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Accentuating Muscular Development Through Active Insufficiency and Passive Tension

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Accentuating Muscular Development Through Active Insufficiency and Passive Tension

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... Muscle hypertrophy is one of the main outcomes that may be obtained with repeated bouts of resistance exercise. Although region-specific hypertrophy is particularly aimed by bodybuilders (1), muscle growth does not occur in the same magnitude in all muscle regions (1,16,20,31), irrespective of the training status (i.e., trained or untrained). Varying exercise choice seems to be a viable strategy for potentiating overall muscle gains in response to a resistance-training program (8). ...
... Varying exercise choice seems to be a viable strategy for potentiating overall muscle gains in response to a resistance-training program (8). In addition, performing the same exercise under different joint positions (which some may consider different exercises as well) has been proposed for obtaining region-specific muscle growth (1,6,7,20). ...
... The soleus is a single-joint plantar flexor, and gastrocnemii are multijoint muscles that cross the knee and the ankle. If varying foot position induces portion-specific hypertrophy of the triceps surae (20), performing different exercises may contribute to its development. This could be particularly important for the gastrocnemius because it is deemed as difficult to respond to hypertrophy stimuli (1,28). ...
Article
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The aim of the present study was to compare the changes in gastrocnemius muscle thickness (MT) between conditions in which foot was pointed outward (FPO), inward (FPI), or forward (FPF). Twenty-two young men (23 ± 4 years) were selected and performed a whole-body resistance training program three times per week for nine weeks, with differences in the exercise specific for calves. Calf-raise exercise was performed unilaterally, in a pin-loaded seated horizontal leg-press machine, in 3 sets of 20-25 repetitions for training weeks 1-3, and 4 sets for weeks 4-9. Each subject's leg was randomly assigned for one of the three groups according to foot position: FPO, FPI, and FPF. Measurements with a B-mode ultrasound were performed to assess changes in MT of medial and lateral gastrocnemius heads. After training period, there were observed increases in MT of both medial (FPO = 8.4%; FPI = 3.8%; FPF = 5.8%) and lateral (FPO = 5.5%; FPI = 9.1%; FPF = 6.4%) gastrocnemius, and significant differences for magnitude of the gains were observed between FPO and FPI conditions (P < 0.05). Positioning FPO potentiated the increases in MT of medial gastrocnemius, while FPI provided greater gains for the lateral head. Our results suggest that head-specific muscle hypertrophy may be obtained selectively for gastrocnemius after nine weeks of calf training in young male adults.
... The barbell hip thrust (BHT) was introduced as a biomechanically efficient means to load the hip extensor muscles (Contreras et al., 2011). Through utilising active insufficiency, the shortening of a two-joint muscle at one of the joints, while muscular contraction is occurring, this horizontally loaded hip extension exercise can decrease hamstring activity, forcing an increase in the contribution of GMax musculature (Schoenfeld, 2002). In the last few years, the increase in the popularity of the BHT among strength and conditioning professionals has led the development of new variations of the exercise, such as the addition of a barbell to the Glute Bridge or Barbell Glute Bridge (BGB). ...
... According to Kwon and Lee (2013) muscular activity of the GMax should not increase once the knee is past 60° of knee flexion during hip extension. Furthermore, hamstring contribution should continue to decrease due to active insufficiency (Schoenfeld, 2002). However, the findings of this study do not support these hypotheses. ...
Article
Hip extensor muscles are critical to sport performance as events requiring sprinting and forceful landings are highly dependent on these muscles. Despite biomechanical differences between the barbell hip thrust (BHT) and the barbell glute bridge (BGB), both are biomechanically efficient ways to load this musculature for training purposes. Research investigating the differences in muscular activity between the BHT and BGB has yet been conducted. The aim of this study was to investigate, through surface electromyography, if one exercise is more optimal than the other in producing greater muscle activation for specific hip extensor muscles. Ten male participants completed a two-part study protocol. Results revealed the BHT elicited significantly greater muscle activity within the vastus lateralis for peak and mean outcomes; however, the BGB elicited significantly greater muscle activity in the upper and lower gluteus maximus for peak and mean outcomes and mean outcome in the gluteus medius. Current findings suggest, the BGB is, at minimum, a superior substitute for the BHT for eliciting a larger magnitude of activity in the gluteus maximus. Future studies between the two exercises are warranted to discern which produces greater hypertrophy and whether adaption of the BHT or BGB transfers more optimally to sport performance.
... As such any training protocol for the PM using a contralateral limb resisted approach should maintain an elbow angle of <135˚ to ensure active insufficiency does not occur (e.g. shortening the muscle to the extent where it cannot contract effectively 30,31 ). In contrast to the AD and PM, the TB showed significantly lower peak RMS amplitude for the ISO testing angles compared to the BP. ...
... Indeed, previous research has reported far greater amplitudes for the TB for the chest press compared to pecdeck, whilst reporting similar values for the AD and PM between said exercises. 31 The sEMG data from the present study suggests that contralateral limb resisted training might be an efficacious tool to activate MUs to catalyse increases in strength and hypertrophy through mechanotransduction. Certainly whilst future research needs to confirm this with a proof-of-principle intervention study, the present data supports this hypothesis. ...
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Objectives: Current protocols for resistance training in space flight are hindered by size, mass, noise, vibration and cost, and potentially still lack efficacy. The purpose of the present study was to examine the muscle activation and force output for con-tralateral limb resisted training compared to traditional resistance training with a view towards the practicality of use in micro-gravity environments. Design: Following ethical approval, employing a within-subject design 12 healthy, resistance-trained males performed a 1-repetition maximum bench press (BP) and three isometric tests at differing elbow joint angles (ISO45˚, ISO90˚, ISO135˚) using a Micro-Gym device. Methods: Surface electromyography (sEMG) was used to assess peak amplitude of the pectoralis major (PM), anterior deltoid (AD) and triceps brachii (TB) muscles. Peak force output for each condition was also measured. Results: Significant effects by condition were found with planned comparisons revealing statistically significant differences for peak sEMG amplitude for TB in addition to peak force between BP and ISO45, ISO90, and ISO135 (p < 0.05). Analyses revealed similar peak sEMG amplitude for PM and AD for BP and isometric conditions (p > 0.05). Conclusions: The present study suggests that a contralateral limb resisted training method could be an efficacious method of recruiting motor units and thus may catalyse muscle fibre adaptations in strength and hypertrophy. This novel method might have considerable application to coaches or trainers not wishing to transport large and heavy equipment or in microgravity environments. (Journal of Trainology 2016;5:46-52)
... Both heads insert at the radius and originates in the scapula, thus acting at two joints (i. e., elbow and shoulder) [23]. When performing the elbow flexion exercise combined with shoulder hyperextension (e. g., incline dumbbell curl), the elbow flexors are passively tensioned due to the stretching of the fibers of these muscle group. ...
... Probably, this causes the sarcomeres to have to produce force in a length above the optimum, taking into account the length-tension relationship [24]. This tension along the entire muscle may have favored the increase in muscle thickness at all measured sites [23,25,26]. ...
Article
The study aimed to compare the effect of performing the same or different exercises for a muscle group on resistance training (RT) sessions on muscle hypertrophy at different sites along muscle length. Twenty-two detrained men (23.3 ± 4.1 years) were randomly allocated to the following groups: a group that performed the same exercises in all training sessions (N-VAR = 11) or one that varied the exercises for the same muscle groups (VAR = 11). All were submitted to 3 weekly sessions for nine weeks. Muscle thickness was assessed at the proximal, middle, and distal sites of the lateral and anterior thigh, elbow flexors, and extensors by B-mode ultrasound. The VAR group significantly increased all the sites analyzed (P < 0.05). Furthermore, the proximal site of the lateral thigh showed a larger relative increase when compared to the middle site (P < 0.05). In contrast, the N-VAR group were not revealed significant improvements only for the middle site of the lateral thigh and the proximal site of the elbow flexors (P > 0.05). Our results suggest that to perform different resistance exercises can induce hypertrophy of all sites assessed in detrained young men.
... Resistance training (RT) has been advocated as a primary strategy to stimulate gains in muscle strength and mass (1,33). These muscular adaptations seem to be affected by the proper manipulation of many variables, including but not limited to exercise selection and order (1,32). General recommendations postulate that RT sessions should involve both multi-joint (MJ) and singlejoint (SJ) exercises, where the MJ exercise involve more than one joint acting dynamically and target several muscle groups at a time, whereas the SJ exercise involve one joint acting dynamically and target a primary muscle group (1). ...
... These discrepancies may be explained by the fact that the long head is a biarticular muscle that has distinct lengthtension implications depending on shoulder positioning, whereas the medial and lateral heads are uniarticular muscles that are pure elbow extensors. Thus, during MJ exercise that involves horizontal abduction of the shoulder (bench press's eccentric movement), the long head of the triceps is shortened and thus becomes actively insufficient in subsequent elbow extension, which in turn allows the remaining heads to accomplish a greater amount of work (32). On the other hand, SJ exercise with the elbow at 90°f lexion (lying triceps extension) may have enabled the long head to maintain an optimal length-tension relationship and hence optimize the interaction among the actin and myosin filaments to produce force. ...
Article
Brandão, L, de Salles Painelli, V, Lasevicius, T, Silva-Batista, C, Brendon, H, Schoenfeld, BJ, Aihara, AY, Cardoso, FN, de Almeida Peres, B, and Teixeira, EL. Varying the order of combinations of single- and multi-joint exercises differentially affects resistance training adaptations. J Strength Cond Res XX(X): 000-000, 2020-Our study aimed to compare the effects of multi-joint (MJ) and single-joint (SJ) exercises, either isolated or in combination, and in different orders, on cross-sectional area (CSA) of the pectoralis major (PM) and different heads of the triceps brachii (TB), as well as on the one-repetition maximum (1-RM) in the bench press and lying barbell triceps press. Forty-three young men were randomly assigned to one of 4 possible RT protocols: barbell bench press plus lying barbell triceps press (MJ + SJ, n = 12); lying barbell triceps press plus barbell bench press (SJ + MJ, n = 10); barbell bench press (MJ, n = 10); or lying barbell triceps press (SJ, n = 11). Results showed significant within-group increases in 1-RM bench press for MJ, MJ + SJ, and SJ + MJ but not for SJ. Conversely, significantly greater within-group increases in elbow extension 1-RM were noted for SJ, MJ + SJ, and SJ + MJ but not for MJ. Significantly greater increases in PM CSA were observed for MJ, MJ + SJ, and SJ + MJ compared with SJ. Significant increases in TB CSA were noted for SJ, MJ + SJ, and SJ + MJ, but not for MJ, without observed between-group differences. Individual analysis of TB heads showed significantly greater CSA increases in the lateral head for MJ, MJ + SJ, and SJ + MJ compared with SJ. Alternatively, significantly greater increases in the long head were observed for SJ, MJ + SJ, and SJ + MJ compared with MJ. CSA increases for the medial head were statistically similar between conditions. Our findings indicate that muscular adaptations are differentially affected by performance of MJ and SJ exercises.
... In addition, Contreras et al. (11) discovered that the gluteus exhibits maximal activation in the top region of the barbell hip thrust exercise which suggests that the gluteus likely is not active on the ascending portion of the curve. Muscles that are active on the ascending portion of the curve often exhibit a trait known as "active insufficiency" in which they shorten to a degree in which little force production is taking place (60). This is exhibited in studies in which the gastrocnemius, a biarticulate muscle wellknown to experience active insufficiency, displays a reduction in muscle activation during ankle plantar flexion with a flexed knee (23). ...
Article
One resistance training variable that may be altered to achieve desired outcomes is the range of motion used in training. Generally, the strength and conditioning field has accepted that using a greater range of motion in strength training exercises results in more substantial muscle hypertrophy outcomes. However, this theory has proved to be inconsistently supported in the literature, and to date, no sufficient explanation exists to explain this phenomenon. This review article seeks to outline a novel approach for potentially describing the disparities seen in range of motion research with respect to hypertrophy outcomes by applying the unique length tension curve of each muscle being examined. As will be discussed in the review, virtually all the results from range of motion studies in various muscles have corresponded to each muscle’s length-tension curve; muscles that are active on the descending limb of the curve appear to garner greater hypertrophy from using larger ranges of motion. Conversely, muscles that are not active on the descending limb exhibit similar adaptations despite alterations in range of motion. A novel hypothesis for applying this information to resistance training programs will be presented and discussed.
... Because the semitendinosus and semimembranosus are biarticulate muscles (crossing 2 joints), their force contribution can be reduced when the joints are closer together, resulting in shortened length of the muscle. This is known as active insufficiency (15). By removing the influence of the semimembranosus and semitendinosus in hip extension, there exists a greater reliance on gluteal activation during the concentric action of the single-leg glute bridge. ...
Article
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The single-leg glute bridge is a variation of the barbell hip thrust that involves unilateral hip extension. Glute bridge exercises are used as a means of strengthening the hip extensors: The gluteal and hamstring muscle groups. In addition to activating the posterior musculature of the hip, single-leg glute bridges require stabilization of both the hip abductors and core muscles through isometric contraction. because strong gluteal and hamstring muscle groups are imperative in lateral stabilization and explosive linear movement, the single-leg glute bridge is beneficial to the general population and athletes in a variety of sports, such as soccer, football, and rugby.
... The ability for single-joint exercises to favorably affect length-tension relationships has implications beyond simply enhancing muscle development. Single joint movements such as seated leg curls, incline arm curls, and overhead triceps extensions place the hamstrings, biceps brachii, and long head of the triceps brachii, respectively, into a position that exceeds resting length, allowing them to be trained while actively stretched (Schoenfeld, 2002). Leonard and Herzog (2010) found that when activated muscle fibers were stretched to the point where no cross bridges remained, titin stiffness contributed significantly to passive tension, thereby protecting against eccentric damage. ...
Article
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FUNCTIONAL TRAINING PROGRAMS TYPICALLY FOCUS ON MULTIJOINT MOVEMENTS. HOWEVER, FUNCTIONAL TRANSFER EXISTS ON A CONTINUUM, WHERE DIFFERENT EXERCISES IMPART VARYING DEGREES OF FUNCTIONAL IMPROVEMENTS DEPENDING ON THE PARTICULAR DEMANDS OF THE TASK. THIS ARTICLE WILL DISCUSS THE POTENTIAL ROLE OF SINGLE-JOINT MOVEMENTS IN FUNCTIONAL TRAINING PROGRAM DESIGN.
... However, the Fonseca et al. [7] study cited to support this statement investigated hypertrophy of the quadriceps. The long head of the triceps is a biarticular muscle that has distinct length-tension implications, whereby the muscle is stretched in shoulder flexion and becomes actively insufficient in shoulder extension [8]. Thus, consistent with the findings of Wakahara et al. [5,6], SJ exercise would provide the ability to take advantage of the length-tension relationship in the triceps brachii and potentially allow for optimal development of the muscle complex. ...
... Because the hamstrings (knee flexors) and gluteal muscles (hip extensors) are involved in the BHT exercise as primary hip extensors (5), it is of interest to examine how performance of these 2 muscles groups as measured with the isokinetic machines correlates with performance in the BHT. However, when performing the BHT exercise, the knee is ;908 bent and the hamstrings length shortens leading to active insufficiency (40), which can increase the mechanical demands of the gluteal musculature. Accordingly, although BHT performances is expected to be correlated with the isolated isokinetic test outcomes of both hip extensors and knee flexors, a stronger relationship is expected with the hip extensors. ...
Preprint
Purpose: The barbell hip thrust (BHT) exercise is growing in popularity as evident by the large increase in research outputs investigating its utility as a training intervention and a testing tool. The aim of this study was to examine the concurrent validity and test-retest reliability of the BHT for the first time. Methods: To establish concurrent validity, the peak force and power measured with the BHT force-velocity profile test of 49 handball athletes, were correlated with peak concentric force of the knee-flexors and hip-extensors measured with an isokinetic device at two different velocities. Test-retest reliability was established by correlating the peak force and power measured with the BHT force-velocity profile test of 20 handball athletes on two separate days. Results: The relationships between the isokinetic testing scores and the BHT force-velocity profile tests were moderate to strong (Pearson r ranges: 0.45-0.86). Test-retest reliability of the BHT force-velocity profile was very high as shown with intra-class correlations of 0.94 and 0.99 for peak force and 0.97 and 0.99 for peak power measures. Conclusion: The BHT force-velocity profile can serve as a tentative substitute in cases that athletes do not have access to an isokinetic device given the moderate to strong correlations between them. Moreover, the BHT force-velocity profile was shown to be very reliable thus providing coaches and scientists a range of day-to-day performance variability in this exercise.
... Because the hamstrings (knee flexors) and gluteal muscles (hip extensors) are involved in the BHT exercise as primary hip extensors (5), it is of interest to examine how performance of these 2 muscles groups as measured with the isokinetic machines correlates with performance in the BHT. However, when performing the BHT exercise, the knee is ;908 bent and the hamstrings length shortens leading to active insufficiency (40), which can increase the mechanical demands of the gluteal musculature. Accordingly, although BHT performances is expected to be correlated with the isolated isokinetic test outcomes of both hip extensors and knee flexors, a stronger relationship is expected with the hip extensors. ...
Article
Dello Iacono, A, Padulo, J, Bešlija, T, and Halperin, I. Barbell hip-thrust exercise: Test-retest reliability and correlation with isokinetic performance. J Strength Cond Res XX(X): 000-000, 2018-The barbell hip-thrust (BHT) exercise is growing in popularity as evident by the large increase in research outputs investigating its utility as a training intervention and a testing tool. The aim of this study was to examine the test-retest reliability of the BHT and its correlation with isokinetic performance. Test-retest reliability was established by correlating the peak force and power outcomes measured with the BHT force-velocity profile test of 20 handball athletes on 2 separate days. The peak force and power measured with the BHT force-velocity profile test of 49 handball athletes were correlated with peak concentric force of the knee flexors and hip extensors measured with an isokinetic device at 2 different velocities (60-180°·s). The correlation between the isokinetic testing scores and the BHT force-velocity profile tests were moderate to large (Pearson r ranges: 0.45-0.86, all p values <0.001). Test-retest reliability of the BHT force-velocity profile was very high as shown with intraclass correlations of 0.94 and 0.99 for peak force and 0.97 and 0.99 for peak power measures. The BHT force-velocity profile can serve as a tentative substitute in cases that athletes do not have access to an isokinetic device, given the moderate to large correlations between them. Moreover, the BHT force-velocity profile was shown to be very reliable, thus providing coaches and scientists a range of day-to-day performance variability in this exercise.
Article
Background/Aims Prone hip extension motion pattern derives from the motor muscle firing pattern, and functional deficits are determined by comparing this pattern with a normal prone hip extension motion muscle recruitment pattern, defined more than 30 years ago by scientifically insufficient methods. The aim of this study was to examine the differences between electromyography recruitment onsets and orders of muscles participating in prone hip extension motion, and to determine whether there is a consistent and dominant motor pattern. Methods The sample consisted of 106 healthy participants. Onset times of semitendinosus, ipsilateral and contralateral erector spinae muscles were determined as 10% of the peak rectified amplitude of the electromyography signal for each of the 18 prone hip extension bilateral repetitions. These values were used to determine the recruitment order for each repetition, as well as to calculate the average ipsilateral and contralatral normalised onset times (ie relative times to firing of the semitendinosus muscle). The main analysis was performed using a one-way analysis of variance. The level of statistical significance was set at P<0.05. Results One-way analysis of variance revealed a significantly delayed onset of prone hip extension of the contralateral erector spinae muscles compared to the other muscles (F=7.02; P<0.001; Cohen's f=0.209). Muscle activation initiated by the semitendinosus and ipsilateral erector spinae muscles was the most common. Conclusions The ipsilateral erector spinae muscle contracts simultaneously with the semitendinosus muscle as a proximal stabiliser, enabling distal hip mobility. The use of the prone hip extension test in recognising dysfunction is limited to when the contralateral erector spinae muscle is initiated first during prone hip extension.
Article
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Fitness professionals routinely employ a variety of resistance training exercises in program design as a strategy to enhance muscular adaptations. However, it remains uncertain whether such an approach offers advantages over a fixed-exercise selection. The objective of this paper was to review the effects of exercise variation on muscle hypertrophy and strength. A search of literature was conducted using PubMed/MEDLINE, Scopus, and Web of Science databases. Eight studies were identified as meeting inclusion criteria. The combined total sample of the studies was n = 241, comprising all young men. The methodological quality of included studies was considered "good" and "excellent" based on the PEDro Scale. The available studies indicate that varying exercise selection can influence muscle hypertrophy and strength gains. Some degree of systematic variation appears to enhance regional hypertrophic adaptations, and maximize dynamic strength, whereas excessive, random variation may compromise muscular gains. We conclude that exercise variation should be approached systematically with a focus on applied anatomical and biomechanical constructs; on the contrary, employing different exercises that provide a redundant stimulus, as well as excessive rotation of different exercises (i.e., high frequency of change), may actually hinder muscular adaptations.
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THE TECHNIQUE OF THE BARBELL HIP THRUST IS DESCRIBED AND DEMONSTRATED THROUGH THE USE OF PHOTOGRAPHS AND VIDEO IN THIS COLUMN. AN EXERCISE PRESCRIPTION IS GIVEN.
Article
Immunoglobulin superfamily members are implicated in immune responses, growth factor signaling, and cell adhesion. IGSF4 (IGSF4A), homologous to IGSF4B, IGSF4C, IGSF4D, PVR, PVRL1, PVRL2, PVRL3 and PVRL4, is down-regulated in lung cancer. IGSF11, homologous to CXADR (CAR), ESAM and ASAM, is up-regulated in the intestinal-type gastric cancer. Here, we identified and characterized a novel member of the immunoglobulin superfamily, TMEM25, by using bioinformatics. BC042896 and AY358919 cDNAs were derived from human TMEM25 gene, while AK002841 cDNA was derived from mouse Tmem25 gene. TMEM25 isoform 1 (BC042896), consisting of exons 1-9, encoded a 366-aa transmembrane protein. TMEM25 isoform 2 (AY358919), consisting of exons 1-4 and 6-9, encoded a 322-aa secreted protein. Human TMEM25 gene was found to encode transmembrane-type as well as secreted-type proteins due to alternative splicing of exon-skipping type. TMEM25 mRNA was expressed in brain, including cerebellar cortex and hippocampus, as well as in neuroblastoma, brain tumors, and gastric cancer. Human TMEM25 isoform 1 showed 91.0% total-amino-acid identity with mouse Tmem25. TMEM25 was identified as a member of immunoglobulin superfamily, because codon 42-112 of TMEM25 was the C-2 type immunoglobulin domain homologous to Hemicentin (Fibulin-6, FIBL6), Titin (TTN), Sialoadhesin (SN) and Nephrin (NEPHS1). Human TMEM25 gene was located at the 11q23.3 oncogenomic recombination hotspot around the MLL amplicon and the neuroblastoma deleted region. TMEM25 is a target of pharmacogenomics in the field of oncology and regenerative medicine.
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Acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) each represent a heterogeneous complex of disorders, which result from diverse mechanisms of leukemogenesis. Modern therapeutic concepts are based on individual risk stratification at diagnosis and during follow-up. For some leukemia subtypes such as AML M3/M3v with t(15;17)/PML-RARA or Philadelphia-positive ALL targeted therapy options are available. Thus, optimal therapeutic conditions are based on exact classification of the acute leukemia subtype at diagnosis and are guided by exact and sensitive quantification of minimal residual disease during complete hematologic remission. Today, a multimodal diagnostic approach combining cytomorphology, multiparameter flow cytometry, chromosome banding analysis, accompanied by diverse fluorescence in situ hybridization techniques, and molecular analyses is needed to meet these requirements. As the diagnostic process becomes more demanding with respect to experience of personnel, time, and costs due to the expansion of methods, algorithms, which guide the diagnostic procedure from basic to more specific methods and which lead finally to a synopsis of the respective results, are essential for modern diagnostics and therapeutic concepts.
To investigate the influence of the various knee angles and ankle angular velocities on synergistic muscle activities, the surface electromyograms (EMG) were recorded from the triceps surae muscles, i.e. lateral gastrocnemius (LG), medial gastrocnemius (MG) and soleus (SOL) muscles. Six healthy young men performed ankle plantarflexions at three ankle angular velocities of 6, 30 and 60° · s−1 and three knee angles of 0, 30 and 60° (0° equalling full extension) under constant load (5% and 10% maximal voluntary contraction). At the fully-extended knee angle (0°), peak values of integrated EMG (peak iEMG) during ankle plantarflexions were significantly increased (P < 0.05) in MG and in LG, but significantly decreased (P < 0.05) in SOL with increasing angular velocity. On the other hand, although the patterns of variation of the peak iEMG in each muscle at flexed knee angles (30 and 60°) were very similar to the patterns seen at the fully-extended knee angle, there were no significant differences among angular velocities. During ankle plantarflexions at any of the angular velocities (6, 30 and 60° · s−1) the peak iEMG were significantly increased (P < 0.05) in SOL, but were significantly decreased (P < 0.05) in MG following increases in the knee angles. These results would suggest the possibility of selective recruitment of motor units in humans depending on the angular velocity; however, this behaviour would appear to be weakened by fixing at flexed knee angles which cause an inhibitory influence on gastrocnemius muscles and a facilitative influence on SOL.
This study concerns the synergy of the elbow extensor muscles during voluntary elbow extension performed at various velocities against different inertia and in a horizontal plane. The quantity of excitation (Q) of the three heads of the triceps brachii muscle increases linearly with the external work (W). On the contrary, the anconeus Q increases rapidly for low values of W while for higher values it increases very slowly but linearly with the W. These results imply a proportionality between Q and W of the different muscles except in the case of anconeus for low values of W. Furthermore, it is shown that the position of the shoulder does not influence the relative contribution of the different muscles to W but leads to an adjustment of the activity of the long head. The different extensor muscles do not come into play simultaneously. The chronology of the muscular activities depends on velocity and inertia. The importance of anconeus activity for slow movements is pointed out, and it is suggested that there exists a specific control of the motoneurons of the different elbow extensor muscles. The limits of the concept of muscle equivalent are also discussed.
Article
Architectural properties of the triceps surae muscles were determined in vivo for six men. The ankle was positioned at 15 degrees dorsiflexion (-15 degrees) and 0, 15, and 30 degrees plantar flexion, with the knee set at 0, 45, and 90 degrees. At each position, longitudinal ultrasonic images of the medial (MG) and lateral (LG) gastrocnemius and soleus (Sol) muscles were obtained while the subject was relaxed (passive) and performed maximal isometric plantar flexion (active), from which fascicle lengths and angles with respect to the aponeuroses were determined. In the passive condition, fascicle lengths changed from 59, 65, and 43 mm (knee, 0 degrees; ankle, -15 degrees) to 32, 41, and 30 mm (knee, 90 degrees ankle, 30 degrees) for MG, LG, and Sol, respectively. Fascicle shortening by contraction was more pronounced at longer fascicle lengths. MG had greatest fascicle angles, ranging from 22 to 67 degrees, and was in a very disadvantageous condition when the knee was flexed at 90 degrees, irrespective of ankle positions. Different lengths and angles of fascicles, and their changes by contraction, might be related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses.
Article
Surface electromyography was performed for both heads of the biceps brachii in 11 healthy men while the muscles were under 30% maximum isometric shoulder flexion and abduction. Elbow related biceps activity was minimized by using a brace locked in neutral forearm rotation. Electromyographic activity was normalized as a percentage of maximal muscle contraction during 24 shoulder motions. Electromyographic activity was detected in all motions examined, suggesting that the biceps muscle acts as a flexor and an abductor of the shoulder. Both heads of the biceps muscle had higher activities during external rotation than during internal rotation for most motions. Activities of both heads increased with arm elevation, but showed little dependence on elbow position. The long head was still active during internal rotation of the shoulder. These findings also suggest that the biceps muscle is a flexor and an abductor of the shoulder, and that the long head can act as a humeral head stabilizer in superior and anterior directions. Muscle fatigue of the biceps and the deltoid muscle also was determined at 30% of maximum isometric flexion. All muscles had significantly decreased mean power frequency and turns count, and increased amplitude and integrated electromyography. The rate of decrease in mean power frequency was larger for the biceps than for the deltoid muscle, and the rate of increase in amplitude was larger for the long head of the biceps than for the short head or for the deltoid muscle. These findings suggest that the long head of the biceps must increase its mechanical output to keep the arm in elevation to a greater extent than do the short head and the deltoid muscle. This may be one of the causes of tendinitis or rupture of the long head.
Brunnstrom's Clinical Kinesiology
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Smith, E., W. Lawrence, D. Lehmkuhl, and L. Smith. Brunnstrom's Clinical Kinesiology. Philadelphia: F.A. Davis, 1996.