QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Nelson, F. E. Articles by Jayne, B. C. Search for Related Content PubMed PubMed Citation Articles by Nelson, F. E. Articles by Jayne, B. C.

The effects of speed on the in vivo activity and length of a limb muscle during the locomotion of the iguanian lizard Dipsosaurus dorsalis

Frank E. Nelson^* and Bruce C. Jayne

Department of Biological Sciences, PO Box 210006, University of Cincinnati, Cincinnati, OH 45221-0006, USA

View larger version (22K): [in a new window]   Fig. 1. Ventral view of the caudofemoralis muscle of the right hindlimb of Dipsosaurus dorsalis with the illiocaudalis and ishiocaudalis removed. The symbols indicate the approximate longitudinal and lateral locations of electromyographic (EMG) electrodes and sonomicrometry crystals. Electrodes were implanted at two sites. AT and PT indicate the auxiliary and primary tendons of the caudofemoralis muscle, respectively, and IL is the illioischiadic ligament.

View larger version (16K): [in a new window]   Fig. 2. A schematic right lateral view of major movements of the right femur. The most dorsal rectangular box represents the pelvis. The long cylinder attached to the pelvis is the femur. The small rectangle on the femur represents the greater trochanter, which is parallel to the black reference line on the distal end of the femur. The more distal cylinder represents the lower leg, and the most ventral rectangle represents the tarsals and metatarsals. For each pair of figures in a row, the figure on the right illustrates the movement relative to the initial position shown on the left. For the sake of simplicity, rotation of the pelvis in the horizontal plane is not shown, but this movement occurs in most lizards and salamanders.

View larger version (32K): [in a new window]   Fig. 3. Angles of the tail and hindlimb, and strain and electromyograms from the caudofemoralis muscle, for one stride cycle for one individual of Dipsosaurus dorsalis at each of three speeds 50 cm s–1 (A), 200 cm s–1 (B) and 350 cm s–1 (C). The muscle strain is expressed as a percentage change from resting length (L0). The elapsed time within each stride shown at the bottom of each panel starts and ends at the beginning (foot-up) of the swing phase (white bar), and the black bar indicates the duration of the stance phase after footfall. The numerals to the left of each electromyogram indicate the longitudinal positions of three different electromyograms electrodes within a single muscle (see Fig. 1), and M and L indicate the medial and lateral locations within a longitudinal position, respectively.

View larger version (13K): [in a new window]   Fig. 4. Mean values (± S.E.M.) of kinematic and electromyographic (EMG) duty factors (A), maximum (Lmax) and (Lmin) minimum muscle strain (B), net muscle strain (Lnet) (C) and average muscle shortening velocity (D) versus speed. All values of strain are given as a percentage of resting muscle length (L0). Mean values were calculated for the total number of strides pooled across three (A) or four (B–D) individuals. W/R, walk–run transition; L, resting length of the caudofemoralis muscle.

View larger version (9K): [in a new window]   Fig. 5. The mean (± S.E.M.) times of electromyographic (EMG) activity, the beginning of swing, the end of stance and shortening of the caudofemoralis muscle (CF) relative to footfall (dashed vertical line) for each of the speeds of locomotion. For each speed, the top and middle rectangles represent the times of electrical activity of the muscle and muscle shortening, respectively. The bottom rectangle represents the stride cycle, for which the swing and stance phases are indicated by white and black, respectively. Mean values of EMG onset and offset were calculated for the total number of strides pooled across three individuals, and all other variables were calculated for all the strides from four individuals.

View larger version (22K): [in a new window]   Fig. 6. Schematic right lateral views showing the effects of speed on the kinematics of the hindlimb. The uppermost cylinder in each figure represents the proximal portion of the tail, and the remaining objects are as in Fig. 2, and from proximal to distal represent the pelvis, the femur, the lower leg and the tarsals and metatarsals, respectively. To facilitate comparison of limb positions, the pelvis is shown at the same height within each row of figures, but in the real lizards the height of the pelvis relative to the tread surface did vary significantly within the stance phase. From left to right within each row that represents a different speed of locomotion, the average limb positions are shown at the beginning of stance and at the times of maximal (Lmax) and minimal (Lmin) length of the caudofemoralis muscle. Each figure illustrates the mean values (using all strides pooled across four individuals) of the dorsal and lateral angles of the proximal tail and the angles of pelvic rotation, femur retraction, femur rotation, femur depression, knee flexion and ankle flexion. The average times of maximum and minimum muscle length occurred within the stance phase when the foot touches the ground; however, this is not apparent in some figures because the height of the pelvis has been standardized and the toes are not shown.

View larger version (23K): [in a new window]   Fig. 7. Effects of femur retraction (B), femur rotation (C) and knee angle (D) on the length (A) of the caudofemoralis muscle of a Dipsosaurus dorsalis. The data shown are from one of the three individuals for which the hindlimb was manipulated while the lizard was anesthetized. The strain of the caudofemoralis muscle is expressed as a percentage change from its resting length (L0).

View larger version (65K): [in a new window]   Fig. 8. Simultaneous lateral and dorsal views of a Dipsosaurus dorsalis running at 350 cm s–1 at the beginning (A) and end (C) of electrical activity and at the maximum (Lmax; B) and minimum (Lmin; D) length of the right caudofemoralis muscle. The images are from the same sequence as shown in Fig. 3C, and the time elapsed since the beginning of the swing phase (foot-up) of the right hind limb is given above each panel. The base of the tail moves away from the side of caudofemoralis activity.