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Aviroop Dutt-Mazumder, Richard L. Segal and Aiko K. Thompson

The Hoffman’s reflex (H-reflex) elicited on soleus is modulated dependent on task and posture ( Capaday & Stein, 1986 ; Hayashi, Tako, Tokuda, & Yanagisawa, 1992 ; Llewellyn, Yang, & Prochazka, 1990 ; Trimble, Brunt, Jeon, & Kim, 2001 ; Zehr, Collins, Frigon, & Hoogenboom, 2003 ). Factors such

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Matthew J. Hodgson, David Docherty and E. Paul Zehr

The contractile history of muscle can potentiate electrically evoked force production. A link to voluntary force production, related in part to an increase in reflex excitability, has been suggested.

Purpose:

Our purpose was to quantify the effect of postactivation potentiation on voluntary force production and spinal H-reflex excitability during explosive plantar fexion actions.

Methods:

Plantar flexor twitch torque, soleus H-reflex amplitudes, and the rate of force development of explosive plantar fexion were measured before and after 4 separate conditioning trials (3 × 5 s maximal contractions).

Results:

Twitch torque and rate of force production during voluntary explosive plantar flexion were significantly increased (P < .05) while H-reflex amplitudes remained unchanged. Although twitch torque was significantly higher after conditioning, leading to a small increase in the rate of voluntary force production, this was unrelated to changes in reflex excitability.

Conclusion:

We conclude that postactivation potentiation may result in a minor increase in the rate of voluntary isometric force production that is unrelated to neural excitability.

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B. Andrew Krause., J. Ty Hopkins, Christopher D. Ingersoll, Mitchell L. Cordova and Jeffrey E. Edwards

Objective:

Correlate skin temperature and motoneuron-pool recruitment during cooling and rewarming.

Design:

Within-subjects, correlational analysis. H reflex was correlated to ankle-skin temperature over time using a Pearson product-moment correlation coefficient and a coefficient of determination (R2).

Subjects:

Ten healthy, physically active college students.

Measurements:

Soleus H reflex and ankle-skin interface temperature were measured during ice application and rewarming. Electrical stimulation was delivered to produce 75% of each subject's maximum H reflex.

Results:

Ankle cooling (r = −.95, P < .05) exhibited a strong inverse relationship with soleus H reflex. A positive correlation was observed between rewarming (r = .74, P < .05) and soleus H reflex.

Conclusions:

Temperature accounts for nearly 90% (R2 = .90) of the variability in the soleus H reflex during cooling and 55% (R2 = .55) during rewarming, suggesting that more motoneurons are recruited as temperature decreases. These interactions appear to involve both local and central nervous system functions.

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Gordon R. Chalmers and Kathleen M. Knutzen

The aim of this study was to determine whether elderly and young adults with similar physical activity levels have similar soleus H-wave maximum/M-wave maximum ratios (H-reflex size) and to determine the relationship between H-reflex size and physical activity level. H-reflex size and physical activity levels were measured in 18 elderly (71 ± 5.7 years) and 20 young (24 ± 4.2) participants. The physical activity levels of the 2 groups were not significantly different. The elderly group had smaller H-rellexes than the young group (elderly. 36% ± 27%; young, 59% ± 17%; p < .05), but the effect of age on H-reflex size was only moderate (omega squared = .19, effect size = .30). There was a weak tendency for higher levels of physical activity to be associated with larger H reflexes (r = .38, p < .05). The findings indicate that soleus H-reflex size is not strongly associated with age or physical activity level.

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Jacob Buus Andersen and Thomas Sinkjaer

Due to the complexity of applying a well-defined stretch during human walking, most of our knowledge about the short latency stretch reflex modulation in humans is based on H-reflex studies. To illuminate the difference between the two methodologies, both types of reflexes were evoked in the same subjects, same experiment. Stretch reflexes were evoked via a stretch device capable of evoking stretch reflexes of the human soleus muscle during walking. H-reflexes were elicited by an electrical stimulation of the tibial nerve at the popliteal fossa at the knee. A significantly different modulation of the two reflexes was found in the late stance where the stretch reflex decreased in relation to the H-reflex. This was consistent with an unloading of the muscle spindles during the push-off in late stance, suggesting a complex alpha-gamma coactivation, if any, at this time of the step. The soleus stretch reflex and H-reflex were compared during the stance phase of walking and sitting at matched soleus EMG activity. No difference was found in the amplitude of the stretch reflex. However, there was a significant decrease of the H-reflex during the stance phase of walking, consistent with a task-specific presynaptic mediated reflex control. It is proposed that the short latency stretch reflex during walking is not sensitive to such a presynaptic inhibition.

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Chetan P. Phadke, Marc Klimstra, E Paul. Zehr, Floyd J. Thompson and Andrea L. Behrman

The purpose of this study was to test the effect of arm swing on modulation of soleus H-reflexes amplitudes during walking. Fifteen subjects walked (1.07 m/s) on a treadmill in 4 arm swing conditions: 1-natural arm swing (control), 2-active restraint, 3-passive restraint, and 4-passive-assisted. Tibial nerve was electrically stimulated and soleus EMG was recorded. H-reflex amplitude was significantly greater during active than during passive restraint (p = .013). Remaining arm swing conditions were not significantly different. We detected a subtle effect of arm swing on soleus H-reflex amplitude. Descending regulation may serve as a gating mechanism to control the effect of arm movements on reflex pathways for leg muscles. This gating mechanism may be impaired postneural injury, potentially enhancing the modulation of peripheral sensory inputs on reflexes in leg muscles during walking. Future experiments to test additional conditions and evoking reflexes in more phases of walking are recommended.

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Koichi Hiraoka, Yuta Chujyo, Sakiko Hatano, Kohei Fukuhara and Yuki Yamanaka

We investigated the effects of contralateral movement on the soleus H-reflex during bilateral movement of the ankles. The soleus H-reflex was evoked during unilateral or in-phase or antiphase bilateral ankle movement in healthy humans. The soleus H-reflex amplitude during antiphase movement was not significantly different from that during in-phase movement. The H-reflex amplitude during inphase movement was not significantly different from that during unilateral movement of the tested ankle. The H-reflex amplitude in the maximal plantar flexion phase of the tested ankle during antiphase movement was significantly smaller than that in the corresponding phase during unilateral movement. The amount of the decrease was 21%. The effect of contralateral movement is prominent during antiphase movement of the ankles.

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Yung-Sheng Chen, Shi Zhou and Colleen Cartwright

This study investigated the effects of ankle joint position and submaximal contraction intensity on soleus (SOL) H-reflex modulation. Twenty young (25.1 ± 4.8 years) and 20 older adults (74.2 ± 5.1 years) performed plantar flexions during 10%, 30% and 50% maximal voluntary contractions (MVC) and at ankle positions of neutral (0°), plantar flexion (20°) and dorsiflexion (–20°) in a sitting position. The SOL H-reflex gain in older adults was relatively lower than that in young adults during 10%, 30% and 50% MVC. The SOL H-reflex gain was significantly affected by the intensity of plantar flexion in the respective ankle joint position in both age groups. The latency of H-reflex was prolonged in older adults and was ankle joint dependent in young adults. Young adults demonstrated a shorter duration of the H-reflex response than that of older adults. The results indicated that there were age-related changes in the SOL H-reflex during the ankle plantar flexors activities.

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Morteza Ahmadi, Giti Torkaman, Sedigheh Kahrizi, Mojdeh Ghabaee and Leila Dadashi Arani

Context:

Despite the widespread use of whole-body vibration (WBV), especially in recent years, its neurophysiological mechanism is still unclear and it is yet to be determined whether acute and short-term WBV exposure produce neurogenic enhancement for agility.

Objective:

To compare the acute and short-term effects of WBV on the H-reflex-recruitment curve and agility.

Design:

Cross-over study.

Setting:

Clinical electrophysiology laboratory.

Participants:

20 nonathlete male volunteers (mean age 24.85 ± 3.03 y).

Main Outcome Measures:

Subjects were randomly divided into 2 groups, H-reflex and agility. In the sham protocol, subjects stood on the turned-off vibration plate while maintaining the semisquat position, and then, after a 2-wk washout, vibration-training sessions were performed in the same position with a frequency of 30 Hz and an amplitude of 3 mm. H-reflex-recruitment curve was recorded and the agility test of a shuttle run was performed before and after the first session and also 48 h after the 11th session in both sham and vibration-training protocols.

Results:

Acute effects of WBV training caused a significant decrease of threshold amplitude and H-max/M-max (P = .01 and P = .04, respectively). Short-term WBV training significantly decreased the threshold intensity of the soleus H-reflex-recruitment curve (P = .01) and caused a decrease and increase respectively, in the threshold intensity and the area under the recruitment curve.

Conclusions:

The results suggest an inhibitory effect of acute WBV training on the H-reflex response.

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Christopher A. Knight

Column-editor : Thomas W. Kaminski