Muscle In Man Research Articles

Evidence of direct connection of corticobulbar fibers to orofacial muscles in man: electromyographic study of individual motor unit responses.

We studied corticobulbar influence on the orbicularis oris (OR) muscles by anodal and magnetic transcranial stimulation and compared it to the corticospinal influence on first dorsal interosseous muscles of healthy human volunteers. We recorded single motor unit (MU) responses and applied peristimulus time histogram (PSTH) technique to determine their properties. Peaks in the PSTHs are assumed to coincide with multiple excitatory postsynaptic potentials (EPSPs) induced at the motoneurons by corticospinal input. We found relatively small latency variation of consecutive single MU responses for both muscles. Additionally, we found a narrow initial peak in five OR MUs after anodal stimulation. This short duration indicates the presence of monosynaptic cortical projection in the lower facial motoneurons. The EPSP amplitudes, estimated on the basis of initial peak, were used as a measure of the synaptic transmission efficiency. Our results support the concept of predominantly monosynaptic transmission at the spinal level.

Evidence of direct connection of corticobulbar fibers to orofacial muscles in man: Electromyographic study of individual motor unit responses

Evidence of direct connection of corticobulbar fibers to orofacial muscles in man: Electromyographic study of individual motor unit responses

Heteronymous influence of masseteric nerve stimulation on temporal muscle in man: A single motor units investigation

Heteronymous influence of masseteric nerve stimulation on temporal muscle in man: A single motor units investigation

Effect of sex and age on bone mass, body composition and fuel metabolism in humans

The mechanism(s) governing the gain of upper-body fat and its relationship to the decrease in bone mass with age is still unclear. Therefore, four groups of subjects matched for weight, height, and body mass index ( n = 119; 60 women, 59 men), but differing in age (above and below 50 y) and sex were investigated using dual-energy x-ray absorptiometry (DXA) to assess body composition (bone, lean, and fat mass as well as its distribution) and indirect calorimetry to determine resting fuel metabolism. Fat mass of trunk and arms ( P < 0.01), but not legs, increased with advancing age in males, resulting in a continuous increase in the ratio of upper- to lower-body fat ( r = 0.45, P < 0.001). In contrast, total fat mass remained stable in women, irrespective of menopause, but a redistribution of fat occurred with advancing age ( r = 0.43, P < 0.001), resulting in a higher upper- to lower-body fat ratio ( P < 0.05) in older than in younger women. Total lean soft-tissue mass of all segments of the body was greater in men than in women irrespective of age ( P < 0.001), and lower in the older groups than in the younger ones irrespective of sex. In males, but not females, lean soft-tissue mass in arms and legs decreased ( r = 0.57, P < 0.001), whereas the ratio of total fat to lean soft-tissue mass increased ( r = 0.53, P < 0.001) with age. Bone mineral content correlated with total body fat in both groups of women and in young males ( r > 0.5, P < 0.001), but not in older males. With advancing age, the proportion of lean soft-tissue mass occupied by total skeleton declined in women ( n = 59, P < 0.001), but remained stable in males. Resting energy expenditure decreased with age in both sexes. Protein and carbohydrate oxidation were similar in all four groups of subjects. Total fat oxidation and fat oxidation per kilogram of lean soft-tissue mass decreased with age ( r > 0.36, P < 0.01) in males, but not in females, whereas it increased with increasing fat mass in females ( r > 0.32, P < 0.03), but not in males. In contrast, fat oxidation per kilogram of fat mass decreased with fat mass in males ( r = 0.61, P < 0.001), but not in females. Our results suggest that aging affects body composition and fuel metabolism differently in each gender, leading to reduced fat oxidation and accumulation of upper-body fat with loss of striated muscle in men, and to an increased ratio of upper- to lower-body fat and bone loss in women, the latter depending on fat mass.

Muscle fibre size and type distribution in thoracic and lumbar regions of erector spinae in healthy subjects without low back pain: normal values and sex differences.

This study sought to investigate the normal muscle fibre size and type distribution of the human erector spinae, both in thoracic and lumbar regions, in a group of 31 young healthy male (n = 17) and female (n = 14) volunteers. Two percutaneous muscle biopsy samples were obtained under local anaesthesia, from the belly of the left erector spinae, at the levels of the 10th thoracic and 3rd lumbar vertebrae. Samples were prepared for routine histochemistry for the identification of fibre types. Fibre size (cross-sectional area (CSA) and narrow diameter (ND)) was quantified using computerised image analysis. The mean CSA/ND for each fibre type was greater in the thoracic than the lumbar region, but there was no difference between the 2 regions either for percentage type I (i.e. percentage distribution by number), percentage type I area (i.e. relative area of the muscle occupied by type I fibres) or the ratio describing the size of the type I fibre relative to that of the type II. Men had larger fibres than women, for each fibre type and at both sampling sites. In the men, each fibre type was of a similar mean size, whereas in the women the type I fibres were considerably larger than both the type IIA and type IIB fibres, with no difference between the latter two. In both regions of the erector spinae there was no difference between men and women for the proportion (%) of a given fibre type, but the percentage type I fibre area was significantly higher in the women. The erector spinae display muscle fibre characteristics which are clearly very different from those of other skeletal muscles, and which, with their predominance of relatively large type I (slow twitch) fibres, befit their function as postural muscles. Differences between thoracic and lumbar fascicles of the muscle, and between the muscles of men and women, may reflect adaptive responses to differences in function. In assessing the degree of any pathological change in the muscle of patients with low back pain, it seems clear that (1) sex cannot be disregarded and (2) 'atrophied' (using the criteria from other muscles) type II fibres are not necessarily abnormal for the erector spinae, particularly in women.

Increased intramuscular concentration of bradykinin increases the static fusimotor drive to muscle spindles in neck muscles of the cat

The aim of the present study was to investigate if increased intramuscular concentrations of bradykinin (BK) in one muscle influence the activity in primary and secondary muscle spindle afferents (MSAs) originating from both ipsi- and contralateral muscles, via fusimotor reflexes. The ipsilateral trapezius (TR) and the splenius (SP) muscles were subjected to sinusoidal stretches and 2–3 MSAs were simultaneously recorded from these muscles. Responses of 29 MSAs (15 SP and 14 TR) were registered in five adult cats lightly anaesthetised with α-chloralose. Intramuscular injections of 0.5 ml BK (6–86 μg/ml) were administered to both the ipsi- and contralateral SP and TR muscles. Similar doses of BK (5–10 μg) have been shown to induce muscle pain when injected into the temporal muscle in man. The responsiveness of the MSAs to the injections of BK was 86% and 87.5% from the contralateral TR and SP muscles, respectively. The effects were predominantly static onto the MSAs. The duration of the effects was on average 3.5–4 min, however some effects lasted for more than 15 min. The effects were always abolished after cutting the nerve to the injected muscle. The large majority of the spindle afferents were unresponsive to i.m. Tyrode injections (23 of 29). For the afferents that were responsive to injection of Tyrode, the effects were always considerably smaller and with shorter duration than those evoked by BK injections. Thus, increased intramuscular concentrations of BK may excite primary and secondary MSAs from ipsi- and contralateral muscles, via fusimotor reflexes evoked most probably by activity in chemosensitive muscle afferents. The results are discussed in relation to a recent hypothesis on pathohysiological mechanisms behind genesis, spread and perpetuation of muscle tension and pain in chronic musculoskeletal pain syndromes.

Blood flow and substrate exchange in skeletal muscle of man: Techniques relevant for use in the study of the ageing process of muscle

Blood flow and substrate exchange in skeletal muscle of man: Techniques relevant for use in the study of the ageing process of muscle

Blood flow and substrate exchange in skeletal muscle of man: Techniques relevant for use in the study of the ageing process of muscle

Blood flow and substrate exchange in skeletal muscle of man: Techniques relevant for use in the study of the ageing process of muscle

Twitch interpolation in the assessment of the maximum force-generating capacity of the jaw-closing muscles in man

The method of twitch interpolation was employed to study the maximum potential bite forces of humans. Transcutaneous electrical stimuli were applied to parts of one or both masseter muscles in eight volunteers while they bit with a variable but controlled isometric force on a uni-directional force transducer held between the anterior teeth. In all participants the twitch force produced by a single 1-ms pulse, of 25–50 mA intensity, was inversely and linearly related to the voluntary bite force. For each participant the slope of the regression between twitch force and bite force depended on the stimulus intensity and not on whether the stimulus was applied to one or both masseters. Extrapolation of the regression lines to zero twitch force showed that they converged towards a bite-force value that, for any given participant varied only a small amount between different stimulus intensities. For most participants this bite force lay above the maximum that they produced voluntarily; voluntary maximum bites ranged from 153 to 593 N, while the extrapolations predicted a narrower and higher potential range of 282–629 N. It was concluded that, for the masseters at least, there is often spare force-generating capacity which individuals are either unable or not prepared to utilize. This method is non-invasive and may help to define better the maximum bite-force potential of humans.

Reproducibility of digital testing of the pelvic floor muscles in men

Objective: To validate the digital testing of pelvic floor muscles in men by evaluating its applicability and the reproducibility of test-retest. Design: Prospective survey on volunteer sample. Blinded between investigators. Setting: University study group with experienced physiotherapists working in a university hospital. Participants: 39 young healthy male volunteers. Intervention: Digital testing of the bulbocavernous muscles, the sphincter and externus, the puborectal muscles. Outcome Measures: Each muscle or muscle group was allocated a tripartite valuation score corresponding with muscle strength, endurance, and exhaustion. The muscle testing was repeated by the same investigator with short (10 seconds), medium (2 hours), and long (>4 hours) intervals. In 9 patients, blinded testing was performed by two independent investigators separately. The results from the different evaluations were statistically compared. Results: Digital testing proved easy to perform and was well tolerated in all patients. Test-retest showed reproducible results with short and long intervals, except for the parameter exhaustion of external anal sphincter and puborectalis muscle as determined with an interval of 2 hours. Between investigators no difference was found between scores except for strength of the bulbocavernous muscle. Conclusion: Digital testing of the pelvic floor muscles, when done by an experienced investigator and with full cooperation of the patient, is reliable and useful for clinical practice in male patients. Intracorporal muscle testing is more reliable than evaluation of superficial muscles.

Resistive loaded breathing changes the motor drive to arm and leg muscles in man

Breathing through inspiratory or expiratory resistive loads activates respiratory afferents. In healthy individuals, we explored the recruitment of motor units in arm (adductor pollicis, AP and biceps brachialis, BB) and leg (vastus lateralis, VL) muscle groups during volutanry contractions sustained at 80% of maximal force. Quantitative EMG analysis consisted of measurement of energies in high (EH) and low (EL) frequency bands. EH and EL changes were measured at constant time, i.e. 10 and 20 s after the onset of plateau contraction. The resistive load was added to the inspiratory or the expiratory circuit for 10-min periods. Its value was high but not enough to induce changes in blood gases and blood pressure. Compared to muscle contractions performed during non-loaded breathing periods, inspiratory loading did not affect BB and VL contractions, whereas it induced significant changes in AP contraction, characterized by enhanced variations in EL value measured at 10 s. Expiratory loading affected solely the VP contraction. Then, EH decreased at 10 and 20 s while it increased always when VP contractions were executed during non-loaded breathing. Expiratory loading elevated the functional residual capacity (FRC), but the load-induced changes in VL contraction persisted when subjects adjusted their FRC to the control level. These data suggest that respiratory afferents influence the skeleto-motor drive. Thus, viscero-somatic reflex may be present in patients with severe obstructive pulmonary disease.

An anatomical analysis of the relationships between the intercostal nerves and the thoracic and abdominal muscles in man. II. Detailed analysis of innervation of the three lateral abdominal muscles.

Minute dissection was performed in one male adult cadaver in order to elucidate the detailed distribution of muscular branches of intercostal nerves within the lateral abdominal muscles as well as the segmental relationships. In the obliquus internus and transversus abdominis, as well as in the upper half of the obliquus externus, each muscle fascicle receives the nerve of the corresponding segmental attachment to the rib. On the other hand, in the lower half, the obliquus externus abdominis receives a twig from the lower adjacent segmental nerve, because within the muscle the corresponding segmental nerve first runs horizontally and enters the upper adjacent fascicle before descending obliquely, parallel to the fiber direction.

An anatomical analysis of the relationships between the intercostal nerves and the thoracic and abdominal muscles in man. I. Ramification of the intercostal nerves.

Minute dissection was performed on the ventral primary rami of the first thoracic to first lumbar nerves in two halves of an adult male cadaver in order to determine points of origins of muscular branches from the intercostal nerves. Generally, the muscular branches originated independently, but the branches supplying the intercostalis intimus and internus tended to originate as a common trunk. The muscular branching patterns were compiled in an illustration, and based on these patterns the serial homology of the thoracic and abdominal muscles was proposed. Although the obliquus externus abdominis has been thought to correspond to the intercostales externi, from these innervation findings it appears to correspond to the intercostales interni. Further, the quadratus lumborum seems homologous to the intercostales externi.

Carrier-mediated fructose uptake significantly contributes to carbohydrate metabolism in human skeletal muscle.

To determine whether fructose can be utilized as a metabolic substrate for skeletal muscle in man, we investigated its incorporation into glycogen, its oxidation and lactate production in isolated human skeletal muscle. Rates of fructose oxidation and incorporation into glycogen increased in the presence of increasing fructose concentrations (0.1-1.0 mM). Lactate production increased 3-fold when extracellular fructose was increased from 0.1 to 0.5 mM. Cytochalasin B, a competitive inhibitor of hexose transport mediated by the GLUT1 and GLUT4 facilitative glucose transporters, completely inhibited insulin-stimulated glucose incorporation into glycogen and glucose oxidation (P < 0.01), but did not alter fructose incorporation into glycogen or fructose oxidation. Insulin (1000 mu-units/ml) increased glucose incorporation into glycogen 2.7-fold and glucose oxidation 2.3-fold, whereas no effect on fructose incorporation into glycogen or fructose oxidation was noted. A physiological concentration of glucose (5 mM) decreased the rate of 0.5 mM fructose incorporation into glycogen by 60% (P < 0.001), whereas fructose oxidation was not altered in the presence of 5 mM glucose. Irrespective of fructose concentration, the majority of fructose taken up underwent non-oxidative metabolism. Lactate production accounted for approx. 80% of the fructose metabolism in the basal state and approx. 70% in the insulin (1000 mu-units/ml)-stimulated state. In the presence of 5 mM glucose, physiological concentrations of fructose could account for approximately 10-30% of hexose (glucose + fructose) incorporation into glycogen under non-insulin-stimulated conditions. In conclusion, fructose appears to be transported into human skeletal muscle via a carrier-mediated system that does not involve GLUT4 or GLUT1. Furthermore, under physiological conditions, fructose can significantly contribute to carbohydrate metabolism in human skeletal muscle.

PS-4-3 Modulation of motor unit firing rates during a sustained submaximal contraction of the soleus muscle in man

PS-4-3 Modulation of motor unit firing rates during a sustained submaximal contraction of the soleus muscle in man

Low intensity electrical stimulation of neck muscles modifies motor neuron excitability of the soleus muscles in man

Low intensity electrical stimulation of neck muscles modifies motor neuron excitability of the soleus muscles in man

Effect of intensive training on the isokinetic strength and structure of lumbar muscles in patients with chronic low back pain.

This study investigated the effects of the intensive physical rehabilitation program on the trunk and knee extensor muscles in patients with chronic low back pain. At baseline and after 3 months, strength was measured and muscle biopsies were taken. To evaluate the effects of strength exercises on the structure of back muscles. Rehabilitation designed for chronic low back pain patients improves trunk muscle strength, mobility of the spine, and the patients' functional capacity. The effects of such programs on the structure of back muscles have not been reported previously. Thirty patients with chronic low back pain volunteered to participate in the study. Biopsies were taken from the multifidus and vastus lateralis muscles. The sizes of Types 1 and 2 muscle fibers were measured. The peak-torques of isokinetic trunk and knee extension were determined at two different angular velocities. Strength increased by 19-22% (P < 0.05) in trunk extension and by 7-11% (P < 0.05) in knee extension. Type 1 fibers maintained their pre-exercise size. The size of Type 2 muscle fibers in men increased by 11% (P < 0.05) in the multifidus and by 8% (P < 0.05) in the vastus lateralis. In women, the corresponding increases were 11% (P = 0.16) and 11% (P < 0.05). The correlation between the size of Type 2 muscle fibers in the multifidus and the strength of trunk extension improved, especially in men at follow-up. The results of the present study suggest that training with maximal or submaximal effort may reverse the selective atrophy of Type 2 fibers in the multifidus muscles in men. Intensive training also can significantly increase the trunk extension strength in women, but women may need a longer training period than men to achieve significant structural changes in their back muscles.

The relationship between the pressor response to involuntary isometric exercise and the contractile protein profile of the active muscle in man.

The present investigation examined the relationship between the pressor response during electrically evoked isometric ankle plantar flexion and the contractile protein profile of the active muscle in seven young men [mean (SD) age, 26 (6) years] and five older men [70 (4) years]. Muscle biopsy samples were taken from lateral gastrocnemius (LG) and soleus (SOL) of each subject. These were analysed for isomyosin composition using non-denaturing pyrophosphate polyacrylamide gel electrophoresis. The degree of association was examined between the cardiovascular changes and the fast isomyosin content of LG and SOL individually and in combination (SOL/LG). In the total subject group there was no association between the heart rate response or the change in systolic blood pressure (BP) and the fast isomyosin composition. However, the change in diastolic BP was significantly associated with the fast isomyosin composition of SOL/LG (delta diastolicBP = 0.31 + 0.045% FM SOL/LG, r = 0.65, P = 0.029). These findings suggest that the magnitude of the peripheral reflex mediated pressor response to isometric exercise and the fast isomyosin content of the active muscle are related.

Segmental reflexes and ankle joint stiffness during co-contraction of antagonistic ankle muscles in man.

The size of soleus H-reflexes and short-latency stretch reflexes was measured at different levels of plantar flexion or co-contraction (simultaneous activation of dorsi- and plantar flexors) in seven healthy subjects. In four of seven subjects the short-latency stretch reflex was smaller during weak co-contraction than during isolated plantar flexion at matched background electromyogram (EMG) levels in the soleus muscle. In three of these four subjects the stretch reflex was larger during strong co-contraction than during plantar flexion, whereas it had the same size during the two tasks in the last subject. In the remaining subjects the stretch reflex either had the same size or was larger at all levels of co-contraction than at similar levels of plantar flexion. In contrast, the H-reflex was found to decrease with co-contraction at all contraction levels in all subjects. The decrease in the reflexes during weak co-contraction might be caused by presynaptic inhibition of Ia afferents. It is unclear why only the H-reflex decreased during strong co-contraction. The stiffness of the ankle joint was measured from the torque increment following the stretch of the plantar flexors divided by the stretch amplitude. In all subjects the total stiffness of the ankle joint was larger during strong co-contraction than during plantar flexion of similar strength. The stiffness was smaller during weak co-contraction than during weak plantar flexion in three out of seven subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Discharge of muscle afferents during voluntary co-contraction of antagonistic ankle muscles in man

The discharge of 38 tibialis anterior (TA) muscle spindle endings was recorded at rest and during isometric voluntary contraction of the ankle joint in eight healthy human subjects. With the ankle joint in 110° plantarflexion, 24 endings (61%) were tonically active in the resting subject. During weak voluntary dorsiflexion, seven additional endings were activated, so that a total of 31 endings were active (82%). 24 of these were either newly recruited or discharged at a faster rate than at rest (average discharge rate 6.6 Hz at rest, 9.7 Hz during contraction). At matched levels of TA EMG, one ending was newly recruited and 10 were more active during co-contraction of dorsi and plantar flexors than during isolated dorsiflexion. 26 endings were equally active during the two tasks and one ending decreased its firing rate with co-contraction. Four of the 11 endings, which had a higher discharge rate during co-contraction than during dorsiflexion, discharged faster during plantarflexion than at rest although slower than during co-contraction. Plantarflexion had no effect on the discharge of three endings. The remaining four endings were not investigated during plantarflexion. It is suggested that the increased discharge rate of muscle endings during co-contraction is caused either by small changes in the length of the TA muscle or by a disproportionately high fusimotor drive during co-contraction.