EMG of serratus anterior and trapezius in the chimpanzee: scapular rotators revisited.

The importance of arm-raising has been a major consideration in the functional interpretation of differences in shoulder morphology among species of nonhuman primates. Among the characters that have been associated with enhancement of the arm-raising mechanism in hominoid primates are the relative enlargement of cranial trapezius and caudal serratus anterior, as the main scapular rotators, as well as changes in scapular morphology associated with their improved leverage for scapular rotation. Yet in an EMG study of cranial trapezius and caudal serratus anterior function in the great apes, Tuttle and Basmajian (Yrbk. Phys. Anthropol. 20:491-497, 1977) found these muscles to be essentially inactive during arm-raising. Although Tuttle and Basmajian suggest that the cranial orientation of the glenoid fossa in apes has reduced the demand for scapular rotation during arm-raising, subsequent EMG studies on other primate species suggest that these muscles do play a significant role in arm motion during active locomotion. This paper presents a reexamination of muscle recruitment patterns for trapezius and caudal serratus anterior in the chimpanzee. All but the lowest parts of caudal serratus anterior were found to be highly active during arm-raising motions, justifying earlier morphological interpretations of differences in caudal serratus anterior development. The lowest digitations of this muscle, while inactive during arm-raising, displayed significant activity during suspensory postures and locomotion, presumably to control the tendency of the scapula to shift cranially relative to the rib cage. Cranial trapezius did not appear to be involved in arm-raising; instead, its recruitment was closely tied to head position.     

Shoulder movements during quadrupedal locomotion in arboreal primates

The kinematics of scapula and shoulder joint movements were analyzed in three species of arboreal quadrupedal primates using cineradiography. Our findings indicate that scapular movement is highly important for forelimb movement in primates with this ancestral mode of locomotion. Retroversion of the scapula (syn. caudal rotation or extension) during the stance phase contributes more than 40% to the stride length of the forelimb. Lateral forelimb excursions, a general feature for arboreal primates, are based on complex three-dimensional scapular movements guided by the clavicle. Humeral abduction is achieved by scapular abduction and transversal rotation of the scapula about its longitudinal axis, and is therefore strikingly different from humeral abduction in humans. At the same time, the movements of the shoulder joint are limited to flexion and extension only.     

Normalization procedures using maximum voluntary isometric contractions for the serratus anterior and trapezius muscles during surface EMG analysis.

The serratus anterior and trapezius muscles are considered to be the only upward rotators of the scapula and are very important for normal shoulder function. A variety of methods have been used to produce a maximum voluntary isometric contraction (MVIC) of these muscles for normalization of EMG data. The purpose of this study was to quantify the surface EMG activity of the serratus anterior muscle and the upper, middle, and lower parts of the trapezius during 9 manual muscle tests performed with maximum effort in 30 subjects. It was found that no one muscle test produced a MVIC for all individuals. Therefore, to perform normalization within each subject, it is suggested that the 2 or 3 tests identified in this study that produce high levels of EMG activity for each muscle be performed. The scapular protraction muscle test that is often used to normalize data for the serratus anterior muscle produced relatively low levels of EMG activity and was not found to be an optimal test. Muscle tests in which an attempt was made to de-rotate the scapula from an upwardly rotated position produced much higher levels of EMG activity in the serratus anterior muscle.     

Rib orientation and implications for orthograde positional behavior in nonhuman anthropoids

Strong caudal obliquity of the lower ribs is one of the assumed characteristics of the thoracic region in hominoids and Ateles. Strong caudal obliquity keeps the scapula of the weight-bearing forelimb on the dorsal surface of the trunk via the serratus anterior muscles during propulsion (Stern et al. 1980). We examined the orientation of odd-numbered ribs in lateral view in remounted thoracic skeletons of fifteen nonhuman anthropoids. Hominoids exhibit pronounced caudal obliquity in the seventh and ninth ribs compared to Old and New World monkeys. The position of the maximum thoracic cage width, which approximates the attachment of the serratus anterior muscle, is more caudally located in Hylobates and Pongo. The overall pattern of rib obliquity is generally similar between New and Old World monkeys, including Ateles. Perhaps not only forelimb suspensory behavior but also various orthograde positional behaviors are related to the strong obliquity of the lower ribs; however, further investigation is necessary.     

Effects of trunk rotation on scapular kinematics and muscle activity during humeral elevation

Trunk rotation often accompanies humeral elevation, during daily activities as well as sports activities. Earlier studies have demonstrated that changes in spinal posture contribute to scapular motion during humeral elevation. However, the effect of trunk rotation on scapular kinematics during humeral elevation has received scant attention. This study aimed to clarify how trunk rotation affects scapular kinematics and muscle activities during humeral elevation. Electromagnetic motion capture and electromyography were used to assess scapular and clavicular motion and muscle activity in the right and left sides of 12 healthy young men. The subjects were seated and instructed to elevate both arms with the trunk in neutral, ipsilaterally rotated, or contralaterally rotated position. Ipsilaterally rotated trunk position decreased the internal rotation (by 5°, relative to neutral trunk position) and increased the upward rotation (by 4°, relative to neutral trunk position) of the scapula. Trunk position did not affect clavicular motion during humeral movement. Electromyography showed that contralaterally rotated trunk position increased the activity of the upper trapezius and serratus anterior muscles and decreased the activity of the lower trapezius. Therapists should consider the importance of trunk rotation, which may be the key to developing more efficient rehabilitation programs.     

Hindlimb dominance during primate high-speed locomotion

Quadrupedal locomotion was mechanically studied for four species of primates, the chimpanzee, the rhesus macaque, the tufted capuchin, and the ring-tailed lemur, from low to high speeds of about two to ten times the anterior trunk length per second. A wide variety of locomotor patterns was observed during the high-speed locomotion of these primates. Positive correlations were observed between the peak magnitude of foot force components and speed. The differentiation of the foot force between the forelimb and the hindlimb did not largely change with a change of speed for each species. The vertical component and the accelerating component for the rhesus macaque were relatively large in the forelimb from low- to high-speed locomotion. The rhesus macaque, which habitually locomotes on the ground, differed in the quadrupedal locomotion from the other relatively arboreal primates, for which the hindlimb was clearly dominant in their dynamic force-producing distribution between the forelimbs and the hindlimbs. The previously reported locomotor difference, which was indicated among primates from the foot force pattern between the forelimb and the hindlimb during walking, also applied to high-speed locomotion.     

Head and shoulder posture affect scapular mechanics and muscle activity in overhead tasks

Forward head and rounded shoulder posture (FHRSP) is theorized to contribute to alterations in scapular kinematics and muscle activity leading to the development of shoulder pain. However, reported differences in scapular kinematics and muscle activity in those with forward head and rounded shoulder posture are confounded by the presence of shoulder pain. Therefore, the purpose of this study was to compare scapular kinematics and muscle activity in individuals free from shoulder pain, with and without FHRSP. Eighty volunteers were classified as having FHRSP or ideal posture. Scapular kinematics were collected concurrently with muscle activity from the upper and lower trapezius as well as the serratus anterior muscles during a loaded flexion and overhead reaching task using an electromagnetic tracking system and surface electromyography. Separate mixed model analyses of variance were used to compare three-dimensional scapular kinematics and muscle activity during the ascending phases of both tasks. Individuals with FHRSP displayed significantly greater scapular internal rotation with less serratus anterior activity, during both tasks as well as greater scapular upward rotation, anterior tilting during the flexion task when compared with the ideal posture group. These results provide support for the clinical hypothesis that FHRSP impacts shoulder mechanics independent of shoulder pain.     

The use of EMG biofeedback for learning of selective activation of intra-muscular parts within the serratus anterior muscle: A novel approach for rehabilitation of scapular muscle imbalance

Motor control and learning possibilities of scapular muscles are of clinical interest for restoring scapular muscle balance in patients with neck and shoulder disorders. The aim of the study was to investigate whether selective voluntary activation of intra-muscular parts within the serratus anterior can be learned with electromyographical (EMG) biofeedback, and whether the lower serratus anterior and the lower trapezius muscle comprise the lower scapula rotation force couple by synergistic activation. Nine healthy males practiced selective activation of intra-muscular parts within the serratus anterior with visual EMG biofeedback, while the activity of four parts of the serratus anterior and four parts of the trapezius muscle was recorded. One subject was able to selectively activate both the upper and the lower serratus anterior respectively. Moreover, three subjects managed to selectively activate the lower serratus anterior, and two subjects learned to selectively activate the upper serratus anterior. During selective activation of the lower serratus anterior, the activity of this muscle part was 14.4 ± 10.3 times higher than the upper serratus anterior activity (P < 0.05). The corresponding ratio for selective upper serratus vs. lower serratus anterior activity was 6.4 ± 1.7 (P < 0.05). Moreover, selective activation of the lower parts of the serratus anterior evoked 7.7 ± 8.5 times higher synergistic activity of the lower trapezius compared with the upper trapezius (P < 0.05). The learning of complete selective activation of both the lower and the upper serratus anterior of one subject, and selective activation of either the upper or lower serratus anterior by five subjects designates the promising clinical application of EMG biofeedback for restoring scapular muscle balance. The synergistic activation between the lower serratus anterior and the lower trapezius muscle was observed in only a few subjects, and future studies including more subjects are required before conclusions of a lower scapula rotation couple can be drawn.     

A Comparison of Qualitative and Quantitative Methodological Approaches to Characterizing the Dorsal Side of the Scapula in Hominoidea and Its Relationship to Locomotion

Hominoidea have adapted to various forms of locomotion, each of which has specific requirements that are reflected in the shape of the scapula. We compared several qualitative and quantitative methods for characterizing the dorsal side of the scapula to detect morphological differences that reflect the adaptations of the scapula to locomotor behaviors. Our sample included 55 specimens of Hominoidea, representing five genera, including Homo, focusing specifically on the relative sizes of the scapular supraspinous and infranspinous fossae. In addition, we weighed the supraspinatus and infraspinatus muscles of 23 of the specimens to examine the feasibility of extrapolating muscle characteristics from osteological data. Our findings confirmed that the five genera exhibit significant differences in the relative size of the supraspinous and the infraspinous fossae that are related to their forms of locomotion. The supraspinous fossa was relatively small in Homo and Pongo but large in Pan, Gorilla, and Hylobates. The analysis of muscle weights showed that a substantial amount of information about soft tissues is lost in osteological analyses, leading us to recommend caution when drawing conclusions regarding forms of locomotion based only on osteological analyses.     

Effects of Kinesio taping on scapular kinematics of overhead athletes following muscle fatigue

Scapular kinematics alterations have been found following muscle fatigue. Considering the importance of the lower trapezius in coordinated scapular movement, this study aimed to investigate the effects of elastic taping (Kinesio taping, KT) for muscle facilitation on scapular kinematics of healthy overhead athletes following muscle fatigue. Twenty-eight athletes were evaluated in a crossover, single-blind, randomized design, in three sessions: control (no taping), KT (KT with tension) and sham (KT without tension). Scapular tridimensional kinematics and EMG of clavicular and acromial portions of upper trapezius, lower trapezius and serratus anterior were evaluated during arm elevation and lowering, before and after a fatigue protocol involving repetitive throwing. Median power frequency decline of serratus anterior was significantly lower in KT session compared to sham, possibly indicating lower muscle fatigue. However, the effects of muscle fatigue on scapular kinematics were not altered by taping conditions. Although significant changes were found in scapular kinematics following muscle fatigue, they were small and not considered relevant. It was concluded that healthy overhead athletes seem to present an adaptive mechanism that avoids the disruption of scapular movement pattern following muscle fatigue. Therefore, these athletes do not benefit from the use of KT to assist scapular movement under the conditions tested.     

Serratus ventralis function in vervet monkeys (Cercopithecus aethiops): are primate quadrupeds unique?

The serratus ventralis in mammals is a fan-shaped scapulo-thoracic muscle that is believed by most morphologists both to support body weight and to rotate the scapula during quadrupedal locomotion. Electromyographic studies of this muscle in cats, dogs and opossums confirm the dual supportive and rotatory roles of the serratus ventralis. Although this muscle has been studied in several primate species, the concentration on arboreal locomotion has resulted in an inadequate data set to permit direct comparisons to non-primate terrestrial quadrupeds. In order to provide a more comparable data set, we examined cranial, mid- and caudal thoracic regions of the serratus ventralis during terrestrial quadrupedalism in the vervet monkey, Cereopithecus aethiops. Our results indicate that the serratus ventralis does support the body during the stance phase of quadrupedalism in this primate. However, unlike several non-primate mammals, it plays a relatively insignificant rotatory role during swing phase.     

Effects of horizontal shoulder abduction and adduction on the activity and strength of the scapular protractors

Increased activity of the serratus anterior (SA) muscle combined with decreased activity of the pectoralis major (PM) muscle during scapular protraction exercise is a widely used method for selective strengthening of the former muscle. However, the role played by the PM during maximal scapular protraction remains unclear. The objective of our study was to investigate the effects of horizontal shoulder abduction (decreasing PM activity) and adduction (increasing activity) on the strength and activity of the scapular protractors (the SA and PM) during maximal protraction. Twenty-nine healthy males performed maximal scapular protraction combined with horizontal shoulder abduction or adduction. The strength and activity of the PM and SA decreased significantly (both p < 0.01) during maximal scapular protraction combined with horizontal shoulder abduction, compared with maximal scapular protraction alone, but increased significantly (both p < 0.01) when maximal scapular protraction was combined with horizontal shoulder adduction. We thus conclude that the PM stabilizes the activated SA during maximal scapular protraction, which effectively increases SA activity and scapular protraction strength in the serratus punch posture.     

Morphology of the shoulder musculature of the American kestrel,Falco sparverius (Aves), with implications for gliding flight

Summary The shoulder morphology of the American kestrel,Falco sparverius, was dissected with an emphasis on the morphological requirements for gliding flight. Kestrels are being used as a model for the study of gliding flight in a non-specialized gliding bird. The kestrel forelimb is relatively generalized in its construction, and does not appear to have any remarkable specializations for gliding. However, several structures found in specialized gliders/soarers which may contribute to gliding were also found in kestrels; these include the presence of a scapular anchor and pectoral muscle fibers inserting onto the tendon of the biceps brachii muscle. This paper is the prelude to an experimental study on the gliding flight in this species and may serve as a basis for future functional or taxonomic comparisons.Abbreviations BB M. biceps brachii - Br M. brachialis - C coracoid - C12 12th cervical vertebra - CBA M. coracobrachialis cranialis - CBC M. coracobrachialis caudalis - DMA M. deltoideus major pars cranialis - DMa M. deltoideus major - DMC M. deltoideus major pars caudalis - DMi M. deltoideus minor - ECU M. extensor carpi ulnaris - EDC M. extensor digitorum communis - EMR M. extensor metacarpi radialis - ES M. expansor secundariorum - EU M. ectopicondylo-ulnaris - F furcula - FAH Facies articularis humeralis - FASc Facies articularis scapularis - FASt Facies articularis sternalis - ECU M. flexor carpi ulnaris - FP Fascia pectoralis - H humerus - HCB humerocarpal band - HS Os humeroscapularc and adjacent shoulder ligaments - K sternal keel - LDA M. latissimus dorsi pars cranialis - LDC M. latissimus dorsi pars caudalis - LMS Ligamentous portion of membrana sternocoracoclavicularis - MC Membrana cristoclavicularis - MS Membrana sternocoracoclavicularis - N Notarium - PB M. tensor propatagialis pars brevis - PC pectoral crest of humerus - PL M. tensor propatagialis pars longa - PP M. pronator profundus - PPB M. pectoralis propatagialis brevis - PPL M. pectoralis propatagialis longus - PS M. pronator superficialis - PT M. pectoralis pars thoracicus - RP M. rhomboideus profundus - RS M. rhomboideus superficialis - SA scapular anchor - SB M. subscapularis - SBe M. subscapularis pars externa - SBi M. subscapularis pars interna - SC M. supracoracoideus - Sc scapula - SHA M. scapulohumeralis cranialis - SHC M. scapulohumeralis caudalis - SP M. serratus profundus - SSA M. serratus superficialis pars cranialis - SSC M. serratus superficialis pars caudalis - SSM M. serratus superficialis pars metapatagialis - ST M. sternocoracoideus - St sternum - SU M. subcoracoideus - Su M. supinator - Sy synsacrum - T M. triceps - TH M. triceps humeralis - TS M. triceps scapularis     

Differential activation of parts of the serratus anterior muscle during push-up variations on stable and unstable bases of support

No studies have examined the effects of an unstable surface on push-up and push-up plus exercises in terms of the two parts of the serratus anterior muscle. We hypothesized that the lower part of the serratus anterior would have greater activity with an unstable surface, which requires stabilizing the scapular position. The present study was performed to investigate the intramuscular differences between parts of the serratus anterior muscle during push-up and push-up plus exercises. Twelve healthy subjects were included in the study. The upper and lower parts of the serratus anterior and upper and lower parts of the trapezius were investigated by surface EMG during four types of exercise. Repeated one-way ANOVA was used for statistical analyses. Maintaining the push-up plus phase caused significant increases in EMG activity of the upper serratus anterior compared with the push-up ascending phase on both of stable and unstable bases (P < 0.05). The lower serratus anterior showed increased activation on an unstable surface, which required more joint stability than did the stable base. Upper trapezius/upper serratus anterior ratio was significantly lower in the PUP than in the PUA phase with both stable and unstable bases of support (P < 0.05).Further studies are required to investigate the intramuscular variation in activation of the serratus anterior during exercises for rehabilitation.     

Relationship between scapular position and structural strength of rib cage in quadruped animals

Determining scapular position is a major issue in reconstructing the skeletal systems of extinct quadruped archosaurs and mammals, because the proximal portion of the scapulae has no direct skeletal joint with the vertebrae or ribs. When quadrupeds stand or walk, their trunk is suspended between the forelimbs by the serratus muscles, which arises from the lateral sides of the “thoracic” ribs and inserts into the proximal portion of the costal surface of the scapula. Therefore, the “thoracic” ribs are subjected to a static or dynamic vertical compression between the lifting force from the muscle and the gravitational force from the vertebral column. To investigate the body support function of the ribs, we analyzed the mechanical strength of the ribs of extant tetrapods by the two‐dimensional finite element method, and compared the degree of strength through their craniocaudal scapular positions. The result of this simulation showed that the “thoracic” ribs of quadrupeds, to which the serratus muscles attach, have a relatively higher strength against compaction than the other ribs. In bipeds, however, we did not find a similar correlation between the strength of ribs and the serratus muscle. This implies that the location of robust ribs is associated with the arrangement of the serratus muscle, and provides a probable candidate for determination of the scapular position for extinct quadruped archosaurs and mammals. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Electromyographic analysis of the serratus anterior and trapezius muscles during push-ups on stable and unstable bases in subjects with scapular dyskinesis

The present study was performed to assess the electromyographic activity of the scapular muscles during push-ups on a stable and unstable surface, in subjects with scapular dyskinesis. Muscle activation (upper trapezius [UT]; lower trapezius [LT]; upper serratus anterior [SA_5th]; lower serratus anterior [SA_7th]) and ratios (UT/LT; UT/SA_5th; UT/ SA_7th) levels were determined by surface EMG in 30 asymptomatic men with scapular dyskinesis, during push-up performed on a stable and unstable surface. Multivariate analysis of variance with repeated measures was used for statistical analyses. The unstable surface caused a decrease in the EMG activity of the serratus anterior and an increase in EMG activity of the trapezius (p = 0.001). UT/SA_5th and UT/ SA_7th ratios were higher during unstable push-ups (p = 0.001). The results suggest that, in individuals with scapular dyskinesis, there is increased EMG activity of the trapezius and decreased EMG activity of the serratus anterior in response to an unstable surface. These results suggest that the performance of the push up exercise on an unstable surface may be more favorable to produce higher levels of trapezius activation and lower levels of serratus anterior activation. However, if the goal of the exercise program is the strengthening of the SA muscle, it is suggested to perform the push up on a stable surface.     

Architectural properties of the musculoskeletal system in the shoulder of two callitrichid primate species derived from virtual dissection

Primates - Callitrichidae are small, arboreal New World primates that utilize a variety of locomotor behaviors including trunk-to-trunk leaping (TTL) and horizontal locomotion which involve...     

Effect of isometric horizontal abduction on pectoralis major and serratus anterior EMG activity during three exercises in subjects with scapular winging

The aim of this study was to determine the effect of isometric horizontal abduction using Thera-Band during three exercises (forward flexion, scaption, and wall push-up plus) in subjects with scapular winging by investigating the electromyographic (EMG) amplitude of the pectoralis major, serratus anterior and the pectoralis major/serratus anterior activity ratio. Twenty-four males with scapular winging participated in this study. The subjects performed the forward flexion, scaption, and wall push-up plus with and without isometric horizontal abduction using Thera-Band. Surface EMG was used to collect the EMG data of the pectoralis major and serratus anterior during the three exercises. Two-way repeated analyses of variance with two within-subject factors (isometric horizontal abduction condition and exercise type) were used to determine the statistical significance of pectoralis major and serratus anterior EMG activity and the pectoralis major/serratus anterior EMG activity ratio. Pectoralis major EMG activity was significantly lower during forward flexion and wall push-up plus with isometric horizontal abduction, and serratus anterior EMG activity was significantly greater with isometric horizontal abduction. Additionally, the pectoralis major/serratus anterior activity ratio was significantly lower during the forward flexion and wall push-up plus with isometric horizontal abduction. The results of this study suggest that isometric horizontal abduction using Thera-Band can be used as an effective method to facilitate the serratus anterior activity and to reduce excessive pectoralis major activity during exercises for activating serratus anterior.     

Kinesiotaping for scapular dyskinesis: The influence on scapular kinematics and on the activity of scapular stabilizing muscles

Scapular dyskinesis is observed in 61% of overhead athletes (Burn et al., 2016). For most of them, it remains asymptomatic. However, scapular dyskinesis is considered a risk factor for shoulder injury by some authors (Clarsen et al., 2014). The aim of this study is to explore the effectiveness of kinesiotaping in modifying scapular kinematics and peri-scapular muscle activity in dyskinetic athletes. The 3-dimensional position and orientation of the scapula as well as the activation of upper trapezius, lower trapezius and serratus anterior were recorded in twenty asymptomatic athletes during shoulder movements (flexion and abduction), in loaded and unloaded conditions and in three circumstances (standard, kinesiotaping 1, kinesiotaping 2). A significant decrease between 9 and 12% in upper trapezius activity was observed with kinesiotaping 1 and 2. Lower trapezius activity was slightly increased with kinesiotaping 1 while it was significantly decreased about 15–20% with kinesiotaping 2. No change was observed in serratus anterior activity, for either kinesiotaping 1 or 2. Considering scapular kinematics, both kinesiotaping 1 and 2 significantly increased posterior tilt and upward rotation. External rotation was decreased with kinesiotaping 2, in comparison to standard condition. Kinesiotaping, and especially taping 1, seems to be an effective method for changing periscapular muscle activity and scapular kinematics.