EMG activity of slow and fast ankle extensors following spinal cord transection

Transformations of slow-twitch fibers to the fast-twitch type following spinal cord transection are thought to be related to a substantial decrease or virtual absence of neuromuscular activity. In this experiment, spontaneous activity levels in spinalized and normal cats, raised under similar conditions, were assessed by integrated electromyography (I-EMG) recorded for 240 min over 24 h from the slow-contracting soleus (SOL) and the fast-contracting lateral gastrocnemius (LG). In the SOL of the spinalized cats, there was a 75% reduction in total I-EMG and a 66% reduction in the total duration of muscle activity. Conversely, the LG showed no significant change in total I-EMG, but there was a 66% reduction in the total duration of muscle activity. Based on muscle property data published in companion studies, there was no significant correlation between the SOL total I-EMG and the reduction in contraction times or the decrease in the percentage of slow-twitch fibers determined histochemically. We conclude that transformations of slow-twitch fibers following spinal transection may be regulated by several factors, among which is the total level of spontaneous daily activity.     

Modulation of the contractile activity of the fast and slow twitch rat muscle during continuous stimulation

The fast- and slow-twitch muscles were tested with single pulses in the course of unfused tetanus formation. The tetanus decreased differences in contractile parameters of the test-twitch contractions and, after continuous stimulation, eliminated them altogether.     

Capillary supply and cross-sectional area of slow and fast twitch muscle fibres in man

Summary The muscles triceps brachii, quadriceps femoris (part vastus lateralis) and soleus were analysed in 6 men and 6 women for fibre composition (% slow twitch, ST-fibres and % fast twitch, FT-fibres), fibre cross sectional areas, and capillarization. Also the fraction of fibres enclosed by their own fibre type was analysed together with the capillary supply of these fibres. Fibre composition was 39(19–60)% ST in m. triceps brachii, 60(29–78)% ST in m. vastus lateralis and 73(49–88)% ST in m. soleus. Fibre areas ranged from 2,320 to 16,667 m² being smallest in m. triceps brachii and largest in m. soleus (p<0.05) and with ST fibres being significantly smaller than FT fibres in some of the muscles. In all muscles the shape of the fibres was elliptical with the larger diameter being about twice the smaller diameter. Capillary density per cross sectional muscle area was not related to the fibre composition and was 379(302–500) cap/mm² in m. triceps brachii, 404(284–529) cap/mm² in m. vastus lateralis and 417(333–592) cap/mm² in m. soleus. However, capillary supply expressed as fibre type area per capillary was up to 40% larger for FT-fibres than for ST-fibres within the same muscle (p<0.05). The capillary supply of enclosed fibres was not different from that of fibres surrounded also by the other fibre type. The results demonstrate that the difference in capillary supply to ST and FT-fibres is less distinct in humans than in other mammals, which is consistent with the metabolic potentials also being more alike.     

Posture-dependent trunk extensor EMG activity during maximum isometrics exertions in normal male and female subjects.

Posture-dependent trunk function data are important for appropriate normalization of submaximal trunk exertions, and is also necessary to define a more precise and specific use for strength testing in the prevention and diagnosis of spinal disorders. The aim of the current study was to quantify maximal effort trunk muscle extensor activity and trunk isometric extension torque over a functional range of sagittal standing postures. Twenty healthy, young adult male and female subjects performed isometric extension tasks over a sagittal posture range of -20 degrees extension to +50 degrees flexion, in 10 degrees increments. Erector spinae muscle activity was recorded bilaterally at the level of L3 using surface EMG electrodes. Isometric trunk extension torque was measured using a trunk dynamometer. EMG and trunk torque differed significantly between genders, but there were no differences between male and female subjects when the data were normalized with respect to the upright posture. For the combined male and female population, upright posture normalized L3 EMG activity (EMGn) and trunk extension torque (Tn) increased 1.7-fold and 3.5-fold, respectively, over the 70 degrees range of sagittal postures examined. The ratio (Tn/EMGn) increased two-fold (0.83 to 1.67) from -20 degrees extension to +50 degrees flexion, indicating that the neuromuscular efficiency increases with flexion. Trunk extension torque normalized with respect to the upright posture was linearly and positively correlated (r = 0.59, P < 0.001) to similarly normalized L3 EMG activity. This relatively weak correlation suggests that trunk muscle synergism and/or intrinsic muscle length-tension relationships are also modulated by posture. This study provides data that can be used to estimate trunk extensor muscle function over a broad range of sagittal postures. Our findings indicate that appropriate postural normalization of trunk extensor EMG activity is necessary for studies where submaximal trunk exertions are performed over a range of upright postures.     

Effect of PNF stretch techniques on knee flexor muscle EMG activity in older adults.

The effects of proprioceptive neuromuscular facilitation (PNF) stretch techniques on older adults are unknown and the physiological changes associated with aging may lead to differential responses to PNF stretching. Therefore, the purpose of this experiment was to examine the effects of PNF stretch techniques and EMG activity in older adults. Three PNF stretch techniques: static stretch (SS), contract-relax (CR), and agonist contract-relax (ACR) were applied to 24 older adults aged 50-75 years. The subjects were tested for knee extension range of motion (ROM) and knee flexor muscle EMG activity. The results indicated that ACR produced 29-34% more ROM and 65-119% more EMG activity than CR and SS, respectively. It was concluded that PNF stretch techniques can increase ROM in older adults. However, a paradoxical effect was observed in that PNF stretching may not induce muscular relaxation even though ROM about a joint increases. Care should be taken when applying PNF stretch techniques to older adults due to age-related alterations in muscle elasticity.     

Effects of stretch on work from fast and slow muscles of mice: damped and undamped energy release

Stretching active muscle increases the work performed during subsequent shortening. The effects of a preceding stretch on work done by the undamped or lightly damped series compliance (SC) and by the contractile component (CC), which includes cross bridges and damped elements, were assessed using mouse soleus (slow) and extensor digitorum longus (fast) muscles with limited tendon. Increasing stretch amplitude (0-10% fibre length) increased work done by the SC up to a limit, but did not effect work done by the CC. Increasing stretch velocity (10-100% Vmax) had almost no effect on work done by either component. Increasing the delay between the end of stretch and onset of shortening (0-60 ms) caused a decrease in SC work, with no effect on CC work. Recoil of the SC was responsible for 50-70% of the total work done during shortening after stretch. Usually only 10-40% of the energy imparted during the stretch was recovered as work during subsequent shortening; large stretches and long delays between stretch and shortening further reduced this recovery by one third to one fifth. Results are interpreted in the context of a loss of energy stored in the SC owing to forcible detachment of cross bridges with large stretches and cyclic detachment with long delays.     

Conditioning of slow electrocortical activity evoked by sensory stimulation and by a reflex movement in man]

Slow cerebral waves are recorded from 10 adults during an experiment consisting of the application of isolated or coupled sensorial stimulations, the weak sound occuring 880 msec prior to the strong light when coupled. Prior to coupling, the stimulations evoke on the vertex generally negative slow waves which would indicate an orientation reaction. After coupling, the responses to sound become constantly negative and are considered as waves described as "negative contingent variations". To the contrary, responses to light are inverted and become constantly positive. Such a phenomenon equally observed during experiments consisting of sound coupled to a reflex movement recalls the resolution of the negative contingent variation, the decision wave and the motor potentiel that accompanies the execution of voluntary movement, however here, it is produced during conditioning which does not require active motor participation by the subject. These results demonstrate that the simple coupling of two stimulations following the protocol developed by Pavlov provokes in man a complex collection of responses containing a motor component analogous to that which one observes in more elaborate experiments destined to prove the anticipation of the decision.     

Potential phasic and tonic muscles express a common set of fast and slow myosin light chains and fast tropomyosin during early development of chick embryo

We investigated the expression of myosin light chains and tropomyosin subunits during chick embryonic development of the anterior (ALD) and posterior (PLD) parts of the latissimus dorsi muscles. As early as day 8 in ovo, both muscles accumulate a common set of myosin light chains (LC) in similar ratios (LC1F: 55 per cent; LC2S: 25 per cent; LC2F: 12 per cent; LC1S: 8 per cent) and a common set of tropomyosin (TM) subunits (beta 2, beta 1, alpha 2F). Later during development, the slow components of the LC regularly disappear in the PLD and the fast components of the LC and the alpha 2FTM disappear in the ALD, so that the adult pattern is almost established at the time of hatching. Thus, early in development, the two muscles accumulate a common set of fast and slow myosin light chains and fast tropomyosin and some isoforms are repressed at a later stage during development. These data might suggest that during development, the regulatory mechanisms of muscle specific isoform expression differ from one contractile protein to another.     

Potential phasic and tonic muscles express a common set of fast and slow myosin light chains and fast tropomyosin during early development of chick embryo

We investigated the expression of myosin light chains and tropomyosin subunits during chick embryonic development of the anterior (ALD) and posterior (PLD) parts of the latissimus dorsi muscles. As early as day 8 in ovo, both muscles accumulate a common set of myosin light chains (LC) in similar ratios (LC1F : 55 per cent; LC2S : 25 per cent; LC2F : 12 per cent ; LC1S : 8 per cent) and a common set of tropomyosin (TM) subunits (β², β¹, α²_F).Later during development, the slow components of the LC regularly disappear in the PLD and the fast components of the LC and the α²_FTM disappear in the ALD, so that the adult pattern is almost established at the time of hatching.Thus, early in development, the two muscles accumulate a common set of fast and slow myosin light chains and fast tropomyosin and some isoforms are repressed at a later stage during development. These data might suggest that during development, the regulatory mechanisms of muscle specific isoform expression differ from one contractile protein to another.     

Pattern and correlation of fast and slow spontaneous unit activity in the visual cortex

Spontaneous unit activity in the visual cortex and its changes during stimulation by continuous light or flashes were investigated in waking rabbits. The study of distributions of adjacent intervals showed that the neurons differ in the ratio of burst (fast, with intervals of up to 15–40 msec) and nonburst (slow) activity and in the character of changes from one type of activity to the other. Of the total number of spikes 63% were outside bursts; the ratio of their number to the number of spikes within bursts consisting of two or of three or more spikes was 27:3:1. The relative stability of the burst structure of spontaneous activity and the limited number of spikes in them (on average 2.4) were demonstrated. Bursts of three or more spikes (mean 3.6) were irregular, and in 79% of them a longer interval (18.6±2.4 msec) was observed before the shortest interval (7.9±0.9 msec). Bursts of spikes of most neurons during photic stimulation contain more spikes with shorter intervals; they also began more frequently with the shortest interval, possibly signifying an increase in the steepness and amplitude of the EPSPs lying at their basis. However, in 20% of neurons spontaneous bursts included more spikes and with shorter intervals than bursts evoked by flash stimulation.Research Institute of Psychiatry, Ministry of Health of the RSFSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 4, pp. 311–320, July–August, 1979.     

Modulation of L-type Ca2+ current by fast and slow Ca2+ buffering in guinea pig ventricular cardiomyocytes.

Free Ca2+ near Ca2+ channel pores is expected to be lower in cardiomyocytes dialyzed with bis-(o-amino-phenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA) than with ethyleneglycol-bis-(beta-aminoethyl)-N,N,N',N'-tetraacetic acid (EGTA) because BAPTA chelates incoming Ca2+ more rapidly. The consequences of intracellular Ca2+ buffering by BAPTA (0.2-60 mM) and by EGTA (0.2-67 mM) on whole-cell L-type Ca2+ current (ICa,L) were investigated in voltage-clamped guinea pig ventricular cardiomyocytes; bulk cytoplasmic free Ca2+ (Cac2+) was monitored using the fluorescent Ca2+ indicator indo-1. ICa,L was augmented by approximately 12-fold when BAPTA in the cell dialysate was increased from 0.2 to 50 mM (half-maximal stimulation at 31 mM), whereas elevating internal EGTA from 0.2 to 67 mM increased ICa,L only by approximately 2-fold. Cac2+ was < 20 nM with internal BAPTA or EGTA > or = 20 mM. While EGTA up to 67 mM had only an insignificant inhibitory effect on the stimulation of ICa,L by 3 microM forskolin, ICa,L in 50 mM BAPTA-dialyzed myocytes was insensitive to forskolin-induced elevation of adenosine 3',5'-cyclic monophosphate (cAMP); conversely, ICa,L in cAMP-loaded cells was unresponsive to BAPTA dialysis. Cell dialysis with BAPTA, but not with EGTA, accelerated the slow component of ICa,L inactivation (tau S) without affecting its fast component (tau F), resembling the effects of cAMP-dependent phosphorylation. BAPTA-stimulated ICa,L was inhibited by acetylcholine and by the cAMP-dependent protein kinase (PKA) blocker H-89. These results suggest that BAPTA-induced lowering of peri-channel Ca2+ stimulates cAMP synthesis and channel phosphorylation by disinhibiting Ca(2+)-sensitive adenylyl cyclase.