Muscle-tendon Architecture Research Articles

Longitudinal changes in Achilles tendon and triceps surae muscle architecture during a 156-km mountain ultramarathon.

This study aimed to assess the longitudinal changes in triceps surae muscle-tendon architecture during a mountain ultramarathon. Experienced trail runners [n = 55, 78% men, age: 45.2 (13.5) yr] participated in a 156-km trail run (6,000 m climbing) consisting of six 26-km laps. The resting architectural properties of triceps surae muscle-tendon were measured using ultrasound imaging for Achilles tendon cross-sectional area (AT CSA), medial gastrocnemius muscle pennation angle, thickness, length, and fiber length. Measurements were performed the day before the race (baseline), at 52 km (T1), at 104 km (T2), at 156 km (T3), and 12 h after the race (H12). Among finishers (n = 41), there was a significant biphasic change in AT CSA during the race (P = 0.001). First, a significant decrease in AT CSA occurred between baseline and T1 (P = 0.006), with a greater decrease for participants averaging speed >8 km/h (P = 0.014). Second, there was a significant increase in AT CSA especially between T2 and T3 (P = 0.006) that was correlated with a decrease in average speed (P = 0.001) and alteration of spaciotemporal running parameters (P < 0.05). Changes in muscle-tendon architecture were not significantly different between finishers (n = 41) and nonfinishers (n = 14). In 47 participants (85.5%) who completed the follow-up, AT CSA at H12 was greater compared with baseline (P = 0.010). The main finding is the significant and biphasic modification of the AT CSA during a 156-km mountain ultramarathon with an initial decrease corresponding to mechanical stress followed by a secondary increase suggesting adaptive mechanotransduction persisting after 12 h.NEW & NOTEWORTHY Achilles tendon cross-sectional area (AT CSA) demonstrated significant adaptive modifications during a 156 km mountain ultramarathon in trained athletes. Initially, a decrease in AT CSA, especially at higher running speeds, is consecutive to the biomechanical stress on the plantar flexor muscle-tendon unit (MTU). Subsequently, there is a significant increase in AT CSA persisting up to 12 h after the race, which likely corresponds to an adaptive process to limit the compressive and tensile load on the tendon.

ArborSim: Articulated, branching, OpenSim routing for constructing models of multi-jointed appendages with complex muscle-tendon architecture.

Computational models of musculoskeletal systems are essential tools for understanding how muscles, tendons, bones, and actuation signals generate motion. In particular, the OpenSim family of models has facilitated a wide range of studies on diverse human motions, clinical studies of gait, and even non-human locomotion. However, biological structures with many joints, such as fingers, necks, tails, and spines, have been a longstanding challenge to the OpenSim modeling community, especially because these structures comprise numerous bones and are frequently actuated by extrinsic muscles that span multiple joints-often more than three-and act through a complex network of branching tendons. Existing model building software, typically optimized for limb structures, makes it difficult to build OpenSim models that accurately reflect these intricacies. Here, we introduce ArborSim, customized software that efficiently creates musculoskeletal models of highly jointed structures and can build branched muscle-tendon architectures. We used ArborSim to construct toy models of articulated structures to determine which morphological features make a structure most sensitive to branching. By comparing the joint kinematics of models constructed with branched and parallel muscle-tendon units, we found that among various parameters-the number of tendon branches, the number of joints between branches, and the ratio of muscle fiber length to muscle tendon unit length-the number of tendon branches and the number of joints between branches are most sensitive to branching modeling method. Notably, the differences between these models showed no predictable pattern with increased complexity. As the proportion of muscle increased, the kinematic differences between branched and parallel models units also increased. Our findings suggest that stress and strain interactions between distal tendon branches and proximal tendon and muscle greatly affect the overall kinematics of a musculoskeletal system. By incorporating complex muscle-tendon branching into OpenSim models using ArborSim, we can gain deeper insight into the interactions between the axial and appendicular skeleton, model the evolution and function of diverse animal tails, and understand the mechanics of more complex motions and tasks.

Intermuscular differences in force generation ability among biarticular hamstring muscles during the late swing phase in maximal speed sprinting

ABSTRACT We aimed to investigate how intermuscular muscle-tendon architectural differences among biarticular hamstring muscles (biceps femoris long head [BFlh], semimembranosus [SM] and semitendinosus [ST]) influence intermuscular differences in muscle force during the late swing phase in maximal speed sprinting. Using a musculoskeletal model, we estimated the muscle-tendon kinematics, muscle force，and force generation ability, defined by force-length-velocity properties and pennation angle, of the biarticular hamstring muscles in 40 male athletes during the late swing phase. SM force generation ability was smaller during the first half of the late swing phase and larger during the second half than the BFlh and ST. The intermuscular differences in force generation ability were caused by the intermuscular differences in time-varying muscle-tendon unit, muscle fibre and tendon lengths, which might be affected by the muscle-tendon architecture of this model, particularly optimal muscle fibre length, tendon slack length and insertion location. Moreover, the peak muscle force was achieved earlier in the BFlh and ST than in the SM. These findings suggest that intermuscular differences in muscle-tendon architecture among the biarticular hamstring muscles can induce intermuscular differences in time-varying muscle force by influencing time-varying force generation ability and muscle-tendon kinematics during the late swing phase.

Is the muscle–tendon architecture of non-athletic Kenyans different from that of Japanese and French males?

BackgroundIn endurance running, elite Kenyan runners are characterized by longer thigh, shank, and Achilles tendon (AT) lengths combined with shorter fascicles and larger medial gastrocnemius (MG) pennation angles than elite Japanese runners. These muscle-tendon characteristics may contribute to the running performance of Kenyans. Furthermore, these specific lower-leg musculoskeletal architectures have been confirmed not only in elite Kenyan runners but also in non-athletic Kenyans since early childhood. However, it remains questionable whether the differences in muscle-tendon architecture between Kenyans and Japanese differ from those of European Caucasians. Therefore, this study aimed to compare anthropometry and muscle–tendon architecture of young non-athletic Kenyan males with their Japanese and French counterparts.MethodsA total of 235 young non-athletic males, aged 17–22 years, volunteered. The anthropometric measures, thigh, and shank lengths, as well as AT and MG muscle architecture, were measured using ultrasonography and a tape measure. Inter-group differences in anthropometry and muscle-tendon architecture were tested using one-way ANOVA and ANCOVA analyses controlling for shank length and muscle thickness.ResultsThe anthropometric and muscle-tendon characteristics of the non-athletic French were closer to those of the Kenyans than to those of the Japanese. However, the ultrasonography analysis confirmed that the non-athletic Kenyans had the longest AT as well as the shortest MG fascicles and the largest pennation angle compared to the French and Japanese, even after controlling for shank length and muscle thickness with ANCOVA, respectively.ConclusionsThese results confirmed the specificity of the muscle-tendon architecture of the triceps surae in Kenyans in comparison to their Japanese and French counterparts in non-athletic adults. This study provides additional support to the fact that Kenyans may have musculotendinous advantages in endurance running.

Comparative Anatomical Studies on the Hand of Human and Two Mammalian Species

Background: Morphologically there is a great similarity in the musculoskeletal pattern in different species of the primates especially the development of hands and digits for better functional adaptation to their environment. The factors involved in evolution of modern hand are muscle-tendon architecture, shape, size of bones and articular surfaces in joints. Human hand is functionally highly evolved with manipulative potential for fast and fine skilled activity especially in thumb and index finger as compared with other species.&#x0D; Aim: Present study was undertaken to compare the hand anatomy of the Baboon and Squirrel with the Human.&#x0D; Methods: Two commonly found mammals in Saudi Arabia i.e. Baboon and Squirrel were selected to reflect the different environmental adaptations. The human hands were provided by the Department of Anatomy. The animals were anesthetized, sacrificed at Anesthesia Department. Fixation done by 9% formaldehyde solution, hands dissected under Zeiss dissecting microscope, Muscle groups identified using 5% iodine stain, Bones and cartilages stained by Alizarin red and Alcian blue stain respectively and photographed (Nikon D3200 digital camera). The hand divided into four parts: Wrist, dorsum of hand, palm and fingers.&#x0D; Results: Human Hand: Wrist is wide, bones arranged in two rows gliding over each other for free movements at hand. Dorsum has thin fatty layer, more wrinkles and fewer hairs. Palm has thick skin without hair and well-developed muscles are arranged in groups (Thenar, Hypothenar, Lumbricals and Interossei). Digits have extensor and flexor tendons up to middle and distal phalanx. Thumb is rotated providing opposition and multiaxial movements.&#x0D; Baboon Hand: Wrist is short, bones arranged in two rows but fewer movements at hand. Dorsum has fewer wrinkles, more hairs. Palm skin has very thick layer, especially at friction pad located below fingers; muscles are arranged in groups but not fully developed as compared to human.&#x0D; Squirrel Hand: Small and close dimensions, five short fingers, pointed, every finger ends with a claw. The skin is thin, covered with hair. Palm is thin but completely free of hair with digital pad. Phalanges are short and all fingers have two phalanges. Thumb has only one phalanx.&#x0D; Conclusions: Human hand structure is evolved for better grip and fine movements of hand providing better functional and artistic capabilities.

Muscle-tendon architecture in Kenyans and Japanese: Potential role of genetic endowment in the success of elite Kenyan endurance runners.

The specificity of muscle-tendon and foot architecture of elite Kenyan middle- and long-distance runners has been found to contribute to their superior running performance. To investigate the respective influence of genetic endowment and training on these characteristics, we compared leg and foot segmental lengths as well as muscle-tendon architecture of Kenyans and Japanese males (i) from infancy to adulthood and (ii) non-athletes versus elite runners. The 676 participants were divided according to their nationality (Kenyans and Japanese), age (nine different age groups for non-athletes) and performance level in middle- and long-distance races (non-athlete, non-elite and elite adult runners). Shank and Achilles tendon (AT) lengths, medial gastrocnemius (MG) fascicle length, pennation angle and muscle thickness, AT moment arm (MAAT ), and foot lever ratio were measured. Above 8years old, Kenyans had a longer shank and AT, shorter fascicle, greater pennation angle, thinner MG muscle as well as longer MAAT , with lower foot lever ratio than age-matched Japanese. Among adults of different performance levels and independently of the performance level, Kenyans had longer shank, AT and MAAT , thinner MG muscle thickness, and lower foot lever ratio than Japanese. The decrease in MG fascicle length and increase pennation angle observed for the adult Japanese with the increase in performance level resulted in a lack of difference between elite Kenyans and Japanese. The specificity of muscle-tendon and foot architecture of elite Kenyan runners could result from genetic endowment and contribute to the dominance of Kenyans in middle- and long-distance races.

Muscle architecture and passive lengthening properties of the gastrocnemius medialis and Achilles tendon in children who idiopathically toe-walk.

Children who idiopathically toe‐walk (ITW) habitually operate at greater plantarflexion angles and thus, at shorter muscle‐tendon unit (MTU) lengths than typically developing (TD) children. Therefore, it is often assumed that habitual use of the gastrocnemius muscle in this way will cause remodelling of the muscle‐tendon architecture compared to TD children. However, the gastrocnemius muscle architecture of children who ITW has never been measured. It is essential that we gain a better understanding of these muscle‐tendon properties, to ensure that appropriate clinical interventions can be provided for these children. Five children who ITW (age 8 ± 2 years) and 14 TD children (age 10 ± 2 years) participated in this study. Ultrasound was combined with isokinetic dynamometry and surface electromyography, to measure muscle architecture at common positions and passive lengthening properties of the gastrocnemius muscle and tendon across full range of motion. Regardless of which common condition groups were compared under, both the absolute and normalised to MTU muscle belly and fascicle lengths were always longer, and the Achilles tendon length was always shorter in children who ITW than TD children (p < 0.05; large effect sizes). The passive lengthening properties of the muscle and tendon were not different between groups (p > 0.05); however, passive joint stiffness was greater in children who ITW at maximum dorsiflexion (p = 0.001) and at a joint moment common to all participants (p = 0.029). Consequently, the findings of this pilot study indicate a remodelling of the relative MTU that does not support the concept that children who ITW commonly experience muscle shortening. Therefore, greater consideration of the muscle and tendon properties are required when prescribing clinical interventions that aim to lengthen the MTU, and treatments may be better targeted at the Achilles tendon in children who ITW.

Does Muscle-Tendon Unit Structure Predispose to Hamstring Strain Injury During Running? A Critical Review.

Hamstring strain injury (HSI) remains the most common muscle injury in high-intensity running in humans. The majority of acute HSI occur specifically within the proximal region of the long head of biceps femoris and there is a sustained interest among researchers in understanding the factors that predispose to HSI. The present critical review describes the current understanding of biceps femoris long head (BFlh) structural features that might influence strain injury risk. Inter-individual differences in muscle-tendon architecture and interactions, muscle fiber type and region-specific innervation are likely to influence biceps femoris long head injury risk and might inform why some individuals are at an increased risk of sustaining a HSI during running. However, more research is needed, with future studies focusing on prospective data acquisition, improved computer simulations and direct imaging techniques to better understand the relationship between structural features, hamstring muscle function, and injury risk.

The comparative and functional anatomy of appendicular musculature of Humboldt’s woolly monkey (Lagothrix lagotricha): What can a (mediocre) suspensory monkey tell us about and human locomotor evolution?

Similar to other members of the platyrrhine subfamily Atelinae, Humboldt’s wooly monkey (Lagothrix lagotricha) isa ‘tail‐assisted’ brachiator that more frequently engages in non‐suspensory forms of locomotion (i.e. quadrupedal climbing). As a group the atelines share a suite of derived forelimb skeletal characters that are specialized for brachiation and that are convergent with ‘richochetal’ brachiating apes (Hylobates, Symphalangus), quadrumanus suspensory apes (Pongo) and secondarily terrestrial apes retaining suspensory capabilities (Pan, Gorilla). The skeletal anatomy of lagothrix is similar to more suspensory atelines (Ateles, Brachyteles) and living apes, but is typically less derived for suspension and many skeletal characters are intermediate between highly suspensory and non‐suspensory anthropoids. While the functional morphology of the ateline skeleton is well documented, relatively little is known about the comparative and functional morphology of the forelimb and hindlimb musculature. Specifically, can locomotor differences between Lagothrix and more suspensory atelines and hylobatids be explained, in part, as a result of differences in muscletendon architecture?This study describes preliminary quantitative data on the muscle–tendon architecture (relative muscle mass and relative physiological cross‐sectional area or PCSA) of the fore‐ and hind‐limbs of Lagothrix lagotricha and Macacasp. (n=9). Despite infrequent brachiation, Lagothrix forelimb relative muscle mass and PCSA is identical to similar results reported for hominoids. In contrast, the relative mass and PCSA of the hind‐limb musculature is most similar to quadrupedal monkeys (i.e. Macaca). Specifically, Lagothrix resembles hylobatids in the concentration of muscle mass and force in the flexor compartments of the arm and forearm but is more similar to Macaca in similar measures associated with the extensor and flexor thigh and leg. This suggests that despite a reduced reliance on suspensory postures and brachiation, Lagothrix forelimb muscle‐tendon architecture may be, at least in part, a response to the minimum functional demands of brachiation but that similar selection pressures are not as prevalent in the hind‐limb.

Morphological and functional outcomes of operatively treated Achilles tendon ruptures

ABSTRACT Objectives: Achilles tendon rupture leads to functional impairments and these may be underpinned by morphological changes in the muscle-tendon unit. The functional performance of the injured limb will be impaired regardless of time since surgery and these impairments occur alongside changes in muscle-tendon morphology. Methods: Following operative treatment of Achilles tendon rupture and short-term immobilization, 12 patients completed a battery of tests during a single visit to the laboratory (performed an average of 4.4 ± 2.6 years post-surgery). Patients completed the Achilles’ tendon rupture score (ATRS), tests of the ankle and hip range of motion (ROM) and ultrasound measurements of muscle-tendon architecture. Data on isokinetic (30°/s, 60°/s) plantar flexion strength, jumping performance and walking-running were also collected on the same visit. Percentage deficits were expressed relative to the non-injured limb and determined for statistical significance (p < 0.05). Relationships between outcome measures and time since surgery were tested using Pearson’s correlation coefficients (p < 0.05). Results: The repaired limb showed a shorter muscle fascicle length (12.1–19.6%), increased fascicle pennation (18.0 ± 22.14%) and reduced muscle thickness (9.1–20.1%) in the gastrocnemius and/or soleus along with greater tendon cross-sectional area (46.7 ± 34.47%). Functionally, the repaired limb displayed lower countermovement jump height (−12.6 ± 15.68%) and longer drop jump contact times (5.5 ± 5.7%). Also, the repaired limb showed reduced hip internal-external ROM (6.3 ± 8.2%) but no differences existed between limbs for plantar flexion ROM and strength or gait characteristics. Good ATRS outcomes were reported (mean: 87.9 ± 16.2, range: 43–100) which related to time since surgery (r = 0.79) but individual ATRS items did not correlate with corresponding objective measures. Conclusion: Plantar flexor atrophy following surgically treated Achilles tendon rupture is partially compensated for by remodeling of the fascicles; however, impairments may still persist many years into the postoperative period although these may be more pronounced in high-velocity activities.

Muscle-specific indices to characterise the functional behaviour of human lower-limb muscles during locomotion

The mechanical output of a muscle may be characterised by having distinct functional behaviours, which can shift to satisfy the varying demands of movement, and may vary relative to a proximo-distal gradient in the muscle-tendon architecture (MTU) among lower-limb muscles in humans and other terrestrial vertebrates. We adapted a previous joint-level approach to develop a muscle-specific index-based approach to characterise the functional behaviours of human lower-limb muscles during movement tasks. Using muscle mechanical power and work outputs derived from experimental data and computational simulations of human walking and running, our index-based approach differentiated known distinct functional behaviours with varying mechanical demands, such as greater spring-like function during running compared with walking; with anatomical location, such as greater motor-like function in proximal compared with the distal lower-limb muscles; and with MTU architecture, such as greater strut-like muscles fibre function compared with the MTU in the ankle plantarflexors. The functional indices developed in this study provide distinct quantitative measures of muscle function in the human lower-limb muscles during dynamic movement tasks, which may be beneficial towards tuning the design and control strategies of physiologically-inspired robotic and assistive devices.

The comparative and functional anatomy of the fore‐ and hind‐limb musculature of Humboldt's woolly monkey (Lagothrix lagotricha): New insights into ape and human evolution from a (mediocre) suspensory platyrrhine

Similar to other members of the platyrrhine subfamily Atelinae, Humboldt's wooly monkey (Lagothrix lagotricha) is a ‘tail‐assisted’ brachiator that more frequently engages in non‐suspensory forms of locomotion (i.e. quadrupedal climbing). As a group the atelines share a suite of derived forelimb skeletal characters that are specialized for brachiation and that are convergent with ‘richochetal’ brachiating apes (Hylobates, Symphalangus), quadrumanus suspensory apes (Pongo) and secondarily terrestrial apes retaining suspensory capabilities (Pan, Gorilla). The skeletal anatomy of lagothrix is similar to more suspensory atelines (Ateles, Brachyteles) and living apes, but is typically less derived for suspension and many skeletal characters are intermediate between highly suspensory and non‐suspensory anthropoids. While the functional morphology of the ateline skeleton is well documented, relatively little is known about the comparative and functional morphology of the forelimb and hindlimb musculature. Specifically, can locomotor differences between Lagothrix and more suspensory atelines and hylobatids be explained, in part, as a result of differences in muscle‐tendon architecture?This study describes preliminary quantitative data on the muscle–tendon architecture (relative muscle mass and relative physiological cross‐sectional area or PCSA) of the fore‐ and hind‐limbs of Lagothrix lagotricha and Macaca sp. (n=9). Despite infrequent brachiation, Lagothrix forelimb relative muscle mass and PCSA is identical to similar results reported for hominoids. In contrast, the relative mass and PCSA of the hind‐limb musculature is most similar to quadrupedal monkeys (i.e. Macaca). Specifically, Lagothrix resembles hylobatids in the concentration of muscle mass and force in the flexor compartments of the arm and forearm but is more similar to Macaca in similar measures associated with the extensor and flexor thigh and leg. This suggests that despite a reduced reliance on suspensory postures and brachiation, Lagothrix forelimb muscle‐tendon architecture may be, at least in part, a response to the minimum functional demands of brachiation but that similar selection pressures are not as prevalent in the hind‐limb.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Differences in in vivo muscle fascicle and tendinous tissue behavior between the ankle plantarflexors during running.

The primary human ankle plantarflexors, soleus (SO), medial gastrocnemius (MG), and lateral gastrocnemius (LG) are typically regarded as synergists and play a critical role in running. However, due to differences in muscle-tendon architecture and joint articulation, the muscle fascicles and tendinous tissue of the plantarflexors may exhibit differences in their behavior and interactions during running. We combined in vivo dynamic ultrasound measurements with inverse dynamics analyses to identify and explain differences in muscle fascicle, muscle-tendon unit, and tendinous tissue behavior of the primary ankle plantarflexors across a range of steady-state running speeds. Consistent with their role as a force generator, the muscle fascicles of the uniarticular SO shortened less rapidly than the fascicles of the MG during early stance. Furthermore, the MG and LG exhibited delays in tendon recoil during the stance phase, reflecting their ability to transfer power and work between the knee and ankle via tendon stretch and storage of elastic strain energy. Our findings add to the growing body of evidence surrounding the distinct mechanistic functions of uni- and biarticular muscles during dynamic movements.

Is the soleus a sentinel muscle for impaired aerobic capacity in heart failure?

Skeletal muscle wasting is well documented in chronic heart failure (CHF). This article provides a more detailed understanding of the morphology behind this muscle wasting and the relation between muscle morphology, strength, and exercise capacity in CHF. We investigated the effect of CHF on lower limb lean mass, detailed muscle-tendon architecture of the individual triceps surae muscles (soleus (SOL), medial gastrocnemius, and lateral gastrocnemius) and how these parameters relate to exercise capacity and strength. Eleven patients with CHF and 15 age-matched controls were recruited. Lower limb lean mass was assessed by dual energy x-ray absorptiometry and the architecture of skeletal muscle and tendon properties by ultrasound. Plantarflexor strength was assessed by dynamometry. Patients with CHF exhibited approximately 25% lower combined triceps surae volume and physiological cross-sectional area (PCSA) compared with those of control subjects (P < 0.05), driven in large part by reductions in the SOL. Only the SOL volume and the SOL and medial gastrocnemius physiological cross-sectional area were statistically different between groups after normalizing to lean body mass and body surface area, respectively. Total lower limb lean mass did not differ between CHF and control subjects, further highlighting the SOL specificity of muscle wasting in CHF. Moreover, the volume of the SOL and plantarflexor strength correlated strongly with peak oxygen uptake (V˙O2peak) in patients with CHF. These findings suggest that the SOL may be a sentinel skeletal muscle in CHF and provide a rationale for including plantarflexor muscle training in CHF care.

Ultrasound Imaging of Muscle-tendon Architecture in Neurological Disease: Theoretical Basis and Clinical Applications

Advances in muscle imaging have led to an increasing number of studies relating non-invasive measurements of muscle-tendon complex architecture parameters. Ultrasonagraphy has been shown to be a feasible method to measure muscle morphological changes after neurological diseases such as stroke, cerebral palsy, and spinal cord injury, thus, may help to enhance the understanding of the mechanism underlying the impaired motor function by the muscle level as well as to evaluate the functional improvement of the affected muscle after an intervention program. Keywords: Ultrasonography, muscle architecture parameters, stroke, cerebral palsy, spinal cord injury.

Leg muscles that mediate stability: mechanics and control of two distal extensor muscles during obstacle negotiation in the guinea fowl

Here, we used an obstacle treadmill experiment to investigate the neuromuscular control of locomotion in uneven terrain. We measured in vivo function of two distal muscles of the guinea fowl, lateral gastrocnemius (LG) and digital flexor-IV (DF), during level running, and two uneven terrains, with 5 and 7 cm obstacles. Uneven terrain required one step onto an obstacle every four to five strides. We compared both perturbed and unperturbed strides in uneven terrain to level terrain. When the bird stepped onto an obstacle, the leg became crouched, both muscles acted at longer lengths and produced greater work, and body height increased. Muscle activation increased on obstacle strides in the LG, but not the DF, suggesting a greater reflex contribution to LG. In unperturbed strides in uneven terrain, swing pre-activation of DF increased by 5 per cent compared with level terrain, suggesting feed-forward tuning of leg impedance. Across conditions, the neuromechanical factors in work output differed between the two muscles, probably due to differences in muscle-tendon architecture. LG work depended primarily on fascicle length, whereas DF work depended on both length and velocity during loading. These distal muscles appear to play a critical role in stability by rapidly sensing and responding to altered leg-ground interaction.

Achilles Tendon Length and Medial Gastrocnemius Architecture in Children With Cerebral Palsy and Equinus Gait

The aim of this study was to examine both the tendon and muscle components of the medial gastrocnemius muscle-tendon unit in children with cerebral palsy (CP) and equinus gait, with or without contracture. We also examined a small number of children who had undergone prior surgical lengthening of the triceps surae to address equinus contracture. Ultrasound was used to measure Achilles tendon length and muscle-tendon architectural parameters in children of ages 5 to 12 years. Muscle and tendon parameters were compared among 4 groups: Control group (N=40 limbs from 21 typically developing children), Static Equinus group (N=23 limbs from 15 children with CP and equinus contracture), Dynamic Equinus group (N=12 limbs from 7 children with CP and equinus gait without contracture), and Prior Surgery group (N=10 limbs from 6 children with CP who had prior gastrocnemius recession or tendo-achilles lengthening). The groups were compared using analysis of variance and Scheffe post hoc tests. The CP groups had longer Achilles tendons and shorter muscle bellies than the Control group (P<0.001). Normalized tendon length was also longer in the Prior Surgery group compared with the Static Equinus group (P<0.001). The Prior Surgery group had larger pennation angles than the CP groups (P< or =0.009) and tended to have shorter muscle fascicle lengths (P< or =0.005 compared with Control and Static Equinus, P=0.08 compared with Dynamic Equinus). Similar results were observed for pennation angles and normalized muscle fascicle lengths throughout the range of motion. Children with spastic CP and equinus gait have longer-than-normal Achilles tendons and shorter-than-normal muscle bellies. These characteristics are observed even in children with dynamic equinus, before contracture has developed. Surgery further lengthens the tendon, restoring dorsiflexion but not normal muscle-tendon architecture. These architectural features likely affect function, possibly contributing to functional deficits such as plantarflexor weakness after surgery. Level II, prospective comparative study.

Functional anatomy of the gibbon forelimb: adaptations to a brachiating lifestyle

It has been shown that gibbons are able to brachiate with very low mechanical costs. The conversion of muscle activity into smooth, purposeful movement of the limb depends on the morphometry of muscles and their mechanical action on the skeleton. Despite the gibbon's reputation for excellence in brachiation, little information is available regarding either its gross musculoskeletal anatomy or its more detailed muscle-tendon architecture. We provide quantitative anatomical data on the muscle-tendon architecture (muscle mass, physiological cross-sectional area, fascicle length and tendon length) of the forelimb of four gibbon species, collected by detailed dissections of unfixed cadavers. Data are compared between different gibbon species and with similar published data of non-brachiating primates such as macaques, chimpanzees and humans. No quantitative differences are found between the studied gibbon species. Both their forelimb anatomy and muscle dimensions are comparable when normalized to the same body mass. Gibbons have shoulder flexors, extensors, rotator muscles and elbow flexors with a high power or work-generating capacity and their wrist flexors have a high force-generating capacity. Compared with other primates, the elbow flexors of gibbons are particularly powerful, suggesting that these muscles are particularly important for a brachiating lifestyle. Based on this anatomical study, the shoulder flexors, extensors, rotator muscles, elbow flexors and wrist flexors are expected to contribute the most to brachiation.

Functional anatomy and muscle moment arms of the pelvic limb of an elite sprinting athlete: the racing greyhound (Canis familiaris)

We provide quantitative anatomical data on the muscle-tendon architecture and geometry of the pelvic limb of an elite sprint athlete, the racing greyhound. Specifically, muscle masses, muscle lengths, fascicle lengths, pennation angles and muscle moment arms were measured. Maximum isometric force and power of muscles, the maximum muscle torque at joints and tendon stress and strain were estimated. We compare data with that published for a generalized breed of canid, and other cursorial mammals such as the horse and hare. The pelvic limb of the racing greyhound had a relatively large volume of hip extensor muscle, which is likely to be required for power production. Per unit body mass, some pelvic limb muscles were relatively larger than those in less specialized canines, and many hip extensor muscles had longer fascicle lengths. It was estimated that substantial extensor moments could be created about the tarsus and hip of the greyhound allowing high power output and potential for rapid acceleration. The racing greyhound hence possesses substantial specializations for enhanced sprint performance.

Functional specialisation of the thoracic limb of the hare (Lepus europeus)

We provide quantitative anatomical data on the muscle-tendon architecture of the hare thoracic limb (specifically muscle mass, fascicle length, pennation angle, tendon mass and length). In addition, moment arms of major thoracic limb muscles were measured. Maximum isometric force and power of muscles, the moment of force about a joint, and tendon stress and strain were estimated. Data are compared with those from other cursorial mammals. The thoracic limb of the hare consists predominantly of extrinsic musculature with long parallel fascicles, specialised for generating force over a large range. A large shoulder flexor/elbow extensor muscle mass is present, in particular Triceps brachii. The pennate nature of the long head of this muscle suggests it has an important role in stabilising the elbow joint during stance, whilst moment arm curves suggest that it may also play a role in initiating shoulder flexion. In addition, Supraspinatus and Infraspinatus are capable of generating high forces, potentially to stabilise the shoulder joint during the stance phase of locomotion. Supraspinatus may in addition play an important role in forelimb protraction. The Subscapularis muscle was capable of generating surprisingly high forces, suggesting that the hare must be able to withstand/produce high forces during activities that need medio-lateral stability, such as turning. Distally, tendons were relatively short, showing little potential for elastic energy storage when compared with both their pelvic limb counterparts and their equivalents in the horse thoracic limb. Thus, a 'stiffer' thoracic limb may be beneficial in terms of behaving like a strut, simply supporting and deflecting the body during high-speed running. This more distal/less proximal distribution of limb mass is also likely to be important in retaining the manipulative/adaptive/non-locomotor capabilities of the limb.