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The relationships between ankle plantar flexor musculotendinous stiffness (MTS) and performance in a countermovement vertical jump (CMJ) and maximal rate of torque development (MRTD) were studied in 27 active men. MTS was studied by means of quick releases at 20 (S0.2), 40 (S0.4), 60 (S0.6), and 80% (S0.8) of maximal voluntary torque (TMVC). CMJ was not correlated with strength indices but was positively correlated with MRTD/BM, S0.4/BM. The slope α2 and intercept β2 of the torque-stiffness relationships from 40 to 80% TMVC were correlated negatively (α2) and positively (β2) with CMJ. The different stiffness indices were not correlated with MRTD. The prediction of CMJ was improved by the introduction of MRTD in multiple regressions between CMJ and stiffness. CMJ was also negatively correlated with indices of curvature of the torque-stiffness relationship. The subjects were subdivided in 3 groups in function of CMJ (groups H, M, and L for high, medium, and low performers, resp.). There was a downward curvature of the torque-stiffness relationship at high torques in group H or M and the torque-stiffness regression was linear in group L only. These results suggested that torque-stiffness relationships with a plateau at high torques are more frequent in the best jumpers. [ABSTRACT FROM AUTHOR]

Abstract: The use of biomechanical methods to quantify functional/physiological parameters in malnourished humans can provide new insights into the understanding of effects of malnutrition on human muscles. Therefore, a transportable ankle ergometer device was developed, which allows the quantification of mechanical properties of the human plantarflexor muscles in field experiments. More precisely, the ergometer quantifies isometric force in static conditions and musculotendinous stiffness in dynamic conditions. This latter parameter is obtained by the quick-release technique. The aim of the study was first to conduct a reproducibility study on musculotendinous stiffness. Seven healthy subjects were tested three times in alternate days. The results showed the well-known linear relationship between musculotendinous stiffness and torque, where the slope was used as a stiffness index (SIMT). Individual regression line comparison indicated that SIMT values were not significantly different between the three repeated measurements (P>0.05). Mean coefficient of variation was 4.5±1.0%. The individual SIMT data were within the range of those reported in the literature. The reproducibility study showed that the quantification of musculotendinous stiffness by means of the quick-release technique is a reliable method, using a transportable ankle ergometer device. [Copyright &y& Elsevier]

The aim of this study was to characterize the influence of intrinsic musculotendinous and musculoarticular stiffness of plantarflexor muscles on (1) the overall musculoskeletal stiffness and (2) the performance during stretch-shortening cycles-type exercise. The influence of plyometric training background on these relationships was also analyzed. Musculotendinous (SIMT), passive ( K P ) and active (SIMA) musculoarticular stiffnesses were quantified, using quick-release and sinusoidal perturbation tests, on nine French elite long or triple jumpers (athlete group, AG) and nine control subjects (CG). These ergometric parameters were related with the lower-limb stiffness ( K leg) and the maximal performance ( H max) measured from a force platform during vertical hopping. AG showed a significantly higher SIMT (2.76 rad−1), K P (55.6 N m rad−1), K leg (30.3 kN m−1) and H max (0.48 m) compared to CG (1.83 rad−1, 37.8 N m rad−1, 19.6 kN m−1 and 0.38 m, respectively). K leg was not significantly correlated with any of the intrinsic stiffness parameters (SIMT, SIMA or K P ). For AG, a strong and negative correlation was observed between H max and K leg. These data indicate that, while elite jumpers presented higher stiffness of both musculotendinous and passive musculoarticular structures, a high compliance of musculoskeletal system was beneficial to optimize the performance in vertical hopping for these athletes. We suggested that neuromuscular strategies were designed to counterbalance this higher intrinsic stiffness to solve the problem of the conflicting requirement of the musculotendinous elements: increase in compliance to enhance the elastic recoil and increase in stiffness for a better force transmission to the periphery. [ABSTRACT FROM AUTHOR]

The present study deals with the question whether 24-week strength training alters neuromechanical properties of plantar flexors in elderly people (73-83 years). The first purpose of the present study was to evaluate the effect of strength training on musculotendinous (MT) stiffness of the triceps surae (TS). The training was performed twice per week and mainly consisted of three series of ten repetitions of calf-rise and leg-press exercises at 75% of the three-repetition maximum. Using quick-release movements at different levels of submaximal torques performed measurements of MT stiffness. Surface electromyograms (EMG) of each part of the TS and the tibialis anterior were also recorded. A stiffness index (SI), defined as the slope of the angular stiffness-torque relationship (SIMT-Torque), was used to quantify changes in MT stiffness. Results showed a significant decrease in SIMT-Torque by 25.2% following training (P<0.05). The second purpose of the study was to evaluate whether neural mechanism has influences on this decrease. Therefore, an activation SI, defined as the slope of the angular stiffness-EMG relationship (SIMT-EMG) was used to overcome the influence of changes in agonist activity, and thus to quantify changes in MT intrinsic elastic properties. SIMT-EMG only decreased by 11.2% following training (P<0.05). The present results underlined that MT stiffness decreases following training in elderly individuals, counterbalancing the effect of ageing. These changes seem not only to be due to peripheral but also to neural adaptations. [ABSTRACT FROM AUTHOR]

Muscle and joint mechanical properties during plantar flexion were investigated in 13 elderly women (EW) (age range 73-83 years) and 15 elderly men (EM) (age range 74-81 years). Maximal torque, at several angular velocities, was measured to construct torque-velocity relationship. This led to the calculation of an index of maximal shortening velocity (VI(max)) at 10% of maximal isometric torque. Two methods were then used to calculate musculotendinous (quick-release movements) and musculoarticular (sinusoidal perturbations) stiffness. In both cases, stiffness was linearly related to torque, and the slope was defined as a stiffness index (SI): SI(MT) and SI(MA), respectively. Maximal torques as well as VI(max) (p <.05) were lower in EW compared with EM. Furthermore, SI(MT) and SI(MA) values were higher for EW than for EM (p <.05). These results are interpreted in terms of possible differences in the muscle mass, fiber-type distribution, and tendons. They may also have implications for daily motor behavior. [ABSTRACT FROM AUTHOR]

Focuses on the quantification of musculotendinous stiffness of the triceps surae muscle group in prepubertal children. Use of quick release movements at different levels of submaximal contractions; Increase of stiffness with age due to maturation of the tissues; Confirmation of the decrease in neuromuscular efficiency.

Studies reflex and elastic properties of the triceps surae on male cosmonauts 28-40 days before a three- to six-month spaceflight. Assessment of reflex excitability by the stretch; Musculotendinous stiffness; Role of musculoarticular structures in the reflex adaptation.

The aim of this study was to measure the effects of hindlimb suspension on mechanical properties of the rat Achilles tendon. Adult male Wistar rats were randomly assigned to groups to be either suspended, or a control. After 21 days, Achilles tendons were removed for mechanical analysis. Classical tests of tensile performance were made, and mechanical parameters were derived from a stress-strain relationship. The tendons of animals that had been suspended presented values for maximal stress and tangent modulus which were 37.5% (P < 0.01) and 41% (P < 0.01), respectively, lower than the tendons of the control rats. In a similar way, the energy absorption capacity had largely decreased in animals that had been suspended. However, the maximal strain was similar in the two groups. These results showed that hindlimb suspension in rats has an important detrimental effect on mechanical properties of the Achilles tendon. Differences in tendon stiffness obtained here, along with those found by other investigators, encourage the hypothesis that homeostatic responses of soft tissues are due to changes in limb loadings. This study may be useful in providing a better understanding of the adaptation of human skeletal muscle when exposed to microgravity. [ABSTRACT FROM AUTHOR]

Abstract: The activation capacities and neuromuscular efficiency (NME) of the triceps surae (TS) of prepubescent children (7–11 years) and adults were evaluated during submaximal and maximal (MVC) isometric plantarflexion to determine whether they varied with age. TS-EMG were obtained by summing-up the rectified electromyograms of the soleus and gastrocnemii muscles; these data were quantified using a sliding average method and normalized with reference to the TS maximal compound action potential (TS-M-wave). The maximal EMG increased significantly with age in the children, but less than MVC, what led to a significant increase in NMEMax (MVC/TS-EMGmax ratio). The EMG–torque relationship indicated an age-related overactivation of TS at low torque, what led to a lower NMESub-max (inverse of the slope of the EMG–torque relationship) for the youngest children. The overactivation of TS was accompanied by contraction of the TA, which decreased with age. The youngest children were also less able to maintain a target torque and muscle activation. Finally, the twitch interpolated method revealed an age-dependant activation deficit. We conclude that central mechanisms are the main cause of the lower torques developed by children and they appear to vary with age in prepubertal children. [Copyright &y& Elsevier]