Muscle-tendon Complex Length Research Articles

Curvature of gastrocnemius muscle fascicles as function of muscle-tendon complex length and contraction in humans.

It has been shown that muscle fascicle curvature increases with increasing contraction level and decreasing muscle-tendon complex length. The analyses were done with limited examination windows concerning contraction level, muscle-tendon complex length, and/or intramuscular position of ultrasound imaging. With this study we aimed to investigate the correlation between fascicle arching and contraction, muscle-tendon complex length and their associated architectural parameters in gastrocnemius muscles to develop hypotheses concerning the fundamental mechanism of fascicle curving. Twelve participants were tested in five different positions (90°/105°*, 90°/90°*, 135°/90°*, 170°/90°*, and 170°/75°*; *knee/ankle angle). They performed isometric contractions at four different contraction levels (5%, 25%, 50%, and 75% of maximum voluntary contraction) in each position. Panoramic ultrasound images of gastrocnemius muscles were collected at rest and during constant contraction. Aponeuroses and fascicles were tracked in all ultrasound images and the parameters fascicle curvature, muscle-tendon complex strain, contraction level, pennation angle, fascicle length, fascicle strain, intramuscular position, sex and age group were analyzed by linear mixed effect models. Mean fascicle curvature of the medial gastrocnemius increased with contraction level (+5 m-1 from 0% to 100%; p = 0.006). Muscle-tendon complex length had no significant impact on mean fascicle curvature. Mean pennation angle (2.2 m-1 per 10°; p < 0.001), inverse mean fascicle length (20 m-1 per cm-1 ; p = 0.003), and mean fascicle strain (-0.07 m-1 per +10%; p = 0.004) correlated with mean fascicle curvature. Evidence has also been found for intermuscular, intramuscular, and sex-specific intramuscular differences of fascicle curving. Pennation angle and the inverse fascicle length show the highest predictive capacities for fascicle curving. Due to the strong correlations between pennation angle and fascicle curvature and the intramuscular pattern of curving we suggest for future studies to examine correlations between fascicle curvature and intramuscular fluid pressure.

Effects of Joint Kinetics on Energy Cost during Repeated Vertical Jumping.

The present study was designed to investigate the effects of lower limb joint kinetics on energy cost during jumping. Eight male middle and long-distance runners volunteered for the study. The subjects were asked to repeat vertical jumps at a frequency of 2 Hz for 3 min on a force platform in three different surface inclination conditions: Incline (+8°), Level (0°), and Decline (-8°). Sagittal plane kinematics were obtained using a high-speed video camera. Simultaneously, ground reaction forces and EMG of the lower limb muscles were recorded. Energy cost was calculated using steady-state oxygen uptake, respiratory ratio, and vertical distance of the body. In all conditions, energy cost correlated positively with total mechanical work of the knee joint (r = 0.636, P < 0.01), but negatively with total mechanical work of the ankle joint (r = -0.584, P < 0.01). The muscle-tendon complex length of the gastrocnemius and soleus muscles were significantly longer in incline than in level and decline. The gastrocnemius muscle showed different activity pattern in decline as compared with the incline and level conditions. The present study revealed that the ankle and knee joint kinematics and, therefore muscles' coordination are associated with energy cost during repeated vertical jumping. The lower limb joints contributed different efficiencies to generate the same total mechanical work in repeated vertical jumping on different surface inclinations. Energy cost was smaller when mechanical work was mainly done by ankle joint. Whereas, when the ankle joint did less mechanical work, the knee and/or hip joints compensated for the lack of mechanical work of the ankle joint and energy cost was increased.

보행과 한발·두발 수직점프 수행 시 내측비복근 근-건 복합체와 근섬유다발의 길이 변화 패턴의 차이

Objective : The purpose of this study was to investigate difference in fascicle behavior of the medial gastrocnemius during the locomotion with varying intensities, such as gait and one-legged and two-legged vertical jumping. Methods : Six subjects (3 males and 3 females; age: <TEX>$27.2{\pm}1.6yrs.$</TEX>, body mass: <TEX>$62.8{\pm}9.8kg$</TEX>, height: <TEX>$169.6{\pm}8.5cm$</TEX>) performed normal gait (G) at preferred speed and maximum vertical jumping with one (OJ) and two (TJ) legs. While subjects were performing the given tasks, the hip, knee and ankle joint motion and ground reaction force was monitored using a 8-infrared camera motion analysis system with two forceplates. Simultaneously, electromyography of the triceps surae muscles, and the fascicle length of the medial gastrocnemius were recorded using a real-time ultrasound imaging machine. Results : Comparing to gait, the kinematic and kinetic parameters of TJ and OJ were found to be significantly different. Along with those parameters, change in the medial gastrocnemius (MG) muscle-tendon complex (MTC) length (<TEX>$50.57{\pm}6.20mm$</TEX> for TJ and <TEX>$44.14{\pm}5.39mm$</TEX> for OJ) and changes in the fascicle length of the MG (<TEX>$18.97{\pm}3.58mm$</TEX> for TJ and <TEX>$20.31{\pm}4.59mm$</TEX> for OJ) were observed. Although the total excursion of the MTC and the MG fascicle length during the two types of jump were not significantly different, however the pattern of length changes were found to be different. For TJ, the fascicle length maintained isometric longer during the propulsive phase than OJ. Conclusion : One-legged and two-legged vertical jumping use different muscle-tendon interaction strategies.

Contraction dynamics and function of the muscle-tendon complex depend on the muscle fibre-tendon length ratio: a simulation study.

Experimental studies show different muscle-tendon complex (MTC) functions (e.g. motor or spring) depending on the muscle fibre-tendon length ratio. Comparing different MTC of different animals examined experimentally, the extracted MTC functions are biased by, for example, MTC-specific pennation angle and fibre-type distribution or divergent experimental protocols (e.g. influence of temperature or stimulation on MTC force). Thus, a thorough understanding of variation of these inner muscle fibre-tendon length ratios on MTC function is difficult. In this study, we used a hill-type muscle model to simulate MTC. The model consists of a contractile element (CE) simulating muscle fibres, a serial element (SE) as a model for tendon, and a parallel elastic element (PEE) modelling tissue in parallel to the muscle fibres. The simulation examines the impact of length variations of these components on contraction dynamics and MTC function. Ensuring a constant overall length of the MTC by L(MTC) = L(SE) + L(CE), the SE rest length was varied over a broad physiological range from 0.1 to 0.9 MTC length. Five different MTC functions were investigated by simulating typical physiological experiments: the stabilising function with isometric contractions, the motor function with contractions against a weight, the capability of acceleration with contractions against a small inertial mass, the braking function by decelerating a mass, and the spring function with stretch-shortening cycles. The ratio of SE and CE mainly determines the MTC function. MTC with comparably short tendon generates high force and maximal shortening velocity and is able to produce maximal work and power. MTC with long tendon is suitable to store and release a maximum amount of energy. Variation of muscle fibre-tendon ratio yielded two peaks for MTC's force response for short and long SE lengths. Further, maximum work storage capacity of the SE is at long relL(SE,0). Impact of fibre-tendon length ratio on MTC functions will be discussed. Considering a constant set of MTC parameters, quantitative changes in MTC performance (work, stiffness, force, energy storage, dissipation) depending on varying muscle fibre-tendon length ratio were provided, which enables classification and grading of different MTC designs.

Movement within foot and ankle joint in children with spastic cerebral palsy: a 3-dimensional ultrasound analysis of medial gastrocnemius length with correction for effects of foot deformation

BackgroundIn spastic cerebral palsy (SCP), a limited range of motion of the foot (ROM), limits gait and other activities. Assessment of this limitation of ROM and knowledge of active mechanisms is of crucial importance for clinical treatment.MethodsFor a comparison between spastic cerebral palsy (SCP) children and typically developing children (TD), medial gastrocnemius muscle-tendon complex length was assessed using 3-D ultrasound imaging techniques, while exerting externally standardized moments via a hand-held dynamometer. Exemplary X-ray imaging of ankle and foot was used to confirm possible TD-SCP differences in foot deformation.ResultsSCP and TD did not differ in normalized level of excitation (EMG) of muscles studied. For given moments exerted in SCP, foot plate angles were all more towards plantar flexion than in TD. However, foot plate angle proved to be an invalid estimator of talocrural joint angle, since at equal foot plate angles, GM muscle-tendon complex was shorter in SCP (corresponding to an equivalent of 1 cm). A substantial difference remained even after normalizing for individual differences in tibia length. X-ray imaging of ankle and foot of one SCP child and two typically developed adults, confirmed that in SCP that of total footplate angle changes (0-4 Nm: 15°), the contribution of foot deformation to changes in foot plate angle (8) were as big as the contribution of dorsal flexion at the talocrural joint (7°). In typically developed individuals there were relatively smaller contributions (10 -11%) by foot deformation to changes in foot plate angle, indicating that the contribution of talocrural angle changes was most important.Using a new estimate for position at the talocrural joint (the difference between GM muscle–tendon complex length and tibia length, GM relative length) removed this effect, thus allowing more fair comparison of SCP and TD data. On the basis of analysis of foot plate angle and GM relative length as a function of externally applied moments, it is concluded that foot plate angle measurements underestimate angular changes at the talocrural joint when moving in dorsal flexion direction and overestimate them when moving in plantar flexion direction, with concomitant effects on triceps surae lengths.ConclusionsIn SCP children diagnosed with decreased dorsal ROM of the ankle joint, the commonly used measure (i.e. range of foot plate angle), is not a good estimate of rotation at the talocrural joint. since a sizable part of the movement of the foot (or foot plate) derives from internal deformation of the foot.

Magnetic Resonance Imaging Assessment of Mechanical Interactions Between Human Lower Leg Muscles in Vivo

Evidence on epimuscular myofascial force transmission (EMFT) was shown for undissected muscle in situ. We hypothesize that global length changes of gastrocnemius muscle-tendon complex in vivo will cause sizable and heterogeneous local strains within all muscles of the human lower leg. Our goal is to test this hypothesis. A method was developed and validated using high-resolution 3D magnetic resonance image sets and Demons nonrigid registration algorithm for performing large deformation analyses. Calculation of strain tensors per voxel in human muscles in vivo allowed quantifying local heterogeneous tissue deformations and volume changes. After hip and knee movement (Δ knee angle ≈ 25 deg) but without any ankle movement, local lengthening within m. gastrocnemius was shown to occur simultaneously with local shortening (maximally by +34.2% and -32.6%, respectively) at different locations. Moreover, similar local strains occur also within other muscles, despite being kept at constant muscle-tendon complex length. This is shown for synergistic m. soleus and deep flexors, as well as for antagonistic anterior crural and peroneal muscle groups: minimum peak lengthening and shortening equaled 23.3% and 25.54%, respectively despite global isometric conditions. These findings confirm our hypothesis and show that in vivo, muscles are in principle not independent mechanically.

ELECTRO-MECHANICAL DELAY IN HILL-TYPE MUSCLE MODELS

In this study, we investigated to which extent Hill-type muscle models can explain the electro-mechanical delay (EMD). The EMD is a phenomenon that has been well examined in muscle experiments. The EMD is the time lag between a change in muscle stimulation and the subsequent measurable change in muscle force. A variety of processes as, e.g., signal conduction and interaction of contractile and elastic muscle structures contribute to the EMD. The relative contributions of the particular processes have not been fully unveiled so far. Thereto, we simulated isometric muscle contractions using two Hill-type muscle models. Their parameters were extracted from experiments on the cat soleus muscle. In agreement with literature data, predicted EMD values depend on muscle-tendon complex (MTC) length and increase when reducing MTC lengths. The highest EMD values (28 and 27 ms) occur at the lowest MTC length examined (78% of optimal length). Above optimal MTC length, we find EMD saturation (2 ms) in one model. In the other model, the EMD slightly re-increases up to 9 ms at the highest length examined (113% of optimal length). The EMD values predicted by the two models were then compared to EMD values found in the same experiments from which the muscle parameters were extracted. At optimal MTC length, the EMD values, mapping ion release and visco-elastic interactions, predicted by both models (3.5 and 5.5 ms) just partly account for the measured value (15.8 ms). The biggest share (about 9 ms) of the remaining 11 ms can be attributed to signal conduction along the nerve and on the muscle surface. Further potential sources of delayed force generation are discussed.

Control of position and movement is simplified by combined muscle spindle and Golgi tendon organ feedback

Whereas muscle spindles play a prominent role in current theories of human motor control, Golgi tendon organs (GTO) and their associated tendons are often neglected. This is surprising since there is ample evidence that both tendons and GTOs contribute importantly to neuromusculoskeletal dynamics. Using detailed musculoskeletal models, we provide evidence that simple feedback using muscle spindles alone results in very poor control of joint position and movement since muscle spindles cannot sense changes in tendon length that occur with changes in muscle force. We propose that a combination of spindle and GTO afferents can provide an estimate of muscle-tendon complex length, which can be effectively used for low-level feedback during both postural and movement tasks. The feasibility of the proposed scheme was tested using detailed musculoskeletal models of the human arm. Responses to transient and static perturbations were simulated using a 1-degree-of-freedom (DOF) model of the arm and showed that the combined feedback enabled the system to respond faster, reach steady state faster, and achieve smaller static position errors. Finally, we incorporated the proposed scheme in an optimally controlled 2-DOF model of the arm for fast point-to-point shoulder and elbow movements. Simulations showed that the proposed feedback could be easily incorporated in the optimal control framework without complicating the computation of the optimal control solution, yet greatly enhancing the system's response to perturbations. The theoretical analyses in this study might furthermore provide insight about the strong physiological couplings found between muscle spindle and GTO afferents in the human nervous system.

Effects of knee joint angle on global and local strains within human triceps surae muscle: MRI analysis indicating in vivo myofascial force transmission between synergistic muscles

PurposeMechanical interactions between muscles have been shown for in situ conditions. In vivo data for humans is unavailable. Global and local length changes of calf muscles were studied to test the hypothesis that local strains may occur also within muscle for which global strain equals zero.MethodsFor determination of globally induced strain in m. gastrocnemius in dissected human cadavers several knee joint angles were imposed, while keeping ankle joint angle constant and measuring its muscle–tendon complex length changes. In vivo local strains in both gastrocnemius and soleus muscles were calculated using MRI techniques in healthy human volunteers comparing images taken at static knee angles of 173° and 150°.ResultsImposed global strains on gastrocnemius were much smaller than local strains. High distributions of strains were encountered, e.g. overall lengthened muscle contains locally lengthened, as well as shortened areas within it. Substantial strains were not limited to gastrocnemius, but were found also in synergistic soleus muscle, despite the latter muscle–tendon complex length remaining isometric (constant ankle angle: i.e. global strain = 0), as it does not cross the knee. Based on results of animal experiments this effect is ascribed to myofascial connections between these synergistic muscles. The most likely pathway is the neurovascular tract within the anterior crural compartment (i.e. the collagen reinforcements of blood vessels, lymphatics and nerves). However, direct intermuscular transmission of force may also occur via the perimysium shared between the two muscles.ConclusionsGlobal strains imposed on muscle (joint movement) are not good estimators of in vivo local strains within it: differing in magnitude, as well as direction of length change. Substantial mechanical interaction occurs between calf muscles, which is mediated by myofascial force transmission between these synergistic muscles. This confirms conclusions of previous in situ studies in experimental animals and human patients, for in vivo conditions in healthy human subjects.

Changes in joint angle, muscle‐tendon complex length, muscle contractile tissue displacement, and modulation of EMG activity during acute whole‐body vibration

It has been suggested that vibration causes small changes in muscle length, but to the best of our knowledge, these have yet to be demonstrated during whole-body vibration (WBV). This was an observational study to determine whether acute WBV would result in muscle lengthening. We hypothesized that acute WBV would increase electromyography (EMG) activity concurrently with measurable changes in muscle contractile length. Nine healthy males performed two conditions on a Galileo vibration machine for 15 s at 0 HZ (resting) and 6 HZ at a set knee angle of 18 degrees. Muscle tendon complex length, contractile tissue displacement of the medial gastrocnemius muscle, and EMG of soleus, tibialis anterior, and vastus lateralis muscles were measured. At 6 HZ the medial gastrocnemius (MG) muscle tendon complex (MTC) amplitude (375 microm) was significantly greater (P < 0.05) compared to 0 HZ (35 microm). The MG contractile length (CD) amplitude at 6 HZ (176 microm) was significantly greater (P < 0.01) compared to 0 HZ (4 microm). Significant increases (P < 0.05) in EMG modulation were found for all muscles during the 6 HZ compared to the 0 HZ condition. The major finding was that approximately 50% of the elongation occurred within the muscle itself and was associated with preceding changes in EMG. This indicates muscle lengthening may be a prerequisite for eliciting stretch reflexes. In conclusion, there is a temporal association between EMG activity and muscle contractile tissue displacement where low-frequency WBV results in small muscle length changes and increases muscle activation.

Vastus Lateralis Fascicle, Muscle-tendon Complex, And Tendon Length During Three Resistance Training Exercises

Vastus Lateralis Fascicle, Muscle-tendon Complex, And Tendon Length During Three Resistance Training Exercises

하지 근골격계질환 평가를 위한 삼차원 근.건모델의 임상적용

Kinematic analysis of MTC (Muscle-Tendon Complex) units is a key indicator for diagnosis of patients with musculoskeletal disorders because the contracture or shortening of musculo-tendinous units is known to produce pathological gaits. Therefore, the principal objective of this study was to assess the length change in the triceps surae prior to and after wearing an AFO (Ankle-Foot Orthoses) in patients with musculoskeletal disorders during a gait. In this study, analyses were conducted using a Muscle Tendon Complex model coupled with the trajectory data from markers attached to anatomical landmarks. As a result, the maximum length change in the triceps surae during a gait was 4.87% when a barefoot walking group and a walking group with AFO were compared. In particular, the difference in length changes between both groups in Soleus MTC units was found to be statistically significant in all gait phases. Our results revealed that MTC length in the AFO walking group was clearly increased over that of the barefoot walking group. In the future, further studies will be required in order to more adequately assess musculoskeletal disorders using many cases studies with regard to agricultural working conditions because this study deals with the kinematic analysis of musculo-tendinous units in the case of clinical experiments.

Effect of the Different Hip Joint Angle Definition on the Estimation of Muscle-Tendon Complex Length of the Hip Extensor Muscles in Counter Movement Jump

The purpose of this study was to consider the discrepancy between the trunk-based and the pelvis-based hip joint angles, and the difference between the MTC lengths estimated on the basis of the two types of hip joint angles during dynamic movement. Ten male athletes performed CMJ. Joint kinematics and the MTC length of long head of biceps femoris were compared between the trunk-based hip angle and the pelvis-based hip angle. In the CMJ, the angular displacements of the trunk-based were significantly higher than that of pelvis-based hip joints. There were no significant correlations between the two types of hip joint angles except at initial position. As for long head of biceps femoris, in contrast with the trunk-based-hip joint angle derived MTC length, which shows stretching in the descending phase and shortening in the ascending phase, the pelvis-based hip joint angle derived MTC length shows little changes. These results suggest that the trunk-based and pelvis-based hip joint angles have similar patterns of fluctuation; however, the angular displacement of each type is not equivalent. These results also suggest that we may misinterpret the type of muscle contraction because the definitions of hip joint angle are different even for the same muscle type.

Vastus Lateralis Fascicle Length Changes During Stair Ascent and Descent

Experimental descriptive laboratory study. To describe the change in fascicle length of the human vastus lateralis (VL) muscle during the stance phase of stair ascent and descent. Muscle fascicle length changes during lower limb functional activities, such as walking and jumping, do not always coincide with joint angle changes. Thirty-three healthy, college-age women walked up and down 4 standard steps. VL fascicle length and pennation angle were measured using real-time ultrasonography. Knee angle was monitored using an electrical goniometer. Foot switches indicated foot contact and release. VL muscle activity was monitored using surface electrodes. The VL muscle-tendon complex and tendon length were calculated based on published models. During initial weight acceptance in stair ascent, the knee joint extended only 3 degrees , VL muscle activity increased to a maximum, VL fascicles shortened, and the tendon lengthened. As the knee extended to ascend the step, the fascicles and tendon shortened throughout the movement. During weight acceptance in stair descent, VL muscle activity increased, VL fascicle length did not change significantly, but the tendon lengthened as 10 degrees of knee flexion occurred. As the knee flexed to complete descent, VL muscle activity peaked, and VL fascicles and tendon lengthened. VL fascicles shorten and lengthen as expected during the respective knee extension and knee flexion phases of stair ascent and descent. However, during initial weight acceptance in both stair ascent and descent, the fascicle length change did not coincide with the knee joint kinematics.

Gastrocnemius Injury during Running: A Case Report

Incidence rate of running related injuries is high but forces acting on the body during injury are hardly known. During a data collection session in the investigator's laboratory, one subject sustained a medial gastrocnemius muscle strain injury while running across a force platform. This case report aimed to investigate the causes of this acute running injury by comparing the running speed, external forces, joint kinetics and kinematics, and muscle-tendon complex length of the injured trial to five preceding noninjured trials. The injured trial was characterized by faster running speed, higher external loading rate, increased muscle-tendon complex length and shortening rate, and indifferent patterns in ground reaction forces, joint angles, moments and powers. Both kinetic and kinematic data suggest that the injury occurred during the early stance phase, which is in agreement with the subject's description. These data are unique and invaluable to the understanding of internal and external loads during acute traumatic running injuries. The findings suggest that the injury occurred soon after touchdown and may be caused by a faster than usual running speed and inappropriate body posture at touchdown, which lead to altered muscle length and actions to attenuate impact shock.

Effects of firing frequency on length-dependent myofascial force transmission between antagonistic and synergistic muscle groups

Effects of stimulation frequency on myofascial force transmission between rat peroneal and triceps surae and antagonistic anterior crural muscles, and between extensor digitorum longus (EDL) and tibialis anterior and extensor hallucis longus (TA + EHL) muscles were investigated for lengthening of all anterior crural muscles. Muscles contracted isometrically at firing rates of 10, 20, 30 and 100 Hz. EDL and TA + EHL were distally lengthened. Peroneal and triceps surae muscles attained a constant muscle-tendon complex length. Peroneal and triceps surae distal active force decreased significantly as a function of anterior crural muscle length, also at submaximal activation. The absolute decrease was highest for 100 Hz (peroneal muscles -0.87 N; triceps surae muscles -0.92 N), but the highest normalized decrease occurred at 10 Hz stimulation (peroneal muscles -34%; triceps surae muscles -18%). At all muscle lengths, a negative proximo-distal difference in EDL active force was present which decreased with lower firing frequencies (from -0.4 N at 100 Hz to -0.03 N at 10 Hz). The passive proximo-distal force difference attained positive values. EDL and TA + EHL length-force characteristics agree with effects of firing frequency, except for 10 Hz stimulation, where active force was higher than expected and optimum length shifted to lower muscle lengths. It is concluded that also at submaximal stimulation frequencies, extramuscular myofascial force transmission between peroneal and triceps surae muscles and antagonistic anterior crural muscles is substantial. Although lengthening of submaximally active anterior crural muscles decreases the net myofascially transmitted load on EDL, myofascial force transmission significantly alters effects of firing frequency on length-force characteristics.

Myofascial force transmission is increasingly important at lower forces: firing frequency‐related length–force characteristics of rat extensor digitorum longus

Effects of submaximal stimulation frequencies on myofascial force transmission were investigated for rat anterior crural muscles with all motor units activated. Tibialis anterior and extensor hallucis longus (TAEHL) muscles were kept at constant muscle-tendon complex length, but extensor digitorum longus muscle (EDL) was lengthened distally. All muscles were activated simultaneously at 10, 20, 30 and 100 Hz within an intact anterior crural compartment. At lower frequencies, significant proximo-distal EDL force differences exist. Absolute EDL proximo-distal active force differences were highest at 100 Hz (deltaF(dist-prox) = 0.4 N). However, the normalized difference was highest at 10 Hz (deltaF(dist-prox) = 30%F(dist)). Firing-frequency dependent shifts of the ascending limb of the EDL length-force curve to higher lengths were confirmed for a muscle within an intact compartment, although effects of firing frequency assessed at proximal and distal EDL tendons differed quantitatively. As EDL was lengthened distally, TAEHL distal isometric active force decreased progressively. The absolute decrease was highest for 100 Hz (deltaF(from initial) = -0.25 N). However, the highest normalized decrease was found for 10 Hz stimulation (deltaF(from initial) = -40%). At submaximal stimulation frequencies, myofascial force transmission is present and the fraction of force transmitted myofascially increases with progressively lower firing frequencies. Evidently, the stiffness of epimuscular myofascial paths of force transmission decreases less than the stiffness of serial sarcomeres and myotendinous pathways. It is concluded that low firing frequencies as encountered in vivo enhance the relative importance of epimuscular myofascial force transmission with respect to myotendinous force transmission.

Intermuscular Interaction between Synergists in Rat Originates from both Intermuscular and Extramuscular Myofascial Force Transmission

The purpose of the present study is to investigate the origin of mechanical interactions between the rat extensor digitorum longus (EDL) muscle and the grouped tibialis anterior and extensor hallucis longus muscles (TA+EHL). The proximal and distal tendons of EDL as well as the tied distal tendons of TA+EHL were transected and connected to force transducers. Connective tissues at the muscle bellies of the anterior crural compartment were left intact. Supramaximal stimulation of the common peroneal nerve activated all muscles maximally and simultaneously. Length-isometric force characteristics of distal TA+EHL were assessed. Simultaneously, forces exerted at the proximal and distal tendons of EDL, kept at constant muscle-tendon complex length and position, were measured. Intermuscular interaction was tested in two conditions: (a) after full longitudinal compartmental fasciotomy, and (b) after blunt dissection of the intermuscular connective tissue linkages between EDL and TA+EHL. Note that in the latter condition, intermuscular myofascial pathways were eliminated. In the initial condition, lengthening TA+EHL by 12 mm increased proximal (by 0.14 N, i.e. 9.5%) and decreased distal EDL force (by 0.21 N, i.e. 11.8%), despite the fact that EDL muscle-tendon complex length was kept constant. Blunt dissection decreased TA+EHL and distal EDL forces at low TA+EHL lengths only, while proximal EDL force decreased for all TA+EHL lengths tested. The dissection caused no changes in the TA+EHL length effects on proximal EDL force. In contrast, the amplitude of change in the distal EDL force curve decreased significantly (by 39%) subsequent to blunt dissection. It is concluded that mechanical interaction between synergists originates from both intermuscular as well as extramuscular connective tissues. The highest contribution, however, should be ascribed to the extramuscular pathway.

Estimation of Passive Ankle Joint Moment during Standing and Walking

This study estimated the passive ankle joint moment during standing and walking initiation and its contribution to total ankle joint moment during that time. The decrement of passive joint moment due to muscle fascicle shortening upon contraction was taken into account. Muscle fascicle length in the medial gastrocnemius, which was assumed to represent muscle fascicle length in plantarflexors, was measured using ultrasonography during standing, walking initiation, and cyclical slow passive ankle joint motion. Total ankle joint moment during standing and walking initiation was calculated from ground reaction forces and joint kinematics. Passive ankle joint moment during the cyclical ankle joint motion was measured via a dynamometer. Passive ankle joint moment during standing and at the time (Tp) when the MG muscle-tendon complex length was longest in the stance phase during walking initiation were 2.3 and 5.4 Nm, respectively. The muscle fascicle shortened by 2.9 mm during standing compared with the length at rest, which decreased the contribution of passive joint moment from 19.9% to 17.4%. The muscle fascicle shortened by 4.3 mm at Tp compared with the length at rest, which decreased the contribution of passive joint moment from 8.0% to 5.8%. These findings suggest that (a) passive ankle joint moment plays an important role during standing and walking initiation even in view of the decrement of passive joint moment due to muscle fascicle shortening upon muscle contraction, and (b) muscle fascicle shortening upon muscle contraction must be taken into account when estimating passive joint moment during movements.

In Vivo Length-Force Relationships on Muscle Fiber and Muscle Tendon Complex in the Tibialis Anterior Muscle

The present study aimed to determine the differences in the length-force relationship between muscle fiber and muscle tendon complex (MTC) and to relate the shape of the length-force relationship to the architectural changes in MTC (the elongation of tendon structures and pennation angle changes). In six male subjects, tetanic contractions (2s at 50Hz) of the tibialis anterior muscle were induced electrically. At a steady state of tetanic contraction, the muscle fiber length and pennation angle were measured from ultrasonic images, and the muscle fiber force, tendon force, MTC length and elongation of tendon structures were calculated. The measured and normalized length-force relationships were clearly different between muscle fiber and MTC, especially on the length axis. The differences could be attributed to the existence of compliant tendon structures and increment of pennation angles related to elongation of tendon structures, suggesting that compliant tendon structures in human muscles influence the length-dependent force generation in both muscle fiber and MTC.