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Biomedical subjects

K Hainaut

Publications and source records attributed to K Hainaut.

At least 37 records · Page 2Linked to original sources
PubMed1988

Training effects of sub-maximal electrostimulation in a human muscle.

This paper compares the effects of 6 wk of sub-maximal training by electrostimulation (100 Hz) and voluntary contractions on the contractile properties of the adductor pollicis muscle in intact man. The daily training program consisted of ten series of twenty 1-s isotonic contractions (60 to 65% of maximum) separated by 1-s intervals. The observed increase in muscle force, tested in maximal voluntary and electrically evoked contractions, appears to be significantly smaller during electrostimulation than during a training session performed by voluntary contractions. The increase in force recorded during electrostimulation is not associated with changes in the tetanus rates of tension development and tension relaxation (dP0/dt). Conversely, the tetanus time course is found to be significantly accelerated in muscles trained by voluntary contractions. No change of the surface action potential total area was observed during both training procedures. Furthermore, electrostimulation does not improve muscle resistance to fatigue, which is observed to be significantly increased after training by voluntary contractions. This study indicates that electrostimulation augments the muscle force of contraction by changing peripheral processes associated with intra-cellular events, without modifying the nervous command of the contraction. The comparison of the peripheral changes recorded during sub-maximal training by electrostimulation and voluntary contractions suggests that electrostimulation is less efficient, but complementary to voluntary training because the number and the type of trained motor units are different in the two procedures.

Adult↗
PubMed1987

Electro-mechanical failures and lactate production during fatigue.

The electrical and mechanical failures observed during sustained and intermittent electrically triggered (30 Hz) contractions of human flexor carpi ulnaris were compared with the blood lactate concentration. The changes recorded during contractions sustained for 60 s were compared with those observed during a series of sixty 1 s contractions separated by 1 s intervals, and also with the changes during the first 30 min of recovery. No significant (P less than 0.05) difference in force reduction or maximal venous lactate concentration was observed in either fatigue test, although electrical failure differed significantly (P less than 0.05). The recovery of electrical failure was poorly correlated with the reduction in lactate concentration following both sustained (r = -0.70) and intermittent contractions (r = 0.72). In contrast, the recovery in tetanic tension, rate of tension development and time to half relaxation correlated closely with the reduction in venous lactate concentration (r = -0.95, -0.93 and 0.96 respectively). It is suggested that, of the peripheral processes which appear to play a dominant role in peripheral fatigue, lactate production controls mechanical failure directly.

Action Potentials↗
PubMed1987

Electrical and mechanical changes in immobilized human muscle.

After forearm fracture, the human thumb was unilaterally immobilized in eight subjects for 6 wk in a standard plaster cast. Changes of contraction properties were studied in the adductor pollicis muscle. The contralateral muscle remained unrestrained and served as control. After immobilization, the maximal voluntary contraction was reduced by 55% (P less than 0.05), and the electrically evoked maximal tetanic contraction (Po) was reduced by 33% (P less than 0.05). The decrease of Po was associated with increased maximal rate of tension development (10%) and decreased maximal rate of tension relaxation (22%). The twitch times to peak and to half relaxation were increased by 16 and 14%, respectively, but the twitch tension (Pt) was not significantly changed and the Pt/Po ratio was increased by 43% after immobilization. The muscle surface action potential presented an increase of its duration (19%) and a decrease of the amplitude and the total area (15 and 26%, respectively). The comparison of the electrical and mechanical alterations recorded during voluntary contractions, and in contractions evoked by electrical stimulation of the motor nerve, suggests that immobilization not only modifies the peripheral processes associated with contraction but also changes central and/or neural command of the contraction. At peripheral sites, it is proposed that the intracellular processes of contraction play the major role in the contractile impairment recorded during immobilization.

Electromyography↗
PubMed1986

Contributions of slow and fast muscles of triceps surae to a cyclic movement.

The relative contribution of synergistic muscles has been studied during pedalling on a bicycle. The electromyographic (EMG) activity of the different components of triceps surae (namely soleus or SOL and medial gastrocnemius or MG) has been recorded and analyzed for increasing pedalling speed performed against increasing resistance. The results indicate that SOL IEMG (integrated EMG) increases linearly (y = 2x-12.1; r = 0.98) with increasing load (10-70 N) at constant speed (60 rpm), whereas no change is noted in MG IEMG below 40 N. In contrast, when the pedalling speed is increased (from 30 to 170 rpm) at constant load, MG IEMG shows the largest increase. Furthermore, although in both muscles EMG activity appears earlier in the movement with increases in load and/or speed, the delay between the onset of both EMGs remains unchanged at constant speed and synchronization of MG with SOL is only observed when speed is increased above 140 rpm. These results suggest that the different muscles of the triceps surae make specific contributions to the development of the mechanical tension required to maintain or increase the speed of movement.

Adult↗
PubMed1986

Nonlinear summation of contractions in striated muscle. I. Twitch potentiation in human muscle.

The adductor pollicis of intact man was electrically stimulated via its motor nerve, with series of two supramaximal pulses delivered at various intervals. Muscle surface action potential, myogram and corresponding first derivative (dPt/dt) were recorded under isometric conditions. When two stimuli are delivered at intervals shorter than 150 ms a more-than-linear summation, or potentiation, is observed. This potentiation of force production by a second stimulus involves both increased duration and acceleration of contraction. The potentiation is larger in muscles with small twitch-to-tetanus ratio (Pt/Po), and is found to decrease or increase when Pt/Po is respectively augmented (for example in positive staircase and in contractile disuse) or reduced (for example in negative staircase and in dynamic training). No significant modification of muscle surface action potential is observed when these contractile changes are present. Combined prolongation and intensification of intracellular processes, associated with muscle excitation-contraction coupling in a twitch, could account for the potentiation observed in nonlinear summation of contractions.

Action Potentials↗
PubMed1986

Nonlinear summation of contractions in striated muscle. II. Potentiation of intracellular Ca2+ movements in single barnacle muscle fibres.

Nonlinear summation of contractions is studied in single barnacle (Balanus nubilus) muscle fibres, loaded with the photoprotein aequorin. The results indicate that nonlinear summation of aequorin transients is indeed present and for short interpulse intervals (25-250 ms), a more-than-linear summation of transients, which suggest an increase of the cytosolic Ca2+ concentration in the second response, is observed. This augmented Ca2+ concentration is not merely due to summation with the preceding conditioning transient, but to an enlargement of the second transient in its own right. Furthermore, the enlargement of the second Ca2+ response is not the result of prolonged release, or slowing of re-uptake by intracellular organelles. On the contrary, Ca2+ release is found to be enhanced and for short depolarizations (20 ms), its time to half re-uptake is reduced. The intensified Ca2+ release, triggered by the second standard depolarization, is related to the level of cytosolic Ca2+ concentration reached in the conditioning response and, for example, appears to be larger in the presence of Dantrolene-sodium, which is known to reduce Ca2+ movements in a single twitch. It is concluded that contractile potentiation observed during nonlinear summation of contractions, is associated with a potentiation of intracellular Ca2+ movements, which interact to regulate the cytosolic Ca2+ concentration during contraction.

Aequorin↗
PubMed1985

Electrical and mechanical failures during sustained and intermittent contractions in humans.

This paper compares the effects of sustained and intermittent contractions on electrical and mechanical failure during muscle fatigue in the human adductor pollicis electrically stimulated at 30 Hz via its motor nerve. Sixty-second sustained contractions are compared with a series of 60 1-s contractions, separated by 2.0-, 1.0-, and 0.5-s intervals for identical duration of tension development. Sixty-second sustained contractions decrease tetanic force to 60% (P less than 0.05) of initial values. No significant difference (P greater than 0.05) of force reduction was observed during intermittent 1-s contractions separated by 1-s intervals (-40%), but final force reduction was found to be significantly smaller (P less than 0.05) for 2-s intervals (-18%) and larger (P less than 0.05) for 0.5-s intervals (-65%). When identical force reduction is present in both fatigue tests, it appears that concomitant electrical failure is considerably different during sustained and intermittent contractions (P less than 0.05). This electromechanical dissociation suggests that slowing of conduction along nerve and muscle membranes, as well as possible increase of synaptic delay, does not explain the observed mechanical failure. It is therefore suggested that intracellular processes play the major role in contractile failure during sustained and intermittent contractions.

Action Potentials↗
PubMed1984

Training effects on muscle fatigue in man.

Effects of 3 months training, on electrical and mechanical failures during fatigue, were studied in human adductor pollicis muscle. Eight subjects carried out a daily training program of 10 series of 20 fast (0.5 s) voluntary contractions, against a load equivalent to 30-40% of the muscle maximal force. Contractile properties in control and trained muscles are tested by delivering supramaximal electrical pulses (30 Hz) to the motor nerve, thereby triggering series of 60 1-s contractions separated by 1-s intervals. Training produces significant increase in tension development during a 30 Hz isometric tetanus (+ 13%; P less than 0.001). Concimitant rates of tension development and of relaxation are respectively augmented by + 18% (P less than 0.001) and + 12% (P less than 0.001). No significant change of surface muscle action potential (SAP) is observed after training. The considerable loss of force recorded during fatigue in control muscles (-36%) is significantly smaller (P less than 0.001) after training (-17%). Slowing of tension development and of tension relaxation, observed during fatigue in control muscles (respectively -47% and -79%) is smaller after training (respectively -28% and -65%). Analysis of electrical failure indicates that training significantly (P less than 0.01) reduces augmentation of muscle SAP duration and area recorded during fatigue. Comparison of time courses of mechanical and electrical failures in control and trained muscles, supports the idea that intracellular processes play the major role in tension decay associated with fatigue in human adductor pollicis muscle.

Action Potentials↗
PubMed1984

Isometric or dynamic training: differential effects on mechanical properties of a human muscle.

This work compares the specific effects of 3 mo of moderate, isometric, or dynamic voluntary exercises on the contractile properties of human adductor pollicis muscle. Isometric training consisted of 10 daily contractions of 5-s duration at the frequency of one contraction per minute. Dynamic training consisted of 10 daily series of 10 fast contractions (less than 0.5-s duration) moving a load of one-third of the maximal muscle strength at a frequency of one series per minute. Both training programs produced a concomitant increase in maximal tetanic tension and in peak rate of tension development (Ro). A larger increase (P less than 0.05) was found after isometric training (20 vs. 11% after dynamic exercises), whereas Ro augmented more (P less than 0.05) after dynamic contractions (31 vs. 18% after isometric training). Enhancements of twitch force (Pt), rates of twitch tension development (Rt), and of relaxation (St) were, respectively, 20, 20, and 12% after isometric training. There was no modification of contraction time and time of half relaxation (T 1/2R). Conversely, dynamic training produced increases of Rt (25%) and St (16%), associated with an apparently paradoxical decrease of Pt (10%) and reductions of contraction time (11%) and T 1/2R (9%). Maximal shortening velocity was only increased after dynamic training (21%), whereas the maximal muscle power presented a large increase (P less than 0.05) after isometric exercises (51 vs. 19% after dynamic exercises) and a shift of its optimal peak toward heavier loads. This study suggests that human muscle adapts differently to isometric or to dynamic training programs and provides evidence that its contractile kinetics can be altered by exercises performed in physiological conditions.

Adolescent↗
PubMed1977

Inhibition of the intracellular release of calcium by Dantrolene in barnacle giant muscle fibres.

1. Ca movements in resting and in activated single giant muscle fibres of the barnacle were analysed before and after exposure to Dantrolene Na, a synthetic hydantoin derivative. 2. In fibres micro-injected with the photoprotein aequorin, the resting rate of light emission (resting glow) reversibly decreased upon exposure to Dantrolene. Similar results were obtained if the fibre had first been equilibrated in a O Ca-1 mM-EGTA medium. 3. The influx of 45Ca into resting muscle fibres was not modified by 35 micronM Dantrolene which also failed to significantly reduce the influx of 45Ca into muscle fibres which had been depolarized by exposure to external solutions in which K+ had been increased to 60 or 200 mM. 4. In fibres micro-injected with 45Ca, the calcium efflux was reversibly decreased by Dantrolene. This effect was still observed in O Ca medium and in O Ca-ONa medium. A possible effect of Dantrolene on the Na-Ca exchange process at the outer membrane was excluded by showing that when the direction of the Ca2+ movement was inverted in aequorin-loaded fibres by the sudden removal of Na+ from the external medium, a marked increase in the resting glow was recorded which was not affected by exposure to Dantrolene. 5. It is argued that the reduction of Ca2+ efflux by Dantrolene does not result from any direct inhibitory effect on the metabolically driven Ca pump at the outer membrane, but that it is rather related to the reduction of the concentration of myoplasmic Ca2+ which is indeed demonstrated by the reduced resting glow. This in turn is thought to result from a shift in the balance between Ca2+ movements into and out of the intracellular storage sites, and namely the sarcoplasmic reticulum (SR). 6. The Ca2+ transient in aequorin-loaded fibres and the force of the isometric contraction elicited by imposed membrane depolarizations were markedly reduced by Dantrolene. The electrochemical threshold for eliciting intracellular Ca2+ release was not significantly modified. The linear relation between membrane depolarization and Ca2+ transient became less steep. The process of sequestration of myoplasmic Ca2+ back into SR was not significantly affected by Dantrolene which appeared to inhibit rather selectively the Ca2+ release from SR into the cytosol.

Animals↗
PubMed1976

[Regulation of ionized calcium in the cytosol of muscle cells during rest: action of dantrolene on the sarcoplasmic reticulum].

Dantrolene sodium, a hydantoin derivative with skeletal muscle relaxant properties, quickly reduces the cytosolic calcium concentration of the Barnacle (Balanus nubilus) giant muscle fibre, by direct action on the sercoplasmic reticulum. This inhibitory effect subsequently reduces the 45Ca efflux out of the cell although the 45Ca influx remains unchanged.

Animals↗
PubMed1976

The effect of A23187 ionophore on calcium movements and contraction processes in single barnacle muscle fibres.

1. Ca movements were studied in single giant muscle fibres of the barnacle before and after exposure to the Ca ionophore A23187. 2. In fibres micro-injected with the photoprotein aequorin, the resting rate of light emission (resting glow) reversibly increased when the external Ca was augmented in the presence of A23187. This resulted from an increased Ca influx through the outer membrane. In zero external Ca, A23187 induced a delayed increase of the resting glow which was related to Ca leakage from intracellular storage sites. 3. When the experiment was carried out at 5 degrees C instead of 22 degrees C, the resting glow about doubled (temperature-sensitive mechanisms for maintaining a low myoplasmic Ca2+ were thus depressed) but A23187 was much less effective in increasing Ca influx in high external Ca. 4. In 45Ca efflux experiments, A23187 increased both the Ca-Ca exchange diffusion and the net Ca outflux at the outer membrane of the fibre. The Na-Ca exchange process was not affected to a significant extent. 5. The Ca2+ transient and the force of the contraction elicited by imposed membrane depolarizations (below the threshold of the propagated action potential) were markedly increased by A23187, but the electromechanical threshold was not significantly modified. The linear relation between membrane depolarizations and the area of the Ca transient became much steeper in the presence of A23187. However the relation between the area of the Ca transient and the force output was not affected which suggests that A23187 specifically involved the Ca2+ intracellular release, but not the subsequent Ca-troponin reaction. 6. A23187 potentiates by ionophoretic action the Ca movements at the outer membrane, and it also acts inside the intact muscle fibre to intensify the intracellular release of Ca.

Aequorin↗