The fatigability of two agonistic muscles in human isometric voluntary submaximal contraction: an EMG study

Maton, B.; Gamet, D.

doi:10.1007/bf00643511

Cited by 123 publications

(99 citation statements)

References 22 publications

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“…To compensate for the reduction in motor unit force, the net muscle force is maintained by a gradual increase in the descending drive that recruits previously inactive motor units (Löscher et al 1996). Once activated, the newly recruited motor units discharge action potentials either repetitively or intermittently (Bawa et al 2006;Carpentier et al 2001;Fallentin et al 1993;Garland et al 1994;Maton and Gamet 1989;Miller et al 1996) and the previously active motor units may either continue to discharge action potentials or cease to discharge action potentials for the remainder of the contraction (Person 1974) or until the motor unit has recovered sufficiently to resume activity (Bawa et al 2006). Riley et al (2008) found that the discharge characteristics of motor units at recruitment could differ substantially, depending on the difference between the recruitment threshold of the motor unit and the target force for the sustained contraction.…”

Section: Introductionmentioning

confidence: 99%

Discharge Characteristics of Biceps Brachii Motor Units at Recruitment When Older Adults Sustained an Isometric Contraction

Pascoe

Holmes

Enoka

2011

Journal of Neurophysiology

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Pascoe MA, Holmes MR, Enoka RM. Discharge characteristics of biceps brachii motor units at recruitment when older adults sustained an isometric contraction. J Neurophysiol 105: 571-581, 2011. First published December 15, 2010 doi:10.1152/jn.00841.2010. The purpose of this study was to compare the discharge characteristics of motor units recruited during an isometric contraction that was sustained with the elbow flexor muscles by older adults at target forces that were less than the recruitment threshold force of each isolated motor unit. The discharge times of 27 single motor units were recorded from the biceps brachii in 11 old adults (78.8 Ϯ 5.9 yr). The target force was set at either a relatively small (6.6 Ϯ 3.7% maximum) or large (11.4 Ϯ 4.5% maximum) difference below the recruitment threshold force and the contraction was sustained until the motor unit was recruited and discharged action potentials for about 60 s. The time to recruitment was longer for the large target-force difference (P ϭ 0.001). At recruitment, the motor units discharged repetitively for both target-force differences, which contrasts with data from young adults when motor units discharged intermittently at recruitment for the large difference between recruitment threshold force and target force. The coefficient of variation (CV) for the first five interspike intervals (ISIs) increased from the small (18.7 Ϯ 7.9) to large difference (35.0 Ϯ 10.2%, P ϭ 0.008) for the young adults, but did not differ for the two target force differences for the old adults (26.3 Ϯ 14.7 to 24.0 Ϯ 13.1%, P ϭ 0.610). When analyzed across the discharge duration, the average CV for the ISI decreased similarly for the two target-force differences (P ϭ 0.618) in old adults. These findings contrast with those of young adults and indicate that the integration of synaptic input during sustained contractions differs between young and old adults.

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Section: Introductionmentioning

confidence: 99%

Discharge Characteristics of Biceps Brachii Motor Units at Recruitment When Older Adults Sustained an Isometric Contraction

Pascoe

Holmes

Enoka

2011

Journal of Neurophysiology

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“…The presence of an initial, brief IPI has been reported to occur during voluntary activation of human motor units [13][14][15]. Therefore, the constant frequency pattern of stimuli that is used during conventional electrical stimulation may not be similar to what occurs under voluntary conditions.…”

Section: Introductionmentioning

confidence: 99%

Variable-frequency-train stimulation of skeletal muscle after spinal cord injury

Bickel¹,

Slade²,

VanHiel³

et al. 2004

JRRD

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-Skeletal muscle, after spinal cord injury (SCI), becomes highly susceptible to fatigue. Variable-frequency trains (VFTs) enhance force in fatigued human skeletal muscle of able-bodied (AB) individuals. VFTs do this by taking advantage of the "catch-like" property of skeletal muscle. However, mechanisms responsible for fatigue in AB and SCI subjects may not be the same, and the efficacy of VFT stimulation after SCI is unknown. Accordingly, we tested the hypothesis that VFT stimulation would augment torque-time integral in SCI subjects. The quadriceps femoris muscle was stimulated with constant frequency trains (CFTs) (six 200 s square wave pulses separated by 70 ms) or VFTs (a train identical to the CFT, except that the first two pulses were separated by 5 ms) in SCI and AB subjects. After 180 contractions (50% duty cycle), isometric peak torque decreased 44, 56, and 67 percent, in the AB (n = 10), acute SCI (n = 10), and chronic SCI (n = 12) groups, respectively. In fatigued muscle, VFTs enhanced the torque-time integral by 18 percent in AB subjects and 6 percent in chronic SCI patients, and had no effect in acute SCI patients when compared to the corresponding CFT. The much faster rise times in SCI subjects (~80 ms vs. 120 ms in AB subjects) probably contributed to the inability of VFTs to enhance torque-time integrals in SCI patients. The results suggest that the use of VFT stimulation in patients with SCI may not be as efficacious as it is in AB persons. Key words: catch-like property, electrical stimulation, fatigue, spinal cord injury, variable frequency train Abbreviations: AB = able-bodied, A/D = analog/digital, CFT = constant-frequency train, IPI = interpulse interval, m. QF = quadriceps femoris muscle, MVC = maximum voluntary contraction, SCI = spinal cord injury, T20-80 = time from 20 to 80 percent of peak torque, VFT = variable-frequency train.

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“…Muscle fatigue causes MU recruitment, and the MU firing rate increases as a function of the elapsed time. These changes are not reflected in the EMG changes which occur during fatiguing isometric contraction of the arm flexors at 20-30% MVC (Maton & Gamet, 1989). However, it was recently found that the changes due to fatigue in the sEMG signal (increased amplitude and decreased frequency) suggest that the recruitment of MU firing rates correlates with sEMG amplitude (Calder et al, 2008).…”

Section: Application Of Emg In Muscle Fatigue Researchmentioning

confidence: 97%

sEMG Techniques to Detect and Predict Localised Muscle Fatigue

Almulla¹,

Sepúlveda²,

Colley³

2012

EMG Methods for Evaluating Muscle and Nerve Function

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The fatigability of two agonistic muscles in human isometric voluntary submaximal contraction: an EMG study

Cited by 123 publications

References 22 publications

Discharge Characteristics of Biceps Brachii Motor Units at Recruitment When Older Adults Sustained an Isometric Contraction

Discharge Characteristics of Biceps Brachii Motor Units at Recruitment When Older Adults Sustained an Isometric Contraction

Variable-frequency-train stimulation of skeletal muscle after spinal cord injury

sEMG Techniques to Detect and Predict Localised Muscle Fatigue

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