Effects of cooking and shearing methodology on variation in Warner-Bratzler shear force values in beef

Longissimus lumborum between the 13th rib and the 4th lumbar vertebra from 57 steers was obtained at 48 h postmortem, stored at 2 degrees C, and frozen after 7 d postmortem. Consecutive 2.54-cm-thick, paired steaks were used to make the following comparisons: Protocol A) steaks were broiled to 70 degrees C, chilled 24 h at 3 degrees C, cored parallel to fiber orientation, and sheared with a Warner-Bratzler attachment to the Instron and Protocol B) steaks were modified-oven-broiled to 65 degrees C, cooled 30 min at 23 degrees C, cored perpendicular to the steak surface, and sheared with a Warner-Bratzler shear machine. Each of the four differences in protocol was subsequently compared one at a time with paired steaks. Protocol A resulted in higher (P < .05) shear force values than Protocol B (6.29 vs 3.60 kg). Neither shearing instrument nor cooling condition contributed to the difference (P > .05) in shear values. However, parallel vs perpendicular core orientation (6.31 vs 4.51 kg, respectively) and broil to 70 degrees C vs modified-oven broil to 65 degrees C cooking method (6.37 vs 5.31 kg, respectively) increased (P < .05) shear force values. Total variance (6.2 vs 1.2 kg2) and the proportion of variance in shear value attributed among animals was greater (P < .05) for Protocol A than for Protocol B (70.0 vs 44.5%). These data indicate that Protocol A resulted in greater animal differences in shear values, and thus was more discriminating than Protocol B.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of 20 weeks basic military training program on body composition, VO2max and aerobic fitness of obese recruits

Forty of the most obese recruits going through a 20 weeks Basic Military Training (BMT) program were selected from a cohort of 197 obese recruits. Their TBW, BF, FFW, VO2max, time taken to achieve VT (VTTime) and maximal heart rate (HRmax) were measured before, in the middle, and at the end of the program. The means for each of these variables measured in the 3 occasions were analysed for significant differences with the repeated measures analysis of variance. Variables that achieved significant difference were further analysed for pairwise difference with the post-hoc Tukey test. The critical value was set at p < 0.05. Mean TBW and BF decreased from 108.33 +/- 13.1 kg to 90.82 +/- 12.3 kg (p < 0.001), and 34.3 +/- 1.2% to 23.9 +/- 2.3% (p 0.001) respectively. Mean FW decreased from 37.4 +/- 4.8 kg to 22.0 +/- 4.5 kg (p < 0.001). FFW decreased slightly from a mean of 71.5 +/- 8.6 kg to 69.2 +/- 8.8 kg, which was not significantly different (p > 0.05). Mean VO2max increased from 28.1 +/- 6.3 ml.kg-1.min-1 to 32.1 +/- 5.1 ml.kg-1.min-1 (p < 0.001), and mean VTTime on similar exercise protocol increased from 13.3 +/- 2.7 minutes to 15.8 +/- 3.8 minutes (p < 0.001). Mean HRmax decreased from 183.5 +/- 12.1 beats.min-1 to 177.3 +/- 10.1 beats.min-1 (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Intrafusal motor innervation: a quantitative histological analysis of tenuissimus muscle spindles in the cat

A quantitative analysis of the motor innervation of intrafusal muscle fibres is described, based on teased silver-impregnated spindles of the tenuissimus muscle of the cat. Included in the analysis are the number and distribution of intrafusal branches of both skeletofusimotor (beta) and purely fusimotor (gamma) axons, and the form of their endings. The number of axonal branches per spindle was found to follow binomial probability distributions, as had previously been shown for the afferent axons. There was a strong correlation between the numbers of gamma intrafusal branches and afferent axons, but none for the intrafusal branches of beta axons. The degree of segregation of gamma input to bag2 and chain fibres was assessed and was found, among other things, to be related to the presence of secondary sensory endings in the same pole. In this and other respects it did not appear to have the properties that would be expected if independent activation of the bag2 and chain fibres were to be functionally important. Morphometric analysis of the motor endings supplied to bag2 or chain fibres by gamma axons revealed some differences between those of intrafusal branches with segregated as opposed to unsegregated distributions, but this cannot be taken as evidence of more than one type of static gamma motoneuron because of the likely contribution of other influential factors such as fibre size. Finally, the relevance of studies on intrafusal motor innervation to the concept of the motor unit and its development are discussed.

Relationship between muscle fiber types and sizes and muscle architectural properties in the mouse hindlimb

Skeletal muscle fiber and architectural properties both contribute to the functional behavior of a muscle. This study uses discriminant analysis and mathematical modeling to identify the structurally and functionally significant properties. The architectural properties of fiber length, muscle length, and pennation angle are found to be the most structurally significant parameters, whereas fiber length, muscle length, and fiber type distribution are found to be most functionally determining. Architectural speed and fiber type do not appear to be complimentary (i.e., the architectural determinant of speed, fiber length, is not associated with fibers of high intrinsic velocity). However, there does seem to be a synergistic relation between the two property classes and force production. Muscles with large physiological cross sectional areas (PCSAs) tend to contain a greater proportion of larger, faster fibers. Structurally or morphologically significant parameters are not always found to have a large functional effect. Pennation angle, though one of the most structurally significant variables, was found to have very little functional effect.

Magnetic resonance imaging of the extensor mechanism

Trauma involving the extensor mechanism of the knee is a fairly common clinical problem, and can be addressed easily with a basic understanding of the anatomy of the involved structures. Injury to the muscles and tendons of this group is categorized broadly into complete versus partial tears based on the respective absence or presence of intact fiber bundles. Acute injuries are associated with edema, hemorrhage, and fluid collections; chronic injuries often demonstrate redundancy, atrophy, and retraction. Fracture of the patella can be related to direct or indirect trauma, and is functionally equivalent to a complete tear of the musculotendinous elements. Tendinitis is a more chronic condition seen with repetitive trauma, and usually affects the proximal aspect of the patellar tendon. Swelling and abnormal intrasubstance signal are commonly associated with this entity.

Effects of distribution of muscle fiber length on active length-force characteristics of rat gastrocnemius medialis

BACKGROUND

The length-force curve of mammalian skeletal muscle is often wider than expected on basis of the optimum length of the muscle fibers. Two important effects may explain this discrepancy: muscle pennation and distribution of fiber lengths in the muscle. In the present study the effects of a Gaussian distribution of fiber lengths on muscle length-force characteristics were investigated in rat gastrocnemius medialis.

METHODS

Fiber length-force characteristics and parameter values of the Gaussian distribution were derived from literature data (Stephenson et al., 1989, J. Physiol., 410:351-366; Heslinga and Huijing, 1990, J. Morph. 206:119-132; Zuurbier and Huijing, 1993, J. Morphol., 218:167-180). Three different constructions of the distribution model were compared with experimental data. Pennation effects were incorporated in the model.

RESULTS

Two constructions gave reasonably good results: 1) the model with a fiber optimum distribution, in which fibers acted at the same absolute length at a given muscle length; 2) the model in which fiber optimum length was uniform but absolute length at a given muscle length was distributed.

CONCLUSIONS

In rat gastrocnemius medialis, the magnitude of the effects of these distributions is similar to pennation effects. The current results help to explain the relative wide working range of skeletal muscles in human movement and the differences in specific muscle tension as affected by muscle type, species, and age.

The detailed neuroanatomy of the human striated urethral sphincter

OBJECTIVE

To study the nerve supply of the striated urethral sphincter.

MATERIALS AND METHODS

The pelvis from six formalin-fixed male cadavers was dissected.

RESULTS

Cadaveric dissection revealed that both the intrinsic and extrinsic segments of the urethral rhabdosphincter receive their innervation from sacral roots S2-S4. The nerve fibres travel to their final destination via both the pudendal nerves and the nerve branches of the sacral roots. The terminal branches of the pudendal nerve enter the sphincteric area from the perineum. They separate shortly after they cross the ischial spine and run further ventromedially. Small branches approach the sphincter after their division from the dorsal nerve of the penis. The course of the pudendal nerve and its branching on the perineum are quite consistent. The pelvic branches travel inside the pelvis above the levator ani muscle. Among the cadavers the number of branches varied markedly, as did their site of termination (2.3 to 3.9 cm from the striated urethral sphincter). A substantial nerve approaching the sphincter from inside the pelvis was found. After it divided from the S2, S3 sacral roots it ran separately, initially just lateral to the fibres of the pelvic plexus and then on the dorsolateral surface of the rectum. In its terminal segment it dived into the levator ani muscle and terminated in the striated urethral sphincter.

CONCLUSIONS

We believe that the nerve supply to the striated urethral sphincter consists of branches from both the pudendal nerve and the 'extrapudendal' nerves that run above the levator ani muscle inside the pelvis. The variations in the course of the latter are remarkable.

The true nature of the adductor brevis dually innervated by the anterior and posterior branches of the obturator nerve in humans

To clarify the true nature and the mechanism of the human adductor brevis (specific adductor brevis, SAB) innervated dually by the anterior and posterior branches of the obturator nerve, we have carried out gross anatomical examination of 100 body halves of 50 adult Japanese cadavers. The SAB was found in 23 of the 100 thighs (23.0%), and its anterior and posterior surfaces received respectively the twigs from the anterior branch of the obturator nerve and the filament(s) from the posterior branch. The filament(s) was either indirectly derived from the medial stratum of the posterior branch through the formation of a common trunk with the twigs distributed in the obturator externus (14/23 thighs, 60.9%) or directly originating in the medial stratum of the posterior branch of the obturator nerve (9/23 thighs, 39.1%). In the close examination of the intramuscular distribution of the nerve to the SAB, the region innervated by the anterior branch of the obturator nerve could clearly be distinguished from that innervated by the posterior branch. The obturator nerve received fibers from L1234 (2/23 thighs) or from L234 (21/23 thighs), and the posterior branch of the obturator nerve ran through the obturator externus (18/23 thighs, 78.3%) or ran over the obturator externus (5/23 thighs, 21.7%), and finally emerged into the thigh. In view of the mode of origin of the filament(s), the structural element of the filament(s), and the pattern of entry of the filament(s) into the SAB, the fasciculus of the SAB, which is innervated by the posterior branch of the obturator nerve, was considered to originate in the obturator externus. Thus, the true nature of the SAB was concluded to be a complex product which was formed by a mechanism in which the fasciculus, which had separated from the obturator externus during the process of ontogeny, fused secondarily to the posterior surface of the regular adductor brevis. From findings in our series of studies, it was estimated that the maximum frequency of occurrence of the SAB could be 56%. Furthermore, from a statistical point of view, the segmental composition or course of the obturator nerve is not considered to be related to either the formation or the incidence of this muscle.

Index finger position and force of the human first dorsal interosseus and its ulnar nerve antagonist

In normal subjects, maximum voluntary contraction (MVC) and electrical ulnar nerve stimulation (UNS; 30-Hz bursts of 0.33 s) were systematically compared with regard to the forces generated in different directions (abduction/adduction and flexion) and at different degrees of index finger abduction. With a "resting" hand position in which there was no index finger abduction, UNS produced about one-half of the abduction force elicited by an MVC (mean ratio 51%). Qualitatively, such a discrepancy would be expected, because UNS activates two index finger muscles with opposing actions in the abduction/adduction plane of torques: the first dorsal interosseus (FDI) and the first palmar interosseus (FPI). The abduction forces produced by MVC and UNS were very sensitive to index finger abduction angle: at a maximum degree of abduction, the UNS-generated force even reversed its direction of action to adduction (with FPI dominating) and the abduction MVC declined to 37% of that in the resting hand position. Inasmuch as these declines in MVC- and UNS-generated abduction force could not be explained by a change in moment arm, the main alternative seemed to be abduction-associated alterations in FDI fiber length (analysis by previously published biomechanical data). The FDI and FPI were further compared by application of a UNS-generated fatigue test (5-min burst stimulation), with the index finger kept at a "neutral" angle, i.e., the abduction angle at which, in the unfatigued state, the forces of the FDI and FPI were in balance (zero net UNS-generated abduction/adduction force).(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of electrostimulation on mechanical and morphological characteristics of the triceps surae

The present study assessed the effects of training using electrostimulation of muscle (EMS) on the torque-angular velocity and torque-angle relationships, and the cross-sectional area (CSA) of the triceps surae. Twelve physical education students, divided into two groups (6 controls, 6 experimental), participated in the experiment. The EMS sessions were undertaken using a 'Complex-type' stimulator. Flexible elastomer electrodes were used. The current used discharged pulses lasting for 200 microseconds at a frequency of 70 Hz. The durations of contraction and rest were 5 and 15 s, respectively. The session lasted for 10 min for each muscle. The training regimen was three sessions per week for 4 weeks. Biomechanical tests were performed with the Biodex (Biodex Corporation, Shirley, NY, USA) isokinetic ergometer. Plantar flexions of the ankle over a concentric range of voluntary contractions were performed at different angular velocities (1.05, 2.10, 3.14, 4.20, 5.23 and 6.28 rad s-1) and maximum voluntary isometric contractions were held for 5 s at several ankle flexion angles (-30 degrees, -15 degrees, 0 degree and 15 degrees; 0 degree corresponds to foot flexion of 90 degrees relative to the leg axis). The peak value of the torque was recorded. Morphological tests consisted of measuring the CSA of the triceps surae on the right leg, 15 cm below the tibial protuberance, by a computerized tomography technique. The torque-velocity relationship was seen to shift significantly upwards after EMS training. The increase in the isometric torque observed after EMS training was greater in dorsiflexion than in plantarflexion.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of anthropometric characteristics in modern pentathlon performance in female athletes

In order to determine the role of body build characteristics in modern pentathletes, 65 female participants at the IXth World Modern Pentathlon Championships, 1989 (Wiener Neustadt, Austria) were investigated. Of these, 54 participate in the competition; the other 11 were reserves. Their mean (+/- S.D.) age was 22.34 +/- 3.97 years (range 16.08-32.58 years). Anthropometric characteristics (body mass, lengths, breadths, girths and skinfolds), somatotype and body composition estimates were determined. Compared with other female athletes (e.g. swimmers, runners, fencers), the elite modern pentathletes were rather tall (x = 168.1 cm) and, as indicated by the body mass index (x = 21.6), they had a high mass relative to their stature. Based on skinfolds, body fat was estimated as 16%, and anthropometrically determined somatotype was on average 2.5-3.9-2.8. The relationship between the athletes' anthropometric characteristics and modern pentathlon performance was investigated by means of Pearson zero-order correlations between the physical traits and the competitive performance scores. Significant correlations were found mainly for the 'fat' variables, such as skinfolds, percent fat and the endomorphy component, r varying from -0.34 to -0.58, which indicated an inverse relationship between the amount of fatness and modern pentathlon performance. To investigate this relationship further, Pearson zero-order correlations were calculated between the respective factors scores, derived from a rotated factor pattern (Varimax) carried out on selected somatic variables, and the performance scores. The results demonstrated that, in relation to anthropometric characteristics, modern pentathlon performance in females is mainly associated with the 'fat development' factor, and to a lesser degree with the 'bone-muscle development' factor. Variables representing linearity of physique seem to be unrelated to modern pentathlon performance. Stepwise regression analysis revealed that 42.4% of the variance in modern pentathlon performance can be explained by the following anthropometric variables: sum of 10 skinfolds, biacromial breadth and humerus diameter. To obtain a high level of modern pentathlon performance, it would seem that a female athlete must above all have a low level of body fatness and, to a lesser degree, a relatively high level of lean body mass.

The fibre type composition of the rabbit latissimus dorsi muscle

The fibre type distribution has been mapped in the latissimus dorsi muscle of the Dutch rabbit. Using the myosin ATPase stain, a distinct border was found to run in a cranial to caudal direction, which effectively divided the muscle into 2 segments of different fibre type proportions. Although both segments contained mostly fast twitch fibres, the medial areas were found to contain approximately 10-20% slow (i.e. type I) fibres while the lateral portions contained very few, if any, slow fibres. Significantly fewer type IIa fibres were also found in the lateral areas of the muscle. These histochemical findings were confirmed by the use of the reverse transcriptase polymerase chain reaction, which demonstrated that more messenger RNA of the slow myosin heavy chain was found in the medial regions compared with the lateral segment. These results demonstrate the importance of choosing well defined sampling sites when evaluating regimes designed to transform this heterogeneous muscle for use in subsequent myoplasty procedures.

Anatomical studies on the extensor carpi radialis longus and brevis muscles in Japanese

In order to determine whether the muscle bellies of the extensor carpi radialis longus and brevis (including additional slips) show laminar disposition, they were observed in 490 upper limbs of 245 Japanese cadavers. The author examined them from the point of view of lamination of the muscle slips (bellies) and classified them into 22 types in this study. The extensor carpi radialis longus muscle consists of five layers (A, B, C, D and E). Their proximal portions are disposed from radial deep to ulnar superficial as A, B, C, D and E, and the distal portions from ulnar deep to radial superficial as A, B, C, D and E. C is the main part of the extensor carpi radialis longus muscle, and A, B, D and E are additional (accessory) slips. The main part (C) is inserted into the second metacarpal bone A and B cross beneath the main part (C) to the ulnar side of the hand and are inserted into the third to second metacarpal bones. D and E pass across on the main part (C) to the radial side of the hand and are inserted into the second to first metacarpal bones. The extensor carpi radialis brevis consists of three layers (X, Y and Z). Their proximal portions are disposed from radial deep to ulnar superficial as X, Y and Z, and the distal portions from ulnar deep to radial superficial as X, Y and Z. Y is the main part of the extensor carpi radialis brevis muscle, and X and Z are additional (accessory) slips. The main part (Y) is inserted into the third metacarpal bone. X passes deep to Y to the ulnar side of the hand and is inserted into the fourth or third metacarpal bone. Z passes superficial to Y to the radial side of the hand and is inserted into the third or second metacarpal bone. The extensor carpi radialis longus muscle showed the normal form (C only present) in 326 of 490 cases, and had the main part (C) and one to three additional slips (A, B, D, E) in 164. The extensor carpi radialis brevis showed the normal form (Y only present) in 389, and had the main part (Y) and one or two accessory slips (X, Z) in 101 of 490 cases.

Effects of testosterone on a sexually dimorphic frog muscle: repeated in vivo observations and androgen receptor distribution

In the present study the sexually dimorphic, androgen-sensitive flexor carpi radialis muscle (FCR) in male Xenopus laevis was viewed repeatedly in vivo to assess the influence of testosterone on muscle fiber size over a period of up to 12 weeks. Regions of the muscle innervated by different spinal nerves responded differently to testosterone treatment. Muscle fibers innervated by spinal nerve 2 (SN2) hypertrophied within 7 days in frogs that had been castrated and given testosterone-filled implants. This initial hypertrophy was followed by a return to normal fiber size a week later, after which fiber size slowly increased again. In castrated males with empty implants, muscle fibers innervated by SN2 gradually atrophied. Fibers innervated by spinal nerve 3 (SN3) were not affected by androgen replacement or withdrawal. The sartorius, a control muscle that is neither sexually dimorphic nor particularly androgen sensitive, was also unaffected. The in vivo observations were confirmed by measurements of muscle fiber cross-sectional areas in frozen sections of whole forelimbs. At 8 and 12 weeks after castration, cross-sectional areas of fibers innervated by SN2 were significantly larger in frogs provided with testosterone than in castrates without testosterone. No difference was found in the SN3 region or in the anconeus caput scapulare (triceps), another control muscle. Immunocytochemistry employing an antibody against the androgen receptor (AR) indicated that the receptor is present in myonuclei of all muscles of the forelimb. While no difference in labeling intensity was detected, the number of AR-containing nuclei per muscle fiber cross-section was higher in fibers innervated by SN2 than in those innervated by SN3, and was yet lower in the triceps. This suggests that regulation of androgen sensitivity may occur via muscle fiber ARs, although an influence of the nerve may also contribute.

Fibre type composition of rabbit tibialis anterior and extensor digitorum longus muscles

Rabbit tibialis anterior (TA) and extensor digitorum longus (EDL) muscles are used extensively in studies of stimulation-induced fibre type transformation, but the proportions and sizes of the 2 main fibre types, and the way in which they are distributed within the muscles, have never been described in any detail. In this study, transverse sections were processed by enzyme histochemical and immunohistochemical techniques and assessed morphometrically. The data were analysed by multivariate methods. In both TA and EDL muscles, the proportion of type 1 fibres varied significantly, and to a similar extent, within a cross-section, from lateral to medial and from superficial to deep parts. The fibre density, an indirect estimate of the mean muscle fibre area, also varied significantly, but not systematically, within a cross-section. For the EDL muscle, the proportion of type 1 fibres was consistently higher in the distal than in the proximal part of the muscle. The proportion of type 1 fibres was also significantly higher in the EDL than in the TA muscle for each of the 6 rabbits. There was no systematic variation between muscles from left and right limbs. The type proportions and fibre densities for both TA and EDL muscles differed significantly between individual rabbits, but not between sexes. The study provides a database that has hitherto been lacking on normal fibre type composition and its variation within and between these experimentally important muscles.

Physique and motor performance characteristics of US national rugby players

Anthropometric and performance data were collected on 65 US rugby players (mean age = 26.3 years) to make comparison on these characteristics by player position and performance level. Anthropometry included stature, body mass, nine skinfolds, two girths and two bone breadths. Skinfold patterns, estimated percent fat and Heath-Carter somatotypes were calculated from anthropometry. Motor performance measures included standing vertical jump, 40 yard dash, 110 yard dash, shuttle run, repeated jump in place, push-up, sit-up and squat thrust. Descriptive statistics were used for the total sample as well as selected sub-groups. Discriminant function analyses were employed to determine which combination of variables best discriminated between position and level of performance for the anthropometric and performance data. The results indicated that forwards were taller, heavier and had more subcutaneous adiposity than backs. Additionally, forwards and backs differed in somatotypes, with forwards being more endo-mesomorphic than backs and with a greater scatter about their mean. The anthropometric variables that best discriminated between backs and forwards were body mass, femur breadth and arm girth, with 88% correctly classified using these variables. The motor performance variables that best discriminated between backs and forwards were repeated jump in place, push-up and standing vertical jump, with 76% correct classification using these variables. Classification into three playing levels was unsatisfactory using either anthropometric or motor performance variables. These data can be used to assess present status and change in players, or potential national players, by position to locate strengths and weaknesses.

Redefining the anatomy of the anterior tibialis tendon

The observation that, when performing a split anterior tibialis tendon transfer, a twist develops as the distal segment is brought into position on the lateral side of the foot led to our hypothesis that, as a consequence of foot rotation during embryologic development, rotation of the tendon of the anterior tibialis muscle also occurs and can be seen in the adult. Ten unembalmed human lower extremities were examined with regard to the macrostructure of the anterior tibialis tendon. In all 10 specimens, the fibers rotated through 90 degrees from the musculotendinous junction to the insertion on the first cuneiform and metatarsal. The tendon was then split, releasing the first metatarsal insertion in five specimens and the first cuneiform insertion in five. Lateral transfer of the first metatarsal-released group produced a crossing over proximally of the tendon as the fibers came from the medial side of the musculotendinous junction. Lateral transfer of the first cuneiform-released group produced no crossing over proximally as the fibers came from the lateral side of the musculotendinous junction. During a split anterior tibialis tendon transfer, release of the cuneiform insertion will avoid the proximal twisting seen with first metatarsal release and allows for a more direct line of pull of the muscle on the tendon.

Metabolic adaptation of skeletal muscles to gravitational unloading

Responses of high-energy phosphates and metabolic properties to hindlimb suspension were studied in adult rats. The relative content of phosphocreatine (PCr) in the calf muscles was significantly higher in rats suspended for 10 days than in age-matched cage controls. The Pi/PCr ratio, where Pi is inorganic phosphate, in suspended muscles was less than controls. The absolute weights of soleus and medial gastrocnemius (MG) were approximately 40% less than controls. Although the % fiber distribution in MG was unchanged, the % slow fibers decreased and the % fibers which were classified as both slow and fast was increased in soleus. The activities (per unit weight or protein) of succinate dehydrogenase and lactate dehydrogenase in soleus were unchanged but those of cytochrome oxidase, beta-hydroxyacyl CoA dehydrogenase, and citrate synthase were decreased following unloading. None of these enzyme activities in MG changed. However, the total levels of all enzymes in whole muscles decreased by suspension. It is suggested that shift of slow muscle toward fast type by unloading is associated with a decrease in mitochondrial biogenesis. Further, gravitational unloading affected the levels of muscle proteins differently even in the same mitochondrial enzymes.

Electromyographic study of the trapezius muscle in free movements of the shoulder

The objective of this study is to analyze the simultaneity of the actions of the three portions of the trapezius (superior portion = TS; middle portion = TM and inferior portion = TI) in elevation, lowering, retraction and protraction of the shoulders. The electromyographic tests were carried out in 20 volunteers using a 4-channel TECA TE 2-7 electromyograph and surface and single coaxial needle electrodes. The electromyographs, obtained with the two types of electrodes, show that in elevation and lowering of the shoulders, TS and TM present increasing and decreasing activity, respectively, from the beginning until the end of these movements. In retraction of the shoulders, TM and TI present increasing activity from the beginning to the end of the movement. In protraction, TS, TM and TI do not show any activity.

Adaptation of rat soleus muscles to 4 wk of intermittent strain

The effect of repeated strains on rat soleus muscles was investigated by stretching active muscles 3 times/wk for 4 wk with two different methods of stretching. The adaptation of myofibers and noncontractile tissue was followed by histochemical techniques and computer-assisted image analysis. Muscle hypertrophy was seen in the slow-stretched muscles, which increased in mass by 13% and increased in myofiber cross-sectional area by 30%. In the fast-stretched muscle, mass increased by 10% but myofiber cross-sectional area actually decreased. This decrease in mean fiber area was the result of a population of very small fibers (population A) that coexisted with slightly smaller normal-sized fibers (population B). Fibers in population A did not have the distribution expected from atrophy compared with atrophic fibers from unloaded muscles; they were much smaller. In addition, there was a 44% increase in noncontractile tissue in the fast-stretched muscles. Thus, soleus muscles subjected to repeated strains respond differently to slow and fast stretching. Slow stretching results in typical muscle hypertrophy, whereas fast stretching produces somewhat larger muscles but with a mixture of small and normal-sized myofibers accompanied by a marked proliferation of noncontractile tissue.

Spatial relationships between neuromuscular junctions and microvessels in hamster cremaster muscle

Acetylcholine (ACh) dilates arterioles in skeletal muscle. Neuromuscular junctions (NMJs) are the known source of ACh in this tissue. We hypothesized that microvascular topology is related to the distribution of NMJs. To test this, the spatial relationships between NMJs, arterioles, and capillaries in the hamster cremaster muscle were investigated. Male hamsters (n = 5, 80-100 g) were anesthetized (sodium pentobarbital, 60 mg/kg) and the cremaster was perfused with fluorescein isothiocyanate-bovine serum albumin (FITC-BSA) and Microfil compound. Excised muscles were stained for NMJs (cholinesterase reaction) and cleared in glycerin. Grid overlays divided each cremaster evenly into proximal and distal regions and 40 numbered 3 x 3-mm study fields. Five fields/region (approximately 25% of muscle area) were chosen randomly. Point counting ("counts") on a coherent test grid (component grid dimensions at x 144 magnification: 150 x 150, 300 x 300, and 450 x 450 microns) quantified NMJs, arterioles, and capillaries, respectively. NMJ:arteriole and NMJ:capillary nearest distances were obtained and arterioles nearest NMJs were classified by branch order. Filling with FITC-BSA vs Microfil indicated that all arterioles and approximately 92% of capillaries were perfused with Microfil. Relative counts (i.e., volume fractions) for capillaries were five- to sixfold greater than those for arterioles, which were two- to fivefold greater than those for NMJs. Capillary counts were similar between muscle regions and did not correlate with NMJ counts. In the distal muscle, arteriole and NMJ counts were correlated (r = 0.55, P < 0.05) and counts for both structures were greater than those in proximal regions. NMJ:capillary distances (proximal, 11.9 +/- 0.9 microns; distal, 14.5 +/- 0.6 microns) were less (P < 0.05) than respective NMJ:arteriole distances (111.1 +/- 7.1 and 89.8 +/- 3.2 microns). Fourth- and fifth-order arterioles accounted for 69% of arterioles nearest NMJs. These findings suggest that NMJs may provide a vasoactive stimulus which varies with muscle region and with location in the microvascular network.

Sensitivity of muscle proton spin-spin relaxation time as an index of muscle activation

The purpose of this study was to determine the minimum number of contractions that are needed to detect an increase in the muscle proton spin-spin relaxation time (T2) at a given exercise intensity. Five healthy human subjects performed five sets of an exercise that included concentric and eccentric contractions of the elbow-flexor muscles with loads that were 25 or 80% of maximum. With the 80% load, the five sets involved 1, 2, 5, 10, or 20 repetitions of the exercise; with the 25% load the five sets were 2, 5, 10, 20, or 40 repetitions. The upper arm of each subject was imaged before and immediately after each set of the exercise. Spin-echo images (repetition time/echo time = 2,000 ms/30, 60, 90, and 120 ms) were collected using an extremity coil, and T2 values were calculated. The signal intensity was measured from the elbow-flexor and -extensor muscles and from the bone marrow of the humerus. With the 80% load, T2 increased in the short head of the biceps brachii after two repetitions of the elbow exercise and after five repetitions in the brachialis and the long head of the biceps brachii. With the 25% load, T2 became longer after five repetitions of the exercise for the short head of the biceps brachii and after 10 repetitions for the brachialis and the long head of the biceps brachii. T2 varied linearly with the number of contraction repetitions for each of the elbow-flexor muscles at either load (r2 > or = 0.97, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of daily mild supine exercise on physical performance after 20 days bed rest in young persons

To investigate the effects of daily mild supine exercise on physical performance capacity identified as maximal oxygen uptake rate (VO2max) after 20 days bedrest, 3 male students performed a supine pedaling at 40% intensity of VO2max for one hour every day, while 6 male and 5 female students were control. Before and after the bedrest, muscle mass and strength of exercising leg and cardiovascular responses during -40mmHg lower body negative pressure (LBNP) and moderate upright cycling exercise were measured. Despite the exercise programme VO2max was similarly decreased to the control subjects after bed-rest. The delta VO2max was correlated to delta % left ventricular fractional shortening during LBNP, and also % delta VO2max to % delta stroke volume of the moderate exercise (both p<0.05). The exercise programme should be too weak to maintain cardiovascular functions and thus to present the decrease in VO2max against prolonged bedrest as well as weightlessness stress.

Differential response of macrophage subpopulations to soleus muscle reloading after rat hindlimb suspension

The hypothesis that distinct populations of macrophages are associated with muscle necrosis and regeneration was examined in Wistar rat soleus muscle after 10 days of hindlimb suspension and 2, 4, and 7 days after the resumption of weight bearing. Necrosis was identified using histological features, such as muscle fiber infiltration, and regeneration was identified using immunohistochemical techniques for developmental myosin heavy chain (dMHC). Light-microscopic observations show that necrotic fibers in 2-day reloaded soleus muscle were invaded by ED1+ and Ia+ macrophages. The number of invaded fibers in muscles reloaded for 2 days increased to 2.8/mm2 compared with 0.2/mm2 in age-matched normal muscle but returned to control values by the 4th day of resumed weight bearing. In the interstitial spaces of 2-day recovery muscle, ED1+ and Ia+ macrophages numbered 369 and 332/mm2, respectively, compared with 12 and 72/mm2, respectively, in control soleus. After 7 days of reloading, the number of ED1+ cells was similar to that of control. Ia+ macrophages decreased to 240/mm2 at 4 days but after 7 days rose above control values to 429/mm2. ED2+ macrophages in 4- and 7-day reloaded soleus increased 70-80% in the interstitial spaces compared with control but were not observed to infiltrate necrotic muscle fibers at any time points. Immunohistochemistry and immunoblots using a monoclonal anti-dMHC antibody demonstrate a greater proportion of myofibers expressing dMHC isoforms after 4 and 7 days of reloading. These findings indicate that macrophage subpopulations are associated with distinct stages during the recovery process from hindlimb suspension: ED1+ macrophages are associated with muscle necrosis, whereas ED2+ cells are associated with muscle regeneration.(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomic evaluation of anterior platysma muscle

The structure of the submental platysma muscle was evaluated in 20 preserved cadavers. Four distinct patterns were identified, depending on the pattern of merging of the right and left platysma bundles. Fifteen percent of cases showed a complete platysma diaphragm submentally, while in the other 85% there was some degree of midline dehiscence. In the 85% of cases where right and left fibers merged or crossed to form a V or U shape, the apex of the V or U was measured relative to the chin point. The distance between right and left fibers was measured at two locations posterior to the chin point. The width of the midline dehiscence (when present) was 6-24 mm (mean 11.8 mm) 1 cm posterior to its apex and 10-44 mm (mean 20.00 mm) 2 cm posterior to the apex. The wider and more divergent the dehiscence and the more U-shaped the dehiscence between left and right platysma bundles, the greater may be the tendency to a "turkey gobbler" deformity with inadequate medial support for the skin and subcutaneous tissues.