Changes in the Inhibitory Control Exerted by the Antagonist Ia Afferents on Human Wrist Extensor Motor Units During an Attention-Demanding Motor Task

Nafati, Gilel; Schmied, Annie; Rossi-Durand, Christiane

doi:10.1152/jn.00996.2004

Cited by 8 publications

(6 citation statements)

References 25 publications

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“…It is possible therefore that older adults have specific impairments in activating areas of the brain associated with high magnification of visual feedback. (3) Greater amount of visual feedback exerts more attentional demands on the nervous system and is more stressful (Nafati et al 2005). There is evidence that when older adults get stressed with noxious electrical stimuli, they exhibit greater impairments in force variability than young adults (Christou et al 2004).…”

Section: Discussionmentioning

confidence: 99%

Magnified visual feedback exacerbates positional variability in older adults due to altered modulation of the primary agonist muscle

2012

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The purpose of this study was to determine whether magnified visual feedback during position-holding contractions exacerbates the age-associated differences in motor output variability due to changes in the neural activation of the agonist muscle in the upper and lower limb. Twelve young (18–35 years) and ten older adults (65–85 years) were instructed to accurately match a target position at 5° of index finger abduction and ankle dorsiflexion while lifting 10 % of their 1 repetition maximum (1RM) load. Position was maintained at three different visual angles (0.1°, 1°, and 4°) that varied across trials. Each trial lasted 25 s and visual feedback of position was removed from 15 to 25 s. Positional error was quantified as the root mean square error (RMSE) of the subject’s performance from the target. Positional variability was quantified as the standard deviation of the position data. The neural activation of the first dorsal interosseus and tibialis anterior was measured with surface electromyography (EMG). Older adults were less accurate compared with young adults and the RMSE decreased significantly with an increase in visual gain. As expected, and independent of limb, older adults exhibited significantly greater positional variability compared with young adults that was exacerbated with magnification of visual feedback (1° and 4°). This increase in variability at the highest magnification of visual feedback was predicted by a decrease in power from 12 to 30 Hz of the agonist EMG signal. These findings demonstrate that motor control in older adults is impaired by magnified visual feedback during positional tasks.

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Section: Discussionmentioning

confidence: 99%

Magnified visual feedback exacerbates positional variability in older adults due to altered modulation of the primary agonist muscle

2012

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“…Inhibition was quantified by examining the influence of stimulation on the mean duration of the interspike interval (Datta and Stephens 1981; Nafati et al 2005). Post-stimulus time histograms were also calculated to permit comparison with previous data (Naito et al (1996).…”

Section: Discussionmentioning

confidence: 99%

“…The degree of inhibition across the motor unit sample was quantified by measuring the prolongation of the interspike interval induced by the radial nerve stimulation (Datta and Stephens 1981; Nafati et al 2005). The three ISIs prior to stimulation were averaged (ISI-pre) and the ISI that included the stimulation (ISI-0) was measured.…”

Section: Methodsmentioning

confidence: 99%

A spinal pathway between synergists can modulate activity in human elbow flexor muscles

et al. 2008

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Electrical stimulation of the brachioradialis branch of the radial nerve has been shown to inhibit the discharge of voluntarily activated motor units in biceps brachii during weak contractions with the elbow flexor muscles. The purpose of the present study was to characterise the inhibitory reflex by comparing its strength in the short and long heads of the biceps brachii and examining the influence of forearm position on the strength of the reflex. Spike-triggered stimulation was used to assess the influence of radial nerve stimulation on the discharge of single motor units in the biceps brachii of 15 subjects. Stimulation of the radial nerve prolonged the interspike interval (P < 0.001) of motor units in the long (n = 31, 4.8 ± 5.6 ms) and short heads (n = 26, 8.1 ± 12.3 ms) of biceps brachii with no difference between the two heads (P = 0.11). The strength of inhibition varied with forearm position for motor units in both heads (n = 18, P < 0.05). The amount of inhibition was greatest in pronation (7.9 ± 8.9 ms), intermediate in neutral (5.8 ± 7.1 ms), and least in supination (2.8 ± 3.4 ms). These findings indicate that the inhibition evoked by afferent feedback from brachioradialis to low-threshold motor units (mean force 3-5% MVC) in biceps brachii varied with forearm posture yet was similar for the two heads of biceps brachii. This reflex pathway provides a mechanism to adjust the activation of biceps brachii with changes in forearm position, and represents a spinal basis for a muscle synergy in humans.

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“…For example, acute deafferentation of the tibialis anterior muscle, which removes the muscle spindle support of a voluntary contraction, reduces the discharge rate of motor neurons during maximal and submaximal voluntary contractions (Macefield et al 1993). Furthermore, afferent input is critical for adjustment of muscle activity during finely controlled movements (Kakuda et al 1996;Nafati et al 2005;Ribot-Ciscar et al 2000), and the gain of the reflex response is heightened during tasks requiring the control of limb position (Akazawa et al 1983). Thus the vibration-induced reduction in afferent input likely contributed to the briefer time to failure during a task that required the maintenance of limb position.…”

Section: Potential Mechanisms Responsible For the Effect Of Vibrationmentioning

confidence: 99%

Prolonged Vibration of the Biceps Brachii Tendon Reduces Time to Failure When Maintaining Arm Position With a Submaximal Load

Mottram¹,

Maluf²,

Stephenson³

et al. 2006

Journal of Neurophysiology

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Prolonged vibration of the biceps brachii tendon reduces time to failure when maintaining arm position with a submaximal load. J Neurophysiol 95: 1185-1193, 2006. First published November 9, 2005 doi:10.1152/jn.00807.2005. Vibration reduces the amplitudes of the tendon jerk response and the Hoffmann and stretch reflexes in the muscle exposed to the vibration, yet does not alter the time to task failure when the task involves exerting a submaximal force against a rigid restraint. Because the amplitude of the stretch reflex is greater when a limb acts against a compliant load than a rigid restraint, the purpose was to determine the influence of prolonged tendon vibration on the time to failure when maintaining limb position with the elbow flexor muscles. Twenty-five healthy men performed the fatiguing contraction by maintaining elbow angle at 1.57 rad until failure while supporting a load equal to 20% of maximal voluntary contraction (MVC) force. The fatiguing contraction was performed on 3 separate days with different levels of vibration applied to the biceps brachii tendon: no vibration, subthreshold for a tonic vibration reflex (TVR), and suprathreshold for a TVR. MVC force before the fatiguing contraction was similar across the three sessions (mean of 3 sessions: 313 Ϯ 54 N, P ϭ 0.83). Despite a similar decline in MVC force after the fatiguing contraction across conditions (-18.0 Ϯ 8.0%, P Ͼ 0.05), the time to task failure was 3.7 Ϯ 1.4 min for the suprathreshold TVR condition, 4.3 Ϯ 2.1 min for the subthreshold TVR condition, and 5.0 Ϯ 2.2 min for the no-vibration condition (P Ͻ 0 0.001). The average EMG of the elbow flexor muscles was similar (P ϭ 0.22) during the fatiguing contractions. However, the fluctuations in limb acceleration at task onset were greater for the suprathreshold TVR condition (P Ͻ 0.01), but were not different between the subthreshold TVR and no-vibration conditions (P Ն 0.22). Furthermore, the difference in the SD of limb acceleration between the no-vibration and vibration conditions was correlated with the difference in time to failure for the no-vibration and subthreshold TVR conditions (P ϭ 0.03; r 2 ϭ 0.22), but not for the no-vibration and suprathreshold TVR conditions (P ϭ 0.90; r 2 ϭ 0.001). These findings indicate that prolonged vibration reduced the time to failure of a sustained contraction when subjects maintained limb position, suggesting that peripheral inputs to the motor neuron pool play a significant role in sustaining a contraction during tasks that require active control of limb position.

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Changes in the Inhibitory Control Exerted by the Antagonist Ia Afferents on Human Wrist Extensor Motor Units During an Attention-Demanding Motor Task

Cited by 8 publications

References 25 publications

Magnified visual feedback exacerbates positional variability in older adults due to altered modulation of the primary agonist muscle

Magnified visual feedback exacerbates positional variability in older adults due to altered modulation of the primary agonist muscle

A spinal pathway between synergists can modulate activity in human elbow flexor muscles

Prolonged Vibration of the Biceps Brachii Tendon Reduces Time to Failure When Maintaining Arm Position With a Submaximal Load

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