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Papers by John Bertram

T h i s study a p p l i e d an e n g i n e e r i n g -fracture nfechanics approach t o the i n v ... more T h i s study a p p l i e d an e n g i n e e r i n g -fracture nfechanics approach t o the i n v e s t i g a t i o n of the f r a c t u r e r e s i s t a n c e of Equine hoof w a l l . The f r a c t u r e mechanics parameters of s t r e s s i n t e n s i t y f a c t o r (K), s t r a i n energy r e l e a s e r a t e (G) and the J i n t e g r a l (J) were used t o determine the e f f e c t of notch o r i e n t a t i o n and specimen h y d r a t i o n on f r a c t u r e , u s i n g the compact t e n s i o n t e s t geometry. The J i n t e g r a l was found t o pr o v i d e the best i n d i c a t i o n of f r a c t u r e behaviour because i t i s not based on s t r i c t l i n e a r e l a s t i c behaviour, as are K and G. Hoof wall has g r e a t e s t f r a c t u r e r e s i s t a n c e f o r c r a c k s running v e r t i c a l l y , p a r a l l e l t o the t u b u l a r s t r u c t u r e s found i n hoof wall k e r a t i n . For f u l l y hydrated m a t e r i a l t e s t e d i n t h i...

Journal of Experimental Biology, 1987

Tensile moduli and J-integral fracture toughness values were determined for horse hoof-wall kerat... more Tensile moduli and J-integral fracture toughness values were determined for horse hoof-wall keratin at four hydration levels. The stiffness of hoof-wall was influenced by water content to a greater degree than is the stiffness of other mammalian hard keratins. Young’s modulus increased from 410 MPa at 100 % relative hydration (RH) to 14·6 GPa at 0% RH. Fracture toughness was maximal (22·8 kJ m−2) at an intermediate hydration (75% RH), which represents a two-fold increase over both fully hydrated and dehydrated material. Maximum fracture toughness occurred at a hydration level which is within the range that has been found in vivo in the hoof wall. These results lead to the hypothesis that the density of secondary bonding sites within the hoof-wall keratin matrix proteins provides the hoof organ with the means to modulate tissue properties, even though this epidermal tissue functions after the cells have died.

Journal of Experimental Biology, 1986

An engineering fracture mechanics approach was applied to the analysis of the fracture resistance... more An engineering fracture mechanics approach was applied to the analysis of the fracture resistance of equine hoof-wall. The relationship between fracture toughness and the morphological organization of the keratin hoof tissue was investigated. Fracture toughness was evaluated using the J-integral analysis method which employs the compact tension test geometry. Tensile tests were also conducted to evaluate the effect of the morphological organization on the stress-strain behaviour. Hoof-wall has greatest fracture resistance for cracks running proximally, parallel to the tubular component of the wall keratin. For fully hydrated material tested in this direction the mean critical J-integral value at failure was 1·19× 104 J m−2. This was nearly three times greater than the value determined for the weakest orientation, in which the crack ran parallel to the material between the tubules. The lower fracture toughness of the intertubular material dominates the fracture behaviour of this tiss...

Journal of Experimental Biology, 2018

This study examined the mechanics of the horizontal to vertical transition used by parkour athlet... more This study examined the mechanics of the horizontal to vertical transition used by parkour athletes in wall climbing. The study serves as an alternative assessment of leg control strategy for a task related to normal running, but where the functional options differ substantially, so can expose the movement control priorities required to successfully complete the task. Ground reaction forces were measured in several expert parkour athletes and centre of mass trajectory was calculated from force plates embedded in the ground and the wall. Empirical measures were compared with movements predicted by a work-based control optimization model. The model captured the fundamental dynamics of the transition, so allowed an exploration of parameter sensitivity for success at the maneuver (run-up speed, foot placement, etc.). The optimal transition of both the model and the parkour athletes used a common intermediate run-up speed and appears determined largely by a trade-off of positive and nega...

2013 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2013

Osteoarthritis and Cartilage, 2013

Objective: Develop a sensitive, functional biomarker of persistent joint pain in a large animal m... more Objective: Develop a sensitive, functional biomarker of persistent joint pain in a large animal model of experimental osteoarthritis. Evaluate Impulse Ratio as a measure of weight distribution among supporting limbs throughout the early natural history of osteoarthritis and with local anaesthesia and analgesia. Design: The distribution of weight bearing in the trot of 11 skeletally-mature dogs was analyzed before and after unilateral surgical intervention (cranial cruciate transection or distal femoral focal impact). The short-term effects of two analgesic treatments (intra-articular lidocaine and intra-dermal meloxicam) were then evaluated as an index of pain relief based on the redistribution of weight-bearing impulse between normal and injured limbs. Results: Impulse Ratio was able to resolve weight redistribution between limbs in both long-term (weekly for over 400 days) and short-term (15 min intervals) joint evaluations. Joint pain relief from lidocaine administration could be reliably tracked over its brief acting time course. Meloxicam administration resulted in ambiguous results, where average weight bearing in the injured limb did not increase, but the variability of limb use changed transiently and reversibly. Conclusion: Joint function and the role of persistent joint pain in the development of osteoarthritis can be investigated effectively and efficiently in a large animal model through the use of Impulse Ratio. Impulse Ratio can be a functionally relevant and sensitive biomarker of locomotion-related joint pain.

Journal of Morphology, 2001

The semispinalis capitis and splenius muscles of the horse were analyzed for gross morphology, mi... more The semispinalis capitis and splenius muscles of the horse were analyzed for gross morphology, microarchitecture, fiber length, and fiber type. Although these two muscles are similar in size and anatomical position, they are very different from one another in structural design and histochemistry, implying diverse functional roles in the animal's behavior. The histochemical staining profile was limited to two fiber types: slow oxidative and fast glycolytic. The splenius muscle has simple architecture, long fibers, and a 60/40 ratio of SO to FG cross-sectional area. The semispinalis capitis has complex architecture with short-fibered, concentric compartments dorsal to its central tendon and longer-fibered compartments ventrally. The entire dorsal region has an increasing gradient of slow oxidative fiber percentage from caudal to cranial (58-71% SO). In contrast, the ventral region has a decreasing gradient of slow oxidative fibers from caudal to cranial (48-67% FG). These patterns can be interpreted within the context of the cervical musculature during locomotion and posture to indicate the functional advantages of this organization.

American Zoologist, 1998

Movement is fundamental to survival and reproduction of all animals. Most animals must possess th... more Movement is fundamental to survival and reproduction of all animals. Most animals must possess the machinery to support and move organelles, cells, parts of the organism, and the entire organism. In multicellular animals support and movement are accomplished by specialized tissues, including, muscles, bones, tendons, and other connective tissues. These tissues must operate as integrated components to provide appropriate functional capabilities to the system. The symposium from which the following several papers are drawn focused on muscle. However the basic philosophy that brought the participants together was that muscle function must be integrated into the context of the multiple systems that are needed to accomplish movement. Only with an integrated approach can we hope to understand the specialization of muscle by natural selection to suit its function in vivo. We are now the beneficiaries of several centuries of investigation into the details of muscle function, with particularly important insight coming in the past 70 years. A change in our understanding of muscle function began in the early part of this century with the pioneering experimental analyses of A. V. Hill. This work denned the basic contractile properties of muscles at a

Summary Surface strains were recorded from four rosette gauges at different sites on the right fo... more Summary Surface strains were recorded from four rosette gauges at different sites on the right forehooves of three ponies running on a treadmill at seven constant speeds and using three gaits. Principal strains determined from the rosette signals indicate that the hoof material is loaded predominantly in compression and that the wall is distorted in a regular, repeatable manner at all speeds and gaits. Peak principal strains reach -5000 f.ie, compared with -2800^(6 reported for the equine radius under similar locomotory conditions. Orientations of peak compressive strains do not correlate strongly with microstructural axes in the material. Comparison of our in vivo strain records with previous in vitro studies of the material properties of the wall shows that hoof keratin behaves as a multidirectional composite, capable of tolerating its usual operating strains in any direction. This mechanical behaviour also allows the material to withstand many unpredictable loading situations whe...

Journal of Experimental Biology, 2007

Journal of Experimental Biology, 2013

Summary As one of the most energetically demanding daily activities, locomotion has attracted sub... more Summary As one of the most energetically demanding daily activities, locomotion has attracted substantial investigative attention. Although legged locomotion has been well described, it is currently not well understood. Looking at energy accounting might be a good pathway with which to solve this problem. One relatively simple way of analyzing energy management is to look directly at the flow of mechanical energy into and out of the system, in terms of costs and losses (with some attention to the mechanisms responsible for this flow). In this commentary we argue that a key source of energetic loss has largely been neglected: the redirection of body motion from downward to upward at each step. We discuss the role of this loss and the compensating energetic costs, identifying some of the general features of the trade-offs that determine gait optimization strategies. We find that even at a conceptual level, a focus on the main mechanism of loss and the strategies available to the organ...

Advances in physiology education, 2002

Proceedings of the Royal Society B: Biological Sciences, 2013

This study compares human walking and running, and places them within the context of other mammal... more This study compares human walking and running, and places them within the context of other mammalian gaits. We use a collision-based approach to analyse the fundamental dynamics of the centre of mass (CoM) according to three angles derived from the instantaneous force and velocity vectors. These dimensionless angles permit comparisons across gait, species and size. The collision angle Φ , which is equivalent to the dimensionless mechanical cost of transport CoT mech , is found to be three times greater during running than walking of humans. This threefold difference is consistent with previous studies of walking versus trotting of quadrupeds, albeit tends to be greater in the gaits of humans and hopping bipeds than in quadrupeds. Plotting the collision angle Φ together with the angles of the CoM force vector Θ and velocity vector Λ results in the functional grouping of bipedal and quadrupedal gaits according to their CoM dynamics—walking, galloping and ambling are distinguished as s...

Journal of The Royal Society Interface, 2011

The analysis of terrestrial locomotion over the past half century has focused largely on strategi... more The analysis of terrestrial locomotion over the past half century has focused largely on strategies of mechanical energy recovery used during walking and running. In contrast, we describe the underlying mechanics of legged locomotion as a collision-like interaction that redirects the centre of mass (CoM). We introduce the collision angle, determined by the angle between the CoM force and velocity vectors, and show by computing the collision fraction, a ratio of actual to potential collision, that the quadrupedal walk and gallop employ collision-reduction strategies while the trot permits greater collisions. We provide the first experimental evidence that a collision-based approach can differentiate quadrupedal gaits and quantify interspecific differences. Furthermore, we show that this approach explains the physical basis of a commonly used locomotion metric, the mechanical cost of transport. Collision angle and collision fraction provide a unifying analysis of legged locomotion whi...

Equine Veterinary Journal, 2007

Reasons for performing study: Racing and training related lesions of the forelimb superficial dig... more Reasons for performing study: Racing and training related lesions of the forelimb superficial digital flexor tendon are a common career ending injury to racehorses but aetiology and/or predisposing causes of the injury are not completely understood. Objectives: Although the injury takes place within the tendon, the lesion must be considered within the context of the function of the complete suspensory system of the distal limb, including the associated muscles. Methods: Both muscle and tendon function were investigated in vivo using implanted strain gauges in 3 Thoroughbred horses walking, trotting and cantering on a motorised treadmill. These data were combined with assessments of muscle architecture and fibre composition to arrive at an overview of the contribution of each muscle-tendon unit during locomotion. Results: The superficial digital flexor muscle has fatigueresistant and high force production properties that allow its tendon to store and return elastic energy, predominantly at the trot. As running speed increases, deep digital flexor tendon force increases and it stabilises hyperextension of the fetlock, thus reinforcing the superficial digital flexor in limb load support. The deep digital flexor muscle has fast contracting properties that render it susceptible to fatigue. Conclusion: Based on these measurements and supporting evidence from the literature, it is proposed that overloading of the superficial digital flexor tendon results from fatigue of the synergistic, faster contracting deep digital flexor muscle. Potential relevance: Future research investigating distal limb system function as a whole should help refine clinical diagnostic procedures and exercise training approaches that will lead to more effective prevention and treatment of digital flexor tendon injuries in equine athletes.

BMC Musculoskeletal Disorders, 2010

BackgroundAs a relatively non-regenerative tissue, articular cartilage has been targeted for cryo... more BackgroundAs a relatively non-regenerative tissue, articular cartilage has been targeted for cryopreservation as a method of mitigating a lack of donor tissue availability for transplant surgeries. In addition, subzero storage of articular cartilage has long been used in biomedical studies using various storage temperatures. The current investigation studies the potential for freeze-thaw to affect the mechanical properties of articular cartilage through direct comparison of various subzero storage temperatures.MethodsBoth subzero storage temperature as well as freezing rate were compared using control samples (4°C) and samples stored at either -20°C or -80°C as well as samples first snap frozen in liquid nitrogen (-196°C) prior to storage at -80°C. All samples were thawed at 37.5°C to testing temperature (22°C). Complex stiffness and hysteresis characterized load resistance and damping properties using a non-destructive, low force magnitude, dynamic indentation protocol spanning a b...

Journal of experimental biology, 1993

Summary Bones are believed to alter their shape in response to changes in tissue strains produced... more Summary Bones are believed to alter their shape in response to changes in tissue strains produced by physical activity and the goal of this study is to examine whether modeling responses of a growing bone to changes in physical exercise are adjusted to maintain a uniform ...

A person constrained to walk at a given speed v on a treadmill, chooses a particular step frequen... more A person constrained to walk at a given speed v on a treadmill, chooses a particular step frequency f and step length d"v/f. Testing over a range of speeds generates a speed}frequency (v}f) relationship. This relationship is commonly posited as a basic feature of human gait. It is often further posited that this curve follows from minimum energy cost strategy. We observed that individuals walking under di!erent constraint circumstances*walking to a range of "xed metronome frequencies ("xed f) or over a range of spaced markers ("xed d)*produce speed}frequency relations distinct from the constrained v relation. We show here that three distinct speed}frequency curves, similar to those observed, are predicted by the assumption that a walking person optimizes an underlying objective function F (v, f) that has a minimum at the preferred gait. Further, the metabolic cost of transport is a reasonable approximate candidate for the function F.