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  • 1
    Electronic Resource
    Electronic Resource
    Motor unit recruitment order during voluntary and electrically induced contractions in the tibialis anterior (1997)
    Springer
    Experimental brain research 114 (1997), S. 117-123 
    Details
    ISSN: 1432-1106
    Keywords: Key words Muscle contraction ; Electrical stimulation ; Motor unit recruitment ; Spike-triggered averaging ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The recruitment order of motor units (MU) was compared during voluntary and electrically induced contractions. With the use of spike-triggered averaging, a total of 302 MUs with recruitment thresholds ranging from 1% to 88% of maximal voluntary contraction were recorded in the human tibialis anterior muscle in five subjects. The mean (±SD) MU force was 98.3±93.3 mN (mean torque 16.8±15.9 mNm) and the mean contraction time (CT) 46.2±12.7 ms. The correlation coefficients (r) between MU twitch force and CT versus the recruitment threshold in voluntary contractions were +0.68 and –0.38 (P〈0.001), respectively. In voluntary contractions, MUs were recruited in order of increasing size except for only 6% of the cases; whereas, during transcutaneous electrical stimulation (ES) at the muscle motor point, MU pairs showed a reversal of recruitment order in 28% and 35% of the observations, respectively, when the pulse durations were 1.0 ms or 0.1 ms. This recruitment reversal during ES was not related to the magnitude of the difference in voluntary recruitment thresholds between MUs. It is concluded that if the reversal of MU recruitment observed during ES is biophysically controlled by differences in their nerve axon input impedance, in percutaneous stimulation at the motor point, other factors such as the size and the morphological organisation of the axonal branches can also influence the order of activation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00005610
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  • 2
    Electronic Resource
    Electronic Resource
    Training effects on muscle fatigue in man (1984)
    Springer
    European journal of applied physiology 53 (1984), S. 248-252 
    Details
    ISSN: 1439-6327
    Keywords: Muscle fatigue ; Training ; Force ; Surface action potential (SAP)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 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〈0.001). Concimitant rates of tension development and of relaxation are respectively augmented by +18% (P〈0.001) and +12% (P〈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〈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〈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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00776598
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of immobilization on electromyogram power spectrum changes during fatigue (1991)
    Springer
    European journal of applied physiology 63 (1991), S. 458-462 
    Details
    ISSN: 1439-6327
    Keywords: Muscle fatigue ; Immobilization ; Electromyography ; Power density spectrum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The maximal force and median frequency (MF) of the electromyogram (EMG) power density spectrum (PDS) have been compared in disused (6 weeks' immobilization) and control (contralateral) human adductor pollicis muscles during fatigue induced by voluntary or electrically-triggered (30 Hz) contractions. The results indicated that after 6 weeks' immobilization, MF was not significantly different in disused and control muscles although the force and integrated EMG were drastically reduced during a maximal voluntary contraction (MVC; by 55% and 45%, respectively,n = 8). During sustained 60 s MVC, the force decreased at the same rate in immobilized and control muscles, but the shift of MF towards lower frequency values was smaller (P〈 0.05) in disused muscle as compared to control by (14% vs 28%, respectively). In electrically-induced fatigue, the force decrease and the MF shift were larger after inactivity (41% and 43% in one subject, and 50% and 54% in the other subject, respectively) as compared to control (29% and 34% in one subject, and 37% and 38% in the other subject, respectively). These results emphasize the caution that should be exercised when EMG signals are quantified by computing the power density spectrum. The different effects of fatigue during voluntary and electrically-imposed contractions in disused and control muscles indicated that immobilization induced changes in the neural command for the contraction which compensated, at least in part, for its decreased contractile efficiency and resistance to fatigue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00868078
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  • 4
    Electronic Resource
    Electronic Resource
    Electro-mechanical failures and lactate production during fatigue (1987)
    Springer
    European journal of applied physiology 56 (1987), S. 287-291 
    Details
    ISSN: 1439-6327
    Keywords: Fatigue ; Muscle contraction ; Lactate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 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〉0.05) difference in force reduction or maximal venous lactate concentration was observed in either fatigue test, although electrical failure differed significantly (P〈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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00690894
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  • 5
    Electronic Resource
    Electronic Resource
    Contributions of slow and fast muscles of triceps surae to a cyclic movement (1986)
    Springer
    European journal of applied physiology 55 (1986), S. 476-481 
    Details
    ISSN: 1439-6327
    Keywords: Cyclic movement ; Synergistic muscles ; Electromyography (EMG) ; Triceps surae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 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, wehen 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00421640
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  • 6
    Electronic Resource
    Electronic Resource
    Muscle stretching and motoneuron excitability (1988)
    Springer
    European journal of applied physiology 58 (1988), S. 47-52 
    Details
    ISSN: 1439-6327
    Keywords: Muscle stretching ; Reflex activities ; Motoneuron excitability ; Flexibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Change of motoneuron excitability has been studied during the three basic modalities of slow or static stretching of the human soleus muscle. Tendon (T) and Hoffmann (H) reflexes were analyzed during static stretching (SS). The H response was compared in SS, in SS preceded by a maximal isometric contraction of the muscle or contraction-relaxation (CR) and during stretching of the muscle by contracting the antagonistic muscles (AC). During progressive dorsiflexion of the foot there is a significant difference (p〈0.05) between T and H reflexes during SS, although the amplitude of direct motor (M) response, evoked by a maximal stimulation of the motor nerve, is not changed. The maximal joint mobilization during SS, CR and AC modalities appears to be closely related to the decrease in the H response during stretching. This decrease is significantly (p〈0.05) smaller in SS than in AC or CR. In this last method, the duration of the maximal isometric contraction does not affect the results. In these three basic stretching procedures, the H reflex quickly recovers as soon as the manoeuvre is interrupted. It is suggested that changes in muscle motoneuron pool excitability closely control joint mobilization during slow or static stretching. The inhibition of the motoneurons observed during SS, CR and AC modalities is limited to the duration of the stretching manoeuvre.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00636602
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