Comparison of viscoelastic characteristics in triceps surae between Black and White athletes

The purpose of the present study was to investigate race differences in viscoelastic characteristics of triceps surae muscle group. Black and white college sprint type athletes (n=44) participated in this study. Viscoelastic properties were assessed using the free vibration technique: subjects sat with their forefeet on the edge of a force-plate (Kistler, Switzerland) and support a frame loaded with weights (0-40 kg) on the knees. Oscillations of the triceps surae and Achilles tendon system were initiated with a hand-held hammer by tapping the weight load. Oscillations occur at frequencies of 3-6 Hz and were slightly damped. The damped oscillations in conjunction with the equation of motion of a damped mass-spring model were used to calculate the viscosity of muscle (b), and the elasticity of muscle fibres (k(d)) and tendon (k(t)) in each subject. There were little significant differences in most of physical characteristic variables between black and white athletes. Black athletes have significantly greater muscle viscosity and elasticity than white athletes while tendon elasticity is equivalent. Thus, muscle stiffness is greater among black athletes. Greater muscle stiffness could contribute to greater sprint/jump performance among black athletes, compared with white athletes, through alteration of foot/ground contact and take-off phases during sprinting/jumping.     

Biomechanical loading of Achilles tendon during normal locomotion.

Direct in vivo Achilles tendon force measurements open up new possibilities for understanding the loading of the Achilles tendon during natural locomotion. This article describes how these human experiments can be performed. The results of these experiments imply that Achilles tendon forces are unexpectedly high in certain activities (e.g., hopping) and that the rates of loading rather than the absolute magnitudes of the recorded forces may be more relevant for clinical purposes as well as for the construction of artificial tendon materials.     

Ultrasonography gives directly but noninvasively elastic characteristic of human tendon in vivo

To obtain an insight into tendon elasticity during human movement, a real-time ultrasonography was applied to the contracting tibialis anterior muscle. The insertion point of fascicles onto the aponeurosis was clearly visualized, and its position relative to a fixed marker on the skin moved proximally (1) according to the increasing dorsiflexion force (F) with a fixed ankle joint. Notably, the 1 – F relationship in the tendon was found to be quadratic in nature (F = c1²; c=1.48 2.24, r=0.985 0.992, n=9) as has been reported in the isolated tendon, although the F – 1 curves were slightly underestimated in comparison with the stiffness constant estimated from tendon architecture. This underestimation might be caused by changes in the height of the foot arch with the application of force.     

In vivo determination of muscle viscoelasticity in the human leg

The purpose of this study was to examine the methodological validity of the free vibration technique for determining individual viscoelastic characteristics of the human triceps surae muscle-tendon complex (MTC) in vivo. Six subjects sat with first phalangeal joint of the forefoot on the edge of a force-plate. The special frame on the knee was loaded with weight (0-40 kg) for testing. Oscillations of the triceps surae MTC system were initiated with a hand-held hammer by tapping the weight. In order to keep the same posture, the output of the force plate was displayed on the oscilloscope and subjects were asked to maintain the beam on the oscilloscope at a particular location in relation to a reference line. The damped oscillations in conjunction with the equation of motion of a damped mass-spring model were used to calculate the viscosity of muscle (b) and the elasticity of muscle fibres and tendon (k) in each subject, considering moment arm of the ankle joint. With this arrangement, we have obtained high reproducibility in this method. The coefficient of variations (CVs) of b and k in five trials at each weight were quite small (range: 0.5-18.7% in b and 1.0-15.1% in k). There were no significant differences in viscoelastic coefficients between right and left legs. Therefore, it appears that free vibration technique, used here, is adequate in describing the viscoelastic characteristics of the triceps surae in vivo in humans.     

In vivo dynamics of human medial gastrocnemius muscle‐tendon complex during stretch‐shortening cycle exercise

The purpose of this study was to investigate the dynamics of human muscle‐tendon complex (MTC) during stretch‐shortening cycle exercises through in vivo observation. A total of seven male subjects performed dorsi flexion followed by plantar flexion at two different frequencies, 0.3 Hz (slow) and 1.0 Hz (fast), in a toe‐standing position. The fascicle length (L_F) of the medial gastrocnemius muscle during the movements was determined using a real‐time ultrasonography in vivo. The L_F at the switching phase from dorsi to plantar flexion was significantly shorter in the fast exercise (54.4 ± 5.5 mm) than in the slow one (58.2 ± 5.4 mm), suggesting that the elongation of tendon structures at that time was significantly greater in the former than in the latter. Furthermore, at the initial stage of plantar flexion during the fast movement, the L_F hardly changed with a rapid shortening of tendon structures at that time. The observed relation between MTC length and force showed that the behaviour of tendon structures contributed to 20.2 and 42.5% of the total amount of work completed during plantar flexion phase in the slow and fast movements, respectively. Thus, the present results suggest that tendon structures make the dynamics of MTC more efficient during stretch‐shortening cycle exercises by changing their lengths.     

Effects of pretension on work and power output of the muscle-tendon complex in dynamic elbow flexion

The purpose of the present study was to investigate the effects of pretension on work and power output of the muscle-tendon complex during dynamic elbow flexion under several submaximal and maximal conditions. The subjects were 10 healthy female students. Randomized trials from 0% to 100% maximal voluntary contraction (MVC) pretension (PT) at 60° elbow flexion were conducted. After about 3 s of static PT, subjects maximally flexed the elbow joint to 90° using a quick release method. The weight was individually selected for each subject to provide an optimal load for the development of maximal power. A Hill-type model was utilized to analyze the performance of the elbow muscle-tendon complex (MTC). PT 0, 30, 60 and 90% MVC data were used for comparison, and all data were expressed as the mean and standard deviation. Multiple paired comparisons between the value of PT 0% MVC and that of the other PT levels were performed post-hoc using Dunnetts method. The work of the series elastic component (SEC) increased gradually with the PT level because elastic energy was stored in the PT phase. However, the work of the contractile component (CC) decreased gradually with an increase in PT level. Moreover, the work of the MTC also decreased, closely related to the CC work decrement. The phenomenon of CC work decrement was caused by force depression and was not related to either the force-length or force-velocity relationships of the CC. EMG activity (agonist and antagonist) showed no significant differences. Muscle geometry changes or intracellular chemical shifts may have occurred in the PT phase.     

In vivo dynamics of human medial gastrocnemius muscle-tendon complex during stretch-shortening cycle exercise

The purpose of this study was to investigate the dynamics of human muscle-tendon complex (MTC) during stretch-shortening cycle exercises through in vivo observation. A total of seven male subjects performed dorsi flexion followed by plantar flexion at two different frequencies, 0.3 Hz (slow) and 1.0 Hz (fast), in a toe-standing position. The fascicle length (LF) of the medial gastrocnemius muscle during the movements was determined using a real-time ultrasonography in vivo. The LF at the switching phase from dorsi to plantar flexion was significantly shorter in the fast exercise (54.4 +/- 5.5 mm) than in the slow one (58.2 +/- 5.4 mm), suggesting that the elongation of tendon structures at that time was significantly greater in the former than in the latter. Furthermore, at the initial stage of plantar flexion during the fast movement, the LF hardly changed with a rapid shortening of tendon structures at that time. The observed relation between MTC length and force showed that the behaviour of tendon structures contributed to 20.2 and 42.5% of the total amount of work completed during plantar flexion phase in the slow and fast movements, respectively. Thus, the present results suggest that tendon structures make the dynamics of MTC more efficient during stretch-shortening cycle exercises by changing their lengths.     

An estimation of the velocities of three take-off phases in 18-m triple jump

The purposes of this study were to estimate the take-off velocities necessary to gain a given distance on the triple jump by adopting three hypotheses and to investigate the external force vectors during the jump's supporting phase. The total distance corresponding to the varying combinations of horizontal and vertical velocities at take-offs were calculated based on these hypotheses. The calculated velocities of the body's center of gravity coincided well with the observed total distance, even though the velocities were slightly underestimated. There was a significant correlation between the run-up velocity and the total distance (r = 0.91, P less than 0.001). From these results, the run-up and take-off velocities and the external force vectors for an 18-m jump were estimated. It might be said that the 18-m jumper must gain great run-up velocity (10.7 m X s-1) and exert forces during each supporting phase which are 3.6-4.4 times the body weight, resulting in a force-vector angle of about 101 degrees at each take-off.     

银杏叶提取物对大鼠高氧肺损伤的影响

目的:明确银杏叶提取物(EGb)能否减轻高氧诱导的大鼠急性肺损伤。方法:SD大鼠随机分为EGb组、高氧组和对照组。EGb组和高氧组大鼠置于>95%氧箱中,对照组置于空气中。实验开始及高氧暴露24 h、48 h时,EGb组大鼠均管饲EGb100 mg/kg,另外两组大鼠予等量生理盐水。检测胸水含量、支气管肺泡灌洗液(BALF)中白细胞和中性粒细胞计数、总蛋白、细胞因子IL-6、IL-1β及TNF-α含量、肺组织丙二醛(MDA)含量以及病理学改变。结果:EGb组大鼠胸水含量和BALF中白细胞、中性粒细胞计数明显低于高氧组(P<0.05)。EGb组和高氧组总蛋白含量差异无统计学意义,均明显高于对照组(P<0.01)。EGb组BALF中IL-6含量显著高于另外两组(P<0.01)。三组大鼠BALF中均未检测到IL-1β和TNF-α,肺组织MDA含量差异无统计学意义。EGb组和高氧组肺组织学评分差异无统计学意义(P>0.05)。结论:EGb可部分减轻高氧诱导的大鼠急性肺损伤,机制可能与促进肺组织IL-6产生有关。     

Clinical Efficacy of Fluvoxamine and Functional Polymorphism in a Serotonin Transporter Gene on Childhood Autism

We studied the correlation between response to fluvoxamine and serotonin transporter gene promoter region polymorphism (5-HTTLPR). Eighteen children with autistic disorder completed a 12-week double-blind, placebo-controlled, randomized crossover study of fluvoxamine. Behavioral assessments were obtained before and at 12 weeks of treatment. 5-HTTLPR (long (l) or short(s)), was analyzed by the PCR method. Ten out of 18 patients responded to fluvoxamine treatment; allele type analysis revealed that clinical global effectiveness was noted significantly more in the l allele than in the s allele. However, with respect to language use, a significant effectiveness was noted in the s allele. 5-HTTLPR may influence the individual responses to fluvoxamine administration.