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Concept: Semitendinosus muscle


BACKGROUND: A common goal of persons post-stroke is to regain community ambulation. The plantar flexor muscles play an important role in propulsion generation and swing initiation as previous musculoskeletal simulations have shown. The purpose of this study was to demonstrate that simulation results quantifying changes in plantar flexor activation and function in individuals post-stroke were consistent with (1) the purpose of an intervention designed to enhance plantar flexor function and (2) expected muscle function during gait based on previous literature. METHODS: Three-dimensional, forward dynamic simulations were created to determine the changes in model activation and function of the paretic ankle plantar flexor muscles for eight patients post-stroke after a 12-weeks FastFES gait retraining program. RESULTS: An median increase of 0.07 (Range [-0.01,0.22]) was seen in simulated activation averaged across all plantar flexors during the double support phase of gait from pre- to post-intervention. A concurrent increase in walking speed and plantar flexor induced forward center of mass acceleration by the plantar flexors was seen post-intervention for seven of the eight subject simulations. Additionally, post-training, the plantar flexors had an simulated increase in contribution to knee flexion acceleration during double support. CONCLUSIONS: For the first time, muscle-actuated musculoskeletal models were used to simulate the effect of a gait retraining intervention on post-stroke muscle model predicted activation and function. The simulations showed a new pattern of simulated activation for the plantar flexor muscles after training, suggesting that the subjects activated these muscles with more appropriate timing following the intervention. Functionally, simulations calculated that the plantar flexors provided greater contribution to knee flexion acceleration after training, which is important for increasing swing phase knee flexion and foot clearance.

Concepts: Knee, Sartorius muscle, Flexion, Extension, Semitendinosus muscle, Semimembranosus muscle, Popliteus muscle, Musculoskeletal system


Forelimb posture has been a controversial aspect of reconstructing locomotor behaviour in extinct quadrupedal tetrapods. This is partly owing to the qualitative and subjective nature of typical methods, which focus on bony articulations that are often ambiguous and unvalidated postural indicators. Here we outline a new, quantitatively based forelimb posture index that is applicable to a majority of extant tetrapods. By determining the degree of elbow joint adduction/abduction mobility in several tetrapods, the carpal flexor muscles were determined to also play a role as elbow adductors. Such adduction may play a major role during the stance phase in sprawling postures. This role is different from those of upright/sagittal and sloth-like creeping postures, which, respectively, depend more on elbow extensors and flexors. Our measurements of elbow muscle moment arms in 318 extant tetrapod skeletons (Lissamphibia, Synapsida and Reptilia: 33 major clades and 263 genera) revealed that sprawling, sagittal and creeping tetrapods, respectively, emphasize elbow adductor, extensor and flexor muscles. Furthermore, scansorial and non-scansorial taxa, respectively, emphasize flexors and extensors. Thus, forelimb postures of extinct tetrapods can be qualitatively classified based on our quantitative index. Using this method, we find that Triceratops (Ceratopsidae), Anhanguera (Pterosauria) and desmostylian mammals are categorized as upright/sagittally locomoting taxa.

Concepts: Knee, Reptile, Hip, Qualitative research, Flexion, Extension, Tetrapod, Semitendinosus muscle


Abstract Characteristics of 32 international and 41 local under-17 (U-17) (14.5-16.5 years) roller hockey players were considered in the context of discrimination by competitive level using training history, anthropometry, skeletal maturation, and several laboratory and field performance tests. More international (42%) than local (22%) players were advanced in maturity status. International players had slightly less hockey experience (years), but had more practice sessions and match time (minutes) during the season. Local players were shorter and attained better performance in the 25-m dash, while international players performed better in sit-ups, ball throw and 20-m shuttle run. The fatigue index derived from the Wingate anaerobic test was higher among local players, while peak torques of knee extension and flexion were greater in international players. Stepwise discriminant function correctly classified 85% of players by competitive level based on grip strength, ratio of eccentric and concentric knee extension, number of training sessions, playing time and fatigue index. The results suggested an interaction among strength, anaerobic fitness and training plus game time as factors in discriminating international from local level players and by inference in the selection and development of youth roller hockey players.

Concepts: Knee, Performance, Flexion, Extension, Discrimination, Semitendinosus muscle, Semimembranosus muscle


The aim of this study was to examine changes in corticomotor excitability to a resting wrist extensor muscle during contralateral rhythmical isotonic and static isometric wrist contractions (flexion/extension) at different loads and positions, using transcranial magnetic stimulation (TMS). TMS-induced motor-evoked potentials (MEPs) were recorded from the relaxed right extensor carpi radialis (ECR) and flexor carpi radialis (FCR) respectively, while the left arm underwent unimanual manipulations. Rhythmical isotonic (0.5Hz) flexion and extension movements of the left wrist under 3 load conditions (no, low and high force) and a frequency matched passive movement condition were collected, along with isometric flexion/extension contractions in each position (low and high force). TMS was delivered at eight positions (4 in the flexion phase and 4 in the extension phase) during the continuous movement conditions and each of these positions was sampled with isometric contraction. The potentials evoked by TMS in right ECR were potentiated when the left ECR was engaged, independent of position within that phase of contraction or contraction type (isotonic and isometric). Motor cortical excitability of the resting right ECR increased as load demands increased to the left wrist. Passive rhythmical movement did not influence excitability to the resting ECR implying that voluntary motor drive is required. Our findings indicated that the increase in corticomotor drive during both rhythmic isotonic and static isometric contractions of the opposite limb is likely mediated by interhemispheric interactions between cortical motor areas. Improving our understanding of these cortical networks can be useful in future methods to enhance neuroplasticity through neurorehabilitation methods.

Concepts: Knee, Transcranial magnetic stimulation, Flexion, Extension, Semitendinosus muscle, Flexor carpi radialis muscle, Extensor carpi radialis longus muscle


The purpose of this study was to investigate changes in muscle oxygenation of knee extensor and plantar flexor muscles during repeated muscle contractions under the same condition. In addition, we compared changes in muscle oxygenation between superficial and deep regions of both muscles.

Concepts: Knee, Muscle contraction, Sartorius muscle, Flexion, Extension, Semitendinosus muscle, Semimembranosus muscle, Popliteus muscle


Manipulating joint range of motion during squat training may have differential effects on adaptations to strength training with implications for sports and rehabilitation. Consequently, the purpose of this study was to compare the effects of squat training with a short vs. a long range of motion. Male students (n = 17) were randomly assigned to 12 weeks of progressive squat training (repetition matched, repetition maximum sets) performed as either a) deep squat (0-120° of knee flexion); n = 8 (DS) or (b) shallow squat (0-60  of knee flexion); n = 9 (SS). Strength (1 RM and isometric strength), jump performance, muscle architecture and cross-sectional area (CSA) of the thigh muscles, as well as CSA and collagen synthesis in the patellar tendon, were assessed before and after the intervention. The DS group increased 1 RM in both the SS and DS with ~20 ± 3 %, while the SS group achieved a 36 ± 4 % increase in the SS, and 9 ± 2 % in the DS (P < 0.05). However, the main finding was that DS training resulted in superior increases in front thigh muscle CSA (4-7 %) compared to SS training, whereas no differences were observed in patellar tendon CSA. In parallel with the larger increase in front thigh muscle CSA, a superior increase in isometric knee extension strength at 75° (6 ± 2 %) and 105° (8 ± 1 %) knee flexion, and squat-jump performance (15 ± 3 %) were observed in the DS group compared to the SS group. Training deep squats elicited favourable adaptations on knee extensor muscle size and function compared to training shallow squats.

Concepts: Muscle, Knee, Thigh, Flexion, Extension, Isometric exercise, Semitendinosus muscle, Semimembranosus muscle


Cervical spinal cord injury (SCI) in humans typically damages both sides of the spinal cord resulting in asymmetrical functional impairments in the arms. Despite this well accepted notion and the growing emphasis on the use of bimanual training strategies, how movement of one arm affects the motion of the contralateral arm after SCI remains unknown. Using kinematics and multi-channel electromyographic (EMG) recordings we studied unilateral and bilateral reach-to-grasp movements of a small and large cylinder in individuals with asymmetric arm impairments due to cervical SCI and age-matched controls. We found that the stronger arm of SCI subjects showed movement durations longer than controls during bilateral compared with unilateral trials. Specifically, movement duration was prolonged when opening and closing the hand when reaching for a large and a small object, respectively, accompanied by deficient activation of finger flexor and extensor muscles. In subjects with SCI, inter-limb coordination was reduced compared with controls, and individuals with lesser coordination between hands were those who showed prolonged times to open the hand. Although the weaker arm showed movement durations during bilateral compared with unilateral trials that were proportional to controls, the stronger arm was excessively delayed during bilateral reaching. Altogether, our findings demonstrate that during bilateral reach-to-grasp movements the more impaired arm has detrimental effects on hand opening and closing of the less impaired arm, and that they are related, at least in part, to deficient control of EMG activity of hand muscles. We suggest that hand opening might provide a time to drive bimanual coordination-adjustments after human SCI.

Concepts: Spinal cord, Knee, Electromyography, Flexion, Extension, Hand, Hand strength, Semitendinosus muscle


How do synergistic muscles interact, when their contraction aims at stabilizing and fine-tuning a movement, which is induced by the antagonistic muscle? The aim of the study was to analyze the interaction of biceps and brachioradialis during fine-tuning control tasks in comparison to load bearing ones. The surface electromyogram of biceps, brachioradialis and triceps were examined in 15 healthy subjects in dynamic flexion and extension movements with different combinations of contraction levels, joint angles and angular velocities. The measurements were conducted in two configurations, where the torque due to an external load opposes the rotational direction of the elbow flexion (load bearing tasks) or the elbow extension (fine-tuning tasks). Whereas during load bearing control tasks, similar muscular activation of biceps and brachioradialis was observed for all joint angles, angular velocities and external loads, during fine-tuning control tasks a significant difference of the muscular activation of both flexors was observed for 1kg, F(3.639,47.305)=2.864, p=0.037, and 5kg of external load, F(1.570,21.976)=6.834, p=0.008. The results confirm the synergistic muscular activation of both flexors during load bearing tasks, but suggest different control strategies for both flexors when they comprise a fine-tuning control task.

Concepts: Muscle, Biceps brachii muscle, Triceps brachii muscle, Knee, Flexion, Extension, Semitendinosus muscle, Brachioradialis


The purpose of this study was to quantify the relative changes in fascicle (FL) and muscle-tendon unit (LMTU) length of the long head of the biceps femoris (BFlh) at different combinations of hip and knee joint positions. Fourteen participants performed passive knee extension trials from 0°, 45° and 90° of hip flexion. FL, LMTU, pennation angle (PA) and effective FL (FL multiplied by the cosine of the PA) of the BFlh were quantified using ultrasonography (US). Three-way analysis of variance designs indicated that at each hip angle, FL and LMTU increased and PA decreased from 90° to 0° of knee flexion. Increasing hip flexion angle from 0° to 90° led to a higher FL and LMTU and a lower PA (p < .05). The average lengthening of the LMTU and effective FL was 28.00 ± 1.82% and 85.88 ± 21.92%, respectively. The average effective FL change accounted for 51.36 ± 7.39% of LMTU change. The relationship between effective FL and LMTU was almost linear with a slope equal to 0.49 ± 0.06 (r2 = 0.52 to 0.97). To achieve greater lengthening of the fascicles of the BFlh, passive stretch with the hip flexed at least 45° and the knee reaching full extension is necessary.

Concepts: Knee, Joint, Sartorius muscle, Flexion, Extension, Semitendinosus muscle, Semimembranosus muscle, Gracilis muscle


The medial hamstring muscle has the potential to prevent excessive dynamic valgus and external rotation of the knee joint during sports. Thus, specific training targeting the medial hamstring muscle seems important to avoid knee injuries.

Concepts: Knee, Anterior cruciate ligament, Joint, Electromyography, Flexion, Extension, Hamstring, Semitendinosus muscle