Muscle In Man Research Articles

Maximal perfusion of skeletal muscle in man.

Five subjects exercised with the knee extensor of one limb at work loads ranging from 10 to 60 W. Measurements of pulmonary oxygen uptake, heart rate, leg blood flow, blood pressure and femoral arterial-venous differences for oxygen and lactate were made between 5 and 10 min of the exercise. Flow in the femoral vein was measured using constant infusion of saline near 0 degrees C. Since a cuff was inflated just below the knee during the measurements and because the hamstrings were inactive, the measured flow represented primarily the perfusion of the knee extensors. Blood flow increased linearly with work load right up to an average value of 5.7 l min-1. Mean arterial pressure was unchanged up to a work load of 30 W, but increased thereafter from 100 to 130 mmHg. The femoral arterial-venous oxygen difference at maximum work averaged 14.6% (v/v), resulting in an oxygen uptake of 0.80 l min-1. With a mean estimated weight of the knee extensors of 2.30 kg the perfusion of maximally exercising skeletal muscle of man is thus in the order of 2.5 l kg-1 min-1, and the oxygen uptake 0.35 l kg-1 min-1. Limitations in the methods used previously to determine flow and/or the characteristics of the exercise model used may explain why earlier studies in man have failed to demonstrate the high perfusion of muscle reported here. It is concluded that muscle blood flow is closely related to the oxygen demand of the exercising muscles. The hyperaemia at low work intensities is due to vasodilatation, and an elevated mean arterial blood pressure only contributes to the linear increase in flow at high work rates. The magnitude of perfusion observed during intense exercise indicates that the vascular bed of skeletal muscle is not a limiting factor for oxygen transport.

Cerebral potentials and electromyographic responses evoked by stretch of wrist muscles in man.

The cerebral evoked potential produced by rapid extension of the wrist was recorded from scalp electrodes in normal subjects while they exerted a small background flexor torque (0.24 Nm) against an electric motor. The initial part of the response consisted of a negative deflection (N1) with an average latency of 24.7 ms. This was followed by a biphasic P1/P2 (32 ms) response and a large later negative wave (N2) (76 ms). Passive wrist extension also evoked reflex EMG responses in the forearm flexor muscles which could be resolved into a short latency (25 ms) and long-latency (52 ms) component. The cerebral responses persisted almost unchanged during complete ischaemic anaesthesia of the hand produced by a pressure cuff around the wrist, and were reduced if the stretch was given during voluntary wrist flexion. The primary component (N1-P1/P2) of the cerebral response probably represents the arrival at the cortex of the muscle afferent volley. However, the significance of the secondary component (P1/P2-N2) is unknown. Under certain conditions, its size was related to the size of the long latency stretch reflex evoked by stretch of the flexor muscles. Thus, increasing the velocity of stretch or decreasing the repetition rate (from 1.0 to 0.15 Hz) at which stretches were applied, increased the size of both the muscle reflex and the cerebral response. The secondary component also could be changed by voluntary reaction to wrist stretch. Changes in the size of the secondary component of the evoked response may represent the earliest cortical sign of interaction between sensory input and motor output.

The effect of long-term circulatory occlusion on pH and energy metabolism of the quadriceps muscle in man.

The effect of up to 2.5 h circulatory occlusion on muscle pH and energy metabolism of the quadriceps muscle was studied in 13 patients operated on for an inveterate knee injury. Muscle samples were taken by the percutaneous needle biopsy technique at different times during the arterial occlusion and after restoration of circulation. Energy was provided by a complete utilization of phosphocreatine and by a low rate of glycolysis during 2 h of occlusion. The ATP level remained unchanged throughout the occlusion period. Muscle pH decreased from 7.0-7.1 to about 6.8 after 2 h occlusion. Muscle pH was essentially normalized within 20 min after restoration of the blood flow.

Glycogen Contents in Skeletal Muscles in Men and Different Species of Experimental Animals

Glycogen Contents in Skeletal Muscles in Men and Different Species of Experimental Animals

Static contraction of the quadriceps muscle in man: cardiovascular control and responses to one-legged strength training.

Knee extension strength training of one leg (ST) (120 maximal contractions per day, 5 days per week for 9 weeks) was performed by 9 healthy young men. Before and after ST, biopsies were obtained from the vastus lateralis muscle of each leg and static quadriceps contractions (SQC) lasting 2 min were performed with each leg under control conditions and after combined vagal and beta-adrenergic blockade with atropine and metoprolol. Maximal voluntary contraction strength (MVC) increased more for the trained leg (TL) than for the untrained leg (UTL) but thigh circumferences and muscle fibre diameters gave little evidence for muscle hypertrophy. In pre- vs. post-training comparisons during SQC at the same relative force (40% of MVC) mean blood pressure (MBP), heart rate (HR) and smoothed rectified electromyographic activity were similar for TL and UTL. Similar findings were obtained for MBP after attenuation of the HR response by autonomic blockade, indicating that MBP, per se, was closely linked to the relative force of SQC. Pre- to post-training reductions in MBP and HR during SQC with each leg at an absolute force of 40% of pre-training MVC were likely due to changes in the pattern of motor unit activation. A lower MBP response to SQC and TL than of UTL after training correlated with a greater capillary density and a lower muscle lactate level for TL.

Facilitation of soleus‐coupled Renshaw cells during voluntary contraction of pretibial flexor muscles in man.

Recurrent inhibition to soleus motoneurones, brought about by a conditioning H-reflex discharge, was estimated in human subjects by a subsequent test H reflex. Changes in recurrent inhibition during voluntary ankle dorsiflexion were evaluated by comparing the amplitude of the test H reflex to a reference H reflex: both reflexes were subjected to the same type of influences which modified soleus monosynaptic reflex excitability during pretibial flexor contraction, but only the test H reflex was subject to the recurrent inhibition evoked by the conditioning H-reflex discharge. During tonic or phasic ramp contractions of the pretibial flexors the inhibition of the test H reflex, as compared to rest, was more marked than that of the reference H reflex. Evidence is presented that this may indicate a facilitation of soleus-coupled Renshaw cells. Since this facilitation of soleus-coupled Renshaw cells was also observed before ramp contraction, it is, at least in part, supraspinal in origin. Within the range of forces studied (8-45% of maximum force) there was no evidence that the facilitation of soleus-coupled Renshaw cells increased along with increased force of the pretibial flexor voluntary contraction. During voluntary phasic ankle dorsiflexion, facilitation of soleus-coupled Renshaw cells was maximum at the moment when soleus motoneurones were most facilitated by the stretch-induced soleus I a discharge. There was no evidence for changes in Renshaw cell excitability during ballistic contractions. It is suggested that this facilitation of soleus-coupled Renshaw cells may be one of the mechanisms preventing the occurrence of a soleus stretch reflex during a voluntary ankle dorsiflexion. Such a mechanism could become important if reciprocal inhibition, via I a inhibitory interneurones, were not strong enough, e.g. because of a weak gamma-drive to the contracting muscles.

From activity to rest: gating of excitatory autogenetic afferences from the relaxing muscle in man

The changes in reflex excitability of the motoneurones to the soleus (Sol) muscle occurring during and after voluntary releases of various duration from a constant plantar-torque level in isometric or isotonic conditions have been investigated in normal humans by means of the H-reflex and T-response. The amplitude of both reflexes during the release phase attains values lower than control (obtained in resting conditions) even in the presence of force and EMG activity; the maximal inhibition is reached at the end of the release; the reflexes recover gradually to control values over several seconds. The more abrupt is the release, the more inhibited is the reflex and the shorter is the time to recovery and vv. These results apply both in isometric and isotonic conditions. Activation of the antagonist muscles, sometimes occurring at the end of the fastest release, does not contribute to the H-reflex inhibition. Tonic isometric contractions and relative releases have also been evoked by the tonic vibration reflex (TVR). The H-reflex during the TVR-induced contractions were lower than control values, at variance with those obtained during the voluntary contractions, but their amplitudes during the releases had similar values and time-courses in both conditions, pointing to a common involved inhibitory mechanism. Any voluntary ballistic or ramp contraction taking place after a preceding release, in the period in which the H-reflexes were still inhibited, was not apparently influenced, despite the fact that H-reflexes evoked during the release-conditioned ramp contractions were significantly lower than when evoked during control ramps of similar characteristics. The results are discussed in terms of a premotoneuronal, possibly presynaptic, inhibitory mechanism.

Bicycle Ergometer For Paralyzed Muscle

A bicycle ergometer for exercising paralyzed muscle in man is described. This system can be used for isotonic training for both the cardiovascular system and skeletal muscle for individuals who are paralyzed. The device cannot be used on individuals who have lower motor neuron lesions. The device is based upon a standard MonarkTM bicycle ergometer. The ergometer has been modified with sensors for feedback of crank position that an Apple IITM computer then uses to coordinate stimulation of muscles. The muscles used in the study are the iliacus and quadriceps. Exercise training to test the device was conducted on four paraplegic and quadriplegic subjects over a period of 30 days. Exercise was induced three times per week for a period of 15 minutes. Results of these experiments show an increase in endurance and muscle size.

The influence of clenching level on the post-stimulus EMG complex, including silent periods, of the masseter muscles in man

Standardized mechanical taps were delivered on an upper central incisor, while the nine subjects investigated maintained constant clenching levels of 5, 10, 20, 40 and 60 per cent of their maximal EMG outputs. Using statistical criteria, a computer program enabled an objective determination of the interaction between the clenching level and the sequence of upward and downward going waves following the stimulus in full-wave rectified and superimposed EMG, called a post-stimulus EMG complex (PSEC). The morphology of the PSEC, including one or two silent periods, was subject-specific and reproducible over one year. The surfaces of the waves were greatly influenced by the clenching level. In general, their total surface decreased as a function of the clenching level. However, the individual waves decreased selectively. The results suggest that the sequence of waves results from overlapping of inhibitory and excitatory inputs. The inhibitory waves, constituting the silent periods, are largely cancelled by the excitatory reflexes of the PSEC.

筋電図積分値と咬合力との関係からみた咀嚼筋の疲労に関する研究

筋電図積分値と咬合力との関係からみた咀嚼筋の疲労に関する研究

Measurement of water filtration in skeletal muscle in man by an osmotic transient method.

Water filtration in the human forearm was determined with a new method using a hyperoncotic transient of albumin solution infused into the brachial artery. Baseline dilution of labelled albumin in deep forearm vein plasma in excess of the contribution from arterial blood and from infusate was assumed to originate from extravascular water filtered into the blood by the transient. The filtration coefficient (Fc) was determined as the ratio between filtered water and increase in colloid osmotic pressure in the blood samples, and gives the filtrative water permeability in the exchange areas of the microcirculation. In 10 normal volunteers, Fc was 0.00082 ml (ml mmHg)-1 (SD=0.00007). Multiplication of Fc by plasma flow in the forearm gave a filtration capacity (Kf) of 0.0036 ml (100 ml tissue min mmHg)-1 (SD=0.00137). This filtration capacity (Kf) represents that of fast flowing regions in the forearm muscles, but it is of the same order of magnitude as the capillary filtration coefficient (CFC) determined plethysmographically for the entire forearm by the venous stasis technique.

Electronic feedback-control of paretic leg muscles in man: Movements controlled from the wrist

Electronic feedback-control of paretic leg muscles in man: Movements controlled from the wrist

Synaptic connection from muscle afferents to the motoneurons of various leg muscles in man

Synaptic connection from muscle afferents to the motoneurons of various leg muscles in man

Growth of the Locomotor Apparatus of the Japanese Macaque: Based on Analysis of Muscular Weights and Limb Segment Lengths

Growth of musculo-skeletal system of Japanese macaques was analysed, on the supposition that the system may grow in concordance with a functional necessity such as locomotion. Growth of bone length shows that the limbs of macaques are not specialized for running or leaping. Growth of muscle weight is remarkable, and the alteration in the weight distribution can be related to the change of locomotor pattern to some extent. Muscle growth of upper and lower limbs differs in their characteristics: growth of lower limb muscles is oriented solely to development for propulsion (pushing the body forward); that of upper limbs is oriented not only to the development of propulsion but also of control, such as rotation. Postnatal growth of muscles in man resembles that of macaque, which suggests that the function is very similar. A large difference in muscle development between man and macaque is in the magnitude of growth, that is, muscle growth in man is more remarkable than in macaque. The difference may be related to the fact that the newborn of man is less mature than that of macaque and/or that changes in the functional necessities of man are greater than those of macaque.

Progressive resistance exercise training of the hypotrophic quadriceps muscle in man. The effects on morphology, size and function as well as the influence of duration of effort

The effects of progressive resistance exercise (PRE) training for 4 weeks on the hypotrophic quadriceps muscle were investigated in 23 young healthy male soccer players, who had been immobilized in a plaster cast 4-6 weeks after knee ligament injuries. The subjects were allocated to two training regimes where the injured leg was trained for periods of varying duration, whereas the intensity and frequency of exercise were alike in the two groups. However no significant differences were detected between the two training groups. In the whole material the lean thigh volume of the injured leg increased from 4.09 to 4.47 litres (p less than 0.001), whereas the fat component of the thigh was unchanged. The dynamic strength (1 RM) of the injured leg increased from 14.0 kg to 27.0 kg and amounted to 87% of the control leg after 4 weeks of training. At this time the maximum isometric strength amounted to 114 Nm, which was 63% of strength in the control leg. Succinate dehydrogenase (SDH) in homogenates of muscle biopsy sample increased (i.e. 20%, p less than 0.05) to the same level as found in the control leg. No changes in phosphofructokinase (PFK) were observed. The type I fibre distribution was lower in the immobilized leg than in the control leg. These results indicate that, following muscular hypotrophy resulting from 4-6 weeks of immobilization, dynamic exercise can restore the oxidative potential, whereas the size and strength are only partly recovered.

Decrease of lipoprotein lipase activity in skeletal muscle in man during a short-term carbohydrate-rich dietary regime. With special reference to HDL-cholesterol, apolipoprotein and insulin concentrations

Seven men took part in a study in which the diet was changed from an ordinary mixed one to a fat-rich diet [>70% energy (E)] for 3 days followed by a carbohydrate-rich diet (>70% E) for 3 days. Blood was drawn and muscle biopsies [for analysis of lipoprotein-lipase (LPL) activity] were taken before the study and at the end of each diet period. Insulin, apolipoprotein (apo) B, A-I and A-II, cholesterol and triglyceride concentrations were determined in serum and the lipids also in the high density lipoproteins (HDL). Serum insulin was higher ( p < 0.01) during the carbohydrate-rich diet than during the fat-rich diet (12.0 ± 0.9 vs. 7.5 ± 0.5 mU/I, mean ± SEM), as were serum-triglycerides ( 2.42 ± 0.27 vs. 0,98 ± 0.07 mmole 1 , p < 0.001 ). Muscle LPL activity, on the other hand, was lower ( p < 0.01), 27.3 ± 6.1 vs. 75.1 ± 13.2 mU/g. HDL-cholesterol was 1.22 ± 0.08 during the carbohydrate-rich diet which was lower ( p < 0.01) than during the fat-rich diet, 1.45 ± 0.11. The concentration of apo A-I and A-II did not vary significantly. It is suggested that the increased insulin concentrations during a short-term, carbohydrate-rich diet may have a down-regulating effect on muscle LPL activity. Low muscle LPL activity may account for part of the elevation of serum triglycerides. An ineffective hydrolysis of VLDL-triglycerides may contribute to the variation in HDL-cholesterol concentration seen under these circumstances.

Extra- and intracellular water spaces in muscles of man at rest and with dynamic exercise

A method was established to analyze the extracellular water space (H2Oe) in small muscle tissue samples as [3H]inulin distribution space. After initial experiments on rats, the method was applied on 13 men and 6 women. Muscles with different fiber compositions (soleus, S; vastus lateralis, (VL; gastrocnemius, G; triceps brachii, TB) were studied at rest. The total water content was the same for all muscles, 320 (313-330) ml/100 g dry wt. However, differences were demonstrated for H2Oe, with 26-34 ml/100 g dry wt in VL and 38-54 ml/100 g dry wt in S, (P less than 0.05); the values for G and TB were in between those for VL and S. The differences in H2Oe were not related to the fiber composition of the muscles. During 3 x 3 min of intense bicycle exercise demanding about 120% VO2 max (6 men), total water content increased in VL from 313 to 359 ml/100 g dry wt and H2Oe increased from 34 to 60 ml/100 g dry wt (P less than 0.05), In TB, which is relatively inactive during bicycle exercise, no such changes occurred. The calculated intracellular lactate concentration increased in VL from 5.7 to 30.6 mmol/l H2Oi. The extracellular lactate concentration amounted to 13.6 mmol/l H2Oe at the end of exercise. The concentration gradient for lactate of 2 from intra- to extracellular space favored a flux of water to the intracellular space. The relative large increase in H2Oe may then be caused by a hydrostatic rather than an osmotic factor.U

The effects of the increase of arterial potassium upon the excitability of normal and dystrophic myotonic muscles in man

Progressively increasing concentrations of potassium chloride were administered intra-arterially to patients affected with dystrophia myotonica (Steinert's disease) and to healthy volunteers before and after parenteral taurine treatment. Changes in the excitability of thenar eminence muscles were related to plasma potassium concentrations. A rise in the plasma potassium brought about a parallel increase of muscular excitability in normal individuals whilst in dystrophic myotonic patients it was associated with a two-phase phenomenon: the severity of myotonia first decreased and then, at higher plasma potassium levels, greatly worsened with the occurrence of spontaneous myotonic discharges. The administration of taurine, a membrane-stabilizing drug, considerably lowered the excitability of both normal and dystrophic myotonic muscles. The effects of potassium and taurine on muscular membrane conductance may explain the observed changes in muscular excitability.

Limitation of jaw movement by antagonist muscle stiffness during unloading of human jaw closing muscles

The unloading reflex in the jaw closing muscles in man was investigated with a view to correlating the jaw closing movement with the timing of the electrical activity of the agonist and antagonist muscles. When the resistance to the forceful isometric bite was suddenly and unexpectedly withdrawn, the closing movement of the mandible was always arrested before the teeth came together. The rapid arrest of the jaw closing movement was not adequately accounted for by the timing of the inhibition of the jaw closing muscles and reflex excitation of the jaw opening muscles. It was observed that the jaw opening muscles, as well as the jaw closing muscles, were always active during the phase of isometric biting on an object between the teeth. It is therefore concluded that the resulting stiffness of the antagonist muscles is the mechanism which is principally responsible for limiting the jaw closing movement after unloading of the agonist muscles.

The disposal of an intravenously administered amino acid load across the human forearm

This study was designed to examine the role of the skeletal muscle in man in the disposal of an intravenously administered L-amino acid solution. Arterio-deep venous differences of amino acids, glucose and lactate, and blood flow across the human forearm were measured in 9 healthy normal male volunteers (age = 27 ± 2 yr, weight = 79 ± 4 kg and height = 180 ± 2 cms) after an overnight fast (12 hr). Glucose and alanine turnover rates were estimated using a continuous infusion of 3- 3H-glucose and U- 14C-alanine isotopes. All measurements were obtained during steady state conditions, basally and two hours after the start of an L-amino acid infusion (8.5% solution). During the control period there was a significant release of total alpha amino nitrogen (AAN) equal to 300 ± 97 nmole 100 g forearm muscle/min with alanine and glutamine accounting for over 80% of that amount ( 260 ± 24 nmole 100 g forearm muscle/min ). The release of the branched chain amino acids (BCAA) was only significant for valine, while the release of each of the keto acids of leucine and valine, α-ketoisocaproate and α-ketoisovalerate ( 37 ± 12 and 36 ± 7 nmole 100 ml forearm muscle/min respectively ) was significant from zero and exceeded the release of the corresponding amino acids ( 13 ± 17 and 24 ± 7 nmole 100 g forearm muscle/min for leucine and valine respectively ). The infusion of the L-amino acid solution resulted in a reversal of amino acid balance across the forearm. There was a net uptake of AAN of 1195 ± 209 nmole 100 g forearm muscle/min with the BCAA accounting for 513 ± 75 nmole 100 g forearm muscle/min or 49 ± 6% of the uptake. The net uptake of BCAA by skeletal muscle did not exceed 35% of the amount infused. The release of α-ketoisocaproate and α-ketoisovalerate showed no significant change from basal levels. The output of alanine and glutamine persisted in response to the infusion; while alanine output dropped by 40%, glutamine output increased by 50% ( 68 ± 23 and 218 ± 42 nmole 100 g forearm muscle/min respectively ), yet the combined release of alanine and glutamine did not change significantly from basal levels. Amino acid infusion resulted in a twofold increase in insulin and glucagon. Plasma glucose fell from 5.3 ± 0.05 mM basally to 5.04 ± 0.06 mM ( p < 0.05), while blood lactate increased from 0.587 ± 0.03 mM to 0.639 ± 0.025 mM ( p < 0.05); similarly there was a time dependent increase in glucose uptake by muscle ( from 0.857 ± 0.08 to 1.27 ± 0.07 μ mole 100 g forearm muscle/min , p < 0.05) and lactate release ( 0.226 ± 0.03 to 0.297 ± 0.045 μ mole 100 g forearm muscle/min, p < 0.05 ). These results indicate that a significant amount of the amino acids infused, and specifically the BCAA are extracted by human skeletal muscle, and mostly retained as such for later use. The data obtained under the conditions of the present study also indicate that tissues other than skeletal muscle are as important in the overall handling of these amino acids. However, it remains to be seen whether these findings can be extrapolated to other physiological conditions.