|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
First published online October 27, 2003
Motor control of locomotor hindlimb posture in the American alligator (Alligator mississippiensis)
1 Department of Biological Sciences, Ohio University, Athens, OH 45701,
USA
2 Department of Biological Sciences, Clemson University, Clemson, SC 29634,
USA
* Author for correspondence (e-mail: rblob{at}clemson.edu)
Accepted 27 August 2003
Crocodilians are unusual among quadrupedal tetrapods in their frequent use of a wide variety of hindlimb postures, ranging from sprawling to a more erect high walk. In this study, we use synchronized kinematic videos and electromyographic recordings to test how the activity patterns of hindlimb muscles in American alligators (Alligator mississippiensis Daudin) differ between sprawling and more upright postures.
Previous force platform analyses suggested that upright posture in alligators would require greater activation by hindlimb extensors to counter increases in the flexor moments exerted about joints by the ground reaction force during upright stance. Consistent with these predictions, ankle extensors (gastrocnemius) and knee extensors (femorotibialis internus and iliotibialis 2) exhibit increases in signal intensity during the use of more upright stance. Bone loading data also predicted that activation patterns for hip adductors spanning the length of the femur would not differ between sprawling and more upright posture. Correspondingly, motor patterns of the adductor femoris were not altered as posture became more upright. However, the adductor puboischiofemoralis externus 3, which inserts far proximally on the femur, displays significant increases in burst intensity that could contribute to the greater femoral adduction that is integral to upright posture.
In contrast to patterns in alligators, in mammals EMG burst intensity typically decreases during the use of upright posture. This difference in the motor control of limb posture between these taxa may be related to differences in the relative sizes of their feet. Alligator feet are large relative to the hindlimb and, as a result, the ground reaction force shifts farther from the limb joints during upright steps than in mammals, increasing flexor moments at joints and requiring alligator extensor muscles to exert greater forces to keep the limb in equilibrium. However, several alligator hindlimb muscles show no differences in motor pattern between sprawling and upright posture. The wide range of motor pattern modulations between different postures in alligators suggests considerable independence of neural control among the muscles of the alligator hindlimb.
Key words: locomotion, biomechanics, kinematics, EMG, muscle, electromyography, modulation, neural control, bone stress, posture, evolution, vertebrate, alligator, Sauria, Crocodylia
This article has been cited by other articles:
|
|
 |
|
  M. T. Butcher and R. W. Blob Mechanics of limb bone loading during terrestrial locomotion in river cooter turtles (Pseudemys concinna) J. Exp. Biol., April 15, 2008; 211(8): 1187 - 1202. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. J. Chen, A. M. Peattie, K. Autumn, and R. J. Full Differential leg function in a sprawled-posture quadrupedal trotter J. Exp. Biol., January 15, 2006; 209(2): 249 - 259. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. Autumn, S. T. Hsieh, D. M. Dudek, J. Chen, C. Chitaphan, and R. J. Full Dynamics of geckos running vertically J. Exp. Biol., January 15, 2006; 209(2): 260 - 272. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. L. Munns, L. K. Hartzler, A. F. Bennett, and J. W. Hicks Terrestrial locomotion does not constrain venous return in the American alligator, Alligator mississippiensis J. Exp. Biol., September 1, 2005; 208(17): 3331 - 3339. [Abstract] [Full Text] [PDF]
|
|
