Development of different types of muscle fiber in the postnatal ontogeny of guinea pigs

As demonstrates estimation of myosin ATPase and SDG activity, the guinea pig is already born with differentiated muscle fibers (MF), and the first histochemical differences between them take place in the uterine 10 days before birth. Tonic oxidative fibers of the first type, arranging hexagonally, develop especially quickly at early stages of postnatal ontogenesis. Their relative contents up to the end of the observations (185 days) do not change, and area of their transversal section increases but slightly in comparison to the phasic fibers. The main age changes of the muscle tissue are connected with formation and rearrangement of the phasic fibers. The most intensive reconstructions of the phasic fibers coincide with the period of game activity and sex maturation. In mixed muscles the part of the glycolytic fibers increase during the postnatal ontogenesis. In the process of ontogenesis the soleus muscle fully consists of oxidative fibers. The definitive level of the MF development is established after the guinea pigs have reached their sex maturation. Comparing the results of the given investigation with the previous data on development of MF in rats, it is possible to conclude that term and premature animals have various rates in development of the muscle system, however, main stages of myogenesis coincide, though they are connected with various phases of ontogenesis.     

Changes in the activity of succinate dehydrogenase in muscle fibers of functionally different muscles in the rat after a reduction in exertion--hypodynamia

In 105 male rats of Wistar strain distal parts of one of the thoracic extremities are amputated with keeping intact the places where the brachial muscle is fixed. This does not restrict the volume of the brachium movements but essentially decreases their dynamic component (power loading). For 45 days dynamics of succinate-dehydrogenase (SDG) activity is being revealed in muscle fibers (MF) of functionally different muscles: m. brachialis, m. serratus ventralis and m. triceps brachii (the medial head). Average tendency of the process, changes in the distribution margins, asymmetry and kurtosis are taken into account. Under hypodynamia reconstruction of the MF has a wavy character with a gradually longer period of fluctuations. In all the muscles appear MF with a greater than in the control SDG activity. In the medial head of the m. triceps brachii the fibers with the lowest SDG activity disappear. The amount of MF with the lowest activity decreases, while those with the higher--increases, the process being more pronounced in the m. triceps brachii. The amount of MF with middle activity of the enzyme remains nearly unchanged. MF with different initial enzymatic activity do not change simultaneously. The degree of the changes in the fibers and the power leading are connected with each other, the fibers with the low initial SDG activity including into the reaction at a sharper decrease of the latter. The changes in quantitative ratio of MF with different SDG activity are not the same in every muscle studied.     

Microvascular architecture of the pampiniform plexus-testicular artery system in the rat: a scanning electron microscope study of corrosion casts

Because the architectural and biochemical properties of skeletal muscle dictate its force, velocity, and displacement properties, the major extensors (triceps brachii) and flexors (biceps brachii, brachialis, and brachioradialis) of the elbow in a primate (cynomolgus, monkey) were studied. Functional cross-sectional areas (CSA) were calculated from muscle mass, mean fiber length (normalized to a 2.20 microns sarcomere length), and angle of fiber pinnation measurements from each muscle. Fiber-type distributions were determined and used as a gross index of the biochemical capacities of the muscle. The extensor group had a shorter mean fiber length (31 vs. 47 mm), a larger CSA (13 vs. 8 cm2), and a higher overall percentage of slow-twitch fibers (47 vs. 26%). Consequently, the elbow extensors had a relatively greater potential for force production and force maintenance than the flexors. In contrast, the flexors were designed to optimize their length-velocity potentials; i.e., they had relatively long fibers and a higher fast-twitch fiber composition than the extensors. These morphologic differences between antagonistic muscle groups should be considered when evaluating the motor control mechanisms regulating reciprocal movements about the elbow.     

Effects of two days of isokinetic training on strength and electromyographic amplitude in the agonist and antagonist muscles

The purpose of this study was to examine the effects of 2 days of isokinetic training of the forearm flexors and extensors on strength and electromyographic (EMG) amplitude for the agonist and antagonist muscles. Seventeen men (mean +/- SD age = 21.9 +/- 2.8 years) were randomly assigned to 1 of 2 groups: (a) a training group (TRN; n = 8), or (b) a control group (CTL; n = 9). The subjects in the TRN group were tested for maximal isometric and concentric isokinetic (randomly ordered velocities of 60, 180, and 300 degrees x s(-1)) torque of the dominant forearm flexors and extensors before (pretest) and after (posttest) 2 days of isokinetic strength training. Each training session involved 6 sets of 10 maximal concentric isokinetic muscle actions of the forearm flexors and extensors at a velocity of 180 degrees x s(-1). The subjects in the CTL group were also tested for strength but did not perform any training. Surface EMG signals were detected from the biceps brachii and triceps brachii muscles during the strength testing. The results indicated that there were no significant (p > 0.05) pre- to post-test changes in forearm flexion and extension torque or EMG amplitude for the agonist and antagonist muscles. Thus, unlike previous studies of the quadriceps femoris muscles, these findings for the forearm flexors and extensors suggested that 2 days of isokinetic training may not be sufficient to elicit significant increases in strength. These results may have implications for the number of visits that are required for rehabilitation after injury, surgery, or both.     

Development of various types of muscle fibers in the quadriceps femoris and the soleus during human ontogenesis

By means of histological methods for revealing adenosine triphosphatase of myosin (pH 4.6) and succinate dehydrogenase activity, using postmortem material, development of various muscle fibers of the femoral m. quadriceps and m. soleus has been studied in human ontogenesis. The first stage of rearrangements lasts from the 5th-6th month of the uterine development up to 2 years of age and is characterized by formation (from non-differentiated) of oxidative, glycolytic and oxidative-glycolytic fibers. During the period from 2 up to 7-8 years of age the ratio in the types changes slightly, but transversal section size of the muscle fiber increases intensively. Then from 11 up to 17 years of age, together with maximal increment of the fibers transversal section, there is an essential change in the type relation. By the 17th years of age, in the femoral m. quadriceps the part of the fibers with glycolytic type of energy supply increases, while in the m. soleus the oxidative fibers become more numerous. By the 70th years of age in the femoral m. quadriceps relative amount of intermediate fibers increases.     

Surface EMG force modeling with joint angle based calibration

In this paper, a calibration method to compensate for changes in SEMG amplitude with joint angle is introduced. Calibration factors were derived from constant amplitude surface electromyogram (SEMG) recordings from the biceps brachii (during elbow flexion) and the triceps brachii (during elbow extension) across seven elbow joint angles. SEMG data were then recorded from the elbow flexors (biceps brachii and brachioradialis) and extensors (triceps brachii) during isometric, constant force flexion and extension contractions at the same joint angles. The resulting force at the wrist was measured. The fast orthogonal search method was used to find a mapping between the system inputs – estimated SEMG amplitudes and joint angle – and the system output – measured force, for both calibrated and non-calibrated SEMG data. Models developed with calibrated data yielded a statistically significant improvement in force estimation compared to models developed with non-calibrated data, suggesting that the calibration method can compensate for changes in the SEMG–force relationship with changing joint angle. It was also found that the number of non-linear, joint angle-dependent terms used in the SEMG–force model was reduced with calibration. Additionally, initial inter-session analysis performed for four subjects suggests that calibration values can be used for subsequent recording sessions, and different output force levels.     

Facilitation of triceps brachii muscle contraction by tendon vibration after chronic cervical spinal cord injury.

One way to improve the weak triceps brachii voluntary forces of people with chronic cervical spinal cord injury may be to excite the paralyzed or submaximally activated fraction of muscle. Here we examined whether elbow extensor force was enhanced by vibration (80 Hz) of the triceps or biceps brachii tendons at rest and during maximum isometric voluntary contractions (MVCs) of the elbow extensors performed by spinal cord-injured subjects. The mean +/- SE elbow extensor MVC force was 22 +/- 17.5 N (range: 0-23% control force, n = 11 muscles). Supramaximal radial nerve stimuli delivered during elbow extensor MVCs evoked force in six muscles that could be stimulated selectively, suggesting potential for force improvement. Biceps vibration at rest always evoked a tonic vibration reflex in biceps, but extension force did not improve with biceps vibration during triceps MVCs. Triceps vibration induced a tonic vibration reflex at rest in one-half of the triceps muscles tested. Elbow extensor MVC force (when >1% of control force) was enhanced by vibration of the triceps tendon in one-half of the muscles. Thus triceps, but not biceps, brachii tendon vibration increases the contraction strength of some partially paralyzed triceps brachii muscles.     

Elbow extensor muscles of the horse: postural and dynamic implications.

Based on histochemical and immunohistochemical evidence, horse elbow extensor muscles are composed of two morphologically distinct muscle groups. The long and lateral heads of the triceps brachii are large, predominantly type II (presumed fast) muscles. The long and lateral heads of the triceps together account for 96% of the weight of the elbow extensors (long head of triceps is 81%). The long and lateral heads contain three histochemical fiber types: types I, IIa and IIb. Type I muscle fibers account for approximately 18 and 27% of the fibers in the long and lateral heads of the triceps, respectively. In the lateral head, type IIa and IIb fibers account equally for the remaining 70%, while in the long head of the triceps type IIb fibers predominate (50%) over type IIa fibers (32%). In contrast, the much smaller medial head of the triceps (2% of triceps mass) and the anconeus (2% of mass) contain almost exclusively type I muscle fibers. It is hypothesized that the medial head and anconeus, with their slow fibers, contribute to the postural maintenance of the forelimb by preventing flexion at the elbow joint during passive stance. The larger long and lateral heads, with their generally fast fiber populations, are most likely important during dynamic activity.     

Succinate dehydrogenase activity of brachial muscle antagonists after decrease in the force load at various times of the day in rats

In 140 male rats of Wistar strain the distal part of one thoracic extremity has been amputated in such a way that places of the brachial muscle fixation remained intact. This resulted in decrease of the force component of muscle contractions (more intensive in the musculus triceps brachii) without essential swing and speed of movements. The operation was performed during one day at three series: at 7 a. m. 3 p. m. and 11 p. m. During following 45 days the muscles developing various contraction force were studied: the medial head of the musculus triceps brachii and brachial muscle. Succinate dehydrogenase (SDG) activity in muscle fibers (MF) was estimated photometrically. In MF initially characterized with various SDG activity, attention was payed to its dynamics and also relation of the fibers number, possessing various level of the enzymatic activity was taken into consideration. SDG activity in MF and relation of various MF change wavy-like, fluctuating from the control meaning and returning to them again. MF with different SDG activity do not similarly react to a sharp decrease of the force loading. Fibers with high enzymatic activity react to changes of the force loading immediately, intensity of the reaction at this stage slightly depends on degree of biomechanical changes; at later stages the response is differentiated: if the loading is decreased considerably (musculus triceps brachii), the process continues developing and increasing uninterruptedly, if it decreases moderately (brachial muscle)--it stabilizes and even has tendency to adaptation and returning towards the control state.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic capacity of individual muscle fibers from different anatomic locations.

We studied muscle fibers by quantitative biochemistry to determine whether metabolic capacity varied among fibers of a given type as a function of their anatomic location. Muscles were selected from both contiguous and diverse anatomic regions within the rats studied. The individual fibers, classified into myosin ATPase fiber types by histochemical means, were assessed for fiber diameters and analyzed for the activities of enzymes representing major energy pathways: malate dehydrogenase (MDH, oxidative), lactate dehydrogenase (LDH, glycolytic), and adenylokinase (AK, high-energy phosphate metabolism). We found that neither the average activities of each of the three enzymes nor the fiber diameters varied in Type I or Type IIa fibers selected from superficial to deep portions of the triceps surae of the hindlimb. However, the IIb fibers in the deep region of this muscle group had significantly greater oxidative capacity, less glycolytic capacity, and smaller diameters than the superficially situated IIb fibers. Type IIa fibers in lateral gastrocnemius, extensor digitorum longus, psoas, diaphragm, biceps brachii, superficial masseter, and superior rectus muscles were highly variable in both diameter and enzyme profiles, with a correlation between MDH activity and fiber diameter. Therefore, our results show that both intermuscular and intramuscular metabolic variations exist in muscle fibers of a given type.     

The fatigability of two agonistic muscles in human isometric voluntary submaximal contraction: an EMG study I. Assessment of muscular fatigue by means of surface EMG

During an external isometric constant torque (25% of the maximal voluntary contraction) maintained until the maximal endurance time (limit time), we analysed and compared the changes in electromyographic (EMG) activity illustrating muscular fatigue simultaneously with mechanical activity (the tangential acceleration theta") related to physiological tremor. The EMG activities recorded were of two agonistic flexors, the biceps brachii (BB) and the brachioradialis (BR) muscles and one of the main extensors, the triceps brachii (TB). The integrated EMG increase and the mean power frequency (MPF) of the power spectrum density function (PSDF) decrease were larger for BR than for BB activity. These two findings suggested a greater BR fatigability. However, it is shown that differences between BB and BR MPF changes could be related to differences in the PSDF upper frequency limit of the two muscles and also to the relative magnitude of their tremor component.     

Age and changes in succinate dehydrogenase activity in functionally different muscles of the young rat

The antigravitational m. triceps brachii, its antagonist m. brachialis and the muscle having a universal functional specialization--m. serratus ventralis--have been studied in 35 male rats of Wistar strain, 60-105-day-old. Succinate dehydrogenase activity is determined in muscle fibers. Changes in the muscle fibers continue after the rats reach their sex maturation. Certain stageness of the process is observed, but the division of the period into separate steps either is absent (m. brachials), or their number is not great as compared to those during the 1st--60th days after birth. The borders of the periods in the muscles studied coinside (the 70th--74th day). Although it is possible to reveal the periods and separate steps in the changes occurring in the muscle fibers and in the muscles of the animals having reached their sex maturation, nevertheless, the borders between them are not distinct, the reconstruction during this age proceeds slower and more smoothely than before the sex maturation. It is possible that in young rats after sex maturation differentiation of the muscle fibers continues and that, in its turn, stimulates further specialization of the muscles as organs. The changes in the muscle fibers revealed histochemically occur most slowly under a low static loading, and when loading of various modality (kinetic and static) are combined, they are mostly pronounced.     

Architectural specialization of the intrinsic thoracic limb musculature of the American badger (Taxidea taxus)

Evaluation of the relationships between muscle structure and digging function in fossorial species is limited. Badgers and other fossorial specialists are expected to have massive forelimb muscles with long fascicles capable of substantial shortening for high power and applying high out‐force to the substrate. To explore this hypothesis, we quantified muscle architecture in the thoracic limb of the American badger (Taxidea taxus) and estimated the force, power, and joint torque of its intrinsic musculature in relation to the use of scratch‐digging behavior. Architectural properties measured were muscle mass, belly length, fascicle length, pennation angle, and physiological cross‐sectional area. Badgers possess hypertrophied shoulder flexors/humeral retractors, elbow extensors, and digital flexors. The triceps brachii is particularly massive and has long fascicles with little pennation, muscle architecture consistent with substantial shortening capability, and high power. A unique feature of badgers is that, in addition to elbow joint extension, two biarticular heads (long and medial) of the triceps are capable of applying high torques to the shoulder joint to facilitate retraction of the forelimb throughout the power stroke. The massive and complex digital flexors show relatively greater pennation and shorter fascicle lengths than the triceps brachii, as well as compartmentalization of muscle heads to accentuate both force production and range of shortening during flexion of the carpus and digits. Muscles of most functional groups exhibit some degree of specialization for high force production and are important for stabilizing the shoulder, elbow, and carpal joints against high limb forces generated during powerful digging motions. Overall, our findings support the hypothesis and indicate that forelimb muscle architecture is consistent with specializations for scratch‐digging. Quantified muscle properties in the American badger serve as a comparator to evaluate the range of diversity in muscle structure and contractile function that exists in mammals specialized for fossorial habits. J. Morphol. 2013. © 2012 Wiley Periodicals, Inc.     

The effect of skinfold on frequency of human muscle mechanomyogram.

The aim of the study was to assess the effect of skinfold thickness on median and peak frequency of mechanomyographic (MMG) signal in relation to subject's age, gender and force during voluntary contraction of elbow flexor and extensor muscles. Seventy-nine healthy subjects participated in the study: 22 young females (age 20.1+/-1.1 years), 22 young males (age 23.4+/-1.1 years), 17 elderly females (age 64.9+/-5.1 years), and 18 elderly males (age 67.4+/-6.2 years). Three identical MMG probes were used to record MMG signals from above the triceps brachii (TB), biceps brachii (BB), and brachioradialis (BR) muscles simultaneously with the force signal. The results showed that the tissue between the muscle and the skin surface has a major contribution to the median and a minor contribution to the peak MMG frequencies independent of subjects' age (with force having more than 2 folds a smaller effect). During antagonistic function of the main elbow flexors and extensors, there is a decreasing effect of skinfold thickness and an increasing effect of force on the MMG frequency, and the relative contribution of both factors to the MMG signal is age related, especially in the TB and BR muscles. The BR muscle differs from the TB and BB muscles in regard to the effects of skinfold thickness and force on the MMG frequency, as well as in the effect of age on the relationship between the MMG frequency and skinfold thickness and force. The effect of age on the relative contribution of skinfolds and force to MMG frequency is specific for muscle and its function. It was concluded that studies that report MMG frequency with different values of skinfold thickness cannot be easily compared, especially when maximally activated prime movers are tested. A use of force and skinfold thickness as covariates is recommended when an MMG frequency is analyzed in subjects differing in the skinfold thickness.     

Trainability of Muscular Activity Level during Maximal Voluntary Co-Contraction: Comparison between Bodybuilders and Nonathletes

Antagonistic muscle pairs cannot be fully activated simultaneously, even with maximal effort, under conditions of voluntary co-contraction, and their muscular activity levels are always below those during agonist contraction with maximal voluntary effort (MVE). Whether the muscular activity level during the task has trainability remains unclear. The present study examined this issue by comparing the muscular activity level during maximal voluntary co-contraction for highly experienced bodybuilders, who frequently perform voluntary co-contraction in their training programs, with that for untrained individuals (nonathletes). The electromyograms (EMGs) of biceps brachii and triceps brachii muscles during maximal voluntary co-contraction of elbow flexors and extensors were recorded in 11 male bodybuilders and 10 nonathletes, and normalized to the values obtained during the MVE of agonist contraction for each of the corresponding muscles (% EMG_MVE). The involuntary coactivation level in antagonist muscle during the MVE of agonist contraction was also calculated. In both muscles, % EMG_MVE values during the co-contraction task for bodybuilders were significantly higher (P<0.01) than those for nonathletes (biceps brachii: 66±14% in bodybuilders vs. 46±13% in nonathletes, triceps brachii: 74±16% vs. 57±9%). There was a significant positive correlation between a length of bodybuilding experience and muscular activity level during the co-contraction task (r = 0.653, P = 0.03). Involuntary antagonist coactivation level during MVE of agonist contraction was not different between the two groups. The current result indicates that long-term participation in voluntary co-contraction training progressively enhances muscular activity during maximal voluntary co-contraction.     

Activity of Motor Units in Human Elbow Flexor and Extensor Muscles during Task-Dependent Unloading

Neurophysiology - Surface EMGs and activity of 73 single motor units (MUs) of the m. triceps brachii caput laterale (TBcl) and 25 units of the m. biceps brachii caput longum (BBcl) were recorded in...     

Studies of human antagonistic muscles after rupture of the tendon of biceps brachii

The fibre type ratio and the cross sectional areas of fibres were studied in triceps brachial muscle after rupture of tendon of the biceps brachial muscle in man. On the healthy and injured sides of the m. triceps brachii, the mean value of type 1 fibres was 51.9% and 52.4%, respectively. The mean cross sectional area of fibre on the two sides of the triceps muscle varied considerably among individuals without any significant correlation to injury of the biceps tendon.     

Control of the Elbow Extensor Muscles in Slow Targeted Extensions of the Arm in Humans

Relations between the kinematic parameters of slow (non-ballistic) targeted extension movements in the elbow joint of humans and characteristics of the movement-related EMG activity in the two heads of the m. triceps brachii were analyzed. Test movements were performed under conditions of application of non-inertional external loadings directed toward flexion. It was shown that the movement-related EMG activity of the elbow extensors, similarly to what was observed in the flexors at flexion movements with the same parameters, demonstrates a complex structure and includes dynamic and stationary phases. In the former phase, in turn, initial and main components can be differentiated. The rising edge and decay of the main component of the dynamic extensor EMG phase could be approximated by exponential functions; this component was never split into a few subcomponents. Dependences between the amplitudes of m. triceps brachii EMG phases and the amplitude of the movement (or external loading) were, as a rule, nonlinear but monotonic. An increase in the test movement velocity led to an increase in the rate of rise of the rising edge of the dynamic EMG phase, while an increment in the amplitude was less significant. Under the used test conditions, the activity of the elbow extensors was usually accompanied by some coactivation of the antagonists (m. biceps brachii). It is concluded that motor commands coming to the elbow extensors at performance of the extension test movements differ from motor commands to the flexors at analogous flexion test movements by a simpler structure and more tonic pattern. Biomechanical specificities of fixation of the mentioned muscle groups to the arm bones (stability of the moment for application of the extensor force under conditions of changing the joint angle vs variable moment of the flexor force) are considered one of the main reasons for such specificity of the patterns of the extensor and flexor motor commands.     

Force generation performance and motor unit recruitment strategy in muscles of contralateral limbs.

The purpose of the present study was to determine whether the motor unit (MU) recruitment strategy of the agonist and antagonist muscles in the dominant arm differs from that in the non-dominant arm. The median frequency (MF) of the power density spectrum (PDS) of the electromyogram (EMG) was used as a tracking parameter to describe the MU recruitment. In 8 subjects the EMG was recorded from the biceps brachii and triceps brachii of each limb during isometric elbow flexion performed in a ramp fashion. Force was increased from 0 to 100% of the maximum voluntary contraction (MVC) in 3 s following a track displayed on an oscilloscope. When comparing the dominant versus non-dominant arm we found no statistical difference in the MU recruitment pattern of the biceps brachii and the triceps. Because the dominant arm was not always the better performing arm, we grouped the data according to the ability of the subjects to track the ramp signal. In this case we found a statistically significant difference between the better and worse performing arm in the full MU recruitment of the biceps. A more precise and accurate control of the increase in force was obtained when the central nervous system selected a slower and prolonged recruitment of MUs in the agonist muscle.     

Peculiarities of Activation of Muscles of the Shoulder Belt in Voluntary Two-Joint Movements of the Upper Limb

We studied coordination of central motor commands (СMCs) coming to muscles of the shoulder and shoulder belt in the course of single-joint and two-joint movements including flexion and extension of the elbow and shoulder joints. Characteristics of rectified and averaged EMGs recorded from a few muscles of the upper limb were considered correlates of the CMC parameters. Special attention was paid to coordination of CMCs coming to two-joint muscles that are able to function as common flexors (m. biceps brachii, caput breve, BBcb) and common extensors (m. triceps brachii, caput longum, TBcl) of the elbow and shoulder joints. Upper limb movements used in the tests included planar shifts of the arm from one spatial point to another resulting from either simultaneous changes in the angles of the shoulder and elbow joints or isolated sequential (two-stage) changes in these joint angles. As was found, shoulder muscles providing movements of the elbow with changes in the angle of the elbow joint, i.e., BBcb and TBcl, were also intensely involved in the performance of single-joint movements in the shoulder joint. The CMCs coming to two-joint muscles in the course of two-joint movements appeared, in the first approximation, as sums of the commands received by these muscles in the course of corresponding single-joint movements in the elbow and shoulder joints. Therefore, if we interpret the isolated forearm movement performed due to a change in the angle of the elbow joint as the main motor event, while the shoulder movement is considered the accessory one, we can conclude that realization of a two-joint movement of the upper-limb distal part is based on superposition of CMCs related to basic movements (main and accessory). Neirofiziologiya/Neurophysiology, Vol. 41, No. 1, pp. 48–56, January–February, 2009.