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Further evidence of functional differentiation within Biceps Brachii
Abstract
This study investigated whether the two heads of Biceps Brachii could be functionally differentiated during rapid supination movements with different degrees of elbow flexion, shoulder axial rotation and load. Surface electromyograms, recorded from the long and short heads of Biceps Brachii, were utilised to identify changes in the intensity of muscle contraction. Based upon an analysis of sixteen subjects, the results indicated that joint position (muscle length), but not load, significantly (p < 0.05) influenced the relationship between the contraction intensities of the two heads. Specifically, increasing the length of the Biceps Brachii promoted increased activation of the long head in relation to the short head in producing rapid supination motions. It was concluded that functional differentiation within the two heads of Biceps Brachii was present in motions involving its distal insertion.
... The anatomical basis for these findings was confirmed by Segal in 1992, who discovered the existence of six parallel individually innervated muscular compartments in each head of the BBM [4] (illustration in Fig 1). In 1996, Brown et al. went on to investigate the amount of differential activation of the BBM during rapid supination movements, and found that joint position had a significant effect on the relative activation of the two heads of the muscle [5]. In the same year, it was shown that the two heads (long and short) contribute in different amount to supination and flexion, however, the relative differences vary largely between subjects [6]. ...
... Overall, there seems to be a complicated functional relationship between the two heads of the BBM. The current understanding indicates that arm posture has a major impact on the amount of differential activation [5]. This was confirmed by Nejat Nahal who showed that changes in arm posture have a large impact on the relative activation of the two heads [7]. ...
A central challenge for myoelectric limb prostheses resides in the fact that, as the level of amputation becomes more proximal, the number of functions to be replaced increases, while the number of muscles available to collect input signals for control decreases. Differential activation of compartments from a single muscle could provide additional control sites. However, such feat is not naturally under voluntary control. In this study, we investigated the feasibility of learning to differentially activate the two heads of the bicep brachii muscle (BBM), by using biofeedback via high-density surface electromyography (HD-sEMG). Using a one degree of freedom Fitts' law test, we observed that eight subjects could learn to control the center of gravity of BBM's myoelectric activity. In addition, we examined the activations patterns of BBM that allow for the decoding of distal hand movements. These patterns were found highly individual, but different enough to allow for decoding of motor volition of distal joints. These findings represent promising venues to increase the functionality of myoelectrically controlled upper limb prostheses.
... 1 To achieve our general aim to determine the dynamic role of the LHBT in the glenohumeral joint, we performed an electromyographic (EMG) analysis of the LHBM in normal volunteers. Our specific aims were (1) to determine LHBM and short head of the biceps muscle (SHBM) activity during a variety of glenohumeral joint motions, (2) to determine whether forearm and elbow immobilization affects this activity, and (3) to determine whether application of a load to the distal humerus affects this activity. ...
... For the LHBM and short head electrodes, if the bulk of the biceps muscle was split into thirds, the LHBM electrodes lay at the junction of the lateral and middle thirds and the short head electrodes lay at the junction of the middle and medial thirds with a minimum of 3 cm between the short and long head electrodes mediolaterally to avoid cross-talk, as previous described. 2,3,14 As an internal check, a cadaveric dissection was performed to confirm that the long and short heads of the biceps had entirely separate muscular fibers until their attachment at the distal tendon. This dissection is shown in Figure 2; the separate heads of the muscle have anatomically distinct fascicles without cross-weaving, with the LHBM being lateral and the SHBM being medial up until they coalesce at the distal tendon. ...
Background:
Optimal treatment of superior labral anterior-posterior (SLAP) tears is controversial, in part because the dynamic role of the long head of the biceps muscle (LHBM) in the glenohumeral joint is unclear. The aim of this study was to determine dynamic LHBM behavior during shoulder activity by studying (1) the electromyographic activity of the LHBM during shoulder motion, (2) the effect of elbow immobilization on this activity, and (3) the effect of a load applied to the distal humerus on this activity.
Hypothesis:
The LHBM would not play a significant role in active glenohumeral range of motion.
Study design:
Controlled laboratory study.
Methods:
Thirteen normal volunteers underwent surface electromyography (EMG) measurement of the LHBM, short head biceps muscle (SHBM), deltoid, infraspinatus, and brachioradialis during shoulder motion from the neutral position (0° of rotation, flexion, and abduction) to 45° of flexion, 90° of flexion, 45° of abduction, and 90° of abduction. These motions were repeated both with and without splint immobilization of the forearm and elbow at 100° of flexion and neutral rotation and with and without a 1-kg weight placed on the lateral distal humerus.
Results:
Mean EMG activity within the LHBM and the SHBM was low (≤11.6% ± 9.1%). LHBM activity was significant increased by flexion and abduction (P < .049 in all cases), while SHBM activity was not. EMG activity from the middle head of the deltoid was significantly increased by loading with the shoulder positioned away from the body (ie, in abduction or flexion). When compared with the unloaded state, the addition of a distal humeral load significantly increased LHBM activity in 45° of abduction (P = .028) and 90° of flexion (P = .033) despite forearm and elbow immobilization. The SHBM showed similar trends.
Conclusion:
In normal volunteers with forearm and elbow immobilization and application of a load to the distal humerus, LHBM EMG activity is increased by both glenohumeral flexion and abduction, suggesting that this muscle plays a dynamic role in glenohumeral motion with higher demand activities.
Clinical relevance:
Biceps tenodesis may result in dynamic change within the glenohumeral joint with higher demand activities.
... For the LHBM and SHBM electrodes, if the bulk of the biceps muscle was split into thirds, the LHBM electrodes lay at the junction of the lateral and middle thirds, and the SHBM electrodes lay at the junction of the middle and medial thirds, with a minimum of 3 cm between the electrodes of the short and long heads mediolaterally to avoid cross-talk as previously described. 6,16,53 Infraspinatus surface electrodes were applied obliquely (ie, at 60°) with respect to the floor, inferior to the trapezius and inferior to the scapular spine. Mediolaterally, if the distance between the medial scapular border and the posterior glenohumeral joint line was divided into thirds, the infraspinatus electrodes were applied at the junction of the middle and medial thirds. ...
... Surface EMG has its shortcomings, especially for muscles in close anatomic proximity, such as the SHBM and LHBM. However, multiple previous studies have described the use of surface EMG for the LHBM and SHBM, 6,16,53 and efforts were taken to ensure adequate electrode spacing. In addition, withinpitcher coefficients of variation were less than 0.22 for all muscle peak amplitudes, and the mean between-pitcher coefficient of variation was significantly less than the mean within-pitcher coefficient of variation. ...
Background:
Superior labral anterior-posterior (SLAP) tears are a common cause of shoulder pain and dysfunction in overhand throwers. Treatment outcomes remain unpredictable, with a large percentage of athletes unable to return to sport. There is considerable debate about the optimal treatment between debridement, repair, and tenodesis.
Hypothesis:
Labral repair more closely restores neuromuscular control and motion during the overhand pitch than tenodesis of the long head of the biceps.
Study design:
Controlled laboratory study.
Methods:
Eighteen pitchers, including 7 uninjured controls, 6 players pitching after SLAP repair, and 5 players pitching after subpectoral biceps tenodesis (BT), underwent simultaneous surface electromyographic measurement at 1500 Hz and motion analysis at 120 Hz with a 14-camera markerless motion analysis system and high-speed video (120 Hz) to confirm accurate motion tracking. Patients had undergone surgery at least 1 year previously and had returned to pitching with a painless shoulder.
Results:
No significant differences were observed in the long head of the biceps muscle, short head of the biceps muscle, deltoid, infraspinatus, or latissimus activity between controls, patients after SLAP repair, and patients after BT. The variability from pitch to pitch for each study participant was similar between groups. Based on visual inspection of the activity time plots, BT appeared to more closely restore the normal pattern of muscular activation within the long head of the biceps muscle than did SLAP repair. There were no significant differences between controls and postoperative patients in the majority of pitching kinematics; however, pitchers after SLAP repair showed significantly altered patterns of thoracic rotation (P = .034) compared with controls and were significantly less likely to fall into previously published normal values for lead knee flexion at front foot contact (P = .019).
Conclusion:
While both BT and SLAP repair can restore physiologic neuromuscular control, pitchers who undergo SLAP repair may exhibit altered patterns of thoracic rotation when compared with controls and pitchers who undergo BT.
Clinical relevance:
While both tenodesis and SLAP repair can restore physiologic neuromuscular control, SLAP repair may alter pitching biomechanics.
... Previous research has shown functional differentiation to be present within segments of single skeletal muscles. 2,3,9,14,16,19 This occurs when segment(s) of a muscle exhibit an earlier onset, higher intensity of activation or some other measured difference in comparison to the remaining muscle segments during a particular motor task. 3,9,19 The evidence of functional differentiation displayed by segments during these studies has been either within the one movement or when movement direction was changed. ...
... 2,3,9,14,16,19 This occurs when segment(s) of a muscle exhibit an earlier onset, higher intensity of activation or some other measured difference in comparison to the remaining muscle segments during a particular motor task. 3,9,19 The evidence of functional differentiation displayed by segments during these studies has been either within the one movement or when movement direction was changed. As a secondary aim of this study the evidence of functional differentiation when contraction intensity is altered for a particular force direction will be investigated. ...
The objectives of this study were two-fold. Firstly we wished to investigate the segmental anatomy, geometry and gross innervation patterns of selected shoulder joint musculature (pectoralis major, latissimus dorsi and deltoid) to establish if these muscles could be anatomically subdivided according to predetermined criteria. We then wished to use this information to help determine if a segments activation pattern was reliant on an efficient line of action and a large moment arm for the intended movement. Surface electromyography was used for this purpose whilst manipulating the independent variable of contraction intensity (% MVC) during two shoulder joint flexion tasks.
For the anatomical portion of the study the dissection of ten cadaveric shoulders revealed the deltoid to consist of seven segments whilst the pectoralis major and the latissimus dorsi were both ascribed six segments according to predetermined anatomical/functional criteria. Primary nerve branching was evident in each muscle but no apparent relationship existed between the designated anatomical segments and the primary nerve branches. Differences were evident in the geometry of each segment in regard to moment arms and orientations of each segments line of action.
The functional portion of this study, which utilized miniature bipolar surface electrodes during the performance of a static shoulder joint flexion task at 75% and 25% MVC, showed significant differences (p<0.05) in the activation patterns of active segments between the two tasks. Specifically, a "drop out" of segments with smaller flexion moment arms and more diverging lines of action in comparison to the movement plane was evident for all subjects in the 25% MVC task in comparison to the 75% MVC task.
... Reported firing rates of these MUs for trapezius Fig. 2. Volume % degenerated fibers in rabbit muscles tibialis anterior (TA) and extensor digitorum longus (EDL) after several days of continuous and intermittent stimulation (data from [80]). muscle and extensor muscles are relatively high (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) [8,127,149] and comparable with firing rates of previously mentioned animal studies. The finding in the study of Lexell et al. [80] that especially muscles subjected to continuous stimulation are at risk for degeneration provides strong support for the ''Cinderella hypothesis''. ...
... This could be the case when type I MUs or mechanically specialized subpopulations of MUs [156] are spatially clustered, such as in muscle compartments that have been identified in animal experiments [151]. In several arm and shoulder muscles, among them the trapezius muscle, indications for compartmentalization have been found [15,50,59,60,92,104]. In addition, prolonged pressure at lower levels (8 h, 30 mmHg) can cause muscle fiber damage at normal blood pressure [46]. ...
A review of the literature on the pathophysiology of upper extremity muscle disorders (UEMDs) was performed. An overview is given of clinical findings and hypotheses on the pathogenesis of UEMDs. The literature indicates that disorders of muscle cells and limitations of the local circulation underlie UEMDs. However, these disorders identified do not necessarily lead to symptoms. The following mechanisms have been proposed in the literature: (1) selective recruitment and overloading of type I (Cinderella) motor units; (2) intra-cellular Ca(2+) accumulation; (3) impaired blood flow; (3b) reperfusion injury; (3.3c) blood vessel-nociceptor interaction; (4a) myofascial force transmission; (4b) intramuscular shear forces; (5) trigger points; (6) impaired heat shock response. The results of the review indicate that there are multiple possible mechanisms, but none of the hypotheses forms a complete explanation and is sufficiently supported by empirical data. Overall, the literature indicates that: (1) sustained muscle activity, especially of type I motor units, may be a primary cause of UEMDs; (2) in UEMDs skeletal muscle may show changes in morphology, blood flow, and muscle activity; (3) accumulation of Ca(2+) in the sarcoplasm may be the cause of muscle cell damage; (4) it seems plausible that suboptimal blood flow plays a role in pathogenesis of UEMDs; (5) since the presence of fiber disorders is not a sufficient condition for the development of UEMSDs additional mechanisms, such as sensitization, are assumed to play a role.
... It is now well accepted that motor units, within individual muscle segments of single skeletal muscles, can be independently controlled by the central nervous system (CNS) to produce particular motor outcomes [3,21]. This phenomenon, which may be termed 'functional differentiation' [18], has been described within a number of individual skeletal muscles, including the Tensor Fascia Latae [18], the Gluteus Maximus and Medius [16], the Triceps Surae [3], the Biceps Brachii [2] and the Pectoralis Major [19]. Ettema et al. [5] has suggested that large absolute differences in moment arms between different segments of a single muscle partially explain this phenomenon. ...
... the activity of muscle segments within adjacent, and more distant muscles, are closely coordinated and, in agreement with Kuechle et al. [12], that the functional classifications of muscle segments were fluid and may change from one motor task to the next. Finally, our results support the contention [2,19,24] that individual skeletal muscles are composed of discrete sub-volumes (segments) of muscle tissue which may be independently controlled by the CNS to produce the desired motor outcome. ...
The aim of the present study was to determine how the intra-muscular segments of three shoulder muscles were coordinated to produce isometric force impulses around the shoulder joint and how muscle segment coordination was influenced by changes in movement direction, mechanical line of action and moment arm (ma). Twenty male subjects (mean age 22 years; range 18-30 years) with no known history of shoulder pathologies, volunteered to participate in this experiment. Utilising an electromyographic technique, the timing and intensity of contraction within 19 muscle segments of three superficial shoulder muscles (Pectoralis Major, Deltoid and Latissimus Dorsi) were studied and compared during the production of rapid (e.g. approximately 400ms time to peak) isometric force impulses in four different movement directions of the shoulder joint (flexion, extension, abduction and adduction). The results of this investigation have suggested that the timing and intensity of each muscle segment's activation was coordinated across muscles and influenced by the muscle segment's moment arm and its mechanical line of action in relation to the intended direction of shoulder movement (e.g. flexion, extension, abduction or adduction). There was also evidence that motor unit task groups were formed for individual motor tasks which comprise motor units from both adjacent and distant muscles. It was also confirmed that for any particular motor task, individual muscle segments can be functionally classified as prime mover, synergist or antagonist - classifications which are flexible from one movement to the next.
... Similar differences in activation patterns have been displayed during elbow flexion exercise, with the long head of the biceps brachii more active during early phase movement and the short head becoming more involved during the latter portion of the ROM. 29 Although EMG findings cannot necessarily be extrapolated to predict long-term hypertrophic outcomes from RT, the possibility remains that a combination of partial and full ROMs may have a synergistic effect on muscle development. ...
The purpose of this study was to systematically review the literature as to the effects of performing exercise with a full vs. partial range of motion (ROM) during dynamic, longitudinal resistance training (RT) programs on changes in muscle hypertrophy. Based on the available evidence, we aimed to draw evidence-based recommendations for RT prescription. Six studies were identified as meeting inclusion criteria: four of these studies involved RT for the lower limbs while the other two focused on the upper extremities. The total combined sample of the studies was n = 135, which comprised 127 men and 8 women. The methodological quality of all included studies was deemed to be “excellent” based on the modified PEDro scale. When assessing the current body of literature, it can be inferred that performing RT through a full ROM confers beneficial effects on hypertrophy of the lower body musculature vs. training with a partial ROM. Alternatively, research on the effects of ROM for the upper limbs is limited and conflicting, precluding the ability to draw strong practical inferences. No study to date has investigated how ROM influences muscle growth of the trunk musculature. Finally, some evidence indicates that the response to variations in ROM may be muscle-specific; however, this hypothesis also warrants further study.
... This muscle is only one part of the four major components of the elbow flexors (short and long heads of BB, BR and brachialis), with the brachialis contributing for almost the same force as the entire BB (Edgerton et al. 1986;Kawakami et al. 1994). In that context, it has been reported that the magnitude of the activation of each elbow flexor muscles can differ in function of the characteristics of the movement (i.e., load, speed, contraction type, muscle length, etc.; see Brown et al. 1993;Kulig et al. 2001). However, despite potential specific training-related adaptations, a similar hypertrophy has been reported for BB, BR and brachialis following 12 weeks of strength training against a load of ~ 70% of 1RM (Erskine et al. 2014). ...
Aim
This study investigated the efficacy of a new strength training method on strength gain, hypertrophy, and neuromuscular fatigability.
Methods
The training exercise consisted of elbow flexion against a load of ~ 70% of one repetition maximal (1RM). A new method (3/7 method) consisting of five sets of an increasing number of repetitions (3 to 7) during successive sets and brief inter-set intervals (15 s) was repeated two times after 150 s of recovery and compared to a method consisting of eight sets of six repetitions with an inter-set interval of 150 s (8 × 6 method). Subjects trained two times per week during 12 weeks. Strength gain [1RM load and maximal isometric voluntary contraction (MVC)], EMG activity of biceps brachii and brachioradialis, as well as biceps’ brachii thickness were measured. Change in neuromuscular fatigability was assessed as the maximal number of repetitions performed at 70% of 1RM before and after training.
Results
Both 3/7 and 8 × 6 methods increased 1RM load (22.2 ± 7.4 and 12.1 ± 6.6%, respectively; p < 0.05) and MVC force (15.7 ± 8.2 and 9.5 ± 9.5%; p < 0.05) with a greater 1RM gain (p < 0.05) for the 3/7 method. Normalized (%Mmax) EMG activity of elbow flexors increased (p < 0.05) similarly (14.5 ± 23.2 vs. 8.1 ± 20.5%; p > 0.05) after both methods but biceps’ brachii thickness increased to a greater extent (9.6 ± 3.6 vs. 5.5 ± 3.7%; p < 0.05) for the 3/7 method. Despite subjects performing more repetitions with the same absolute load after training, neuromuscular fatigability increased (p < 0.05) after the two training methods.
Conclusion
The 3/7 method provides a better stimulus for strength gain and muscle hypertrophy than the 8 × 6 method.
... Por ejemplo, en un curl de bíceps, la cabeza larga se activa en mayor medida al inicio del movimiento y la cabeza corta lo hace en mayor media al final del recorrido (J. Brown, Solomon, & Paton, 1993), pudiendo generar diferentes adaptaciones el hecho de trabajar en una zona del recorrido u otra. ...
Variables de influencia en el proceso de hipertrofia en adultos sanos y su importancia en la elaboración de programas de entrenamiento
... These results are similar to those of Brown et al. [17], who reported that more activity is found in the SH of the biceps during a rapid supination movement of the hand with surface electrodes, as well as to those of Romeny et al. [13], who found more activity in the medial (electrodes #4 and #5 here) than in the lateral portion (electrodes #6 and #7 here) of the LH during supination with wire electrodes. The data acquired in the present study were from normal subjects because they are considered to be the best candidates for demonstrating whether anatomical biceps partitions can be voluntarily activated. ...
The latest myoelectric prostheses have several degrees of freedom and therefore require a large number of myoelectric signals to fully exploit their capabilities. Muscle compartments, which are intra-muscular subdivisions innervated by an individual muscle nerve branch, can be exploited to provide additional independent muscle control sites to operate such prostheses. To explore whether muscle compartments can be voluntarily controlled, electromyographic (EMG) signals are recorded from an array of seven pairs of equally spaced surface electrodes positioned across the biceps brachii of four healthy subjects. The EMG signals are collected in two positions: 1) with the subject seated, right elbow flexed ~100°, and 2) with the subject standing with the right arm extended horizontally in the coronal plane (out to the side). In both positions, the hand is either fully supinated, neutral, or fully pronated. The average root mean square value of the EMG signals obtained from three pairs of electrodes positioned over the biceps short head are compared with the average obtained for the three pairs placed over the biceps long head. Out of the nine hand position/load pairs examined, two pairs are found to elicit larger EMG activity in the long head or in the short head. The potential to preferentially activate either the short or the long head of the biceps suggests that the selective activation of muscle compartments is a promising strategy for facilitating the control of myoelectric prostheses capable of generating many types of movement.
... This observation is supported by findings that single muscles are sub-divided into neuromuscular compartments, 8 that motor units form ''task groups'' within single muscles for specific joint movements, 17 that skeletal muscle is anatomically segmented 12 and that fast-and slow-twitch muscle fibres are not uniformly distributed throughout a muscle's belly. 14 Although the ''function'' of muscle segments within single skeletal muscles has been extensively assessed, 3,14,19,31,35 there has been little effort to quantify muscle segment contractile properties and their muscle fibre type distributions. Given that muscle segments have been shown to have large and absolute differences in moment arms, 10,36 it is probable that muscle segments may have their own unique contractile characteristics and distributions of fast-and slowtwitch muscle fibres to support their individual roles in producing torque across a joint. ...
The aim of this investigation was to determine the contractile properties of motor units within 3 segments of the gluteus maximus utilizing a laser-based mechanomyographic (MMG) technique. The intention was to determine whether there were segmental differences in motor unit contractile properties and whether these differences may be related to the muscle segment's function and its fibre type composition.
Ten subjects were recruited from the student population at the University of Wollongong. Maximal percutaneous neuromuscular stimulation (PNS) was delivered to the medial and lateral portions of three (cranial, middle, caudal) muscle segments of the gluteus maximus by an MMG stimulator. An MMG laser sensor measured the lateral displacement of the muscle segment belly resulting from the development of maximal isometric tension. Parameters characterizing the MMG waveforms were statistically compared to determine variations in contractile properties both within (medial to lateral) and between segments.
Our results indicated that the contractile properties of motor units varied significantly (p < 0.05) between, but not within (medial to lateral), the three segments of the gluteus maximus. Most the gluteus maximus. Most notably, segment contraction time (tc) decreased significantly (p < 0.05) in a cranio to caudal direction suggesting a variation in muscle fibre type composition within the three segments of the muscle. Even when corrected for differences in muscle belly displacement between subjects, the cranial segment was found to have a significantly (p < 0.05) longer contraction time than the two more caudal segments. The results suggest that the gluteus maximus was composed of muscle segments that were physiologically, as well as anatomically, designed to fulfil particular roles during everyday motor tasks. Based upon these results, the MMG technique appears to have considerable utility for the non-invasive assessment of muscle segment contractile properties for both laboratory and clinical applications.
... Numerous studies have confirmed that single human skeletal muscles can be subdivided into smaller independently controlled muscle segments during a motor task (Johnson & Bogduk, 1994; Wickham & Brown, 1998; Mc Andrew et al. 2006). Although the 'function' of muscle segments within single skeletal muscles has been extensively assessed (Lindman et al. 1990; Brown et al. 1993 ), there has been little effort to quantify the contractile properties and muscle fiber type distributions that may be found within single skeletal muscle segments. The fiber type proportions differ within different muscle segments and depend not only on their functional role, but on other factors, such as innervation and the pattern of mechanical stimuli as well (Staron et al. 1984; Pette & Vrbova, 1989; Goldspink et al. 1992). ...
Keywords:
histochemistry;tensiomyography;vastus medialis longus;vastus medialis obliquus
Abstract
The aim of this study was to show the connection between structure (anatomical and histochemical) and function (muscle contraction properties) of vastus medialis obliquus (VMO) and vastus medialis longus (VML). The non-invasive tensiomyography (TMG) method was used to determine the contractile properties (contraction time; Tc) of VML and VMO muscle, as a reflection of the ratio between the slow and fast fibers in two groups of nine young men. VML and VMO significantly (P < 0.01) differ in the proportion of type 1 (59.6: 44%) and type 2b (6.3: 15%) fibers. The VML muscle is almost entirely composed of type 1 and type 2a fibers. In many samples of this muscle no type 2b fibers were found. The proportion of slow-twitch type 1 fibers is nearly twice as high as the proportion of fast-twitch type 2a fibers. These observations indicate that VML is a slower and more fatigue-resistant muscle than VMO muscle. These characteristics correspond to the different functions of the VML, which is an extensor of the knee, and to the VMO, which maintains the stable position of the patella in the femoral groove. Our results obtained by TMG provided additional evidence that muscle fibers within the segments of VM muscle were not homogenous with regard to their contractile properties, thereby confirming the histochemical results. Tc can be attributed to the higher percentage of slow-twitch fibers – type 1. The statistically shorter Tc (P ≤ 0.001) of VMO (22.8 ± 4.0 ms) compared with VML (26.7 ± 4.0 ms) in our study is consistent with previously found differences in histochemical, morphological and electrophysiological data. In conclusion, the results of this study provide evidence that the VML and VMO muscles are not only anatomically and histochemically different muscles, but also functionally different biological structures.
... 17 Electrode placement sites were based on previous studies. [18][19][20] Insertion of intramuscular-needle electrodes (for supraspinatus, brachialis, and subscapularis) was performed by a researcher trained in intramuscular electromyography (RG) using a sterile technique. Ultrasonography was used to locate the deep target muscles, allowing accurate electrode insertion. ...
Testing procedures for SLAP lesions of the shoulder can combine resisted elbow flexion, forearm pronation and supination, and glenohumeral glides. These procedures reproduce symptoms by increasing biceps long head active tension or passive torsion, and by placing the shoulder in an unstable position. We compared activation of biceps long head and pain intensity, between supinated and pronated forearm positions, between different glides, and between individuals with and without shoulder impairment. A case control study. Twelve participants with suspected SLAP lesions and twelve with no history of shoulder injury volunteered. Electromyography measured muscle activity in biceps long head, normalised against maximum voluntary isometric contraction (MVIC). Subjective pain intensity scores were recorded. Biceps long head activity was greater in forearm supination (mean 39% MVIC) than pronation (mean 24% MVIC), but pain was higher in pronation (mean 4.5/10) than supination (3.2/10). Biceps long head activity was greater when testing without a glide, but there was no difference in pain comparing the glide conditions. The impaired group experienced more pain (mean 3.9/10) than controls (mean 0.3/10) but there was no difference in shoulder muscle activity. No one combination of testing procedures appeared to be diagnostic of SLAP lesions in our sample. This study supports the theory that biceps long head acts as a stabiliser of the shoulder, and suggests that clinical testing procedures for SLAP lesions may need to inhibit biceps long head activity. The addition of glides to SLAP testing procedures did not affect the reproduction of pain.
... Recently, the mechanical specialisation of the biceps brachii, whereby distinct insertion sites have been proposed for each head of the biceps brachii (Athwal et al. 2007; Eames et al. 2007), provides a scenario in which the long and short head may change length independently of each other. Accordingly, Brown et al. (1993) report the SBB is shorter when compared with the LBB during supination. During supination, the SBB's insertion, the proximal radial tuberosity, is externally rotated likely resulting in a greater relative shortening of the SBB when compared with the LBB, which inserts on the distal radial tuberosity. ...
In the biceps brachii, age-related differences in synaptic excitability and muscle architecture may affect motor unit (MU) activity differently depending on the position of the forearm. It was hypothesised that as a result of these age-related differences, greater changes in MU activity would accompany a change in forearm position in old when compared with young men. Six young (22 +/- 3 years) and six old (84 +/- 3 years) men maintained isometric elbow flexion at 10% of maximal voluntary contraction (MVC) during changes in forearm position. Forty-nine MUs in the short (SBB) and long (LBB) heads of the biceps brachii were followed. Motor unit recruitment and de-recruitment thresholds, motor unit discharge rates (MUDRs), and MU discharge variability were measured. Although an age-related decrease in MU recruitment thresholds, and increase in MU discharge variability was evident, changes in forearm position influenced MUDRs similarly in young and old men (P = 0.27). Motor unit recruitment thresholds of the SBB were highest in the pronated position (8.2 +/- 2.9 %MVC), whereas in the LBB they were highest in the supinated position (8.6 +/- 2.0 %MVC). Motor unit discharge rates of the LBB did not change with forearm position. In the SBB, MUDRs were highest when the forearm was supinated, and also greater when compared with the LBB in this position. No position-dependent changes were observed for MU discharge variability in the LBB, but the SBB exhibited greatest MU discharge variability in the pronated position. The results suggest that MU activity is modulated following a change in forearm position, but the response is similar in young and old adults.
... These three-bar type configuration electrodes with silver contact material and interelectrode distance of 10 mm are designed to minimize crosstalk between muscles of close proximity. Electrode placement was based on previous studies for both heads of biceps brachii (Brown et al., 1993) and for anterior and middle deltoid (Delagi and Perotto, 1980). Intramuscular electrodes for the more deeply located supinator and brachialis muscles were placed according to descriptions by Delagi and Perotto (1980), and were inserted using ultrasound guidance by a qualified examiner. ...
The majority of clinical tests used to diagnose superior labral anterior to posterior (SLAP) lesions of the shoulder have poor diagnostic accuracy, possibly related to a lack of anatomical validity for test procedures. The resisted supination external rotation (RSER) test is suggested to reproduce symptoms associated with a SLAP lesion by placing stress on the labrum through increasing tension in biceps brachii long head. The test requires supination of the forearm against resistance, while the shoulder is externally rotated passively. It was hypothesized that the RSER would increase activity in biceps brachii long head, thereby providing evidence of the anatomical validity of the test. Electromyography (EMG) was used to measure activity in biceps brachii long head and five other muscles potentially recruited during the RSER test in 12 healthy subjects. EMG amplitude was normalized against maximum voluntary isometric contraction for each muscle. Muscle activity values were averaged across five RSER trials and graded descriptively. Moderately strong activity was recorded in biceps brachii long head and supinator muscle throughout all phases of the RSER test. Brachialis was minimally active throughout the test. The results provide support for the anatomical basis of the RSER test, with the resisted forearm supination component of the test recruiting moderately strong levels of activity in biceps brachii long head throughout the test. Although the evidence of anatomical validity provides support for the RSER test as a clinical test for SLAP lesions of the shoulder, further tests of diagnostic accuracy are required.
... As all of the muscles examined are subcutaneous, double differential surface electrodes (to minimize crosstalk between muscles of close proximity) were placed over the belly of tested muscles. Electrode placement was based on previous studies (Brown et al., 1993;Perotto, 2005). Using established protocols (Wickham and Brown, 1998), participants completed three 3-sec maximum voluntary contraction (MVC) trials for each muscle by contracting maximally against a fixed resistance in 908 shoulder abduction (middle deltoid), 908 shoulder flexion (anterior deltoid), and 908 elbow flexion (long and short heads of biceps). ...
Both Biceps Load tests I and II rely on an increase in tension in the long head of biceps to identify a superior labral anterior and posterior (SLAP) lesion. This study aimed to evaluate the anatomical basis of Biceps Load tests I and II by measuring activity in the long head of biceps in the two clinical tests. Activity in the long head of biceps was measured in 12 healthy young participants using surface electromyography. Activity was only minimally increased in both Biceps Load I and II compared with the resting position. In the absence of convincing support for the anatomical basis of the test, investigations of diagnostic accuracy need to be replicated in order for the reported high accuracy of Biceps Load I and II tests to be supported with confidence.
Summary of the doctoral thesis Introduction: In many sports, strength is considered an important basis for performance. One factor affecting strength is muscle mass. Therefore, it may be necessary to increase muscle mass in athletes through resistance training. However, the most effective strategy to gain muscle mass has not yet been clearly identified. Many methods used in practice are based on anecdotal evidence rather than empirical data. For this reason, different approaches to hypertrophy training were examined in this thesis based on three studies. The methods and most important results of these studies are summarized in the following. Methods: In the first study, adolescent American football players completed a 12-week resistance training program with three total-body training sessions per week using either Block Periodization (BLOCK) or Daily Undulating Periodization (DUP). The aim was to investigate the effects of the different periodization strategies on muscle mass and athletic performance. The second study assessed the impact of a three-week detraining period (DTR) on anthropometric measures and sport performance. In a third study, highly trained male subjects completed a six-week low-intensity calf resistance training intervention either without (noBFR) or with blood flow restriction (BFR). Before and after the intervention, 1-RM calf raise, calf volume, muscle thickness of the gastrocnemius, and leg stiffness were recorded. Results: At the end of the first intervention, both periodization groups showed significantly higher muscle mass and thickness, as well as athletic performance without differences between groups. Following DTR, fat mass increased significantly, and fat-free mass was reduced. All other measures were unchanged after DTR. Both BFR and NoBFR training resulted in significant increases in 1-RM and muscle thickness without differences between groups. Calf volume and leg stiffness remained unchanged in both conditions. Conclusions: In adolescent American football players, the structure of periodization does not appear to have any effect on muscle growth. Furthermore, a three weeks DTR does not result in negative effects. Both results provide new insights that can be helpful when creating training programs as well as for planning training-free periods. The currently frequently investigated BFR training does not show higher effects on muscle growth of the lower extremities than conventional low-intensity resistance training.
DEVELOPING MUSCLE CROSSSECTIONAL AREA HAS THE POTENTIAL TO ENHANCE PERFORMANCE FOR MANY ATHLETES. BECAUSE EMERGING EVIDENCE CHALLENGES TRADITIONAL BELIEFS REGARDING THE PRESCRIPTION OF HYPERTROPHYFOCUSED TRAINING PROGRAMS, THIS REVIEW PROVIDES AN OVERVIEW OF THE CURRENT LITERATURE RELATING, SPECIFICALLY, TO PROGRAMMING VARIABLES. EVIDENCE-BASED RECOMMENDATIONS ARE PROVIDED FOR THE DESIGN OF EFFECTIVE RESISTANCE-TRAINING PROGRAMS, WITH THE GOAL OF INCREASING AN ATHLETE'S SKELETAL MUSCLE MASS. © National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
To facilitate the use of upper limb myoelectric prostheses, we investigated if and how muscle compartments, i.e intra-muscular subdivisions each innervated by a nerve branch, could be voluntarily contracted. Five pairs of electrodes were positioned across the short head of the biceps brachii and 5 others across its long head. Electromyographic signals from 4 able subjects were collected. They produced voluntary isometric and isotonic contractions with the arm kept in different positions while the hand was either fully supinated, neutral or fully pronated. Root mean square value of the signals, from the 5 electrode pairs across the long and short heads were averaged. Depending on the task, activity was found larger in one head or in the other. Being able to activate either head of the biceps, while not yet completely independently, suggests that the selective use of compartments could be a possible avenue for controlling myoelectric prostheses.
Relevance of Electromyography in Kinesiology Typical Acquisition Settings Study of Motor Control Strategies Investigation on the Mechanical Effect of Muscle Contraction Gait Analysis Identification of Pathophysiologic Factors Workload Assessment in Occupational Biomechanics Biofeedback The Linear Envelope Information Enhancement through Multifactorial Analysis References
Immediate and delayed-onset muscle soreness differ mainly in chronology of presentation. Both conditions share the same quality of pain, eliciting and relieving activities and a varying degree of functional deficits. There is no single mechanism for muscle soreness; instead, it is a culmination of 6 different mechanisms. The developing pathway of DOMS begins with microtrauma to muscles and then surrounding connective tissues. Microtrauma is then followed by an inflammatory process and subsequent shifts of fluid and electrolytes. Throughout the progression of these events, muscle spasms may be present, exacerbating the overall condition. There are a multitude of modalities to manage the associated symptoms of immediate soreness and DOMS. Outcomes of each modality seem to be as diverse as the modalities themselves. The judicious use of NSAIDs and continued exercise are suggested to be the most reliable methods and recommended. This review article and each study cited, however, represent just one part of the clinician's decisionmaking process. Careful affirmation of temporary deficits from muscle soreness is not to be taken lightly, nor is the advisement and medical management of muscle soreness prescribed by the clinician.
The aim of this investigation was to determine whether functional differentiation was present within the radiate muscle, pectoralis major, by determining whether motor units within individual muscular segments were independently controlled by the central nervous system (CNS) during a series of isometric muscle actions. Six miniature surface electrode pairs were placed along the origin of the pectoralis major of eight male subjects. Electromyographic (EMG) potentials were then recorded during isometric shoulder actions in various planes and at two levels of contraction intensity. The EMG waveforms were integrated (IEMG) and then normalized. The normalized IEMG waveforms (nIEMG) were then statistically compared to determine whether motor units within the detection area of each electrode pair had varied their contribution to the total activity of the muscle from one isometric action to another. An alteration in the contribution of each electrode site (muscular segment) to the total activity of the pectoralis major was taken to be indicative of functional differentiation. The results of this study indicated that the muscular segments of pectoralis major were controlled independently during performance of the isometric tasks. Isometric shoulder adduction saw moderate to high levels of activation expand from the inferior segments of the muscle to all segments, excluding the clavicular head, as the position of the upper limb changed from 90° to 0° of abduction. The most inferior muscular segments of pectoralis major were utilized preferentially when the subjects performed shoulder extension motions from a flexed shoulder position. Conversely, shoulder flexion motions utilized the superior segments of the muscle. Finally, horizontal flexion of the shoulder joint elicited activity from the middle segments of the muscle regardless of the degree of shoulder flexion. The results of this study support the notion that the CNS 'fine tunes' the activation patterns of muscular segments within pectoralis major to maximize the muscle's potential to contribute efficiently to isometric actions of the shoulder.
The quest to increase lean body mass is widely pursued by those who lift weights. Research is lacking, however, as to the best approach for maximizing exercise-induced muscle growth. Bodybuilders generally train with moderate loads and fairly short rest intervals that induce high amounts of metabolic stress. Powerlifters, on the other hand, routinely train with high-intensity loads and lengthy rest periods between sets. Although both groups are known to display impressive muscularity, it is not clear which method is superior for hypertrophic gains. It has been shown that many factors mediate the hypertrophic process and that mechanical tension, muscle damage, and metabolic stress all can play a role in exercise-induced muscle growth. Therefore, the purpose of this paper is twofold: (a) to extensively review the literature as to the mechanisms of muscle hypertrophy and their application to exercise training and (b) to draw conclusions from the research as to the optimal protocol for maximizing muscle growth.
Surface electromyographic (EMG) amplitude from the upper trapezius muscle is widely used as a measure of shoulder-neck load in ergonomic studies. A variety of methods for normalizing EMG amplitude from the upper trapezius (EMGamp(ut)) have been presented in the literature. This impedes meta-analyses of, for instance, upper trapezius load in relation to development of shoulder-neck disorders. The review offers a thorough discussion of different normalization procedures for EMGamp(ut). The following main issues are focused: output variable, location of electrodes, posture and attempted movement during normalization, load and duration of reference contractions, signal processing and test-retest repeatability. It is concluded that translations of EMGamp(ut) into biomechanical variables, for example relative force development in the shoulder or in the upper trapezius itself, suffer from low validity, especially if used in work tasks involving large and/ or fast arm movements. The review proposes a standard terminology relating to normalization of EMGamp(ut) and concludes in a concrete suggestion for a normalization procedure generating bioelectrical variables which reflect upper trapezius activation.
During voluntary arm movements, the medial back muscles are differentially active. It is not known whether differential activity also occurs when the trunk is perturbed unpredictably, when the earliest responses are initiated by short-latency spinal mechanisms rather than voluntary commands. To assess this, in unpredictable and self-initiated conditions, a weight was dropped into a bucket that was held by the standing subject (n = 7). EMG activity was recorded from the deep (Deep MF), superficial (Sup MF) and lateral (Lat MF) lumbar multifidus, the thoracic erector spinae (ES) and the biceps brachii. With unpredictable perturbations, EMG activity was first noted in the biceps brachii, then the thoracic ES, followed synchronously in the components of the multifidus. During self-initiated perturbations, background EMG in the Deep MF increased two- to threefold, and the latency of the loading response decreased in six out of the seven subjects. In Sup MF and Lat MF, this increase in background EMG was not observed, and the latency of the loading response was increased. Short-latency reflex mechanisms do not cause differential action of the medial back muscles when the trunk is loaded. However, during voluntary tasks the central nervous system exerts a 'tuned response', which involves discrete activity in the deep and superficial components of the medial lumbar muscles in a way that varies according to the biomechanical action of the muscle component.
The electromyographic activity of the biceps brachii--BB (long head), triceps brachii--TB (long head) and deltoideus--DA (clavicular portion) muscles, during the going (G) and return (R) phases in "front support" exercise, as well the efficacy of this exercise for the development of these muscles strength were studied in 10 male volunteers. The values were normalized through maximum voluntary isometric contraction (MVIC = 100%) and statistically analyzed using the Friedman, DMS and Wilcoxon non-parametric test. A value of p < or = 0.05 indicated significance (Campos, 1983). All the muscles presented higher electromyographic activity in the return phase of the movement. The triceps brachii was the muscle which had higher activity in both phases of the movement. It was concluded that the "front support" exercise is efficient for strength development mainly in the triceps brachii muscle.
Despite the functional importance of the human quadriceps femoris in movements such as running, jumping, lifting and climbing, and the known effects of muscle architecture on muscle function, no research has fully described the complex architecture of this muscle group. We used ultrasound imaging techniques to measure muscle thickness, fascicle angle and fascicle length at multiple regions of the four quadriceps muscles in vivo in 31 recreationally active, but non-strength-trained adult men and women. Our analyses revealed a reasonable similarity in the superficial quadriceps muscles, which is suggestive of functional similarity (at least during the uni-joint knee extension task) given that they act via a common tendon. The deep vastus intermedius (VI) is architecturally dissimilar and therefore probably serves a different function(s). Architecture varies significantly along the length of the superficial muscles, which has implications for the accuracy of models that assume a constant intramuscular architecture. It might also have consequences for the efficiency of intra- and intermuscular force transmission. Our results provide some evidence that subjects with a given architecture of one superficial muscle, relative to the rest of the subject sample, also have a similar architecture in other superficial muscles. However, this is not necessarily true for vastus lateralis (VL), and was not the case for VI. Therefore, the relative architecture of one muscle cannot confidently be used to estimate the relative architecture of another. To confirm this, we calculated a value of whole quadriceps architecture by four different methods. Regardless of the method used, we found that the absolute or relative architecture of one muscle could not be used as an indicator of whole quadriceps architecture, although vastus medialis, possibly in concert with VL and the anterior portion of VI, could be used to provide a useful snapshot. Importantly, our estimates of whole quadriceps architecture show a gender difference in whole quadriceps muscle thickness, and that muscle thickness is positively correlated with fascicle angle whereas fascicle length is negatively, although weakly, correlated with fascicle angle. These results are supportive of the validity of estimates of whole quadriceps architecture. These data are interpreted with respect to their implications for neural control strategies, region-specific adaptations in muscle size in response to training, and gender-dependent differences in the response to exercise training.
The aim of this study was to determine, by a non-invasive whole muscle mechanomyographic technique (wMMG), how muscle segment contractile properties varied within the segments of the multifunctional deltoid muscle, and how such variations in contractile properties may reflect the muscle segment’s function and fibre type composition. We hypothesised that muscle segment contractile properties, consistent with slower twitch muscle fibre populations, would be associated with the deltoid’s prime mover abductor muscle segment (middle head), rather than the prime mover flexor and extensor muscle segments (anterior and posterior heads). Eighteen healthy and athletic University students (nine males and nine females; mean age 20–24 years) volunteered for this study. Each subject’s right upper limb was secured with the forearm flexed to 30° and the shoulder in 45° of abduction. The wMMG laser sensor was positioned perpendicular to the middle of each muscle segment, to record the involuntary lateral displacement of the muscle belly following a maximal, single twitch, percutaneous neuromuscular stimulation (PNS) [180 V (max.); 80 mA (max.); 50 μs]. Ten trials were recorded from each of the seven deltoid segments for a total of 70 trials per subject. From each segment, eight variables were analysed from the recorded wMMG waveforms; maximal displacement (D
max); delay time (T
d); contraction time (T
c); sustain time (T
s); relaxation time (T
r) and half relaxation time (½T
r), average rate of contraction (ARC) and the average rate of relaxation (ARR). The results indicated that the contractile properties of the seven segments of the deltoid muscle showed significant (P < 0.05) variation in a medial to lateral direction. Medially the strap-like segments of the anterior (S1, S2) and posterior heads (S4–S7), with larger moment arms for shoulder flexion and extension respectively, had the fastest contractile properties. In contrast the multipennate segment 3, with the largest moment arm for shoulder abduction, had the slowest contractile properties (P < 0.05). Muscle segment contractile properties were matched to the biomechanical and architectural characteristics of the individual muscle segments.
It has been suggested that the positive position of the O'Brien test (shoulder flexion, horizontal adduction, and internal rotation) tensions the bicipital labral complex relative to the negative position (shoulder flexion, horizontal adduction, and external rotation). This study measured active and passive tension in the long head of biceps in the 2 positions of the O'Brien test to validate the proposed anatomic basis of the test. Active tension was measured using surface electromyography of the long head of biceps in 12 healthy young adults. Passive tension was measured using a load cell attached to the intracapsular tendon of the long head of biceps in 5 cadaver specimens. Active and passive tension were higher in the negative position, thus refuting the proposed anatomic basis of the test. Although there may be an alternative basis for the test, the failure to support the proposed anatomic basis may partly explain the variable likelihood ratios obtained in clinical accuracy studies of the O'Brien test. The results of this study reinforce the need for anatomic validation during the development of clinical testing procedures.
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