Principal Tensile Strain Research Articles

Changes in proximal femoral strain after insertion of uncemented standard and customised femoral stems. An experimental study in human femora.

We have compared the changes in the pattern of the principal strains in the proximal femur after insertion of eight uncemented anatomical stems and eight customised stems in human cadaver femora. During testing we aimed to reproduce the physiological loads on the proximal femur and to simulate single-leg stance and stair-climbing. The strains in the intact femora were measured and there were no significant differences in principal tensile and compressive strains in the left and right femora of each pair. The two types of femoral stem were then inserted randomly into the left or right femora and the cortical strains were again measured. Both induced significant stress shielding in the proximal part of the metaphysis, but the deviation from the physiological strains was most pronounced after insertion of the anatomical stems. The principal compressive strain at the calcar was reduced by 90% for the anatomical stems and 67% for the customised stems. Medially, at the level of the lesser trochanter, the corresponding figures were 59% and 21%. The anatomical stems induced more stress concentration on the anterior aspect of the femur than did the customised stems. They also increased the hoop strains in the proximomedial femur. Our study shows a consistently more physiological pattern of strain in the proximal femur after insertion of customised stems compared with standard, anatomical stems.

Changes in proximal femoral strain after insertion of uncemented standard and customised femoral stems

We have compared the changes in the pattern of the principal strains in the proximal femur after insertion of eight uncemented anatomical stems and eight customised stems in human cadaver femora. During testing we aimed to reproduce the physiological loads on the proximal femur and to simulate single-leg stance and stair-climbing. The strains in the intact femora were measured and there were no significant differences in principal tensile and compressive strains in the left and right femora of each pair. The two types of femoral stem were then inserted randomly into the left or right femora and the cortical strains were again measured. Both induced significant stress shielding in the proximal part of the metaphysis, but the deviation from the physiological strains was most pronounced after insertion of the anatomical stems. The principal compressive strain at the calcar was reduced by 90% for the anatomical stems and 67% for the customised stems. Medially, at the level of the lesser trochanter, the corresponding figures were 59% and 21%. The anatomical stems induced more stress concentration on the anterior aspect of the femur than did the customised stems. They also increased the hoop strains in the proximomedial femur. Our study shows a consistently more physiological pattern of strain in the proximal femur after insertion of customised stems compared with standard, anatomical stems.

Micromechanical Modeling of a Composite Containing Piezoelectric and Shape Memory Alloy Inclusions

Macroscopic constitutive relations based on the mean-field theory and the Mori–Tanaka method are derived for a 3-phase composite consisting of a polymer matrix and shape memory alloy (SMA) and piezoceramic (PZT) inclusions. Effective moduli are computed for likewise oriented spherical and cylindrical inclusions. Results are also computed for cylindrical PZT and ellipsoidal SMA inclusions. Even though the PZT and the matrix materials are assumed to be linear, the overall response of the composite is nonlinear because of the phase transformations in the SMA inclusions. The 3-phase composite exhibits pyroelectric effects even when none of its constituents is pyroelectric. It is found that the spherical inclusions are more effective than the cylindrical inclusions in the sense that lower values of the average axial stress induce phase transformations in the SMA inclusions, and the maximum principal tensile strain induced in the PZT inclusions is only about 7% of the average axial strain. However, spherical PZT inclusions require a very high value of the electric field to induce any noticeable axial strain in the hybrid composite.

Modeling Shear Behavior of Hybrid RCS Beam-Column Connections

A model to predict the shear strength versus shear distortion response of hybrid connections between reinforced concrete columns and steel (RCS) beams is presented. Based on a preestablished maximum attainable joint shear deformation, design equations were developed for use in both interior and exterior RCS connections in buildings located in high seismic risk zones. The proposed model is based on the definition of the state of plane strain in the joint through the development of a ratio between the principal tensile and compression strains. The strength of the joints is given by contributions from the steel web panel and concrete diagonal struts. The joint model is capable of predicting the shear force, and stirrup and concrete strains at any level of joint shear distortion for exterior joints. In addition, the use of the proposed design equations led to excellent agreement between predicted and measured shear strength for both interior and exterior RCS joints.

Seismic detailing of reinforced concrete beam-column connections

A simplified analysis procedure utilizing the strut-tie modeling technique is developed to take a close look into the post-elastic deformation capacity of beam-column connections in ductile reinforced concrete frame structures. Particular emphasis is given to the effect of concrete strength decay and quantity and arrangement of joint shear steel. For this a fan-shaped crack pattern is postulated through the joints. A series of hypothetical rigid nodes are assumed through which struts, ties and boundaries are connected to each other. The equilibrium consideration enables all forces in struts, ties and boundaries to be related through the nodes. The boundary condition surrounding the joints is obtained by the mechanism analysis of the frame structures. In order to avoid a complexity from the indeterminacy of the truss model, it is assumed that all shear steel yielded. It is noted from the previous research that the capacity of struts is limited by the principal tensile strain of the joint panel for which the strain of the transverse diagonal is taken. The post-yield deformation of joint steel is taken to be the only source of the joint shear deformation beyond the elastic range. Both deformations are related by the energy consideration. The analysis is then performed by iteration for a given shear strain. The analysis results indicate that concentrating most of the joint steel near the center of the joint along with higher strength concrete may enhance the post-elastic joint performance.

Loading conditions and cortical bone construction of an artiodactyl calcaneus.

Customary nonuniform distributions of physiological bone strains are thought to evoke heterogeneous material adaptation in diaphyseal cortices of some limb bones. Recent studies of artiodactyl calcanei have suggested that the regional prevalence of specific mechanical strain features such as mode and magnitude correlate with specific variations in cortical bone ultrastructure, microstructure and mineralization. These data are also consistent with predictions of current algorithms of mechanically induced bone adaptation. However, detailed characterization of the customary functional strain environment of these bones is needed to understand better the mechanisms of these adaptations. An in vitro loading method and rosette strain gauges were used to record principal strains, maximum shear strains and principal strain angles at multiple locations on ten calcanei of adult male mule deer (Odocoileus hemionus hemionus). Each hind limb was fixed in an apparatus to mimic the mid-support phase of the gait and loaded via the Achilles tendon over a broad range of functional loads (0 to 2943 N). Strains were recorded on the craniolateral, craniomedial, caudal, medial and lateral cortices at mid-diaphysis. Loading variations included the progressive elimination of the ligament and tendon along the caudal calcaneus. The results showed that the cranial cortex experiences longitudinal compressive strains that are nearly equal to the principal minimum strains and that the caudal cortex receives longitudinal tensile strains that are nearly equal to the principal maximum strains. With a 981 N load, the mean principal compressive strain on the cranial cortex was -636+/-344 micro(&egr;) (mean +/- s.d., N=9) and the mean principal tensile strain on the caudal cortex was 1112+/-68 micro;(&egr;)x (N=9). In contrast to the cranial and caudal cortices, principal strains in the medial and lateral cortices displayed relatively large deviations from the longitudinal axis (medial, 24 degrees cranial; lateral, 27 degrees caudal). Although shear strains predominated at all gauge sites, variations in maximum shear strains showed no apparent regional pattern or consistent regional predominance. The plantar ligament and tendon of the superficial digital flexor muscle were shown to have important load-sharing functions. These results demonstrate that the functionally loaded artiodactyl calcaneus generally behaves like a cantilevered beam with longitudinal compression and tension strains predominating in opposing cranial and caudal cortices, respectively. Differences in osteon remodeling rates, osteon morphology and mineral content reported previously between the cranial and caudal cortices correlate, in part, with the magnitudes of the principal compressive and tensile strains, respectively. However, material differences that distinguish the medial and lateral cortices from the cranial and caudal cortices could not be primarily attributed to locally increased shear strains as previously suggested. Variations in osteon and/or collagen fiber orientation may correlate more strongly with principal strain direction.

Seismic analysis of arch dams?a continuum damage mechanics approach

In this paper, the non-linear seismic response of arch dams is presented using the concept of Continuum Damage Mechanics (CDM). The analysis is performed using the finite element technique and appropriate non-linear material and damage models in conjunction with the α-algorithm for time marching. Because of the non-linear nature of the discretizied equations of motion, modified Newton–Raphson approach has been used at each time step. Damage evolution based on tensile principal strain using mesh-dependent hardening modulus technique is adopted to ensure the mesh objectivity and to calculate the accumulated damage. The methodology employed is shown to be computationally efficient and consistent in its treatment of both damage growth and damage propagation. As an application of the proposed formulation, a double curvature arch dam has been analysed and the results are compared with the solutions from linear analysis and it is shown that the structural response of arch dams varies significantly in terms of damage evolution. Copyright © 1999 John Wiley & Sons, Ltd.

Non-linear seismic behaviour of concrete gravity dams using coupled finite element?boundary element technique

In this paper, the seismic response of concrete gravity dams is presented using the concept of Continuum Damage Mechanics (CDM) and adopting the hybrid Finite Element–Boundary Element technique (FE–BE). The finite element method is used for discretization of the near field and the boundary element method is employed to model the semi-infinite far field. Because of the non-linear nature of the discretizied equations of motion modified Newton–Raphson approach has been used at each time step to linearize them. Damage evolution based on tensile principal strain using mesh-dependent hardening modulus technique is adopted to ensure the mesh objectivity and to calculate the accumulated damage. The methodology employed is shown to be computationally efficient and consistent in its treatment of both damage growth and damage propagation in gravity dams. Other important features considered in the analysis are: (1) realistic damage modelling for concrete that allows isotropic as well as anisotropic damage state and exhibits stiffness recovery upon load reversals. (2) softening initiation and strain softening criteria for concrete, and (3) proper modelling of semi-infinite foundation using FE–BE method that allows to consider dam–foundation interaction analysis. As an application of the proposed formulation a gravity dam has been analysed and the results are compared with different foundation stiffnesses. The results of the analysis indicate the importance of including rock foundation in the seismic analysis of dams. Copyright © 1999 John Wiley & Sons, Ltd.

Examination of a Rock Failure Criterion Based on Circumferential Tensile Strain

—Uniaxial compression, triaxial compression and Brazialian tests were conducted on several kinds of rock, with particular attention directed to the principal tensile strain. In this paper we aim to clarify the effects of the experimental environment—such as confining pressure, loading rate, water content and anisotropy—on the critical tensile strain, i.e., the measured principal tensile strain at peak load.¶It was determined that the chain-type extensometer is a most suitable method for measuring the critical tensile strain in uniaxial compression tests. It is also shown that the paper-based strain gage, whose effective length is less than or equal to a tenth of the specimen’s diameter and glued on with a rubber-type adhesive, can be effectively used in the Brazilian tests.¶The effect of confining pressure P C on the critical tensile strain ɛ TC in the brittle failure region was between −0.02 × 10−10 Pa−1 and 0.77 × 10−10 Pa−1. This pressure sensitivity is small compared to the critical tensile strain values of around −0.5 × 10−2. The strain rate sensitivities ∂ɛ TC /∂{log(d|ɛ|/dt)} were observed in the same way as the strength constants in other failure criteria. They were found to be from −0.10 × 10−3 to −0.52 × 10−3 per order of magnitude in strain rate in the triaxial tests. The average magnitude of the critical tensile strain ɛ TC increased due to the presence of water by 4% to 20% for some rocks, and decreased by 22% for sandstone. It can at least be said that the critical tensile strain is less sensitive to water content than the uniaxial compressive strength under the experimental conditions reported here. An obvious anisotropy was observed in the P-wave velocity and in the uniaxial compressive strength of Pombetsu sandstone. It was not observed, however, in the critical tensile strain, although the data do show some variation.¶A "tensile strain criterion" was proposed, based on the above experimental results. This criterion signifies that stress begins to drop when the principal tensile strain reaches the critical tensile strain. The criterion is limited to use within the brittle failure region. The critical tensile strain contains an inelastic strain component as well as an elastic one. It is affected by the strain rate, however, it is relatively insensitive to the confining pressure, the presence of water and anisotropy.

Polymers under mechanical stress: Deformation of the nanostructure of isotactic polypropylene revealed by scanning force microscopy

AbstractScanning force microscopy (SFM) was used to study the lamellar morphology of α and β spherulites in bulk intruded isotactic polypropylene (iPP) samples deformed under shear stress. The iPP specimens were sheared at a constant shear rate at room temperature. Just beyond yielding, at a shear strain level of 0.5, the lamellar structure of the α‐spherulites resembles that for unsheared iPP; few cracks are observed along the interfaces between neighboring α‐spherulites: this behavior is attributed to a “cross‐hatched” lamellar texture of the α‐spherulites. In β‐spherulites, at the same shear strain, SFM observations reveal the presence of nanocracks perpendicular to the principal tensile strain axis, going through stacks of crystalline lamellae. Profuse local lamellar kinkings occur along the principal compressive strain axis and few nanocracks parallel to the molecular axis are seen in individual lamellae that lie along the shear direction. Neither particular preferred lamellar orientation nor localization of deformation within shear bands has been detected.

The effect of shoe gear on human tibial strains recorded during dynamic loading: a pilot study.

The study was conducted to test the hypothesis that alterations in shoe gear can affect tibial strains in the human during dynamic loading. Rosette strain gauges were mounted on the medial border of the mid-diaphysis in two human subjects with a new strain gauge bonding technique using methyl methacrylate. Strain measurements were made at this site, the most frequent location for stress fractures in the Israeli Army during treadmill walking and free running while wearing various sport shoes (Rockport ProWalkers and New Balance NBX 900) and army boots (light Israeli infantry, double layered sole Israeli infantry, and Zohar infantry boots). Data were analyzed for only one of the subjects because strain gauge bonding was found to be inadequate at the time of surgical removal in the other subject. No single shoe lowered both the principal tibial compression and tensile strains, and the shear strains. The Zohar boot had the lowest principal compression strains during treadmill walking and mobile running, despite its relatively higher weight and sole durometry.

Crush-crack': a non-local damage model for concrete

SUMMARY A model is presented based on the non-local damage theory. It sets out to describe the behavior of concrete under free-variable loads, which are constant in sign. Its purpose is to analyze shear behavior and high strain-gradient localized problems, and it takes Mazar’s model as a starting point with reference to the basic idea of a scalar isotropic non-local damage controlled by principal tensile strains. In addition, the other two main features are an internal variable denoted to the control or reversible volumetric expansion in compression, and irreversible strains aimed at modelling crushing in compression and cracks both in tension and compression. As a consequence, induced-anisotropy, dilatancy and path-dependency can be reproduced. In particular, the modelling of micro- and macrocracks makes it possible to capture mixed-mode cracking as well as aggregate interlock, which requires a residual stiffness to guarantee the transmission of transversal and normal stresses for assigned slips.The model requires the knowledge of the material response in uniaxial tension and compression, and biaxial compression tests which can be introduced directly by adopting experimental curves, or by means of a reduced number of parameters. The effectiveness of the model is shown through comparisons with several sets of experimental tests on both small specimens, assumed to be homogeneous, and boundary value problems.

Crush‐crack': a non‐local damage model for concrete

A model is presented based on the non-local damage theory. It sets out to describe the behavior of concrete under free-variable loads, which are constant in sign. Its purpose is to analyze shear behavior and high strain-gradient localized problems, and it takes Mazar's model as a starting point with reference to the basic idea of a scalar isotropic non-local damage controlled by principal tensile strains. In addition, the other two main features are an internal variable denoted to the control or reversible volumetric expansion in compression, and irreversible strains aimed at modelling crushing in compression and cracks both in tension and compression. As a consequence, induced-anisotropy, dilatancy and path-dep endency can be reproduced. In particular, the modelling of micro- and macrocracks makes it possible to capture mixed-mode cracking as well as aggregate interlock, which requires a residual stiffness to guarantee the transmission of transversal and normal stresses for assigned slips. The model requires the knowledge of the material response in uniaxial tension and compression, and biaxial compression tests which can be introduced directly by adopting experimental curves, or by means of a reduced number of parameters. The effectiveness of the model is shown through comparisons with several sets of experimental tests on both small specimens, assumed to be homogeneous, and boundary value problems.

Adaptive changes in trabecular architecture in relation to functional strain patterns and disuse.

Principal strains and their orientation, determined from in vivo and in situ strains recorded from the lateral cortical surface of the calcaneus of potoroos (a small marsupial) during treadmill exercise and tension applied via the Achilles tendon, were compared with the underlying trabecular architecture and its alignment to test Wolff's "trajectorial theory" of trabecular alignment. In vivo and in situ principal compressive strains (-800 to -2000 mu e) were found to be aligned (mean 161 +/- 7 degrees) close to the preferred alignment (160 degrees) of underlying trabeculae within the calcaneal metaphysis [a second trabecular arcade was closely aligned (70 degrees) with the direction (71 degrees) of principal tensile strain]. This finding represents quantitative verification of Wolff's trajectorial theory of trabecular alignment. These trabecular alignments, as measured by trabecular anisotropy (TbAn, the ratio of horizontal: vertical intercepts), remained unchanged (p > 0.05) after 8 weeks of disuse. However, trabecular bone volume fraction (BV/TV, -35%), trabecular thickness (TbTh, -25%), and trabecular number (TbN, -16%) were reduced for the tenotomized calcaneii relative to their contralateral controls (p < 0.001 to < 0.003). The reduction in trabecular number was associated with a corresponding increase in trabecular spacing (TbSp, +30%). Together, these results suggest that once trabecular alignment is established during growth (along the directions of principal strain during locomotion), it is not altered when functional strains are removed.

Low-frequency Raman spectroscopy of plastically deformed poly(methyl methacrylate)

The low-frequency Raman scattering (2–200 cm −1 range) of poly(methyl methacrylate) (PMMA) specimens plastically deformed in pure shear is compared to that of non-deformed specimens. The main experimental feature is an excess of Raman scattering in the 30–50 cm −1 spectral range induced by plastic deformation. This excess appears to be strongly anisotropic and is maximum when the light polarization is orthogonal to the principal tensile strain component, i.e. to the chain orientation direction. The effect is still present, but with a weaker anisotropy, after mechanical cycling when the macroscopic deformation is brought back to zero by application of an opposite stress. These observations are interpreted in terms of the non-continuous nature of the disordered network on the nanometric scale. The orientation of macromolecular strands induced by plastic deformation is shown to be higher in the less cohesive spaces.

Surface strain on the dorsomedial metacarpus of yearling Thoroughbreds at different speeds and gaits on a treadmill

SummaryStacked rectangular rosette strain gauges were used to measure surface bone strain on the dorsomedial cortex of the third metacarpal bones in 6 yearling (16 to 19 months old) Thoroughbred horses during exercise on a treadmill. The peak principal compressive and tensile strains, angle of the peak strains and strain rate during loading were calculated and compared with speed and gait. At speeds ranging from 4 to 16.5 m/s there was compression of the dorsomedial cortex of the metacarpus and the magnitude of compression and rate of compression were proportional to the speed of exercise. At the walk (2 m/s) tension was recorded in some strides. The mean maximum compressive strains in the 6 horses were −966 μstrain at 2 m/s; −1630 μstrain at 4 m/s; −2172 μstrain at 6 m/s; −2857 μstrain at 8 m/s; −3500 μstrain at 10 m/s; and −3911 μstrain at 12 m/s. Recordings from 3 horses gave a mean −5028 μstrain at 14 m/s. One horse gave a mean −6296 μstrain at 16.5 m/s. These strains were all about 25% higher than those recorded from the metacarpus of adult Thoroughbreds under similar exercise conditions. It was concluded that the higher strains may predispose the young Thoroughbred racehorse to dorsal metacarpal disease.

Homogenization theory and digital imaging: A basis for studying the mechanics and design principles of bone tissue

Bone tissue is a complex multilevel composite which has the ability to sense ad respond to its mechanical environment. It is believed that bone cells called osteocytes within the bone matrix sense the mechanical environment and determine whether structural alterations are needed. At present it is not known, however, how loads are transferred from the whole bone level to cells. A computational procedure combining representative volume element (RVE) based homogenization theory with digital imaging is proposed to estimate strains at various levels of bone structure. Bone tissue structural organization and RVE based analysis are briefly reviewed. The digital image based computational procedure was applied to estimate strains in individual trabeculae (first-level microstructure). Homogenization analysis of an idealized model was used to estimate strains at one level of bone structure around osteocyte lacunae (second-level trabecular microstructure). The results showed that strain at one level of bone structure is amplified to a broad range at the next microstructural level. In one case, a zeor-level tensile principal strain of 495 muE engendered strains ranging between -1000 and 7000 muE in individual trabeculae (first-level microstructure). Subsequently, a first-level tensile principal strains of 1325 muE within an inidividual trabecula engendered strains ranging between 782 and 2530 muE around osteocyte lacunae. Lacunar orientation was found to influence strains around osteocyte lacunae much more than lacunar ellipticity. In conclusion, the computational procedure combining homogenization theory with digital imaging can proveide estimates of cell level strains within whole bones. Such results may be used to bridge experimental studies of bone adaptation at the whole bone and cell culture level. (c) 1994 John Wiley & Sons, Inc.

Investigation of Laboratory Fatigue Testing Procedures for Asphalt Aggregate Mixtures

The primary purpose of this paper is to evaluate laboratory test procedures for measuring the fatigue response of asphalt paving mixtures. Available test methods are conveniently classified into the following categories: simple flexure, supported flexure, direct axial, diametral, triaxial, fracture mechanics, and wheel‐track testing. Criteria used to evaluate each method for its potential use as a laboratory standard included: (1) Ability to simulate field conditions; (2) applicability of test results for use in modeling pavement performance; and (3) simplicity. The three most promising methods are considered to be simple flexure, diametral fatigue, and tests based on fracture mechanics principles. Although not a fatigue test in itself, direct tension testing offers considerable potential as a simple surrogate for more complex fatigue tests. Finally, in most prior work, the maximum principal tensile strain has been used as the cause or determinant of fatigue damage. Other damage determinants, such as work...

Pectoralis Muscle Force and Power Output During Different Modes of Flight in Pigeons (Columba Livia)

ABSTRACT In vivo measurements of pectoralis muscle force during different modes of free flight (takeoff, level flapping, landing, vertical ascending and near vertical descending flight) were obtained using a strain gauge attached to the dorsal surface of the delto-pectoral crest (DPC) of the humerus in four trained pigeons (Columbalivia). In one bird, a rosette strain gauge was attached to the DPC to determine the principal axis of strain produced by tension of the pectoralis. Strain signals recorded during flight were calibrated to force based on in situ measurements of tetanic force and on direct tension applied to the muscle’s insertion at the DPC. Rosette strain recordings showed that at maximal force the orientation of tensile principal strain was −15° (proximo-anterior) to the perpendicular axis of the DPC (or +75° to the longitudinal axis of the humerus), ranging from +15 to −25° to the DPC axis during the downstroke. The consistency of tensile principal strain orientation in the DPC confirms the more general use of single-element strain gauges as being a reliable method for determining in vivo pectoralis force generation. Our strain recordings show that the pectoralis begins to develop force as it is being lengthened, during the final one-third of the upstroke, and attains maximum force output while shortening during the first one-third of the downstroke. Force is sustained throughout the entire downstroke, even after the onset of the upstroke for certain flight conditions. Mean peak forces developed by the pectoralis based on measurements from 40 wingbeats for each bird (160 total) were: 24.9±3.1N during takeoff, 19.7±2.0N during level flight (at speeds of about 6–9 ms−1 and a wingbeat frequency of 8.6±0.3Hz), 18.7±2.5N during landing, 23.7±2.7N during near-vertical descent, and 26.0±1.8N during vertical ascending flight. These forces are considerably lower than the maximum isometric force (67N, P0) of the muscle, ranging from 28% (landing) to 39% (vertical ascending) of P0. Based on estimates of muscle fiber length change determined from high-speed (200frames s−1) light ciné films taken of the animals, we calculate the mass-specific power output of the pigeon pectoralis to be 51 W kg−1 during level flight (approximately 8ms−1), and 119W kg−1 during takeoff from the ground. When the birds were harnessed with weighted backpacks (50% and 100% of body weight), the forces generated by the pectoralis did not significantly exceed those observed in unloaded birds executing vertical ascending flight. These data suggest that the range of force production by the pectoralis under these differing conditions is constrained by the force–velocity properties of the muscle operating at fairly rapid rates of shortening (4.4 fiberlengths s−1 during level flight and 6.7fiberlengths s−1 during takeoff).

Surface strain on the dorsal metacarpus of thoroughbreds at different speeds and gaits.

Stacked rectangular rosette strain gages were used to measure surface bone strain on the dorsomedial cortex of the third metacarpal bones in 6 adult Thoroughbred horses during treadmill exercise. The peak principal compressive and tensile strains, angle of the peak strains and strain rate during loading were calculated and compared with speed and gait. At speeds from 4 to 14 m/s loading on the metacarpus resulted in compression of the dorsomedial cortex. Tension only occurred consistently in 1 forelimb of 1 horse at the walk (2 m/s). The angle of peak compression was within 10 degrees of the longitudinal axis of the bone, and the magnitude of compression was proportional to the speed of exercise. Mean maximum compressive strains in the 6 horses at 2 m/s were -668 mu strain, -1,204 mu strain at 4 m/s; -1,617 mu strain at 6 m/s; -2,127 mu strain at 8 m/s, and -2,533 mu strain at 10 m/s. Recordings from 3 horses gave a mean -3,206 mu strain at 12 m/s, and strains at 14 m/s approached -4,000 mu strain. Peak strains were similar in both forelimbs at the canter while strain rate tended to be higher in the leading forelimb.