Position dependence of stretch reflex dynamics at the human ankle

1986 ◽  
Vol 63 (1) ◽  
Author(s):  
P.L. Weiss ◽  
R.E. Kearney ◽  
I.W. Hunter
Keyword(s):  
Stretch Reflex ◽  
Human Ankle ◽  
Position Dependence ◽  
Stretch Reflex Dynamics

Nonlinear identification of stretch reflex dynamics

1988 ◽  
Vol 16 (1) ◽  
pp. 79-94 ◽  
Author(s):  
Robert E. Kearney ◽  
Ian W. Hunter
Keyword(s):  
Stretch Reflex ◽  
Nonlinear Identification ◽  
Stretch Reflex Dynamics

Nonlinear behavior of muscle reflexes at the human ankle joint

1995 ◽  
Vol 73 (1) ◽  
pp. 65-72 ◽  
Author(s):  
R. B. Stein ◽  
R. E. Kearney
Keyword(s):  
Ankle Joint ◽  
Stretch Reflex ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Random Perturbations ◽  
Hydraulic Actuator ◽  
Voluntary Activity ◽  
Highly Nonlinear ◽  
Human Ankle

1. Pulse inputs (similar to tendon jerks) were applied to the human ankle joint with the use of a hydraulic actuator. Inputs of only 1-2 degrees could elicit large responses (> 20% of maximum voluntary contraction). The magnitude of the response depended nonlinearly on a number of factors: the amplitude, direction, and duration of the pulse; the angle of the ankle; and the level of voluntary activation of the ankle muscles. 2. Pulses that flexed or extended the ankle could both produce reflex torques in the same direction (extensor torque). Although an extension of the ankle did not itself produce a response, it could affect the response to a subsequent flexion for up to 1 s. 3. The influence of random perturbations on the stretch reflex at the ankle was assessed. Responses to pulse displacements alone and to pulses superimposed on random perturbations were compared at the same level of voluntary activity. Reflex responses decreased in a graded manner with increasing amplitude or bandwidth of the random perturbations. 4. These results demonstrate that stretch reflexes can generate substantial torques, but in a highly nonlinear manner. In particular, passive joint movements markedly alter stretch reflex gain, and these changes must be considered in interpreting the functional significance of reflex actions.

Age-related changes of the stretch reflex excitability in human ankle muscles

2010 ◽  
Vol 20 (1) ◽  
pp. 55-60 ◽  
Author(s):  
Hiroki Obata ◽  
Noritaka Kawashima ◽  
Masami Akai ◽  
Kimitaka Nakazawa ◽  
Tatsuyuki Ohtsuki
Keyword(s):  
Stretch Reflex ◽  
Reflex Excitability ◽  
Age Related ◽  
Ankle Muscles ◽  
Human Ankle ◽  
Age Related Changes

Modulation of Stretch Reflexes During Imposed Walking Movements of the Human Ankle

1999 ◽  
Vol 81 (6) ◽  
pp. 2893-2902 ◽  
Author(s):  
Robert E. Kearney ◽  
Mireille Lortie ◽  
Richard B. Stein
Keyword(s):  
Stretch Reflex ◽  
Swing Phase ◽  
Hydraulic Actuator ◽  
Step Cycle ◽  
Stretch Reflexes ◽  
Mechanical Responses ◽  
Human Ankle ◽  
Peripheral Afferents ◽  
Central Factors

Modulation of stretch reflexes during imposed walking movements of the human ankle. Our overall objectives were to examine the role of peripheral afferents from the ankle in modulating stretch reflexes during imposed walking movements and to assess the mechanical consequences of this reflex activity. Specifically we sought to define the changes in the electromyographic (EMG) and mechanical responses to a stretch as a function of the phase of the step cycle. We recorded the ankle position of a normal subject walking on a treadmill at 3 km/h and used a hydraulic actuator to impose the same movements on supine subjects generating a constant level of ankle torque. Small pulse displacements, superimposed on the simulated walking movement, evoked stretch reflexes at different phases of the cycle. Three major findings resulted: 1) soleus reflex EMG responses were influenced strongly by imposed walking movements. The response amplitude was substantially smaller than that observed during steady-state conditions and was modulated throughout the step cycle. This modulation was qualitatively similar to that observed during active walking. Because central factors were held constant during the imposed walking experiments, we conclude that peripheral mechanisms were capable of both reducing the amplitude of the reflex EMG and producing its modulation throughout the movement. 2) Pulse disturbances applied from early to midstance of the imposed walking cycle generated large reflex torques, suggesting that the stretch reflex could help to resist unexpected perturbations during this phase of walking. In contrast, pulses applied during late stance and swing phase generated little reflex torque. 3) Reflex EMG and reflex torque were modulated differently throughout the imposed walking cycle. In fact, at the time when the reflex EMG response was largest, the corresponding reflex torque was negligible. Thus movement not only changes the reflex EMG but greatly modifies the mechanical output that results.

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