Behavior Of Muscle-tendon Unit Research Articles

Effects of gait retraining using minimalist shoes on the medial gastrocnemius muscle-tendon unit behavior and dynamics during running.

The effects of a 12-week gait retraining program on the adaptation of the medial gastrocnemius (MG) and muscle-tendon unit (MTU) were investigated. 26 runners with a rearfoot strike pattern (RFS) were randomly assigned to one of two groups: gait retraining (GR) or control group (CON). MG ultrasound images, marker positions, and ground reaction forces (GRF) were collected twice during 9 km/h of treadmill running before and after the intervention. Ankle kinetics and the MG and MTU behavior and dynamics were quantified. Runners in the GR performed gradual 12-week gait retraining transitioning to a forefoot strike pattern. After 12-week, (1) ten participants in each group completed the training; eight participants in GR transitioned to non-RFS with reduced foot strike angles; (2) MG fascicle contraction length and velocity significantly decreased after the intervention for both groups, whereas MG forces increased after intervention for both groups; (3) significant increases in MTU stretching length for GR and peak MTU recoiling velocity for both groups were observed after the intervention, respectively; (4) no significant difference was found for all parameters of the series elastic element. Gait retraining might potentially influence the MG to operate at lower fascicle contraction lengths and velocities and produce greater peak forces. The gait retraining had no effect on SEE behavior and dynamics but did impact MTU, suggesting that the training was insufficient to induce mechanical loading changes on SEE behavior and dynamics.

Medial gastrocnemius muscle fascicles shorten throughout stance during sprint acceleration.

The compliant nature of distal limb muscle-tendon units is traditionally considered suboptimal in explosive movements when positive joint work is required. However, during accelerative running, ankle joint net mechanical work is positive. Therefore, this study aims to investigate how plantar flexor muscle-tendon behavior is modulated during fast accelerations. Eleven female sprinters performed maximum sprint accelerations from starting blocks, while gastrocnemius muscle fascicle lengths were estimated using ultrasonography. We combined motion analysis and ground reaction force measurements to assess lower limb joint kinematics and kinetics, and to estimate gastrocnemius muscle-tendon unit length during the first two acceleration steps. Outcome variables were resampled to the stance phase and averaged across three to five trials. Relevant scalars were extracted and analyzed using one-sample and two-sample t-tests, and vector trajectories were compared using statistical parametric mapping. We found that an uncoupling of muscle fascicle behavior from muscle-tendon unit behavior is effectively used to produce net positive mechanical work at the joint during maximum sprint acceleration. Muscle fascicles shortened throughout the first and second steps, while shortening occurred earlier during the first step, where negative joint work was lower compared with the second step. Elastic strain energy may be stored during dorsiflexion after touchdown since fascicles did not lengthen at the same time to dissipate energy. Thus, net positive work generation is accommodated by the reuse of elastic strain energy along with positive gastrocnemius fascicle work. Our results show a mechanism of how muscles with high in-series compliance can contribute to net positive joint work.

Importance of Maximal Strength and Muscle-Tendon Mechanics for Improving Force Steadiness in Persons with Parkinson's Disease.

Although plantar flexion force steadiness (FS) is reduced in persons with Parkinson’s disease (PD), the underlying causes are unknown. The aim of this exploratory design study was to ascertain the influence of maximal voluntary contraction (MVC) force and gastrocnemius-Achilles muscle-tendon unit behaviour on FS in persons with PD. Nine persons with PD and nine age- and sex-matched non-PD controls (~70 years, 6 females per group) performed plantar flexion MVCs and sub-maximal tracking tasks at 5, 10, 25, 50 and 75% MVC. Achilles tendon elongation and medial gastrocnemius fascicle lengths were recorded via ultrasound during contraction. FS was quantified using the coefficient of variation (CV) of force. Contributions of MVC and tendon mechanics to FS were determined using multiple regression analyses. Persons with PD were 35% weaker during MVC (p = 0.04) and had 97% greater CV (p = 0.01) with 47% less fascicle shortening (p = 0.004) and 38% less tendon elongation (p = 0.002) than controls. Reduced strength was a direct contributor to lower FS in PD (ß = 0.631), and an indirect factor through limiting optimal muscle-tendon unit interaction. Interestingly, our findings indicate an uncoupling between fascicle shortening and tendon elongation in persons with PD. To better understand limitations in FS and muscle-tendon unit behavior, it is imperative to identify the origins of MVC decrements in persons with PD.

Altered Achilles tendon function during walking in people with diabetic neuropathy: implications for metabolic energy saving.

The Achilles tendon (AT) has the capacity to store and release elastic energy during walking, contributing to metabolic energy savings. In diabetes patients, it is hypothesized that a stiffer Achilles tendon may reduce the capacity for energy saving through this mechanism, thereby contributing to an increased metabolic cost of walking (CoW). The aim of this study was to investigate the effects of diabetes and diabetic peripheral neuropathy (DPN) on the Achilles tendon and plantarflexor muscle-tendon unit behavior during walking. Twenty-three nondiabetic controls (Ctrl); 20 diabetic patients without peripheral neuropathy (DM), and 13 patients with moderate/severe DPN underwent gait analysis using a motion analysis system, force plates, and ultrasound measurements of the gastrocnemius muscle, using a muscle model to determine Achilles tendon and muscle-tendon length changes. During walking, the DM and particularly the DPN group displayed significantly less Achilles tendon elongation (Ctrl: 1.81; DM: 1.66; and DPN: 1.54 cm), higher tendon stiffness (Ctrl: 210; DM: 231; and DPN: 240 N/mm), and higher tendon hysteresis (Ctrl: 18; DM: 21; and DPN: 24%) compared with controls. The muscle fascicles of the gastrocnemius underwent very small length changes in all groups during walking (~0.43 cm), with the smallest length changes in the DPN group. Achilles tendon forces were significantly lower in the diabetes groups compared with controls (Ctrl: 2666; DM: 2609; and DPN: 2150 N). The results strongly point toward the reduced energy saving capacity of the Achilles tendon during walking in diabetes patients as an important factor contributing to the increased metabolic CoW in these patients. NEW & NOTEWORTHY From measurements taken during walking we observed that the Achilles tendon in people with diabetes and particularly people with diabetic peripheral neuropathy was stiffer, was less elongated, and was subject to lower forces compared with controls without diabetes. These altered properties of the Achilles tendon in people with diabetes reduce the tendon's energy saving capacity and contribute toward the higher metabolic energy cost of walking in these patients.

Muscle-Tendon Unit Behavior During Constant Torque Stretching

Muscle-Tendon Unit Behavior During Constant Torque Stretching

The influence of loading intensity on muscle–tendon unit behavior during maximal knee extensor stretch shortening cycle exercise

Tendon stiffness increases as the magnitude and rate of loading increases, according to its viscoelastic properties. Thus, under some loading conditions tendons should become exceptionally stiff and act almost as rigid force transducers. Nonetheless, observations of tendon behavior during multi-joint sprinting and jumping tasks have shown that tendon strain increases whilst muscle strain decreases as the loading intensity increases. The purpose of the current study was to examine the influence of external loading intensity on muscle-tendon unit (MTU) behavior during a high-speed single-joint, stretch-shortening cycle (SSC) knee extension task. Eighteen men (n = 9) and women (n = 9) performed single-leg, maximum intensity SSC knee extensions at loads of 20, 60 and 90% of their one repetition maximum. Vastus lateralis fascicle length (L(f)) and velocity (v(f)) as well as MTU (L(MTU)) and tendinous tissue (L(t)) length were measured using high-speed ultrasonography (96 Hz). Patellar tendon force (F(t)) and rate of force development (RFDt) were estimated using inverse dynamics. Results showed that as loading intensity increased, concentric joint velocity and shortening v f decreased whilst F t and RFDt increased, but no significant differences were observed in eccentric joint velocity or peak L(MTU) or L(f). In addition, the tendon lengthened significantly less at the end of the eccentric phase at heavier loads. This is the first observation that tendon strain decreases significantly during a SSC movement as loading intensity increases in vivo, resulting in a shift in the tendon acting as a power amplifier at light loads to a more rigid force transducer at heavy loads.

Neural Modulation of Muscle–Tendon Control Strategy after a Single Practice Session

The purpose of the present study was to examine a hypothesis that the musculotendinous behavior during a propelling action with a countermovement can be altered by a single practice session through modulation of neuromuscular activities. Eight males performed unilateral maximal plantarflexion with (CMJ) and without (noCMJ) countermovement before and after a practice consisting of six sets of three repetitions of unilateral CMJ exercises. Measurements included EMG activities of the triceps surae and tibialis anterior muscles and the fascicle behavior of the gastrocnemius by ultrasonography, and impulse was calculated from the force-time data. The change in tendon length was also estimated. The impulse in CMJ increased after the practice, but that in noCMJ did not. After the practice, the magnitude of fascicle lengthening and shortening in CMJ decreased, which was accompanied by an increase in tendon shortening without change in the ankle joint range of motion. The time lag from the onset of reaction force to that of EMG activities of the triceps surae muscles was shortened after the practice. The results support the hypothesis and indicate that, as a neural modulation through a single practice, the muscle-tendon unit behavior during CMJ can be optimized to improve the performance.

Muscle Fascicle Behavior During Cross-country Skiing

The repetitive extension/flexion patterns are typical of muscle stretch-shortening cycles (SSC) and are commonly observed in sport movements such as running, jumping. In cross-county (x-c) skiing, relatively little evidence collected with kinematics, ground reaction force and electromyography (EMG) recordings suggests that SSC-like behavior can be identified in diagonal stride of classical technique x-c skiing. PURPOSE: The purpose of the present study was to examine the muscle-tendon unit (MTU) and muscle fascicle behaviors simultaneously during the diagonal stride of classical technique x-c skiing. METHODS: The muscle fascicle behavior was measured by the portable ultrasound machine (Prosound C3cv, Aloka Japan) in natural skiing conditions in the Vuokatti ski tunnel. The ultrasound machine with the weight of 5 kg was put on the rucksack of the skier and the probe was attached on the skin of the following muscles: vastus lateralis, rectus femoris, triceps brachii, medial gastrocnemius and soleus. Each fascicle behavior during skiing was studied separately using the same skiing speed of 4.5 m s-1, approximately. An experienced skier was used as a subject. The measurements included also EMGs from the same muscles as the ultrasound scanning was recorded. The 3D kinematics and the ground reaction force recordings were also preformed. RESULTS: Most of the measured fascicles were stretched in the MTU stretching phase followed by shortening in the MTU shortening phase. However, the relative stretching and shortening amplitudes of the fascicles and MTU were muscle specific. Additionally, the rectus femoris muscle showed interesting activation patterns and fascicle behavior during x-c skiing. SSC type behavior was observed in two different phases of the stride, emphasizing the role of the rectus femoris both in knee extension and hip flexion. The knee extension occurred from the end of the braking phase to the early push-off phase and the hip flexion during the early swing phase immediately following the push-off phase. This can explain quite logically why rectus femoris may show greater fatigue as compared to the vastus lateralis and medialis muscles in x-c skiing. CONCLUSIONS: Our results clearly showed the SSC-type fascicle and MTU behavior during x-c skiing as well as the double SSC behavior of the rectus femoris

Mechanical behavior of the quadriceps femoris muscle tendon unit during low-load contractions

We examined the relationships between morphology and muscle-tendon dynamics of the quadriceps femoris muscle of 11 men using velocity-encoded phase-contrast magnetic resonance imaging (MRI). Thigh muscle electromyography and joint range of motion were first measured outside the MRI scanner during knee extension-flexion tasks that were performed at a rate of 40 times/min with elastic bands providing peak resistance of 5.2 kp (SD 0.4) to the extension. The same movement was repeated inside the MRI scanner bore where tissue velocities and muscle morphology were recorded. The average displacement in the proximal and distal halves of the rectus femoris and vastus intermedius aponeuroses was different (P = 0.049), reflecting shortening (1.6%), but the tensile strain along the length of the aponeuroses was uniform. The aponeurosis behavior varied among individuals, and these individual patterns were best explained by the differences in relative cross-sectional area of rectus femoris to vastus muscles (r = 0.71, P = 0.014). During dynamic contraction, considerable deformation of muscles in the axial plane caused an anatomic measure such as muscle thickness to change differently (decrease or increase) in different sites of measurement. For example, when analyzed from the axial images, the vastus lateralis thickness did not change (P = 0.946) in the frontal plane through femur but increased in a 45 degrees oblique plane between the frontal and sagittal planes (P = 0.004). The present observations of the heterogeneity and individual behavior emphasize the fact that single-point measurements do not always reflect the overall behavior of muscle-tendon unit.