Variability in the interpolated twitch torque for maximal and submaximal voluntary contractions

2003 ◽  
Vol 95 (4) ◽  
pp. 1648-1655 ◽  
Author(s):  
M. A. E. Oskouei ◽  
B. C. F. van Mazijk ◽  
M. H. C. Schuiling ◽  
W Herzog
Keyword(s):  
Muscle Activation ◽  
Knee Extensor ◽  
Voluntary Contraction ◽  
Twitch Force ◽  
Actual Force ◽  
Before And After ◽  
Target Force ◽  
The Mean ◽  
Voluntary Contractions ◽  
Maximal Effort

The superimposed twitch technique is frequently used to study the degree of motor unit activation during voluntary effort. This technique is one of the preferred methods to determine the activation deficit (AD) in normal, athletic, and patient populations. One of the limitations of the superimposed twitch technique is its variability under given contractile conditions. The objective of this research was to determine the source(s) of variability in the superimposed twitch force (STF) for repeat measurements. We hypothesized that the variability in the AD measurements may be caused by the timing of the twitch force relative to the onset of muscle activation, by force transients during the twitch application, by small variations in the actual force from the nominal target force, and by variations in the resting twitch force. Twenty-eight healthy subjects participated in this study. Sixteen of these subjects participated in a protocol involving contractions at 50% of their maximal voluntary contraction (MVC) effort, whereas the remaining 12 participated in a protocol involving contractions at 100% of their MVC. Doublet-twitch stimuli were superimposed onto the 50 and 100% effort knee extensor muscle contractions, and the resting twitch forces, voluntary knee extensor forces, and STFs were then measured. The mean resting twitch forces obtained before and after 8 s of 50% of MVC were the same. Similarly, the mean STFs determined at 1, 3, 5, and 7 s into the 50% MVC were the same. The variations in twitch force were significantly smaller after accounting for the actual force at twitch application than those calculated from the prescribed forces during the 50% MVC protocol ( P < 0.05). Furthermore, the AD and the actual force showed statistically significant negative correlations for the 50% MVC tests. The interpolated twitch torque determined for the maximal effort contractions ranged from 1 to 70%. In contrast to the protocol at 50% of MVC, negative correlations were only observed in 5 of the 12 subjects during the 100% effort contractions. These results suggest that small variations in the actual force from the target force can account for the majority of the variations in the STFs for submaximal but not maximal effort contractions. For the maximal effort contractions, large variations in the STF exist due to undetermined causes.

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.

Fatigue of intermittent submaximal voluntary contractions: central and peripheral factors

1986 ◽  
Vol 61 (2) ◽  
pp. 421-429 ◽  
Author(s):  
B. Bigland-Ritchie ◽  
F. Furbush ◽  
J. J. Woods
Keyword(s):  
No Reduction ◽  
Rest Period ◽  
Central Fatigue ◽  
Voluntary Contraction ◽  
Adductor Pollicis ◽  
M Wave ◽  
Generating Capacity ◽  
Target Force ◽  
Voluntary Contractions ◽  
Muscle Contractile

Central and peripheral factors were studied in fatigue of submaximal intermittent isometric contractions of the human quadriceps and soleus muscles. Subjects made repeated 6 s, 50% maximal voluntary contractions (MVC) followed by 4 s rest until the limit of endurance (Tlim). Periodically, a fatigue test was performed. This included a brief MVC, either a single shock or 8 pulses at 50 Hz during a rest period and a shock superimposed on a target force voluntary contraction. At Tlim, the MVC force had declined by 50%, usually in parallel with the force from stimulation at 50 Hz. The twitches superimposed on the target forces declined more rapidly, disappearing entirely at Tlim. In similar experiments on adductor pollicis, no reduction of the evoked M wave was seen. The results suggest that, during fatigue of quadriceps and adductor pollicis induced by this protocol, no central fatigue was apparent, but some was seen in soleus. Thus the reduced force-generating capacity could result mainly or entirely from failure of the muscle contractile apparatus.

Mechanical behavior of skeletal muscle during intermittent voluntary isometric contractions in humans

1997 ◽  
Vol 83 (5) ◽  
pp. 1557-1565 ◽  
Author(s):  
N. K. Vøllestad ◽  
I. Sejersted ◽  
E. Saugen
Keyword(s):  
Skeletal Muscle ◽  
Mechanical Behavior ◽  
Recovery Period ◽  
Oscillation Amplitude ◽  
Voluntary Contraction ◽  
Knee Extensors ◽  
Isometric Contractions ◽  
Target Force ◽  
The Mean ◽  
Type Of Exercise

Vøllestad, N. K., I. Sejersted, and E. Saugen. Mechanical behavior of skeletal muscle during intermittent voluntary isometric contractions in humans. J. Appl. Physiol. 83(5): 1557–1565, 1997.—Changes in contractile speed and force-fusion properties were examined during repetitive isometric contractions with the knee extensors at three different target force levels. Seven healthy subjects were studied at target force levels of 30, 45, and 60% of their maximal voluntary contraction (MVC) force. Repeated 6-s contractions followed by 4-s rest were continued until exhaustion. Contractile speed was determined for contractions elicited by electrical stimulation at 1–50 Hz given during exercise and a subsequent 27-min recovery period. Contraction time remained unchanged during exercise and recovery, except for an initial rapid shift in the twitch properties. Half relaxation time (RT1/2) decreased gradually by 20–40% during exercise at 30 and 45% of MVC. In the recovery period, RT1/2 values were not fully restored to preexercise levels. During exercise at 60% MVC, the RT1/2 decreased for twitches and increased for the 50-Hz stimulation. In the recovery period after 60% MVC, RT1/2 values declined toward those seen after the 30 and 45% MVC exercise. The force oscillation amplitude in unfused tetani relative to the mean force increased during exercise at 30 and 45% MVC but remained unaltered during the 60% MVC exercise. This altered force-fusion was closely associated with the changes in RT1/2. The faster relaxation may at least partly explain the increased energy cost of contraction reported previously for the same type of exercise.

Impulse propagation and muscle activation in long maximal voluntary contractions

1989 ◽  
Vol 67 (5) ◽  
pp. 1835-1842 ◽  
Author(s):  
C. K. Thomas ◽  
J. J. Woods ◽  
B. Bigland-Ritchie
Keyword(s):  
Tibialis Anterior ◽  
Muscle Activation ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Mass Action ◽  
M Wave ◽  
Force Reduction ◽  
Small Decline ◽  
Voluntary Contractions ◽  
Do So

With fatigue, force generation may be limited by several factors, including impaired impulse transmission and/or reduced motor drive. In 5-min isometric maximal voluntary contraction, no decline was seen in the peak amplitude of the tibialis anterior compound muscle mass action potential (M wave) either during or immediately after the voluntary effort, provided maximal nerve stimulation was retained. For first dorsal interosseous (FDI) muscle, M wave amplitudes declined by 19.4 +/- 1.6% during the first 2 min but did not change significantly thereafter, despite the continued force reduction (up to 94% in 5 min for both muscles). The duration of the FDI M waves increased (greater than 30%), suggesting that the small decline in amplitude was the result of increased dispersion between the responses of different motor units. Some subjects kept FDI maximally activated throughout, but when they used tibialis anterior, twitch occlusion and tetanic muscle stimulation showed that most subjects were usually only able to do so for the first 60 s and thereafter only during brief “extra efforts.” Thus force loss during isometric voluntary contractions sustained at the highest intensities results mainly from failure of processes within the muscle fibers.

Postactivation potentiation in a human muscle: effect on the load-velocity relation of tetanic and voluntary shortening contractions

2007 ◽  
Vol 103 (4) ◽  
pp. 1318-1325 ◽  
Author(s):  
Stéphane Baudry ◽  
Jacques Duchateau
Keyword(s):  
Angular Velocity ◽  
Muscle Activation ◽  
Electrical Stimulus ◽  
Voluntary Contraction ◽  
Muscle Performance ◽  
Postactivation Potentiation ◽  
Muscle Twitch ◽  
Velocity Relation ◽  
Voluntary Contractions ◽  
Shortening Contractions

Recently it was demonstrated that postactivation potentiation (PAP), which refers to the enhancement of the muscle twitch torque as a result of a prior conditioning contraction, increased the maximal rate of torque development of tetanic and voluntary isometric contractions ( 3 ). In this study, we investigated the effects of PAP and its decay over time on the load-velocity relation. To that purpose, angular velocity of thumb adduction in response to a single electrical stimulus (twitch), a high-frequency train of 15 pulses at 250 Hz (HFT250), and during ballistic voluntary shortening contractions, performed against loads ranging from 10 to 50% of the maximum torque, were recorded before and after a conditioning 6-s maximal voluntary contraction (MVC). The results showed an increase of the peak angular velocity for the different loads tested after the conditioning MVC ( P < 0.001), but the effect was greatest for the twitch (∼182%) compared with the HFT250 or voluntary contractions (∼14% for both contraction types). The maximal potentiation occurred immediately following the conditioning MVC for the twitch, whereas it was reached 1 min later for the tetanic and ballistic voluntary contractions. At that time, the load-velocity relation was significantly shifted upward, and the maximal power of the muscle was increased (∼13%; P < 0.001). Furthermore, the results also indicated that the effect of PAP on shortening contractions was not related to the modality of muscle activation. In conclusion, the findings suggest a functional significance of PAP in human movements by improving muscle performance of voluntary dynamic contractions.

Motor unit firing rates during isometric voluntary contractions performed at different muscle lengths

2004 ◽  
Vol 82 (8-9) ◽  
pp. 769-776 ◽  
Author(s):  
Alejandro Del Valle ◽  
Christine K Thomas
Keyword(s):  
Motor Unit ◽  
Muscle Activation ◽  
Muscle Length ◽  
Surface Emg ◽  
Voluntary Contraction ◽  
Force Frequency ◽  
Triceps Brachii ◽  
Firing Rates ◽  
Motor Unit Firing ◽  
Voluntary Contractions

Firing rates of motor units and surface EMG were measured from the triceps brachii muscles of able-bodied subjects during brief submaximal and maximal isometric voluntary contractions made at 5 elbow joint angles that covered the entire physiological range of muscle lengths. Muscle activation at the longest, midlength, and shortest muscle lengths, measured by twitch occlusion, averaged 98%, 97%, and 93% respectively, with each subject able to achieve complete activation during some contractions. As expected, the strongest contractions were recorded at 90° of elbow flexion. Mean motor unit firing rates and surface EMG increased with contraction intensity at each muscle length. For any given absolute contraction intensity, motor unit firing rates varied when muscle length was changed. However, mean motor unit firing rates were independent of muscle length when contractions were compared with the intensity of the maximal voluntary contraction (MVC) achieved at each joint angle.Key words: muscle activation, length–tension relationships, force–frequency relationships.

scholarly journals Voluntary movement and repetitive transcranial magnetic stimulation over human motor cortex

2009 ◽  
Vol 106 (5) ◽  
pp. 1593-1603 ◽  
Author(s):  
Gabrielle Todd ◽  
Nigel C. Rogasch ◽  
Stanley C. Flavel ◽  
Michael C. Ridding
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Motor Cortex ◽  
Magnetic Stimulation ◽  
Voluntary Movement ◽  
Repetitive Transcranial Magnetic Stimulation ◽  
Voluntary Contraction ◽  
Human Motor Cortex ◽  
Before And After ◽  
Human Motor ◽  
Voluntary Contractions

Repetitive transcranial magnetic stimulation (rTMS) can induce short-term reorganization of human motor cortex. Here, we investigated the effect of rTMS during relaxation and weak voluntary muscle contraction on motor cortex excitability and hand function. Subjects ( n = 60) participated in one of four studies. Single transcranial magnetic stimuli were delivered over the motor area of the first dorsal interosseus for measurement of motor evoked potential (MEP) size before and after real or sham rTMS delivered at an intensity of 80% of active motor threshold. rTMS involved trains of stimuli applied at 6 Hz for 5 s and repeated every 30 s for 10 min. Resting MEP size was suppressed for 15 min after rTMS during relaxation. However, MEP suppression was abolished when additional brief voluntary contractions were performed before and after rTMS ( study 1). Resting MEP size was suppressed for 30 min after rTMS during weak voluntary contraction. MEP suppression was present even though voluntary contractions were performed before and after rTMS ( study 2). The MEP suppression most likely reflects a decrease in motor cortical excitability. Surprisingly, rTMS during voluntary contraction did not alter maximal finger tapping speed or performance on a grooved pegboard test, object grip and lift task ( study 3), and visuomotor tracking task ( study 4). These studies document the complex relationship between voluntary movement and rTMS-induced plasticity in motor cortex. This work has implications for the optimization of rTMS parameters for improved efficacy and potential therapeutic applications.

Sex differences in the fatigability of arm muscles depends on absolute force during isometric contractions

2001 ◽  
Vol 91 (6) ◽  
pp. 2686-2694 ◽  
Author(s):  
Sandra K. Hunter ◽  
Roger M. Enoka
Keyword(s):  
Muscle Activation ◽  
Pressor Response ◽  
Voluntary Contraction ◽  
Elbow Flexor ◽  
Endurance Time ◽  
Muscle Activation Patterns ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Target Force ◽  
The Absolute

Women are capable of longer endurance times compared with men for contractions performed at low to moderate intensities. The purpose of the study was 1) to determine the relation between the absolute target force and endurance time for a submaximal isometric contraction and 2) to compare the pressor response and muscle activation patterns of men [26.3 ± 1.1 (SE) yr] and women (27.5 ± 2.3 yr) during a fatiguing contraction performed with the elbow flexor muscles. Maximal voluntary contraction (MVC) force was greater for men (393 ± 23 vs. 177 ± 7 N), which meant that the average target force (20% of MVC) was greater for men (79.7 ± 6.5 vs. 36.7 ± 2.0 N). The endurance time for the fatiguing contractions was 118% longer for women (1,806 ± 239 vs. 829 ± 94 s). The average of the rectified electromyogram (%MVC) for the elbow flexor muscles at exhaustion was similar for men (31 ± 2%) and women (30 ± 2%). In contrast, the heart rate and mean arterial pressure (MAP) were less at exhaustion for women (94 ± 6 vs. 111 ± 7 beats/min and 121 ± 5 vs. 150 ± 6 mmHg, respectively). The target force and change in MAP during the fatiguing contraction were exponentially related to endurance time ( r 2 = 0.68 and r 2 = 0.64, respectively), whereas the change in MAP was linearly related to target force ( r 2 = 0.51). The difference in fatigability of men and women when performing a submaximal contraction was related to the absolute contraction intensity and was limited by mechanisms that were distal to the activation of muscle.

Anaerobic capacity and muscle activation during horizontal and uphill running

1997 ◽  
Vol 83 (1) ◽  
pp. 262-269 ◽  
Author(s):  
Mark A. Sloniger ◽  
Kirk J. Cureton ◽  
Barry M. Prior ◽  
Ellen M. Evans
Keyword(s):  
Lower Extremity ◽  
Muscle Activation ◽  
Anaerobic Capacity ◽  
Magnetic Resonance Images ◽  
Muscle Volume ◽  
Treadmill Running ◽  
Oxygen Deficit ◽  
Before And After ◽  
The Mean ◽  
Exercise Induced

Sloniger, Mark A., Kirk J. Cureton, Barry M. Prior, and Ellen M. Evans. Anaerobic capacity and muscle activation during horizontal and uphill running. J. Appl. Physiol. 83(1): 262–269, 1997.—Anaerobic capacity as measured by the maximal or peak oxygen deficit is greater during uphill than during horizontal running. The objective of this study was to determine whether the greater peak oxygen deficit determined during uphill compared with horizontal running is related to greater muscle volume or mass activated in the lower extremity. The peak oxygen deficit in 12 subjects was determined during supramaximal treadmill running at 0 and 10% grade. Exercise-induced contrast shifts in magnetic resonance images were obtained before and after exercise and used to determine the percentage of muscle volume activated. The mean peak oxygen deficit determined for uphill running [2.96 ± 0.63 (SD) liters or 49 ± 6 ml/kg] was significantly greater ( P < 0.05) than for horizontal running (2.45 ± 0.51 liters or 41 ± 7 ml/kg) by 21%. The mean percentage of muscle volume activated for uphill running [73.1 ± 7.4% (SD)] was significantly greater ( P < 0.05) than for horizontal running (67.0 ± 8.3%) by 9%. The differences in peak oxygen deficit (liters) between uphill and horizontal running were significantly related ( y = 8.05 × 10−4 x + 0.35; r = 0.63, SE of estimate = 0.29 liter, P < 0.05) to the differences in the active muscle volume (cm3) in the lower extremity. We conclude that the higher peak oxygen deficit during uphill compared with horizontal running is due in part to increased mass of skeletal muscle activated in the lower extremity.

scholarly journals Motoneuron excitability of the quadriceps decreases during a fatiguing submaximal isometric contraction

2018 ◽  
Vol 124 (4) ◽  
pp. 970-979 ◽  
Author(s):  
Harrison T. Finn ◽  
David M. Rouffet ◽  
David S. Kennedy ◽  
Simon Green ◽  
Janet L. Taylor
Keyword(s):  
Motor Evoked Potentials ◽  
Femoral Nerve ◽  
Silent Period ◽  
Knee Extension ◽  
Voluntary Contraction ◽  
Knee Extensors ◽  
Cortical Input ◽  
Motoneuron Excitability ◽  
Before And After ◽  
Voluntary Contractions

During fatiguing voluntary contractions, the excitability of motoneurons innervating arm muscles decreases. However, the behavior of motoneurons innervating quadriceps muscles is unclear. Findings may be inconsistent because descending cortical input influences motoneuron excitability and confounds measures during exercise. To overcome this limitation, we examined effects of fatigue on quadriceps motoneuron excitability tested during brief pauses in descending cortical drive after transcranial magnetic stimulation (TMS). Participants ( n = 14) performed brief (~5-s) isometric knee extension contractions before and after a 10-min sustained contraction at ~25% maximal electromyogram (EMG) of vastus medialis (VM) on one ( n = 5) or two ( n = 9) days. Electrical stimulation over thoracic spine elicited thoracic motor evoked potentials (TMEP) in quadriceps muscles during ongoing voluntary drive and 100 ms into the silent period following TMS (TMS-TMEP). Femoral nerve stimulation elicited maximal M-waves (Mmax). On the 2 days, either large (~50% Mmax) or small (~15% Mmax) TMS-TMEPs were elicited. During the 10-min contraction, VM EMG was maintained ( P = 0.39), whereas force decreased by 52% (SD 13%) ( P < 0.001). TMEP area remained unchanged ( P = 0.9), whereas large TMS-TMEPs decreased by 49% (SD 28%) ( P = 0.001) and small TMS-TMEPs by 71% (SD 22%) ( P < 0.001). This decline was greater for small TMS-TMEPs ( P = 0.019; n = 9). Therefore, without the influence of descending drive, quadriceps TMS-TMEPs decreased during fatigue. The greater reduction for smaller responses, which tested motoneurons that were most active during the contraction, suggests a mechanism related to repetitive activity contributes to reduced quadriceps motoneuron excitability during fatigue. By contrast, the unchanged TMEP suggests that ongoing drive compensates for altered motoneuron excitability. NEW & NOTEWORTHY We provide evidence that the excitability of quadriceps motoneurons decreases with fatigue. Our results suggest that altered intrinsic properties brought about by repetitive activation of the motoneurons underlie their decreased excitability. Furthermore, we note that testing during voluntary contraction may not reflect the underlying depression of motoneuron excitability because of compensatory changes in ongoing voluntary drive. Thus, this study provides evidence that processes intrinsic to the motoneuron contribute to muscle fatigue of the knee extensors.

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