Feedback and communication of model results. Section Two: Biomechanics of musculoskeletal injury. Injuries in sport. Properties of materials. Calculating the loads. Biomechanical factors affecting sports injury. Customer Reviews Average Review. See All Customer Reviews. Shop Textbooks. Add to Wishlist. USD Ship This Item — This item is available online through Marketplace sellers.
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Temporarily Out of Stock Online Please check back later for updated availability. Overview This advanced text is the companion volume to Introduction to Sports Biomechanics , also written by Roger Bartlett. Product Details Table of Contents.
Table of Contents Section One: Biomechanical analysis and optimisation of sports techniques. Average Review. Write a Review. Related Searches. Furthermore, muscle and reflex properties and the central nervous system interact in determining how stiffness affects the control of movement Gottlieb, The mechanisms thought to be involved are elastic energy storage and release mostly in tendon , and reflex potentiation e. Komi, The stretch-shortening effect has not been accurately measured or fully explained. It is important not only in research but also in strength and power training for athletic activities.
Some evidence shows that muscle fibres may shorten whilst the whole muscle-tendon unit lengthens. Furthermore, the velocity of recoil of the tendon during the shortening phase may be such that the velocity of the muscle fibres is less than that of the muscle-tendon unit. The result would be a shift to the right of the force-velocity curve of the contractile element Gregor, , similar to Figure 1. These interactions between tendinous structures and muscle fibres may substantially affect elastic and reflex potentiation in the stretchshortening cycle, whether or not they bring the muscle fibres closer to their optimal length and velocity Huijing, There have been alternative explanations for the phenomenon of the stretch-shortening cycle e.
Differences of opinion also exist on the amount of elastic energy that can be stored compare van Ingen Schenau, with Alexander, and its value in achieving maximal performance e. Zajac, The creation of larger muscle forces in, for example, a countermovement jump compared with a squat jump is probably important both in terms of the pre-load effect e. Force enhancement occurs in dynamic concentric contractions after stretch, such that the force-velocity relationship shifts towards increasing forces at any given velocity Chapman, Figure 1.
Sports biomechanics : reducing injury risk and improving
The effects of this force enhancement on the tension-velocity and tension-length curves of human muscle in vivo has yet to be fully established. The elastic modulus of the anterior longitudinal ligament of the spine is Obviously, the mechanical properties of ligaments, and other biological tissues, vary with species, donor history and age, and testing procedures.
As with cartilage Figure 1. The histological make-up of ligaments varies from those having largely elastic fibres, such as the ligamentum flavum, to cord-like thickenings of collagen. Because of their non-linear tensile properties Figure 1. The stiffness of the ligament initially increases with the force applied to it.
The tropocollagen molecules are organised into cross-striated fibrils, which are arranged into fibres. When unstressed, the fibres have a crimped pattern owing to cross-linking of collagen fibres with elastic and reticular ones. This crimped pattern is crucial for normal joint mobility as it allows a limited range of almost unresisted movement.
If displaced towards the outer limit of movement, collagen fibres are recruited from the crimped state to become straightened, which increases resistance and stabilises the joint. In addition, ligament mechanoreceptors may contribute to maintenance of joint integrity by initiating the recruitment of muscles as dynamic stabilisers Grabiner, Daily activities, such as walking and jogging, are usually in the toe of the stress—strain curve Figure 1. Strenuous activities are normally in the early part of the linear region Hawkings, The ratedependent behaviour of ligaments may be important in cyclic activities where ligament softening—the decrease in the peak ligament force with successive cycles—may occur.
The implications of this for sports performance are not yet known Hawkings, Tendon tissue is similar to that of fascia, having a large collagen content. Collagen is a regular triple helix with cross-links, giving a material and associated structures of great tensile strength that resists stretching if the fibres are correctly aligned. Tendons are strong; however, no consensus exists on the ultimate tensile stress of human tendon.
The value of between 49 MPa and 98 MPa for mammalian tendon cited in Curwin and Stanish is less than the value of MPa reported by them for the Achilles tendon in fast running, assuming a cross-sectional area of 75mm2. This discrepancy was attributed by them to the strain-rate-dependent properties of tendon.
However, the value is within the band of 45— MPa reported by Woo for human tendon. Tendon is a relatively stiff material, having an elastic modulus of MPa—2GPa. The stiffness is smaller for low loads as the collagen crimping pattern causes a less steep gradient of the load—extension and stress—strain curves in the toe region Figure 1. The compliance elasticity of tendon is important in how tendon interacts with the contraction of muscle tissue. When the tendon compliance is high, the change in muscle fibre length will be small compared to the length change of the whole muscle— tendon unit.
As well as having a relatively high tensile strength and stiffness, tendon is resilient, having a relative hysteresis of only 2. Within the physiological range, this represents a limited viscoelastic behaviour for a biological material Herzog and Loitz, Because of this, tendon is often considered the major site within the muscle-tendon unit for the storage of elastic energy. It should be noted that the energy storage is likely to be limited unless the tendon is subject to large forces, as in the eccentric phase of the stretch-shortening cycle Huijing, Immobilisation of ligaments causes a reduction in both their failure strength and the energy absorption before failure.
Sports Biomechanics : Reducing Injury Risk and Improving Sports Performance
This leads to an increase in joint stiffness and injury susceptibility, and it takes longer to regain than to lose tissue strength Hawkings, Immobilisation of bone weakens the cortex and thereby affects the strength of the ligament—bone junction. The effects of immobilisation on bone are generally the opposite to the beneficial effects of exercise see below. Bone atrophy occurs, with the mass and size of the bone decreasing through the loss of equal proportions of bone matrix and mineral content Booth and Gould, Significant individual age and sex variations occur, in both the rate of development and the final mass and density.
Some disagreement exists about whether bone mass peaks at a particular age or simply reaches a plateau starting from an age of 20—25 years and ending at 35— The loss of cortical bone density 1. Continuous excessive pressure on bones causes atrophy; intermittent pressure leads to the formation of spurs and bridges arthritis to compensate for deterioration of cartilage.
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As bones age they experience a decrease in compressive strength and fracture more easily; this is more marked in females than in males. The loss of strength is a combination of the bones becoming thinner and an increasing number of calcified osteons leading to brittleness Edington and Edgerton, The mechanical properties of collagenous tissue show increases in ultimate stress and elastic modulus during growth.
Sports biomechanics : reducing injury risk and improving sports performance
Reductions in these properties, owing to fewer cross-links, occur during further ageing. The decrease in stiffness and the lower failure load with ageing for ligaments, for example, may be linked to a decrease in physical activity. Degeneration begins early, with the central artery disappearing from tendons as early as the age of Until this time, tendon is more resistant to tension than is bone; this explains the increased frequency of avulsion fractures in the young.
Preventive training includes training of muscle, mobility and flexibility, and coordination. Warm-up and cool-down are also considered to be important features of injury prevention Kannus, a , although there are few conclusive laboratory and clinical studies to show that these do prevent injury Best and Garrett, a.
Attention needs to be paid not only to the intensity and duration of training, but also to the repetitions within an exercise period and the rest between periods, because of the reduced ultimate strength of tissues for repeated compared with single loading Nigg, Normal compressive forces, and tensile forces caused by muscle action, create an electrical potential which induces bone growth.
This may explain why people who are physically active have significantly greater bone densities than those who are less active Kannus, b. The long bones of the extremities, in particular, are highly responsive to changes in mechanical loading—they increase in both size and mineralisation and undergo substantial cortical remodelling.
How mechanical change affects remodelling, and the identity and manner of the response of cells initially receptive to that change, remain to be fully established. Cyclic bending strain may be a mechanism to account for selective bone remodelling Zernicke, It has been reported that high intensity training leads to an increase in bone density, but that low to moderate intensity training has no such effect. Low intensity training promotes increases in bone length and growth in the growing athlete, but relatively high intensity training inhibits these Booth and Gould, It has often been reported e.
Booth and Gould, that exercise leads to hypertrophy of ligaments and tendons, with increased stiffness, ultimate strength and energy-to-failure, as well as some increase in mass. Junction strength changes are related to the type of exercise regimen as well as its duration; endurance training before trauma may lead to increased junction strength after repair Booth and Gould, Within its elastic limits, cartilage increases in thickness with short-and long-term exercise, and this is accompanied by an increased elasticity Nigg, Connective tissue can experience stress relaxation and creep during exercise.
Cyclic loading of such tissues with a fixed displacement, as through activities such as running and swimming, can lead to stress relaxation and a reduction of tissue load. Increased ligamentous laxity after exercise is an example of the creep properties of tissue Best and Garrett, a. Training can increase muscle strength though physiological adaptations, related to an increase in muscle mass, an improved recruitment pattern and a change in fibre orientation Nigg, The physiological mechanisms stimulated depend on the specific form of training, as this affects the patterns of motor unit activation Kraemer et al.
Kawakami et al. The muscle force-time curve is sensitive to heavy resistance and explosive training, which has even more effect on the force-time curve than on muscle structure Komi, The length-feedback component of the muscle spindle response has been claimed to be trainable, increasing the muscle spindle discharge for the same stretch.
It has also been hypothesised that training can decrease the force-feedback component of the Golgi tendon organs. Neural adaptations also occur to muscle with training Enoka and Fuglevand, These include increases in the maximal voluntary contraction MVC , without any size increase of the muscle, with short-term training and after mental MVC training. Passive stretching of the muscle-tendon unit can alter its failure properties, with stress relaxation being greatest during the early part of the stretch. A series of short stretches results in greater adaptation than one held over a longer time.
Stretching also increases the length of ligaments. The maximum isometric force developed by a muscle changes little with temperature, although the contraction speed increases and the time to reach peak tension decreases as the temperature is raised.
The mechanical properties of connective tissue can be altered, through combined temperature and load changes, to increase joint range of motion; this might support the use of a warm-up routine followed by stretching Best and Garrett, a. In this chapter the biomechanical reasons why injuries occur in sport were covered. The most important mechanical properties of sports materials were considered. Viscoelasticity, and its significance for biological materials, was explained. The composition and biomechanical properties of bone, cartilage, ligament and tendon, and their behaviour under various forms of loading, were considered.
Muscle elasticity contractility, the generation of maximal force in a muscle, muscle activation, muscle stiffness and the importance of the stretch-shortening cycle were all described. Finally, the ways in which various factors—immobilisation, age, sex, exercise and training—affect the properties of biological tissue were outlined. Provide a biomechanical subdivision of the factors that affect injury and list the factors in each category.
Give your opinion about which of these are intrinsic and which extrinsic to the sports participant. Define stress and strain and provide clear diagrams of the different types of loading. Using a clearly labelled stress-strain diagram for a typical non-biological material, explain the material properties related to elasticity and plasticity. List, and briefly explain, what would be the most important properties for materials for use in: a vaulting pole, a racing bicycle frame, the frame of a squash racket, rowing oars, skis.