Twitch Interpolation in Human Muscles: Mechanisms and Implications for Measurement of Voluntary Activation

1999 ◽  
Vol 82 (5) ◽  
pp. 2271-2283 ◽  
Author(s):  
R. D. Herbert ◽  
S. C. Gandevia
Keyword(s):  
Time Course ◽  
Full Range ◽  
Electrical Stimulus ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Time To Peak ◽  
Motoneuron Pool ◽  
Twitch Interpolation ◽  
Muscle Nerve ◽  
Force Drop

An electrical stimulus delivered to a muscle nerve during a maximal voluntary contraction usually produces a twitchlike increment in force. The amplitude of this “interpolated twitch” is widely used to measure voluntary “activation” of muscles. In the present study, a computer model of the human adductor pollicis motoneuron pool was used to investigate factors that affect the interpolated twitch. Antidromic occlusion of naturally occurring orthodromic potentials was modeled, but reflex effects of the stimulus were not. In simulations, antidromic collisions occurred with probabilities of between ∼16% (in early recruited motoneurons) and nearly 100% (in late recruited motoneurons). The model closely predicted experimental data on the amplitude and time course of the rising phase of interpolated twitches over the full range of voluntary forces, except that the amplitude of interpolated twitches was slightly overestimated at intermediate contraction intensities. Small interpolated twitches (4.7% of the resting twitch) were evident in simulated maximal voluntary contractions, but were nearly completely occluded when mean peak firing rate was increased to ∼60 Hz. Simulated interpolated twitches did not show the marked force drop that follows the peak of the twitch, and when antidromic collisions were excluded from the model interpolated twitch amplitude was slightly increased and time-to-peak force was prolonged. These findings suggest that both antidromic and reflex effects reduce the amplitude of the interpolated twitch and contribute to the force drop that follows the twitch. The amplitude of the interpolated twitch was related to “excitation” of the motoneuron pool in a nonlinear way, so that at near-maximal contraction intensities (>90% maximal voluntary force) increases in excitation produced only small changes in interpolated twitch amplitude. Thus twitch interpolation may not provide a sensitive measure of motoneuronal excitation at near-maximal forces. Increases in the amplitude of interpolated twitches such as have been observed in fatigue and various pathologies may reflect large reductions in excitation of the motoneuron pool.

scholarly journals Velocity of the muscle tendon unit is sex-dependent and not altered with acute static stretch

2018 ◽  
Vol 43 (3) ◽  
pp. 227-232 ◽  
Author(s):  
Carey L. Simpson ◽  
Rowan R. Smart ◽  
Dylan E.E. Melady ◽  
Jennifer M. Jakobi
Keyword(s):  
Plantar Flexion ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Plantar Flexors ◽  
Shortening Velocity ◽  
Static Stretch ◽  
Twitch Interpolation ◽  
Tendon Lengthening ◽  
The Individual ◽  
The Relationship

Contraction velocity of a muscle tendon unit (MTU) is dependent upon the interrelationship between fascicles shortening and the tendon lengthening. Altering the mechanical properties of these tissues through a perturbation such as static stretching slows force generation. Females, who have inherently greater compliance compared with males, have slower velocity of MTU components. The addition of a static stretch might further exacerbate this sex difference. The purpose of this study was to investigate the velocity of fascicle shortening and tendon lengthening in males and females during isometric maximal voluntary contraction (MVC) of the plantar flexors prior to and following an acute static stretch. The MTU was imaged with ultrasound and voluntary activation tested with twitch interpolation for the 5-s plantar flexion MVC, which proceeded and followed an acute stretch. For the 3-min stretch the ankle was passively rotated to maximal dorsi-flexion. The males were stronger (128.71 ± 7.88 Nm) than the females (89.92 ± 4.70 Nm) but voluntary activation did not differ. Tendon lengthening velocity (p = 0.001) and fascicle shortening velocity (p = 0.01) were faster in males than females. Tendon velocity was positively and significantly correlated with fascicle velocity, (r2 = 0.307, p = 0.02). Although sex was significant as a predictor (p = 0.05) time was not independently significant. Thus, stretch did not alter this relationship in either sex (p = 0.6). The velocity of the individual components of the MTU is slower in females when compared with males; however, acute stretch does not alter the relationship between these components in males or females.

Effects of caffeine on neuromuscular function

1999 ◽  
Vol 87 (2) ◽  
pp. 801-808 ◽  
Author(s):  
J. M. Kalmar ◽  
E. Cafarelli
Keyword(s):  
Repeated Measures ◽  
Isometric Force ◽  
Neuromuscular Function ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Knee Extensors ◽  
Double Blind ◽  
Twitch Interpolation ◽  
Motor Unit Firing ◽  
The Right

This double-blind, repeated-measures study examined the effects of caffeine on neuromuscular function. Eleven male volunteers [22.3 ± 2.4 (SD) yr] came to the laboratory for control, placebo, and caffeine (6 mg/kg dose) trials. Each trial consisted of 10 × 1-ms stimulation of the tibial nerve to elicit maximal H reflexes of the soleus, four attempts at a maximal voluntary contraction (MVC) of the right knee extensors, six brief submaximal contractions, and a 50% MVC held to fatigue. Isometric force and surface electromyographic signals were recorded continuously. The degree of maximal voluntary activation was assessed with the twitch-interpolation technique. Single-unit recordings were made with tungsten microelectrodes during the submaximal contractions. Voluntary activation at MVC increased by 3.50 ± 1.01 (SE) % ( P < 0.01), but there was no change in H-reflex amplitude, suggesting that caffeine increases maximal voluntary activation at a supraspinal level. Neither the force-EMG relationship nor motor unit firing rates were altered by caffeine. Subjects were able to hold a 50% MVC for an average of 66.1 s in the absence of caffeine. Time to fatigue (Tlim) increased by 25.80 ± 16.06% after caffeine administration ( P < 0.05). There was no significant change in Tlim from pretest to posttest in the control or placebo trials. The increase in Tlim was associated with an attenuated decline in twitch amplitude, which would suggest that the mechanism is, at least in part, peripheral.

scholarly journals Exercise-Induced Muscle Damage and Recovery in Young and Middle-Aged Males with Different Resistance Training Experience

Sports ◽  
2019 ◽  
Vol 7 (6) ◽  
pp. 132 ◽  
Author(s):  
John Fernandes ◽  
Kevin Lamb ◽  
Craig Twist
Keyword(s):  
Resistance Training ◽  
Muscle Damage ◽  
Peak Power ◽  
Time Course ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Knee Extensors ◽  
Middle Aged ◽  
Training Experience ◽  
Exercise Induced

This study compared the time course of recovery after a squatting exercise in trained young (YG; n = 9; age 22.3 ± 1.7 years) and trained (MT; n = 9; 39.9 ± 6.2 years) and untrained (MU; n = 9; age 44.4 ± 6.3 years) middle-aged males. Before and at 24 and 72 h after 10 × 10 squats at 60% one-repetition maximum (1RM), participants provided measurements of perceived muscle soreness (VAS), creatine kinase (CK), maximal voluntary contraction (MVC), voluntary activation (VA), and resting doublet force of the knee extensors and squatting peak power at 20% and 80% 1RM. When compared to the YG males, the MT experienced likely and very likely moderate decrements in MVC, resting doublet force, and peak power at 20% and 80% 1RM accompanied by unclear differences in VAS, CK, and VA after the squatting exercise. MU males, compared to MT, experienced greater alterations in peak power at 20% and 80% 1RM and VAS. Alterations in CK, MVC, VA, and resting doublet force were unclear at all time-points between the middle-aged groups. Middle-aged males experienced greater symptoms of muscle damage and an impaired recovery profile than young resistance trained males. Moreover, regardless of resistance training experience, middle-aged males are subject to similar symptoms after muscle-damaging lower-body exercise.

scholarly journals Sensitivity of 24-h EMG duration and intensity in the human vastus lateralis muscle to threshold changes

2010 ◽  
Vol 108 (3) ◽  
pp. 655-661 ◽  
Author(s):  
Cliff S. Klein ◽  
Lillian B. Peterson ◽  
Sean Ferrell ◽  
Christine K. Thomas
Keyword(s):  
Vastus Lateralis ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Vastus Lateralis Muscle ◽  
Twitch Interpolation ◽  
Before And After ◽  
Compound Action Potentials ◽  
Small Change ◽  
Electromyographic Signals ◽  
Compound Action

Few studies have quantified lower limb muscle activity over 24 h using electromyographic signals (EMG). None have described the changes in EMG duration and intensity when data are analyzed with different thresholds. Continuous bilateral EMG recordings were made from vastus lateralis (VL) in 10 subjects (20–48 yr) for 24 h. Before and after this recording, voluntary quadriceps forces and VL EMG at 25%, 50%, 75%, and 100% of the maximal voluntary contraction (MVC), percentage voluntary activation (twitch interpolation), and compound action potentials (M-waves) were recorded. Offline, the 24-h EMG integrals (IEMG, 10-ms time constant) were normalized to the MVC IEMG. Total EMG duration and mean IEMG ranged from 1–3 h and 3.2–12.1% MVC, respectively, when the data were analyzed using the baseline (+3 SD) as threshold. When analysis was done with progressively higher thresholds, from baseline up to 4% MVC, the total EMG duration declined curvilinearly. In some cases the decline in duration was 50–60% for a 1% MVC threshold increment. The mean 24-h IEMG increased by 1.5–2% MVC for each 1% MVC threshold increment. Hence, a small change in the analysis threshold may result in large changes in 24-h EMG duration but moderate changes in mean IEMG. Our findings suggest that VL was active for a short amount of time and at low intensities over 24 h.

Failure of prostaglandins to modulate the time course of blood flow during dynamic forearm exercise in humans

1996 ◽  
Vol 81 (4) ◽  
pp. 1516-1521 ◽  
Author(s):  
J. K. Shoemaker ◽  
H. L. Naylor ◽  
Z. I. Pozeg ◽  
R. L. Hughson
Keyword(s):  
Blood Flow ◽  
Brachial Artery ◽  
Time Course ◽  
Forearm Blood Flow ◽  
Voluntary Contraction ◽  
Double Blind ◽  
Rate Of Increase ◽  
Forearm Exercise ◽  
Blind Manner ◽  
Exercise In Humans

Shoemaker, J. K., H. L. Naylor, Z. I. Pozeg, and R. L. Hughson. Failure of prostaglandins to modulate the time course of blood flow during dynamic forearm exercise in humans. J. Appl. Physiol. 81(4): 1516–1521, 1996.—The time course and magnitude of increases in brachial artery mean blood velocity (MBV; pulsed Doppler), diameter ( D; echo Doppler), mean perfusion pressure (MPP; Finapres), shear rate (γ˙ = 8 ⋅ MBV/ D), and forearm blood flow (FBF = MBV ⋅ π r 2) were assessed to investigate the effect that prostaglandins (PGs) have on the hyperemic response on going from rest to rhythmic exercise in humans. While supine, eight healthy men performed 5 min of dynamic handgrip exercise by alternately raising and lowering a 4.4-kg weight (∼10% maximal voluntary contraction) with a work-to-rest cycle of 1:1 (s/s). When the exercise was performed with the arm positioned below the heart, the rate of increase in MBV and γ˙ was faster compared with the same exercise performed above the heart. Ibuprofen (Ibu; 1,200 mg/day, to reduce PG-induced vasodilation) and placebo were administered orally for 2 days before two separate testing sessions in a double-blind manner. Resting heart rate was reduced in Ibu (52 ± 3 beats/min) compared with placebo (57 ± 3 beats/min) ( P < 0.05) without change to MPP. With placebo, D increased in both arm positions from ∼4.3 mm at rest to ∼4.5 mm at 5 min of exercise ( P < 0.05). This response was not altered with Ibu ( P > 0.05). Ibu did not alter the time course of MBV or forearm blood flow ( P > 0.05) in either arm position. The γ˙ was significantly greater in Ibu vs. placebo at 30 and 40 s of above the heart exercise and for all time points after 25 s of below the heart exercise ( P < 0.05). Because PG inhibition altered the time course ofγ˙ at the brachial artery, but not FBF, it was concluded that PGs are not essential in regulating the blood flow responses to dynamic exercise in humans.

scholarly journals Sodium and calcium currents in dispersed mammalian septal neurons.

1991 ◽  
Vol 97 (2) ◽  
pp. 303-320 ◽  
Author(s):  
A Castellano ◽  
J López-Barneo
Keyword(s):  
Time Constant ◽  
Time Course ◽  
Calcium Currents ◽  
Closing Time ◽  
Patch Clamp Technique ◽  
Average Value ◽  
Time To Peak ◽  
Time Courses ◽  
Fast Activation ◽  
Septal Neurons

Voltage-gated Na+ and Ca2+ conductances of freshly dissociated septal neurons were studied in the whole-cell configuration of the patch-clamp technique. All cells exhibited a large Na+ current with characteristic fast activation and inactivation time courses. Half-time to peak current at -20 mV was 0.44 +/- 0.18 ms and maximal activation of Na+ conductance occurred at 0 mV or more positive membrane potentials. The average value was 91 +/- 32 nS (approximately 11 mS cm-2). At all membrane voltages inactivation was well fitted by a single exponential that had a time constant of 0.44 +/- 0.09 ms at 0 mV. Recovery from inactivation was complete in approximately 900 ms at -80 mV but in only 50 ms at -120 mV. The decay of Na+ tail currents had a single time constant that at -80 mV was faster than 100 microseconds. Depolarization of septal neurons also elicited a Ca2+ current that peaked in approximately 6-8 ms. Maximal peak Ca2+ current was obtained at 20 mV, and with 10 mM external Ca2+ the amplitude was 0.35 +/- 0.22 nA. During a maintained depolarization this current partially inactivated in the course of 200-300 ms. The Ca2+ current was due to the activity of two types of conductances with different deactivation kinetics. At -80 mV the closing time constants of slow (SD) and fast (FD) deactivating channels were, respectively, 1.99 +/- 0.2 and 0.11 +/- 0.03 ms (25 degrees C). The two kinds of channels also differed in their activation voltage, inactivation time course, slope of the conductance-voltage curve, and resistance to intracellular dialysis. The proportion of SD and FD channels varied from cell to cell, which may explain the differential electrophysiological responses of intracellularly recorded septal neurons.

Neuromuscular Fatigue in Individuals With Intellectual Disability: Comparison Between Sedentary Individuals and Athletes

Motor Control ◽  
2021 ◽  
Vol 25 (2) ◽  
pp. 264-282
Author(s):  
Rihab Borji ◽  
Firas Zghal ◽  
Nidhal Zarrouk ◽  
Sonia Sahli ◽  
Haithem Rebai
Keyword(s):  
Intellectual Disability ◽  
Recovery Period ◽  
Voluntary Contraction ◽  
Neuromuscular Fatigue ◽  
Voluntary Activation ◽  
Peripheral Fatigue ◽  
Typical Development ◽  
Activation Level ◽  
Voluntary Activation Level ◽  
Voluntary Contractions

The authors explored neuromuscular fatigue in athletes with intellectual disability (AID) compared with sedentary individuals with intellectual disability (SID) and individuals with typical development. Force, voluntary activation level, potentiated resting twitch, and electromyography signals were assessed during isometric maximal voluntary contractions performed before and immediately after an isometric submaximal exhaustive contraction (15% isometric maximal voluntary contractions) and during recovery period. AID presented shorter time to task failure than SID (p < .05). The three groups presented similar isometric maximal voluntary contraction decline and recovery kinetic. Both groups with intellectual disability presented higher voluntary activation level and root mean square normalized to peak-to-peak M-wave amplitude declines (p < .05) compared with individuals with typical development. These declines were more pronounced in SID (p < .05) than in AID. The AID recovered their initial voluntary activation level later than controls, whereas SID did not. SID presented lower potentiated resting twitch decline compared with AID and controls with faster recovery (p < .05). AID presented attenuated central fatigue and accentuated peripheral fatigue compared with their sedentary counterparts, suggesting a neuromuscular profile close to that of individuals with typical development.

Initial phase of maximal voluntary and electrically stimulated knee extension torque development at different knee angles

2004 ◽  
Vol 97 (5) ◽  
pp. 1693-1701 ◽  
Author(s):  
C. J. de Ruiter ◽  
R. D. Kooistra ◽  
M. I. Paalman ◽  
A. de Haan
Keyword(s):  
Muscle Activation ◽  
Knee Extensor ◽  
Surface Emg ◽  
Knee Extension ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Knee Angle ◽  
Time Integral ◽  
Voluntary Contractions ◽  
Torque Development

We investigated the capacity for torque development and muscle activation at the onset of fast voluntary isometric knee extensions at 30, 60, and 90° knee angle. Experiments were performed in subjects ( n = 7) who had high levels (>90%) of activation at the plateau of maximal voluntary contractions. During maximal electrical nerve stimulation (8 pulses at 300 Hz), the maximal rate of torque development (MRTD) and torque time integral over the first 40 ms (TTI40) changed in proportion with torque at the different knee angles (highest values at 60°). At each knee angle, voluntary MRTD and stimulated MRTD were similar ( P < 0.05), but time to voluntary MRTD was significantly longer. Voluntary TTI40 was independent ( P > 0.05) of knee angle and on average (all subjects and angles) only 40% of stimulated TTI40. However, among subjects, the averaged (across knee angles) values ranged from 10.3 ± 3.1 to 83.3 ± 3.2% and were positively related ( r2 = 0.75, P < 0.05) to the knee-extensor surface EMG at the start of torque development. It was concluded that, although all subjects had high levels of voluntary activation at the plateau of maximal voluntary contraction, among subjects and independent of knee angle, the capacity for fast muscle activation varied substantially. Moreover, in all subjects, torque developed considerably faster during maximal electrical stimulation than during maximal voluntary effort. At different knee angles, stimulated MRTD and TTI40 changed in proportion with stimulated torque, but voluntary MRTD and TTI40 changed less than maximal voluntary torque.

Sign in / Sign up

Export Citation Format

Share Document