Force Regulation of Ankle Extensor Muscle Activity in Freely Walking Cats

2009 ◽  
Vol 101 (1) ◽  
pp. 360-371 ◽  
Author(s):  
J. M. Donelan ◽  
D. A. McVea ◽  
K. G. Pearson
Keyword(s):  
Muscle Activity ◽  
Force Feedback ◽  
Muscle Length ◽  
Medial Gastrocnemius ◽  
Strongly Correlated ◽  
Experimental Conditions ◽  
Hind Foot ◽  
Feedback Pathway ◽  
Total Muscle ◽  
Medial Gastrocnemius Muscle

To gain insight into the relative importance of force feedback to ongoing ankle extensor activity during walking in the conscious cat, we isolated the medial gastrocnemius muscle (MG) by denervating the other ankle extensors and measured the magnitude of its activity at different muscle lengths, velocities, and forces accomplished by having the animals walk up and down a sloped pegway. Mathematical models of proprioceptor dynamics predicted afferent activity and revealed that the changes in muscle activity under our experimental conditions were strongly correlated with Ib activity and not consistently associated with changes in Ia or group II activity. This allowed us to determine the gains within the force feedback pathway using a simple model of the neuromuscular system and the measured relationship between MG activity and force. Loop gain increased with muscle length due to the intrinsic force–length property of muscle. The gain of the pathway that converts muscle force to motoneuron depolarization was independent of length. To better test for a causal relationship between modulation of force feedback and changes in muscle activity, a second set of experiments was performed in which the MG muscle was perturbed during ground contact of the hind foot by dropping or lifting the peg underfoot. Collectively, these investigations support a causal role for force feedback and indicate that about 30% of the total muscle activity is due to force feedback during level walking. Force feedback's role increases during upslope walking and decreases during downslope walking, providing a simple mechanism for compensating for changes in terrain.

Contribution of Force Feedback to Ankle Extensor Activity in Decerebrate Walking Cats

2004 ◽  
Vol 92 (4) ◽  
pp. 2093-2104 ◽  
Author(s):  
J. M. Donelan ◽  
K. G. Pearson
Keyword(s):  
Muscle Activity ◽  
Force Feedback ◽  
Muscle Length ◽  
Medial Gastrocnemius ◽  
Loop Gain ◽  
Afferent Pathways ◽  
Golgi Tendon Organs ◽  
Length Dependence ◽  
Feedback Pathway ◽  
Positive Force

Previous investigations have demonstrated that feedback from ankle extensor group Ib afferents, arising from force-sensitive Golgi tendon organs, contributes to ankle extensor activity during the stance phase of walking in the cat. The objective of this investigation was to gain insight into the magnitude of this contribution by determining the loop gain of the positive force feedback pathway. Loop gain is the relative contribution of force feedback to total muscle activity and force. In decerebrate cats, the isolated medial gastrocnemius muscle (MG) was held at different lengths during sequences of rhythmic contractions associated with walking in the other three legs. We found that MG muscle activity and force increased at longer muscle lengths. A number of observations indicated that this length dependence was not due to feedback from muscle spindles. In particular, activity in group Ia afferents was insensitive to changes in muscle length during the MG bursts, and electrical stimulation of group II afferents had no influence on the magnitude of burst activity in other ankle extensors. We concluded that the homonymous positive force feedback pathway was isolated from other afferent pathways, allowing the use of a simple model of the neuromuscular system to estimate the pathway loop gain. This gain ranged from 0.2 at short muscle lengths to 0.5 at longer muscle lengths, demonstrating that force feedback was of modest importance at short muscle lengths, accounting for 20% of total activity and force, and of substantial importance at long muscle lengths, accounting for 50%. This length dependence was due to the intrinsic force-length property of muscle. The gain of the pathway that converts muscle force to motoneuron depolarization was independent of length. We discuss the relevance of this conclusion to the generation of ankle extensor activity in intact walking cats. These findings emphasize the general importance of feedback in generating ankle extensor activity during walking in the cat.

Recovery of medial gastrocnemius muscle grafts in rats: implications for the plantar flexor group

1994 ◽  
Vol 77 (6) ◽  
pp. 2773-2777 ◽  
Author(s):  
S. W. Miller ◽  
C. A. Hassett ◽  
T. P. White ◽  
J. A. Faulkner
Keyword(s):  
Group Structure ◽  
Muscle Group ◽  
Medial Gastrocnemius ◽  
Maximum Force ◽  
Plantar Flexor ◽  
Flexor Muscle ◽  
And Function ◽  
Total Muscle ◽  
Medial Gastrocnemius Muscle ◽  
Degree Of Recovery

Medial gastrocnemius (MGN) muscles were grafted in 18 rats and evaluated at 60, 90, and 120 days after the operation. Our purpose was to investigate the degree of recovery of the vascularized MGN grafts and the entire plantar flexor muscle group. Compared with control values, muscle mass and maximum force of MGN grafts were decreased by 33 and 38% at 60 days, 22 and 32% at 90 days, and 13 and 15% at 120 days. At 60 and 90 days, the deficits in maximum force for the entire plantar flexor muscle group, including the graft, were 29 and 17%, respectively. No difference was observed at 120 days. At 60 days, the deficit in the total mass of the plantar flexor group was 14% compared with control values, but by 90 days no deficit was observed. The restoration of normal plantar flexor group structure and function indicates that the degree of recovery attained by MGN grafts, although not complete, was sufficient to ensure that the performance of the total muscle group was not compromised.

Control of ankle extensor muscle activity in walking cats

2012 ◽  
Vol 108 (10) ◽  
pp. 2785-2793 ◽  
Author(s):  
Kathrin Hatz ◽  
Katja Mombaur ◽  
J. Maxwell Donelan
Keyword(s):  
Muscle Activity ◽  
Neural Control ◽  
Stance Phase ◽  
Force Feedback ◽  
Afferent Feedback ◽  
Proprioceptive Feedback ◽  
Medial Gastrocnemius ◽  
Model Parameters ◽  
Small Contribution ◽  
Central Drive

Our objective was to gain insight into the relative importance of feedforward control and different proprioceptive feedback pathways to ongoing ankle extensor activity during walking in the conscious cat. We asked whether the modulation of stance phase muscle activity is due primarily to proprioceptive feedback and whether the same proprioceptive gains and feedforward commands can automatically generate the muscle activity required for changes in walking slope. To test these hypotheses, we analyzed previously collected muscle activity and mechanics data from cats with an isolated medial gastrocnemius muscle walking along a sloped pegway. Models of proprioceptor dynamics predicted afferent activity from the measured muscle mechanics. We modeled muscle activity as the weighted sum of the activity predicted from the different proprioceptive pathways and a simple model of central drive. We determined the unknown model parameters using optimization procedures that minimized the error between the predicted and measured muscle activity. We found that the modulation of muscle activity within the stance phase and across walking slopes is indeed well described by neural control that employs constant central drive and constant proprioceptive feedback gains. Furthermore, it is force feedback from Ib afferents that is primarily responsible for modulating muscle activity; group II afferent feedback makes a small contribution to tonic activity, and Ia afferent feedback makes no contribution. Force feedback combined with tonic central drive appears to provide a simple control mechanism for automatically compensating for changes in terrain without requiring different commands from the brain or even modification of central nervous system gains.

Medial Gastrocnemius Muscle Activity during Single-Leg Hopping to Exhaustion

2019 ◽  
Vol 52 (5) ◽  
pp. 601-611
Author(s):  
Kurt L. Mudie ◽  
Peter J. Clothier ◽  
Ryan J. Hilliard ◽  
Amitabh Gupta
Keyword(s):  
Muscle Activity ◽  
Gastrocnemius Muscle ◽  
Medial Gastrocnemius ◽  
Medial Gastrocnemius Muscle

Regional Variability of Stretch Reflex Amplitude in the Cat Medial Gastrocnemius Muscle During a Postural Task

1997 ◽  
Vol 78 (2) ◽  
pp. 1150-1154 ◽  
Author(s):  
Janice J. Eng ◽  
J. A. Hoffer
Keyword(s):  
Stretch Reflex ◽  
Gastrocnemius Muscle ◽  
Muscle Length ◽  
Medial Gastrocnemius ◽  
Regional Variability ◽  
Reflex Amplitude ◽  
Local Reflex ◽  
Whole Muscle ◽  
Postural Task ◽  
Medial Gastrocnemius Muscle

Eng, Janice J. and J. A. Hoffer. Regional variability of stretch reflex amplitude in the cat medial gastrocnemius muscle during a postural task. J. Neurophysiol. 78: 1150–1154, 1997. The relationship between local fibre stretch velocity (mechanical input) and the corresponding local reflex electromyographic (EMG) amplitude (a measure of the neural output) was assessed to determine the contribution of muscle spindle feedback in postural control. We hypothesized that traditionally measured input variables (e.g., the velocity of an external movement or whole muscle velocity) may not accurately represent the mechanical input to the muscle spindles, especially when the background forces are small. Three cats were trained to stand on pedestals while ankle rotations were applied to the left hindlimb. EMG and fiber movement in both proximal and distal regions of the muscle were recorded in addition to muscle length and tendon force. We found that local muscle velocity was correlated poorly with whole muscle velocity, demonstrating that internal and external muscle movements are often dissimilar, particularly during tasks that involve modest levels of muscle activation. Local EMG reflex amplitudes were correlated well with the corresponding local fiber stretch velocities ( R values ranging from 0.5 to 0.8) but not with muscle stretch velocity. The lack of crossed correlations between fiber stretch velocities and reflex EMG amplitudes measured in proximal versus distal regions of the muscle suggests the presence of a local reflex component. It is concluded that changes in local muscle fiber length represent the mechanical input to spindles better than changes in the total muscle length. Additionally, spindles have a specific role in the reflex activation of nearby muscle fibers.

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