Can passive stretch inhibit motoneuron facilitation in the human plantar flexors?

Trajano, Gabriel S., Seitz, Laurent B., Nosaka, Kazunori, & Blazevich, Anthony J. (2014) Can passive stretch inhibit motoneuron facilitation in the human plantar flexors? Journal of Applied Physiology, 117(12), pp. 1486-1492.

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Abstract

The purpose of the present study was to examine the possible inhibitory effect of passive plantar flexor muscle stretching on the motoneuron facilitatory system. Achilles tendon vibration (70 Hz) and triceps surae electrical stimulation (20 Hz) were imposed simultaneously in 11 subjects to elicit contraction through reflexive pathways in two experiments. In experiment 1, a vibration-stimulation protocol was implemented with the ankle joint plantar flexed (+10°), neutral (0°), and dorsiflexed (−10°). In experiment 2, the vibration-stimulation protocol was performed twice before (control), then immediately, 5, 10, and 15 min after a 5-min intermittent muscle stretch protocol. Plantar flexor torque and medial and lateral gastrocnemius and soleus (EMGSol) EMG amplitudes measured during and after (i.e., self-sustained motor unit firing) the vibration protocol were used as an indicator of this facilitatory pathway. In experiment 1, vibration torque, self-sustained torque and EMGSol were higher with the ankle at −10° compared with 0° and +10°, suggesting that this method is valid to assess motoneuronal facilitation. In experiment 2, torque during vibration was reduced by ∼60% immediately after stretch and remained depressed by ∼35% at 5 min after stretch (P < 0.05). Self-sustained torque was also reduced by ∼65% immediately after stretch (P < 0.05) but recovered by 5 min. Similarly, medial gastrocnemius EMG during vibration was reduced by ∼40% immediately after stretch (P < 0.05), and EMGSol during the self-sustained torque period was reduced by 44% immediately after stretch (P < 0.05). In conclusion, passive stretch negatively affected the motoneuronal amplification for at least 5 min, suggesting that motoneuron disfacilitation is a possible mechanism influencing the stretch-induced torque loss.

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ID Code: 96716
Item Type: Journal Article
Refereed: Yes
Keywords: Ia afferent; persistent inward current; muscle force
DOI: 10.1152/japplphysiol.00809.2014
ISSN: 1522-1601
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Current > Schools > School of Exercise & Nutrition Sciences
Copyright Owner: Copyright 2016 The American Physiological Society
Deposited On: 07 Jul 2016 23:22
Last Modified: 13 Jul 2016 04:49

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