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Agonist Muscle

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Evangelos A. Christou – One of the best experts on this subject based on the ideXlab platform.

  • Long-term adaptations differ for shortening and lengthening contractions
    European Journal of Applied Physiology, 2012
    Co-Authors: Osmar Pinto Neto, Hillary Lindheim, Ana Carolina Miranda Marzullo, Harsimran S. Baweja, Evangelos A. Christou
    Abstract:

    The purpose of this study was to determine whether practice of a sinusoidal task induces different neural adaptations for shortening and lengthening contractions performed within a task. Fourteen young adults were instructed to accurately match a sinusoidal target by lifting and lowering a light load (15% of 1 repetition maximum; 1-RM) with their index finger for 35 s. Each subject performed a total of 50 practice trials during the practice session. After 48 h, subjects performed five trials with the same sinusoidal target at each of three loading conditions: 15% (retention/savings), 7.5% (transfer to a lighter load), and 30% (transfer to a heavier load) of 1-RM. Movement error was quantified as the root meanmean square error of the movement trace from the target, while movement variability was quantified as the standard deviation of the acceleration of the index finger. First dorsal interosseus Muscle activation was recorded using surface electromyography (EMG). The frequency structure of the acceleration and EMG signals were obtained using wavelets. Subjects were able to retain the trained task for both shortening and lengthening contractions; however, they exhibited better savings for the shortening contractions. Additionally, for the lowering segments of the task subjects exhibited better transfer to the lighter load. Short-term adaptation and transfer results may be related to changes in the Agonist Muscle neural activation. Finally, we found greater movement variability during lengthening contractions which was related to both the frequency structure of the acceleration and EMG signals.

  • Magnified visual feedback exacerbates positional variability in older adults due to altered modulation of the primary Agonist Muscle
    Experimental Brain Research, 2012
    Co-Authors: Harsimran S. Baweja, Minhyuk Kwon, Evangelos A. Christou
    Abstract:

    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 meanmean 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.

  • Greater amount of visual information exacerbates force control in older adults during constant isometric contractions
    Experimental Brain Research, 2011
    Co-Authors: Deanna M. Kennedy, Evangelos A. Christou
    Abstract:

    The purpose of this study was to compare control of force and modulation of Agonist Muscle activity of young and older adults when the amount of visual feedback was varied at two different force levels. Ten young adults (25 years ± 4 years, 5 men and 5 women) and ten older adults (71 years ± 5 years, 4 men and 6 women) were instructed to accurately match a constant target force at 2 and 30% of their maximal isometric force with abduction of the index finger. Each trial lasted 35 s, and the amount of visual feedback was varied by changing the visual angle at 0.05, 0.5, and 1.5°. Each subject performed three trials for each visual angle condition. Force variability was quantified as the standard deviation and coefficient of variation (CV) of force. Modulation of the Agonist Muscle activity was quantified as the normalized power spectrum density of the EMG signal recorded from two pairs of bipolar electrodes placed on the first dorsal interosseus Muscle. The frequency bands of interest were between 5 and 100 Hz. There were significant age-associated differences in force control with changes in the amount of visual feedback. The CV of force did not change with visual angle for young adults, whereas it increased for older adults. Although older adults exhibited similar CV of force to young adults at 0.05° (5.95 ± 0.67 vs. 5.47 ± 0.5), older adults exhibited greater CV of force than young adults at 0.5° (8.49 ± 1.34 vs. 5.05 ± 0.5) and 1.5° (8.23 ± 1.12 vs. 5.49 ± 0.6). In addition, there were age-associated differences in the modulation of the Agonist Muscle activity. Young adults increased normalized power in the EMG signal from 13 to 60 Hz with an increase in visual angle, whereas older adults did not. These findings suggest that greater amount of visual information may be detrimental to the control of a constant isometric contraction in older adults, and this impairment may be due to their inability to effectively modulate the motor neurneuron pool of the Agonist Muscle.

Jayne S Garland – One of the best experts on this subject based on the ideXlab platform.

Dawson J. Kidgell – One of the best experts on this subject based on the ideXlab platform.

Harsimran S. Baweja – One of the best experts on this subject based on the ideXlab platform.

  • Long-term adaptations differ for shortening and lengthening contractions
    European Journal of Applied Physiology, 2012
    Co-Authors: Osmar Pinto Neto, Hillary Lindheim, Ana Carolina Miranda Marzullo, Harsimran S. Baweja, Evangelos A. Christou
    Abstract:

    The purpose of this study was to determine whether practice of a sinusoidal task induces different neural adaptations for shortening and lengthening contractions performed within a task. Fourteen young adults were instructed to accurately match a sinusoidal target by lifting and lowering a light load (15% of 1 repetition maximum; 1-RM) with their index finger for 35 s. Each subject performed a total of 50 practice trials during the practice session. After 48 h, subjects performed five trials with the same sinusoidal target at each of three loading conditions: 15% (retention/savings), 7.5% (transfer to a lighter load), and 30% (transfer to a heavier load) of 1-RM. Movement error was quantified as the root mean square error of the movement trace from the target, while movement variability was quantified as the standard deviation of the acceleration of the index finger. First dorsal interosseus Muscle activation was recorded using surface electromyography (EMG). The frequency structure of the acceleration and EMG signals were obtained using wavelets. Subjects were able to retain the trained task for both shortening and lengthening contractions; however, they exhibited better savings for the shortening contractions. Additionally, for the lowering segments of the task subjects exhibited better transfer to the lighter load. Short-term adaptation and transfer results may be related to changes in the Agonist Muscle neural activation. Finally, we found greater movement variability during lengthening contractions which was related to both the frequency structure of the acceleration and EMG signals.

  • Magnified visual feedback exacerbates positional variability in older adults due to altered modulation of the primary Agonist Muscle
    Experimental Brain Research, 2012
    Co-Authors: Harsimran S. Baweja, Minhyuk Kwon, Evangelos A. Christou
    Abstract:

    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.

  • The interaction of respiration and visual feedback on the control of force and neural activation of the Agonist Muscle
    Human movement science, 2011
    Co-Authors: Harsimran S. Baweja, Osmar Pinto Neto, Bhavini K. Patel, Evangelos A. Christou
    Abstract:

    Abstract The purpose of this study was to compare force variability and the neural activation of the Agonist Muscle during constant isometric contractions at different force levels when the amplitude of respiration and visual feedback were varied. Twenty young adults (20–32 years, 10 men and 10 women) were instructed to accurately match a target force at 15% and 50% of their maximal voluntary contraction (MVC) with abduction of the index finger while controlling their respiration at different amplitudes (85%, 100% and 125% normal) in the presence and absence of visual feedback. Each trial lasted 22 s and visual feedback was removed from 8–12 and 16–20 s. Each subject performed three trials with each respiratory condition at each force level. Force variability was quantified as the standard deviation of the detrended force data. The neural activation of the first dorsal interosseus (FDI) was measured with bipolar surface electrodes placed distal to the innervation zone. Relative to normal respiration, force variability increased significantly only during high-amplitude respiration (∼63%). The increase in force variability from normal- to high-amplitude respiration was strongly associated with amplified force oscillations from 0 to 3 Hz ( R 2 ranged from .68 to .84, p R 2  = .82) and weakly associated with greater power from 12 to 30 Hz ( R 2  = .24) in the EMG of the Agonist Muscle. Our findings demonstrate that high-amplitude respiration and visual feedback of force interact and amplify force variability in young adults during moderate levels of effort.

Joel Mason – One of the best experts on this subject based on the ideXlab platform.

  • Modulation of intracortical inhibition and excitation in Agonist and antAgonist Muscles following acute strength training
    European Journal of Applied Physiology, 2019
    Co-Authors: Joel Mason, Glyn Howatson, Ashlyn K. Frazer, Alan J. Pearce, Shapour Jaberzadeh, Janne Avela, Dawson J. Kidgell
    Abstract:

    Purpose Transcranial magnetic stimulation (TMS) usually investigates the corticospinal responses of the Agonist Muscle to strength training, despite the role of the antAgonist Muscle in strength development. We examined the intracortical responses from an Agonist and antAgonist Muscle following a single session of heavy-loaded strength training (dominant-arm only) to identify the early antAgonistic responses to a single session that may accompany improvements in strength. Methods Corticospinal and motor cortical excitability and inhibition was collected from Agonist and antAgonist Muscles prior to and following a single session of heavy-loaded wrist flexor training in 18 individuals. Training consisted of four sets 6–8 repetitions at 80% of 1-repetition maximum (1-RM). Recruitment curves for corticospinal excitability and inhibition of the right wrist flexor and wrist extensor Muscles were constructed and assessed by examining the area under the recruitment curve. Intracortical measures were obtained using paired-pulse TMS. Results Following a single training session, increases in corticospinal excitability were observed in both the Agonist and antAgonist Muscles. This was accompanied by decreases in corticospinal inhibition in both Muscles. Intracortical inhibition was reduced and intracortical facilitation was increased for the Agonist Muscle only. Intracortical measures in the antAgonist Muscle remained unchanged after training. Conclusions These findings indicate that the corticospinal responses to a single session of strength training are similar between Agonist and antAgonist Muscles, but the intrinsic cortico-cortical circuitry of the antAgonist remains unchanged. The corticospinal responses are likely due to increased involvement/co-activation of the antAgonist Muscle during training as the Agonist Muscle fatigues.

  • Modulation of intracortical inhibition and excitation in Agonist and antAgonist Muscles following acute strength training
    European journal of applied physiology, 2019
    Co-Authors: Joel Mason, Glyn Howatson, Ashlyn K. Frazer, Alan J. Pearce, Shapour Jaberzadeh, Janne Avela, Dawson J. Kidgell
    Abstract:

    Transcranial magnetic stimulation (TMS) usually investigates the corticospinal responses of the Agonist Muscle to strength training, despite the role of the antAgonist Muscle in strength development. We examined the intracortical responses from an Agonist and antAgonist Muscle following a single session of heavy-loaded strength training (dominant-arm only) to identify the early antAgonistic responses to a single session that may accompany improvements in strength. Corticospinal and motor cortical excitability and inhibition was collected from Agonist and antAgonist Muscles prior to and following a single session of heavy-loaded wrist flexor training in 18 individuals. Training consisted of four sets 6–8 repetitions at 80% of 1-repetition maximum (1-RM). Recruitment curves for corticospinal excitability and inhibition of the right wrist flexor and wrist extensor Muscles were constructed and assessed by examining the area under the recruitment curve. Intracortical measures were obtained using paired-pulse TMS. Following a single training session, increases in corticospinal excitability were observed in both the Agonist and antAgonist Muscles. This was accompanied by decreases in corticospinal inhibition in both Muscles. Intracortical inhibition was reduced and intracortical facilitation was increased for the Agonist Muscle only. Intracortical measures in the antAgonist Muscle remained unchanged after training. These findings indicate that the corticospinal responses to a single session of strength training are similar between Agonist and antAgonist Muscles, but the intrinsic cortico-cortical circuitry of the antAgonist remains unchanged. The corticospinal responses are likely due to increased involvement/co-activation of the antAgonist Muscle during training as the Agonist Muscle fatigues.

  • Adaptations in corticospinal excitability and inhibition are not spatially confined to the Agonist Muscle following strength training.
    European journal of applied physiology, 2017
    Co-Authors: Joel Mason, Glyn Howatson, Ashlyn K. Frazer, Alan J. Pearce, Janne Avela, Deanna Horvath, Dawson J. Kidgell
    Abstract:

    Purpose We used transcranial magnetic stimulation (TMS) to determine the corticospinal responses from an Agonist and synergist Muscle following strength training of the right elbow flexors.