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

First published online March 14, 2008
Journal of Experimental Biology 211, 1148-1162 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.012419

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 Moreno, C. A. Articles by Biewener, A. A. Search for Related Content PubMed PubMed Citation Articles by Moreno, C. A. Articles by Biewener, A. A.

Variability in forelimb bone strains during non-steady locomotor activities in goats

Carlos A. Moreno^1,*, Russell P. Main² and Andrew A. Biewener¹

¹ Concord Field Station, Department of Organismic and Evolutionary Biology, Harvard University, 100 Old Causeway Road, Bedford, MA 01730, USA
² Sibley School of Mechanical and Aerospace Engineering, 222 Upson Hall, Cornell University, Ithaca, NY 14853, USA

View larger version (34K): [in this window] [in a new window]   Fig. 1. Outdoor experimental setup. (A) Video stills of outdoor locomotor behaviors, depicting gallops and trots on the level, jumping on to and off of the platform, and running up and down the ramp. (B) Diagram of the outdoor arena showing the location of the ramp and platform. Goats were freely chased around in the arena while trailing a data cable to record in vivo bone strains. Kinematics were recorded from behind a clear plastic barrier.

View larger version (20K): [in this window] [in a new window]   Fig. 2. (A) Parameter space used to evaluate and represent the variability in loading pattern. The x axis is the orientation of the tensile principal strain relative to the long axis of the bone (TSO). The y axis is the fractional measure of the dominant strain type (FTSR): values greater than 0.5 indicate that tension>compression whereas values less than 0.5 indicate compression>tension. The broken outlines delineate zones in which we expect the majority of loading events to occur, either tension>compression and TSO aligned near the long axis (zone 1), or compression>tension and principal compression angle aligned near the long axis (TSO closer to 90°; zone 2). Between 22.5° and 67.5° the TSO is closer to the diagonal (45°) than to either the long or transverse axis of the bone, and compression and tension magnitudes are approximately equal (e.g. this would be the case for torsion). (B) Illustrations of the radius and metacarpus, with medio-lateral (M-L) and cranio-caudal (C-C) curvature values from each aspect. The cranial and caudal surfaces are labeled with the loading zone where strain data from that surface would be expected to occur for a typical loading cycle. Tensile strain orientation (TSO) is the angle () between the principal tensile strain and the longitudinal axis. All illustrations are drawn to scale.

View larger version (45K): [in this window] [in a new window]   Fig. 3. (A) Representative strain record showing principal tensile (black) and compressive (grey) strains from the caudal surface of the radius during one trial lasting about 30 s. Strains are shown during the contact phase of identified loading cycles (swing phase and non-analyzed footfalls have been discarded). (B) Expanded view of five footfalls, showing a range of natural locomotor behaviors. (C) Two-dimensional scatterplot depicting the loading pattern for this surface (caudal radius, black diamonds), as well as the opposite surface (cranial radius, white diamonds; strain trace not shown), during this representative trial. (D) Principal tensile (black) and compressive (grey) strains for cranial, caudal and medial surfaces (medial surfaces show axial strains) for the metacarpus and radius during representative treadmill footfalls. Each panel shows three consecutive walks, trots and gallops from one goat during different trials. Note the difference in y axis scale for each surface.

View larger version (16K): [in this window] [in a new window]   Fig. 4. 2D scatterplot of loading pattern for all loading cycles from outdoor (grey) and treadmill (black) locomotion, showing fractional tensile strain ratio (FTSR) plotted against tensile strain orientation (TSO) for the cranial and caudal midshaft surfaces of both bones. Variability in pattern was greater during outdoor, non-steady behaviors than during steady treadmill locomotion (for descriptive statistics, see Table 2). Mean values for FTSR and TSO were nearly identical between outdoor and treadmill conditions. On average, the radius had a significantly higher percentage of footfalls that landed within the expected loading zones.

View larger version (17K): [in this window] [in a new window]   Fig. 5. Composite measures of variability in loading pattern, shown for the cranial and caudal midshaft surfaces of both bones during outdoor (grey) and treadmill (black) locomotion. (A) Participation ratio (PR) and (B) Distance to Individual Mean (DIM) are measures of two-dimensional spread, and (C) percentage of footfalls that land in the expected loading zone indicates how consistently individual footfalls land within the expected range of TSO and FTSR. For both measures of 2D spread (A,B), outdoor footfalls are more variable than those of treadmill locomotion, but not all comparisons are significant because of low degrees of freedom (*significant difference, P<0.05). (C) For both bones the percentage of footfalls landing in the expected loading zone is not significantly different between outdoor and treadmill conditions. Values shown are means ± s.e.m.

View larger version (21K): [in this window] [in a new window]   Fig. 6. Within-individual variability in loading pattern in terms of (A) variance in tensile strain orientation (TSO; normalized to 90°) and (B) variance in fractional tensile strain ratio (FTSR). Values are shown when outdoor (grey) and treadmill (black) data for the cranial and caudal surfaces of both bones were available for an individual. In most of the within-individual comparisons (TSO: 3 of 5 metacarpus, 8 of 9 radius; FTSR: 4 of 5 metacarpus, 8 of 9 radius), the variance in these dimensions during outdoor locomotion is significantly greater than during treadmill locomotion (*significant difference in variances, according to F-tests). (C) Variance in TSO averaged across individuals for the cranial and caudal surfaces of each bone was not significantly different between the metacarpus (MC) and radius (Rad) for either experimental condition. (D) Variance in FTSR averaged across individuals for the cranial and caudal surfaces was low and not significantly different between bones during treadmill locomotion, but was significantly lower (P=0.037) in the radius during outdoor locomotion.

View larger version (21K): [in this window] [in a new window]   Fig. 7. Frequency distributions of strain magnitudes for the cranial, caudal and medial surfaces of the metacarpus, for both outdoor and treadmill locomotion. Peak principal strain magnitudes (absolute magnitudes of compressive or tensile principal strains) are shown for cranial and caudal surfaces (A–D) and peak axial strain magnitudes are shown for medial surfaces (E,F). These distributions contain pooled data across all behaviors and individuals, providing an estimate of the distribution pattern for the population of strains recorded at each bone surface. During both outdoor and treadmill locomotion, strains in all three surfaces appeared to be log-normally distributed, although only in the cases where P>0.05 (caudal outdoor, C, and medial treadmill, F) was the fit not significantly different from a standard lognormal distribution. The pooled sample size and the median are shown, as well as the D-statistic from the KSL goodness-of-fit test, which indicates that the outdoor data had smaller deviations from the best-fit lognormal curves than the treadmill data.

View larger version (20K): [in this window] [in a new window]   Fig. 8. Frequency distributions of strain magnitudes for the cranial, caudal and medial surfaces of the radius. Details of these distributions and the values shown are the same as in Fig. 7. Though all six distributions are skewed to the right and appear to fit a lognormal distribution, only the caudal surface during outdoor locomotion (C; P=0.15) and the medial surface during treadmill locomotion (F, P=0.15) are not significantly different than a standard lognormal distribution. As in the metacarpus, all of the outdoor distributions had smaller deviations (according to the D statistic) from the log-normal curves than the corresponding treadmill distributions, probably because the larger sample size for the outdoor data.

View larger version (7K): [in this window] [in a new window]   Fig. 9. (A) Axial versus bending strain components for the metacarpus and the radius during outdoor activities. Although axial strain components did not differ between bones, bending strain in the radius (white bars) was significantly greater than in the metacarpus (hatched bars). (B) The coefficient of variation (CV) of the axial and bending strain components for both bones during outdoor activities. Variability in axial strains was similar between bones, but the variability in bending strain was significantly greater in the straighter metacarpus versus the curved radius.

View larger version (34K): [in this window] [in a new window]   Fig. 10. (A–D) FTSR versus TSO for outdoor loading events having magnitudes greater than the pooled median, plotted within bins representing normalized strain magnitudes, where cool colors are lower magnitudes and warm colors are higher magnitudes, quantified as a percentage of the maximum value recorded for each bone site. The minimum (median) and maximum strain values are shown for each bone surface. (E) Variability in strain pattern expressed as distance to the bin mean (DBM) regressed against bin magnitude, represented as a percentage of the maximum strain recorded. DBM values were averaged across the cranial and caudal midshaft surfaces for the metacarpus and the radius.