Muscular Insertions Research Articles

Strain pattern in the upper facial skeleton: Preliminary model development

In the human upper facial skeleton, the patterns of strain caused by physiological loading are not known. It is generally accepted that these patterns can be predicted based on the morphology of the bone, but this is not necessarily the case. The elucidation of these patterns of strain has a significant impact on the plating techniques of facial fractures, the development of bone substitutes and tissue-engineered bone, and the understanding of facial development. The goal of this study was to initiate the development of a model that could be used to measure strain magnitude and direction in the upper facial skeleton from physiological loading of facial musculature. A strain gauge was bonded to the lateral orbital rim of a cadaveric skull that had been dissected, leaving only muscular origins and insertions intact. Braided nylon straps were sutured to the origins and insertions of the masseter and levator labii superioris, and these were pulled individually using a hydraulic testing machine. When the masseter origin was pulled, the recorded strain increased with increasing force and the angle of the strain corresponded directly to the angle of pull. When the levator labii superioris origin was pulled, the angle of strain was directed anteriorly and inferiorly, but did not correspond with the axis of the muscle or the axis of the lateral orbital rim where the strain gauge was located. It was concluded that this model is reliable and reproducible for investigating strain magnitude and direction in the human upper facial skeleton.

Cognitive-Behavioural Treatment of Chronic Pain in Primary Care

Objectives: To analyse the frequencies of, and the clinical risk factors for, full-time sick leave (100% sick leave) in the past month after cognitive-behavioural treatment of young persons at risk of permanent disability.Patients and methods: Persons aged 16-45 years on more than six weeks of sick leave for benign disorders were asked to participate in a four-week treatment programme in primary care. It included weekly patient-doctor dialogues on worries about pain, and daily training. Mental and somatic health and psychosocial stressors were assessed. Locations of muscular insertion lesions (enthesopathies) were counted. Pain behaviour was defined as ≥1.5 points on the University of Alabama scale. Self-reported inability to work, pain anxiety, pain behaviour and depression were evaluated before and after the treatment.All variables were categorised. Non-parametric tests were used to detect group differences and changes in related dichotomous variables. The variables that were significantly related to 100% sick leave at the three-month, one-year and three-year follow-ups were used as independent variables in multinomial logistic regression calculations of odds ratios (ORs) with 95% confidence intervals (95% CI) for 100% sick leave in the past month. Also, three or more enthesopathy locations and previous 100% sick leave of more than three months were chosen as independent variables. The ORs were adjusted for age and sex.Results: Two Swedes and 149 immigrants participated; nearly all were working in the service sector. Long periods of sick leave were common, on average 47 weeks. All reported pain as their major problem, mostly in the back and shoulders, and 27.8% had three or more locations of enthesopathies. Pain anxiety (76% to 50%), self-reported inability to work (75% to 60%) and pain behaviour (68% to 54%) were common but diminished after treatment (p<0.001). The frequency of 100% sick leave in the past month decreased at the follow-ups, from 76% at the start to 48%, 44% and 51%, respectively (p<0.001). Persons with self-reported inability to work had ORs of 3.04 (95% CI 1.22-7.56) at the three-month follow-up, and 3.13 after one year (95% CI 1.26-7.80) for being on 100% sick leave, while persons with three or more enthesopathy locations had an OR of 2.98 (95% CI 1.19-7.44) after three years. Previous durations of 100% sick leave of more than three months had significant ORs varying from 5.19 to 2.89.Conclusion: The number of persons on 100% sick leave declined significantly after this treatment. The risk factors for future 100% sick leave were, in the short term, self-reported inability to work and, in the long term, multiple enthesopathies.

Cirurgias de músculos retos horizontais: análise de planejamentos e resultados

Objetivo: Estudo retrospectivo dos resultados de cirurgias para correção de estrabismo horizontal num hospital-escola. Métodos: Selecionados casos de eso ou exotropias aproximadamente concomitantes, sem sinais evidentes de paralisias musculares ou de processos de contenção das rotações oculares, em que se realizaram, apenas, cirurgias de recuo dos retos mediais (grupo A), ou laterais (grupo C), ou de recuo e ressecção em esotropias (grupo B), ou exotropias (grupo D), com ou sem transposições das inserções dos músculos operados. Resultados: Esotropias foram mais freqüentes que exotropias (nA = 66; nB = 28; nC = 27; nD = 22) e cirurgias com transposições (96) superaram as sem (47). A distribuição dos ângulos pré-operatórios (m = 42,49D, s = 11,68D nas esotropias; m = 35,39D; s = 9,93D nas exotropias) e a das correções obtidas (m = 38,95D, s = 13,57D nas esotropias; m = 31,64D, s = 14,58D nas exotropias) são praticamente equivalentes e, além disso, altas correlações foram observadas entre o ângulo pré-operatório e a quantidade da operação respectiva. Todavia, as correlações entre os ângulos pré-operatórios e os resultados proporcionais da cirurgia (em D/mm) foram, todas, baixas. As quantidades de correções adequadas quando considerados ângulos residuais de desvio de ±5D, ±10D e ±15D, foram respectivamente de 31,9%, 62,8%, e 80,8% nas esotropias e 40,8%, 55,1% e 73,5% nas exotropias. Conclusões: Embora planejamentos cirúrgicos e suas execuções produzam resultados coletivos satisfatórios, os individuais mostram ainda uma imprevisibilidade muito alta.

Normal anal sphincter anatomy and age- and sex-related variations at high-spatial-resolution endoanal MR imaging.

To describe the various patterns of normal sphincter anatomy as seen at endoanal magnetic resonance (MR) imaging and to assess sex- and age-related variations in the dimensions of the anal sphincter to refine the diagnosis of sphincter disorders. Endoanal MR imaging (1.5 T) was performed in 100 healthy volunteers (50 women, 50 men) evenly distributed between ages 20 and 85 years. The essential anatomic structures were evaluated, and various patterns in men and women were recorded. The thickness of the anal sphincter muscles and the length of the anal canal were measured, and age- and sex-related correlations were studied. Sex-related differences included a significantly shorter external sphincter in women than in men both laterally (mean, 27.1 mm +/- 5.4 vs 28.6 mm +/- 4.3; P: <.05) and anteriorly (mean, 14.0 mm +/- 3.0 vs 27.0 mm +/- 53.0; P: <.051). The superficial transverse perineal muscle is located more superiorly in women than in men. The central perineal tendon in men is a central muscular insertion point; in women, it represents an area where muscle fibers imbricate. Age-related variations included a significant decrease in the thickness of the external sphincter in men (P: <.01). Significant decrease in the thickness of the longitudinal muscle and increase in the thickness of the internal sphincter were noted in both sexes (P: <.01). High-spatial-resolution endoanal MR imaging provides excellent visualization of pelvic floor structures. Severe atrophy as it occurs in incontinent patients should be differentiated from physiologic, age-related thinning of the external sphincter and longitudinal muscle.

Dual origin and segmental organisation of the avian scapula

Bones of the postcranial skeleton of higher vertebrates originate from either somitic mesoderm or somatopleural layer of the lateral plate mesoderm. Controversy surrounds the origin of the scapula, a major component of the shoulder girdle, with both somitic and lateral plate origins being proposed. Abnormal scapular development has been described in the naturally occurring undulated series of mouse mutants, which has implicated Pax1 in the formation of this bone. Here we addressed the development of the scapula, firstly, by analysing the relationship between Pax1 expression and chondrogenesis and, secondly, by determining the developmental origin of the scapula using chick quail chimeric analysis. We show the following. (1) The scapula develops in a rostral-to-caudal direction and overt chondrification is preceded by an accumulation of Pax1-expressing cells. (2) The scapular head and neck are of lateral plate mesodermal origin. (3) In contrast, the scapular blade is composed of somitic cells. (4) Unlike the Pax1-positive cells of the vertebral column, which are of sclerotomal origin, the Pax1-positive cells of the scapular blade originate from the dermomyotome. (5) Finally, we show that cells of the scapular blade are organised into spatially restricted domains along its rostrocaudal axis in the same order as the somites from which they originated. Our results imply that the scapular blade is an ossifying muscular insertion rather than an original skeletal element, and that the scapular head and neck are homologous to the 'true coracoid' of higher vertebrates.

Skull Shape, Masticatory Apparatus, and Diet of Vassallia and Holmesina (Mammalia: Xenarthra: Pampatheriidae): When Anatomy Constrains Destiny

The form and function of the masticatory apparatus of the fossil genera Vassallia and Holmesina are analyzed so that the possible dietary behaviors of these pampathere xenarthrans might be inferred. Analysis is based on comparisons of dental morphology and skeletal features (through RFTRA) associated with the masticatory musculature among the pampatheres, the extant dasypodids Euphractus and Dasypus, and the glyptodont Propalaeohoplophorus. A method is proposed for generating a moment arm of the massetericus independently of the muscle's line of action, which allows direct comparison among extant and fossil mammals. The masticatory apparatus of the pampatheres strongly resembles that of Euphractus among extant forms, but the development of muscular attachment sites indicates a more powerful musculature, particularly the massetericus; the taxa differ most markedly in dental morphology. Long moment arms about the jaw joint and large ratios of muscle to bite moments indicate forceful rather than quick movements. The various skeletal and dental features analyzed suggest that the masticatory apparatus of the pampatheres was more powerful and efficient in transverse chewing than in dasypodids and that they were primarily grazers consuming mainly coarse vegetation. These features, some shared with herbivorous ungulates, include wide, relatively flat mandibular condyles; condyles well dorsal to muscular insertion sites; expanded angular processes; unfused symphysis; a posteriorly extended tooth row; open-rooted teeth; mesial teeth that bear mainly transverse striations; distal teeth that are mesiodistally elongated, bear basined occlusal surfaces, and in Vassallia possess a central island of resistant dentine that acted as a functional analogue of an ectoloph; and teeth with a stepwise arrangement. The results of this study indicate that detailed analysis and comparison of morphology lead to useful predictions of behavior.

Lengths and lever arms of hip joint muscles: geometrical analyses using a human multibody model

Abstract Multibody analysis was applied in order to construct a model of the human body including the large joints and 31 muscles crossing the hip and knee. The model represents the 50th percentile rank of a male adult. The model was used to study the influence of hip joint angles on the distances between muscular insertions and origins and on muscular lever arms. Maximum and minimum muscle lengths were determined during inplane and combined hip joint motions. Maximum and minimum lever arms and their flexion/extension, abduction/adduction and rotation components during inplane hip motions were computed. A good qualitative agreement was obtained with the literature data; being suitably compared with the results presented here. It is concluded that a large geometrical data base on hip joint muscle lengths and lever arms is provided which was not previously available and which may be of significant value in morphometry, musculoskeletal research and biomechanical modelling.

Musculature of the soft palate: clinico-anatomic correlations and therapeutic implications in the treatment of cleft palates.

Hypoplasia of the maxilla, often described as a classic sequela to surgical repair of the cleft palate, has been rare in our experience. We believe that our surgical technique, which includes dividing the nasal mucosa and the abnormal muscular insertions at the posterior border of the hard palate, is an important factor in preventing this sequela. We compared the anatomy of 12 normal palates in cadavers to the anatomy of cleft palates seen at operation and to the anatomy of one cleft palate in a fetus aged 34 weeks. In cleft palates, the muscular fibres have an abnormal sagittal orientation, inserting on the posterior border of the hard palate. The division of both the nasal mucosa and these abnormal muscular insertions at the posterior border of the hard palate enables the surgeon to eliminate the abnormal posterior pull of these fibers on the maxilla.

Associations between self-rated psychosocial work conditions and musculoskeletal symptoms and signs. Stockholm MUSIC I Study Group.

The aim was to study the associations between self-rated psychosocial work conditions and the characteristics and location of musculoskeletal symptoms, signs, and syndromes. Perceived psychosocial work conditions were recorded in a cross-sectional study with 358 men and women in various occupations. Symptoms were recorded from the musculoskeletal system with a questionnaire, and signs were detected in a medical examination of all body regions. The analyses of statistical associations between the psychosocial factors and musculoskeletal disorders were performed with control for age, gender, and physical load. The most consistent and pronounced associations were mainly seen between poor psychosocial work conditions and coexisting symptoms and signs of the neck and back regions. Poor psychosocial work conditions were more consistently and strongly associated with signs of muscular (soft tissue) tenderness than with signs of tenderness in the joints, tendons, or muscular insertions or signs in nerve compression tests. Mainly low social support at work, but also high psychological demands and high job strain, were associated with such symptoms and signs, whereas decision latitude at work showed few associations with musculoskeletal disorders. Perceived poor psychosocial work conditions are statistically associated mainly with symptoms and signs of muscular tenderness in the central body regions. Studies on associations between psychosocial work conditions and musculoskeletal disorders should separate effect measures of different clinical signs and different body regions in order to avoid attenuation of the risk estimates.

Three-dimensional Reconstruction of the Human Fetal Philtrum

The anatomy of the philtrum is incompletely understood because it is difficult to analyze three-dimensionally. Previous anatomic studies suggested that the philtral ridges are formed by the dermal insertion of the orbicularis oris muscle and musculis nasalis decussating across the midline, with the philtral dimple an area of few muscular insertions. This theory is inconsistent with the usual finding of a normal-appearing philtrum contralateral to the cleft in patients with unilateral cleft lip. Using a microcomputer and three-dimensional software, we have created a three-dimensional model of the philtrum from digitized images of sequential transverse histological sections from a third-trimester fetus. Our studies demonstrate that the philtral ridges are formed by thickened dermis and dermal appendages. The labial levators are the predominant muscles associated with the philtrum throughout its length; their fibers insert into the dermis lateral to the philtral ridges. Crossing muscle fibers of the orbicularis oris pars marginalis only appear below the vermilion-cutaneous junction, caudal to the philtral ridges.

Entrapment of the popliteal artery and its surgical management in a 20-year period

This study was a retrospective review of 19 patients with popliteal artery entrapment syndrome (PAES) treated in a 20-year interval. The Heidelberg classification of PAES was used, which differentiates three categories of entrapment: in type I the popliteal artery has an atypical course, in type II the muscular insertion is atypical, and in type III both conditions are present. Besides decompression of the popliteal artery the commonest operative reconstruction used was resection of the atherosclerotic part of the artery and autologous vein interposition grafting (n = 12). Local thromboendarterectomy was done in seven cases, six with a vein patch angioplasty repair. Follow-up ranged from 6 months to 20 years (mean 9.5 years). There was no limb loss. The rate of complications was lowest after primary venous interposition (two of 12) compared with five of 11 when venous interposition was not used (P < 0.01). Autologous saphenous vein interposition grafting seems to be the best treatment for PAES.

Transmanubrial Osteomuscular Sparing Approach for Apical Chest Tumors

The transclavicular approach improved the treatment of apical chest tumors. However, removing the internal half of the clavicle and sectioning its muscular insertions led to serious postoperative alterations. We propose a transmanubrial approach, through a manubrial L-shaped transection and first costal cartilage resection, which allows retraction of an osteomuscular flap including but sparing the clavicle and all its muscular insertions. The elevation of the osteomuscular flap affords excellent access to the subclavicular region with safe control and resection of neurovascular outlet structures during the resection of apical chest tumors. Shoulder articulations and stability of the scapular girdle are respected, thus avoiding functional and cosmetic consequences of clavicle resection.(Ann Thorac Surg 1997;63:563–6)

Gracilis Muscle Dynamic Urethral Sphincter Myoplasty: Rat Model Experience

Purpose Dynamic urethral sphincter myoplasty (skeletal muscle urinary sphincter reconstruction) using a neurovascularly intact gracilis muscle was investigated in a rat model. Materials and Methods In female Sprague-Dawley rats, a unilateral gracilis anticus muscle flap was dissected from the medial thigh, preserving the medial muscular insertion, vascular flow, and innervation. This muscle graft was used to completely encircle the urethra and was fixed in position. Urodynamic leak point pressure (LPP) and bladder volume at leakage were measured with cystometry after 1 month, using an 18 gauge catheter placed through the bladder dome with a constant infusion rate of 0.2 ml. per minute. In addition, the effect of electrical stimulation of the gracilis myoplasty (current parameters: 1 to 10 mA, 1 to 60 Hz, 0.05 to 1 msec. duration) on intravesical leak point pressure was noted during cystometry. Results The gracilis muscle measured 3.8 plus/minus 0.3 cm. in length, 0.5 plus/minus 0.1 cm. in width and 0.2 plus/minus 0.1 cm. in thickness. Blood flow rates to the grafted and contralateral gracilis myoplasty were similar at 43 plus/minus 26 and 51 plus/minus 30 g.cm. 3, respectively (p = 0.46). The leak point pressure (LPP) of control, unstimulated gracilis myoplasty and gracilis myoplasty with electrical stimulation were 28 plus/minus 8, 32 plus/minus 12, and 85 plus/minus 27 mm.Hg (p less than 0.01). Bladder volumes at LPP in the 3 respective groups were 0.5 plus/minus 0.2, 0.6 plus/minus 0.3 and 1.2 plus/minus 0.6 ml (p less than 0.01). Conclusions Gracilis myoplasty is not obstructive, as substantiated by unchanged leak point pressure and leak point capacity. Myoplasty with low current stimulation, however, significantly increased LPP and leak point capacity.

Locomotor differentiation and different skeletal morphologies in mangabeys (Lophocebus and Cercocebus).

The postcranial morphology of the arboreal white-cheeked mangabey (Lophocebus albigena) differs from that of partly terrestrial Cercocebus mangabeys (C. torquatus, C. galeritus). Its humerus has a reduced greater tuberosity, weak muscular insertions on the humeral shaft, less salient trochlear keels, a thinner diaphysis and less retroflexed medial epicondyle. The femur of L. albigena is characterized by a lowered greater trochanter, a thinner shaft, a flattened distal epiphysis and a wide and shallow patellar surface. The forelimb is short relative to other limb segments. L. albigena has attained these skeletal features by deducting the ancestral terrestrial adaptations, such as skeletal robusticity and joint restriction. Influence of phylogenetic inertia on the development of skeletal morphology are discussed.

Bilateral Gluteus Maximus V-Y Advancement Musculocutaneous Flaps for the Coverage of Large Sacral Pressure Sores: Revisit and Refinement

Surgical management of the sacral defect using the gluteal muscle or musculocutaneous flap has been well accepted over the years. In this study, refinements in the bilateral gluteus maximus V-Y advancement musculocutaneous flaps were made. These refinements include having sharper angle (60 degrees or less) at the donor sites of the flap, cutting the edges of the gluteal muscle of 3 cm beyond the skin flap, and cutting most parts of the gluteal muscle at a depth of only 2.5 cm (at the level of upper third portion). These improvements result in less tension closure of the donor site, easier closure of the advanced flaps in two planes without tension, and better preservation of most parts of the gluteal muscular insertions to the femur and their functions. The design of V-Y advancement has successfully maintained the superior and inferior gluteal vessels and inferior gluteal nerve. In this study, the average sacral defect was more than 12 cm in diameter, and each advanced flap was 15 x 12 x 3 cm in size. Of the 63 consecutive patients undergoing bilateral gluteus maximus V-Y advancement musculocutaneous flaps with refinements for coverage of large sacral pressure sores, 59 (93%) achieved complete healing after an average follow-up period of 28 months. Only 4 patients had recurrences of sacral sore. In this study, the duration of hospital stay for flap coverage averaged 38.5 days. Four patients (6%) had superficial dehiscences of the donor site requiring skin grafting. Ten patients (16%) developed stitch abscesses and 9 patients (14%) had wound infections, but no flap was lost. No significant functional impairment related to the flap procedure was noted. The operative technique described in this paper is not only simple and noninvasive, but with our refinements of flap design, the bilateral gluteus maximus V-Y advancement musculocutaneous flaps also provide reliable and durable coverage for large sacral pressure sores.

Popliteal artery entrapment syndrome. Anatomic and embryologic bases, diagnostic and therapeutic considerations following a series of 15 cases with a review of the literature.

We report 15 examples of popliteal artery entrapment syndrome observed in 11 patients. The anatomical causes were as follows: in one case, the popliteal artery presented an aberrant course medially to the medial head of the gastrocnemius muscle. In 5 cases, there was a small fibrous band linking the medial head of the gastrocnemius muscle to the lateral condyle and crossing behind the popliteal artery; in 5 cases this anomaly was also found in association with an abnormally high and/or internal insertion of the medial head of gastrocnemius muscle. In the last 4 cases, there was a muscular insertion anomaly associated with muscular hypertrophy causing arterial compression. Arteriography performed in the 11 patients showed evocative signs of the diagnosis in all cases where the artery was patent. Two popliteal arteries were occluded. CT scan and MRI examination of the popliteal fossa enabled us to define the muscular origin of the popliteal compression. All of the patients were operated upon; two received a reversed saphenous bypass and all of the others were treated by liberation of the popliteal artery and/or vein by a posterior approach. Follow-up in all patients at long term showed good prognosis. All of the patients were able to take up their previous physical activities without sequelae. Our review of the literature, which is based on 374 cases of popliteal artery entrapment observed in 280 patients, made it possible to define the frequency of the various anomalies observed, their symptoms and the different therapeutic possibilities. The multiple anatomical classifications as well as the arterial and muscular embryology are also described.

Osteitis pubis in collegiate football players

Osteitis pubis in athletes is an inflammatory condition of the pubic symphysis and surrounding muscular insertions. It is of uncertain etiology, however, and is seen particularly in those sports requiring sprinting and sudden changes of direction. There is a paucity of literature of this condition occurring in players of American football. This report presents two such cases and details proposed etiology and a specific management protocol.

Histomorphometric analyses of cancellous bone from COSMOS 2044 rats.

The influence of 14 days of spaceflight on cancellous bone of male Wistar rats was assessed by histomorphometric analysis. In proximal tibia, no difference was found between flight, synchronous, vivarium, and basal groups for epiphyseal bone volume or trabecular arrangement. In metaphysis, primary spongiosa width was reduced in flight rats, suggesting an alteration in bone longitudinal growth. In flight rats, secondary spongiosa evidenced a trend toward decreased bone mass, trabecular number and thickness, and osteoid surfaces, whereas there was a tendency toward increased osteoclast number compared with vivarium control but not with synchronous rats. In femoral fossa trochanteri, an area facing deep muscular insertions, no changes in bone volume or structure were noted among the different groups. However, a reduction of osteoid surfaces was seen in flight and synchronous groups compared with the other groups. Resorption activity was increased in flight rats compared with control rats. In thoracic vertebral body, osteoblastic surfaces decreased similarly in flight and synchronous rats. In lumbar vertebral body, decreased osteoblastic surfaces and increased osteoclastic parameters were observed in flight and synchronous rats. The more striking effects of spaceflight were the decrease in tibial primary spongiosa width and the increase in resorption activity of the femoral fossa trochanteri. In all other sites, cellular alterations appeared similar in flight and synchronous rats, suggesting a role for physiological stress. The time course of events would depend on initial growth and turnover rates of bone, its weight-bearing function on earth, and the presence of muscular insertions.

Microgravity and bone adaptation at the tissue level.

Our knowledge of the adaptation of human bone microgravity remains poor despite long-term Russian spaceflights and the recent use of accurate techniques for bone mass measurements. The extent of bone deficits in the adaptation of the whole skeleton is not clear. At the tissue level, bone resorption and formation activities have been studied only in bones from rats after spaceflights lasting a few days to 3 weeks. In these animals, architectural features consistent with osteoporosis have been found in the proximal tibia. In pregnant animals the osteoclast population is increased at other skeletal sites. In areas of weight-bearing bones that are not protected by muscular insertions, bone resorption is not markedly altered after 7 days of spaceflight and bone formation is reduced. In areas of weight-bearing bones with muscular insertions and in non-weight-bearing bones, similar changes in bone cell activity are delayed. The severity of the response seems to vary with the location of the bone in the skeleton and its initial level of bone turnover. After 12.5 days the acute bone changes are less and no additional changes are observed after 21 days in space. We conclude that generalized bone deficits do not appear to be a consequence of microgravity but occur in localized areas according to the level of modeling and remodeling and of the support function of each bone at 1 g.

Chest wall and trunk muscle activity during inspiratory loading.

We measured the electromyographic (EMG) activity in four chest wall and trunk (CWT) muscles, the erector spinae, latissimus dorsi, pectoralis major, and trapezius, together with the parasternal, in four normal subjects during graded inspiratory efforts against an occlusion in both upright and seated postures. We also measured CWT EMGs in six seated subjects during inspiratory resistive loading at high and low tidal volumes [1,280 +/- 80 (SE) and 920 +/- 60 ml, respectively]. With one exception, CWT EMG increased as a function of inspiratory pressure generated (Pmus) at all lung volumes in both postures, with no systematic difference in recruitment between CWT and parasternal muscles as a function of Pmus. At any given lung volume there was no consistent difference in CWT EMG at a given Pmus between the two postures (P > 0.09). However, at a given Pmus during both graded inspiratory efforts and inspiratory resistive loading, EMGs of all muscles increased with lung volume, with greater volume dependence in the upright posture (P < 0.02). The results suggest that during inspiratory efforts, CWT muscles contribute to the generation of inspiratory pressure. The CWT muscles may act as fixators opposing deflationary forces transmitted to the vertebral column by rib cage articulations, a function that may be less effective at high lung volumes if the direction of the muscular insertions is altered disadvantageously.