The role of short latency reflexes in the motor control of quadriceps in humans

Khademi-Kalantari, Khosro (2002) The role of short latency reflexes in the motor control of quadriceps in humans. PhD thesis, University of Glasgow.

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Abstract

A total of 34 volunteer subjects participated in a series of experiments. These experiments were designed to investigate the characteristics and functional role of an excitatory reflex pathway linking the pretibial muscles to quadriceps (CPQ reflex). The CPQ reflex was evoked by low intensity electrical stimulation of common peroneal nerve (CPN) at the level of caput fibulae. The reflex was observed in averaged EMG of rectus femoris (RF) and vastus medialis (VM). Voluntary contraction of Q was needed to reveal the reflex and no responses were detected in the recordings from relaxed muscle. The peak to peak amplitude and area of the responses were measured in non-rectified and rectified averaged EMG. The stability of the CPQ reflex was investigated in the first series of experiments. Nine trials were distributed across three sessions with the perceptive caution to keep the stimulating and recording conditions similar. A constant contraction (20% of maximum voluntary contraction) in quadriceps was maintained by the subjects during the tests. Constant stimulus intensity to evoke maximum reflex was applied in all trials. The result suggested that the peak- peak amplitude and the threshold of the CPQ reflex was extremely consistent with-in session and between sessions of the experiment. Graded stimulus intensities between 0.9 and 1.5xmotor threshold (MT) in tibialis anterior (TA) were applied to CPN in the second series of experiments while the quadriceps (Q) was contracted at a level of 20% of maximum voluntary contraction (MVC). The electrical stimulation of the CPN evoked excitatory responses in all the subjects with a latency of about 30+/-2.1ms (mean +/- ISD). The responses were regarded significant with amplitude beyond 2 standard deviation (SD) of the mean. The mean was calculated from 30ms pre-stimulus averaged EMG. In three subjects making contractions at 20% of MVC significant CPQ reflexes were recorded with stimulation at an intensity of 0.9xMT. The extrapolation of the pooled data also suggests an electrical threshold of around O.8xMT. This low threshold and the short latency strongly suggest the participation of group I afferent types in this reflex pathway. Maximum response was evoked by stimulus intensity of about 1.3XMT. The changes in the reflex magnitude in different knee and hip joint positions were also investigated in another series of experiments. The knee positioning was shown to affect the reflex amplitude in all subjects. The reflex became smaller towards more flexed position of the knee joint. Two patterns of reaction were recognised among the subjects. One group showed a very significant and abrupt reduction in the magnitude of the reflex after 10

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: R H Baxendale
Keywords: Kinesiology
Date of Award: 2002
Depositing User: Enlighten Team
Unique ID: glathesis:2002-72136
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 12:50
Last Modified: 17 May 2019 12:50
URI: http://theses.gla.ac.uk/id/eprint/72136

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