achilles tendon during the endurance test was measured via ultrasonography. Compared to the resting level, the THb and StO(2) of the tendon increased significantly after SC, but not after LC. On the other hand, Achilles tendon became more compliant after LC, but not after SC. These results suggested that duration of contraction affected not only elasticity, but also blood volume and oxygen saturation of tendons.

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Study design: Cross-sectional study. Objectives: To determine the effect of injury duration on plantar-flexor elastic properties in individuals with chronic spinal cord injury (SCI) and spasticity. Setting: National Rehabilitation Center for Persons with Disabilities, Japan. Methods: A total of 16 chronic SCI patients (age, 33 ± 9.3 years; injury localization, C6-T12; injury duration, 11-371 months) participated. Spasticity of the ankle plantar-flexors was assessed using the Modified Ashworth Scale (MAS). The calf circumference and muscle thickness of the medial gastrocnemius (MG), lateral gastrocnemius and soleus were assessed using tape measure and ultrasonography. In addition, the ankle was rotated from 10°plantar-flexion to 20°dorsiflexion at 5 deg s −1 with a dynamometer, and the ankle angle and torque were recorded. After normalizing the data (the initial points of angle and torque were set to zero), we calculated the peak torque and energy. Furthermore, angle-torque data (before and after normalization) were fitted with a second-and fourth-order polynomial, and exponential (Sten-Knudsen) models, and stiffness indices (SI SOP, SI FOP, SI SK ) and Angle SLACK (the angle at which plantar-flexor passive torque equals zero) were calculated. The stretch reflex gain and offset were determined from 0-10°d orsiflexion at 50, 90, 120 and 150 deg s −1 . After logarithmic transformation, Pearson's correlation coefficients were calculated. Results: MAS, calf circumference, MG thickness, peak torque and SI FOP significantly decreased with injury duration (r loglog = − 0.63, − 0.69, − 0.63, − 0.53 and − 0.55, respectively, Po0.05). The peak torque and SI FOP maintained significant relationships even after excluding impacts from muscle morphology. Conclusion: Plantar-flexor elasticity in chronic SCI patients decreased with increased injury duration.

Transcranial magnetic stimulation (TMS) to the cerebral cortex is a major in vitro technique that is used in the field of neurophysiology. The magnitude of the motor-evoked potentials (MEP) that are elicited by TMS to the primary motor cortex reflect the excitability of the corticospinal pathway. MEPs are very sensitive to the scalp location of the stimulus coil, especially when corticospinal excitability is recorded during walking or other dynamic motions. In this study, we created a coil navigational system that consisted of three-dimensional motion analysis cameras, rigid bodies on the head and coil, and programming software. In order to evaluate the feasibility of the use of our system, pseudo TMS was applied during treadmill walking with or without the navigational system. As a result, we found that the variances due to coil location and/or distance from the target site were reduced with our system. This technique enabled us to realize high precision and accuracy in coil placement, even during dynamic motion.

Transcranial magnetic stimulation (TMS) is one of the useful tools as an electrophysiological technique to elucidate neural mechanism underlying human behavior. In order to acquire validated motor evoked potentials (MEPs) during dynamic motion such as walking, it is necessary to precisely place TMS coil to the target on subjects' scalp. In this study, we developed a coil navigation system for accomplishing precise coil placement even though the subject's head is moved. Since the system enables us to record the coil position data, it is possible to ascertain whether the coil is suitably placed on the target or not. In order to evaluate the feasibility of the use of our system, sham TMS was applied during treadmill walking with or without using the developed system. The results demonstrated that the variances of coil location and distance from the target site (consistent error) could be minimized with using the system. Our developed coil navigation system enabled us to realize high precision and accuracy in TMS coil placement even during walking.

This study aimed to identify the stiffness and natural length of the human plantar aponeurosis (PA) during quiet standing using ultrasound shear wave elastography. The shear wave velocity (SWV) of the PA in young healthy males and females (10 participants each) was measured by placing a probe in a hole in the floor plate. The change in the SWV with the passive dorsiflexion of the metatarsophalangeal (MP) joint was measured. The Young’s modulus of the PA was estimated to be 64.7 ± 9.4 kPa, which exponentially increased with MP joint dorsiflexion. The PA was estimated to have the natural length when the MP joint was plantarflexed by 13.8°, indicating that the PA is stretched by arch compression during standing. However, the present study demonstrated that the estimated stiffness for the natural length in quiet standing was significantly larger than that in the unloaded condition, revealing that the PA during standing is stiffened by elongation and through the possible activation of intrinsic muscles. Such quantitative information possibly contributes to the detailed biomechanical modeling of the human foot, facilitating an improved understanding of the mechanical functions and pathogenetic mechanisms of the PA during movements.