scholarly journals Motor units of the fourth deep lumbrical muscle of the adult rat: isometric contractions and fibre type compositions.

1991 ◽  
Vol 443 (1) ◽  
pp. 193-215 ◽  
Author(s):  
H J Gates ◽  
R M Ridge ◽  
A Rowlerson
Keyword(s):  
Fibre Type ◽  
Motor Units ◽  
Isometric Contractions ◽  
Adult Rat ◽  
Lumbrical Muscle

Determining patterns of motor recruitment during locomotion

2002 ◽  
Vol 205 (3) ◽  
pp. 359-369 ◽  
Author(s):  
James M. Wakeling ◽  
Motoshi Kaya ◽  
Genevieve K. Temple ◽  
Ian A. Johnston ◽  
Walter Herzog
Keyword(s):  
Motor Unit ◽  
Frequency Band ◽  
Fibre Type ◽  
Low Frequency ◽  
Motor Units ◽  
Motor Unit Recruitment ◽  
Medial Gastrocnemius ◽  
Fibre Types ◽  
Myoelectric Signals ◽  
Frequency Bands

SUMMARY Motor units are the functional units of muscle contraction in vertebrates. Each motor unit comprises muscle fibres of a particular fibre type and can be considered as fast or slow depending on its fibre-type composition. Motor units are typically recruited in a set order, from slow to fast, in response to the force requirements from the muscle. The anatomical separation of fast and slow muscle in fish permits direct recordings from these two fibre types. The frequency spectra from different slow and fast myotomal muscles were measured in the rainbow trout Oncorhynchus mykiss. These two muscle fibre types generated distinct low and high myoelectric frequency bands. The cat paw-shake is an activity that recruits mainly fast muscle. This study showed that the myoelectric signal from the medial gastrocnemius of the cat was concentrated in a high frequency band during paw-shake behaviour. During slow walking, the slow motor units of the medial gastrocnemius are also recruited, and this appeared as increased muscle activity within a low frequency band. Therefore, high and low frequency bands could be distinguished in the myoelectric signals from the cat medial gastrocnemius and probably corresponded, respectively, to fast and slow motor unit recruitment. Myoelectric signals are resolved into time/frequency space using wavelets to demonstrate how patterns of motor unit recruitment can be determined for a range of locomotor activities.

Change in Muscle Fascicle Length Influences the Recruitment and Discharge Rate of Motor Units During Isometric Contractions

2005 ◽  
Vol 94 (5) ◽  
pp. 3126-3133 ◽  
Author(s):  
Benjamin Pasquet ◽  
Alain Carpentier ◽  
Jacques Duchateau
Keyword(s):  
Motor Unit ◽  
Ankle Joint ◽  
Discharge Rate ◽  
Motor Units ◽  
Motor Unit Recruitment ◽  
Isometric Contractions ◽  
Neutral Position ◽  
Proprioceptive Information ◽  
Fascicle Length ◽  
Muscle Fascicle

This study examines the effect of fascicle length change on motor-unit recruitment and discharge rate in the human tibialis anterior (TA) during isometric contractions of various intensities. The torque produced during dorsiflexion and the surface and intramuscular electromyograms (EMGs) from the TA were recorded in eight subjects. The behavior of the same motor unit ( n = 59) was compared at two ankle joint angles (+10 and −10° around the ankle neutral position). Muscle fascicle length of the TA was measured noninvasively using ultrasonography recordings. When the ankle angle was moved from 10° plantarflexion to 10° dorsiflexion, the torque produced during maximal voluntary contraction (MVC) was significantly reduced [35.2 ± 3.3 vs. 44.3 ± 4.2 (SD) Nm; P < 0.001] and the average surface EMG increased (0.47 ± 0.08 vs. 0.43 ± 0.06 mV; P < 0.05). At reduced ankle joint angle, muscle fascicle length declined by 12.7% ( P < 0.01) at rest and by 18.9% ( P < 0.001) during MVC. Motor units were activated at a lower recruitment threshold for short compared with long muscle fascicle length, either when expressed in absolute values (2.1 ± 2.5 vs. 3.6 ± 3.7 Nm; P < 0.001) or relative to their respective MVC (5.2 ± 6.1 vs. 8.8 ± 9.0%). Higher discharge rate and additional motor-unit recruitment were observed at a given absolute or relative torque when muscle fascicles were shortened. However, the data indicate that increased rate coding was mainly present at low torque level (<10% MVC), when the muscle-tendon complex was compliant, whereas recruitment of additional motor units played a dominant role at higher torque level and decreased compliance (10–35% MVC). Taken together, the results suggest that the central command is modulated by the afferent proprioceptive information during submaximal contractions performed at different muscle fascicle lengths.

scholarly journals Motor unit recruitment strategies investigated by surface EMG variables

2002 ◽  
Vol 92 (1) ◽  
pp. 235-247 ◽  
Author(s):  
Dario Farina ◽  
Mauro Fosci ◽  
Roberto Merletti
Keyword(s):  
Biceps Brachii ◽  
Motor Units ◽  
Surface Emg ◽  
Recruitment Strategy ◽  
Isometric Contractions ◽  
Size Principle ◽  
Constant Torque ◽  
Emg Signal ◽  
Power Spectral ◽  
The Central Nervous System

During isometric contractions of increasing strength, motor units (MUs) are recruited by the central nervous system in an orderly manner starting with the smallest, with muscle fibers that usually show the lowest conduction velocity (CV). Theory predicts that the higher the velocity of propagation of the action potential, the higher the power at high frequencies of the detected surface signal. These considerations suggest that the power spectral density of the surface detected electromyogram (EMG) signal may give indications about the MU recruitment process. The purpose of this paper is to investigate the potential and limitations of spectral analysis of the surface EMG signal as a technique for the investigation of muscle force control. The study is based on a simulation approach and on an experimental investigation of the properties of surface EMG signals detected from the biceps brachii during isometric linearly increasing torque contractions. Both simulation and experimental data indicate that volume conductor properties play an important role as confounding factors that may mask any relation between EMG spectral variables and estimated CV as a size principle parameter during ramp contractions. The correlation between spectral variables and CV is thus significantly lower when the MU pool is not stable than during constant-torque isometric contractions. Our results do not support the establishment of a general relationship between spectral EMG variables and torque or recruitment strategy.

scholarly journals Decomposition of surface EMG signals from cyclic dynamic contractions

2015 ◽  
Vol 113 (6) ◽  
pp. 1941-1951 ◽  
Author(s):  
Carlo J. De Luca ◽  
Shey-Sheen Chang ◽  
Serge H. Roy ◽  
Joshua C. Kline ◽  
S. Hamid Nawab
Keyword(s):  
Motor Units ◽  
Surface Emg ◽  
Machine Learning Algorithms ◽  
Isometric Contractions ◽  
Semg Signal ◽  
Emg Signal ◽  
Verification Methods ◽  
Flexion Extension ◽  
Dynamic Contractions ◽  
Cyclic Contractions

Over the past 3 decades, various algorithms used to decompose the electromyographic (EMG) signal into its constituent motor unit action potentials (MUAPs) have been reported. All are limited to decomposing EMG signals from isometric contraction. In this report, we describe a successful approach to decomposing the surface EMG (sEMG) signal collected from cyclic (repeated concentric and eccentric) dynamic contractions during flexion/extension of the elbow and during gait. The increased signal complexity introduced by the changing shapes of the MUAPs due to relative movement of the electrodes and the lengthening/shortening of muscle fibers was managed by an incremental approach to enhancing our established algorithm for decomposing sEMG signals obtained from isometric contractions. We used machine-learning algorithms and time-varying MUAP shape discrimination to decompose the sEMG signal from an increasingly challenging sequence of pseudostatic and dynamic contractions. The accuracy of the decomposition results was assessed by two verification methods that have been independently evaluated. The firing instances of the motor units had an accuracy of ∼90% with a MUAP train yield as high as 25. Preliminary observations from the performance of motor units during cyclic contractions indicate that during repetitive dynamic contractions, the control of motor units is governed by the same rules as those evidenced during isometric contractions. Modifications in the control properties of motoneuron firings reported by previous studies were not confirmed. Instead, our data demonstrate that the common drive and hierarchical recruitment of motor units are preserved during concentric and eccentric contractions.

scholarly journals Modulation of passive force in single skeletal muscle fibres

2005 ◽  
Vol 1 (3) ◽  
pp. 342-345 ◽  
Author(s):  
Dilson E Rassier ◽  
Eun-Jeong Lee ◽  
Walter Herzog
Keyword(s):  
Skeletal Muscle ◽  
Sarcomere Length ◽  
Fibre Length ◽  
Muscle Fibres ◽  
Isometric Contractions ◽  
Passive Force ◽  
Length Relationship ◽  
Lumbrical Muscle ◽  
Single Fibres ◽  
Skeletal Muscle Fibres

In this study, we investigated the effects of activation and stretch on the passive force–sarcomere length relationship in skeletal muscle. Single fibres from the lumbrical muscle of frogs were placed at varying sarcomere lengths on the descending limb of the force–sarcomere length relationship, and tetanic contractions, active stretches and passive stretches (amplitudes of ca 10% of fibre length at a speed of 40% fibre length/s) were performed. The passive forces following stretch of an activated fibre were higher than the forces measured after isometric contractions or after stretches of a passive fibre at the corresponding sarcomere length. This effect was more pronounced at increased sarcomere lengths, and the passive force–sarcomere length relationship following active stretch was shifted upwards on the force axis compared with the corresponding relationship obtained following isometric contractions or passive stretches. These results provide strong evidence for an increase in passive force that is mediated by a length-dependent combination of stretch and activation, while activation or stretch alone does not produce this effect. Based on these results and recently published findings of the effects of Ca 2+ on titin stiffness, we propose that the observed increase in passive force is caused by the molecular spring titin.

Muscle fiber recruitment and blood pressure response to isometric exercise

1981 ◽  
Vol 50 (1) ◽  
pp. 32-37 ◽  
Author(s):  
J. S. Petrofsky ◽  
C. A. Phillips ◽  
M. N. Sawka ◽  
D. Hanpeter ◽  
A. R. Lind ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Blood Pressure Response ◽  
Pressor Response ◽  
Venous Blood ◽  
Isometric Exercise ◽  
Motor Units ◽  
Medial Gastrocnemius ◽  
Isometric Contractions ◽  
Slow Twitch ◽  
K Concentration

Blood pressure was recorded during fatiguing and nonfatiguing isometric contractions of a slow-twitch muscle (the soleus) and a mixed muscle (the medial gastrocnemius) of the cat. Four tensions were examined in each muscle; 10, 25, 40, and 70% of the muscle's initial strength (tetanic tension of the unfatigued muscle). All experiments were also repeated at two muscle temperatures, 28 and 38 degrees C. For the soleus muscle, there was no change in the blood pressure during isometric contractions. For the medial gastrocnemius muscle, both the systolic and diastolic blood pressure increased markedly when either all or just the fast-twitch motor units were stimulated; however, when only the slow-twitch motor units were stimulated, a lower pressor response was observed. Venous blood samples were drawn before, during, and after fatiguing and nonfatiguing contractions of both muscles to determine the K+ concentration in the venous blood. The mean increase in the K+ concentration during contractions was 0.6 meq/l for the slow-twitch motor units of the soleus and 5.1 meq/l for the motor units in the medial gastrocnemius.

Na+–K+ ATPase concentration in different adult rat skeletal muscles is related to oxidative potential

1993 ◽  
Vol 71 (8) ◽  
pp. 615-618 ◽  
Author(s):  
E. R. Chin ◽  
H. J. Green
Keyword(s):  
Fibre Type ◽  
Citrate Synthase ◽  
Vastus Lateralis ◽  
Maximal Activity ◽  
Type I ◽  
Oxidative Potential ◽  
Adult Rat ◽  
Primary Determinant ◽  
Male Wistar Rats ◽  
Wet Weight

To investigate the relationship among fibre type, oxidative potential, and Na+–K+ ATPase concentration in skeletal muscle, adult male Wistar rats weighing 259 ± 8 g [Formula: see text] were sacrificed and the soleus (SOL), extensor digitoram longus (EDL), red vastus lateralis (RV), and white vastus lateralis (WV) removed. These muscles were chosen as being representative of the two major fibre type populations: slow twitch (SOL) and fast twitch (EDL, RV, WV) and exhibiting either a high (SOL, EDL, RV) or low (WV) oxidative potential. Na+–K+ ATPase concentration (pmol∙g−1 wet weight), measured by the [3H]ouabain binding technique, differed (p < 0.01) only between the WV (238 ± 7.9) and the SOL (359 ± 9.6), EDL (365 ± 10), and RV (403 ± 12). Similarly, muscle oxidative potential as measured by the maximal activity of citrate synthase was different (p < 0.01) only between the WV and the other three muscles. Citrate synthase activity (μmol∙min−1∙g−1 wet weight) was 4.0 ± 0.7, 12.3 ± 0.9, 9.1 ± 0.7, and 11.3 ± 1.0 in the WV, SOL, EDL, and RV, respectively. These results indicate that Na+–K+ ATPase concentration is not related to the speed of contraction but to the oxidative potential of the muscle. Since chronic activity is a primary determinant of oxidative potential, it would be expected that increases in Na+–K+ ATPase would accompany increases in muscle utilization.Key words: Na+–K+ ATPase, citrate synthase, type I and type II fibres.

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