Search results for "jäykkyys"

Mechanical properties of natural fiber composites produced using dynamic sheet former

2018

Composites formed from wood fibers and man-made cellulosic fibers in PLA (polylactic acid) matrix, manufactured using sheet forming technique and hot pressing, are studied. The composites have very low density (due to high porosity) and rather good elastic modulus and tensile strength. As expected, these properties for the four types of wood fiber composites studied here improve with increasing weight fraction of fibers, even if porosity is also increasing. On the contrary, for man-made cellulosic fiber composites with circular fiber cross-section, the increasing fiber weight fraction (accompanied by increasing void content) has detrimental effect on stiffness and strength. The differences …

Structure and function of human triceps surae muscle and tendon in aging

2016

Age-related muscle activation profiles and joint stiffness regulation in repetitive hopping

2011

It is well documented that increasing effort during exercise is characterized by an increase in electromyographic activity of the relevant muscles. How aging influences this relationship is a matter of great interest. In the present study, nine young and 24 elderly subjects did repetitive hopping with maximal effort as well as with 50%, 65%, 75% and 90% intensities. During hopping joint kinematics were measured together with electromyographic activity (EMG) from the soleus, gastrocnemius medialis, gastrocnemius lateralis and tibialis anterior muscles. The results showed that agonist activation increased in both age groups with increasing intensity. The highest jumping efficiency (EMG ratio …

Repeatability and sensitivity of passive mechanical stiffness measurements in the triceps surae muscle‐tendon complex

2021

Measurements of muscle-tendon unit passive mechanical properties are often used to illustrate acute and chronic responses to a training stimulus. The purpose of this study was to quantify the inter-session repeatability of triceps surae passive stiffness measurements in athletic and non-athletic populations, with the view to discussing its usefulness both as a muscle-tendon profiling tool and a control measure for studies with multiple data collection sessions. The study also aimed to observe the effects of quiet standing on passive stiffness parameters. Twenty-nine men (10 cyclists, nine triathletes, 10 controls) visited the laboratory on three separate occasions, where passive stiffness t…

Viscoelastic properties of the Achilles tendon in vivo

2013

It has been postulated that human tendons are viscoelastic and their mechanical properties time-dependent. Although Achilles tendon (AT) mechanics are widely reported, there is no consensus about AT viscoelastic properties such as loading rate dependency or hysteresis, in vivo. AT force-elongation characteristics were determined from 14 subjects in an ankle dynamometer at different loading rates using motion capture assisted ultrasonography. AT stiffness and elongation were determined between 10 – 80% of maximum voluntary contraction (MVC) force at fast and slow loading rates. As subjects were unable to consistently match the target unloading rate in the slow condition, AT hysteresis was on…

Towards modern understanding of the Achilles tendon properties in human movement research

2023

The Achilles tendon (AT) is the strongest tendon in humans, yet it often suffers from injury. The mechanical properties of the AT afford efficient movement, power amplification and power attenuation during locomotor tasks. The properties and the unique structure of the AT as a common tendon for three muscles have been studied frequently in humans using in vivo methods since 1990's. As a part of the celebration of 50 years history of the International Society of Biomechanics, this paper reviews the history of the AT research focusing on its mechanical properties in humans. The questions addressed are: What are the most important mechanical properties of the Achilles tendon, how are they stud…

Muscle-tendon morphomechanical properties of non-surgically treated Achilles tendon 1-year post-rupture

2022

Background\ud Achilles tendon rupture appears to alter stiffness and length of the tendon. These alterations may affect the function of tendon in force transmission and in energy storage and recovery. We studied the mechanical properties of the Achilles' tendon post-rupture and their association with function.\ud Methods\ud Twenty-four (20 males, 4 females) participants (mean age: 43 y, 176 cm, 81 kg) were recruited. Ultrasonography and dynamometry were used to assess the muscle-tendon unit morphological and mechanical properties of non-surgically treated patients 1-year post rupture.\ud Findings\ud Injured tendons were longer with difference of 1.8 cm (95%CI: 0.5–1.9 cm; P < 0.001), and th…

Lihastonuksen yhteys hermolihasjärjestelmän suorituskykyyn

2005

Haverinen, Marko. 2005. Lihastonuksen yhteys hermolihasjärjestelmän suorituskykyyn. Valmennus-ja testausopin Pro gradu -tutkielma. Jyväskylän yliopisto. Liikuntabiologian laitos. 96 s.Lihastonusta on tutkittu aikaisemmin lähinnä kliinisessä diagnosointi-, kuntoutus- ja tutkimuskäytössä eripotilasryhmillä ja kvantitatiivisesti mitattavana ilmiönä se ei ole ollut käytössä kovin kauan. Tämän tutkimuksentarkoituksena oli kuvata lihastonusta ilmiönä, selvittää miten se muuttuu ikääntymisen myötä jaon yhteydessä eri ikäisten ei-harjoittelevien henkilöiden neuromuskulaariseen suorituskykyyn. Tarkoituksenaoli tutkia myös miten lihastonus ilmenee eri harjoitustaustan omaavilla henkilöillä sekä selvi…

Venyttelyn akuutit vaikutukset juoksun taloudellisuuteen

2005

Tämän tutkimuksen tarkoituksena oli selvittää ennen suoritusta tehdyn venyttelyn akuutteja vaikutuksia juoksun taloudellisuuteen. Samalla tutkittiin venyttelyn vaikutuksia liikkuvuuteen ja askelmuuttujiin, joten voitiin nähdä ovatko taloudellisuuden mahdolliset muutokset yhteydessä liikkuvuuden tai askelmuuttujien mahdollisiin muutoksiin. Tutkimuksen koehenkilöinä oli 8 miespuolista kestävyysjuoksijaa (ikä 23.9 ± 5.1 vuotta). Jokainen koehenkilö harjoitteli aktiivisesti tulevan kesän kilpailuja varten. Juoksijoiden ennätykset olivat 800m:llä välillä 1min50s – 2min3s ja/tai 1500m:llä välillä 3min53 – 4min5s. Koehenkilöt tekivät samanlaiset juoksun taloudellisuutta mittaavat testit kahtena er…

Effect of Training-Induced Changes in Achilles Tendon Stiffness on Muscle–Tendon Behavior During Landing

2018

During rapid deceleration of the body, tendons buffer part of the elongation of the muscle–tendon unit (MTU), enabling safe energy dissipation via eccentric muscle contraction. Yet, the influence of changes in tendon stiffness within the physiological range upon these lengthening contractions is unknown. This study aimed to examine the effect of training-induced stiffening of the Achilles tendon on triceps surae muscle–tendon behavior during a landing task. Twenty-one male subjects were assigned to either a 10-week resistance-training program consisting of single-leg isometric plantarflexion (n = 11) or to a non-training control group (n = 10). Before and after the training period, plantarf…