Biomechanics of Sports Injury

Sports biomechanics has often been described as having two aims that may
be incompatible: the reduction of injury and the improvement of performance.
The former may involve a sequence of stages that begins with a description
of the incidence and types of sports injury. The next stage is to identify the
factors and mechanisms that affect the occurrence of sports injury. This relates
to the properties of biological materials (Chapter 1), the mechanisms of injury
occurrence (Chapter 2) and the estimation of forces in biological structures
(Chapter 4). The final stage in the prevention sequence relates to measures to
reduce the injury risk. Some of the most important ones from a biomechanical
point of view are considered in Chapter 3. Where necessary, basic
mathematical equations have been introduced, although extensive
mathematical development of the topics covered has been avoided.
In Chapter 1, the load and tissue characteristics involved in injury are
considered along with the terminology used to describe injuries to the human
musculoskeletal system. The most important mechanical properties of
biological and non-biological sports materials are covered. Viscoelasticity
and its significance for biological materials is explained. The composition
and biomechanical properties of bone, cartilage, ligament and tendon, and
their behaviour under various forms of loading, are considered. Muscle
elasticity, contractility, the generation of maximal force in a muscle, muscle
activation, muscle stiffness and the importance of the stretch-shortening cycle
are all described. The chapter concludes with an outline of the ways in which
various factors—immobilisation, age and sex, and exercise—affect the
properties of biological tissue.
Chapter 2 covers the biomechanical reasons why injuries occur in sport,
and the distinction between overuse and traumatic injury is made clear. An
understanding is provided of the various injuries that occur to bone and soft
tissues, including cartilage, ligaments and the muscle-tendon unit, and how
these depend on the load characteristics. The sports injuries that affect the major joints of the lower and upper extremities, and the back and neck, are
also covered. Finally, the effects that genetic, fitness and training factors have
on injury are considered. A glossary of possibly unfamiliar terminology is
provided at the end of this chapter.
Chapter 3 includes a consideration of the important characteristics of a
sports surface and how specific sports surfaces behave. Such surfaces are
often designed with ‘performance enhancement’ as the primary aim rather
than injury reduction. The methods used to assess sports surfaces
biomechanically and the injury aspects of sports surfaces are covered. The
biomechanical requirements of a running shoe are considered, including the
structure of a running shoe and the contribution of its various parts to
achieving the biomechanical requirements of the shoe. The influence of
footwear on injury in sport and exercise, with particular reference to impact
absorption and rearfoot control, is also covered. Attention is given to the
injury moderating role of other sport and exercise protective equipment. The
chapter concludes by providing an understanding of the effects of technique
on the occurrence of musculoskeletal injury in a variety of sports and exercises.
In Chapter 4 the difficulties of calculating the forces in muscles and
ligaments are considered, including typical simplifications made in inverse
dynamics modelling. The equations for planar force and moment calculations
from inverse dynamics for single segments and for a segment chain are
explained, along with how the procedures can be extended to multi-link
systems. The various approaches to overcoming the redundancy (or
indeterminacy) problem are described. The method of inverse optimisation is
covered, and attention is given to an evaluation of the various cost functions
used. The uses and limitations of EMG in estimating muscle force are outlined.
Finally a rare example of muscle force calculations from a cine film recording
of an activity where an injury occurred is considered. The limitations that
exist, even when this information is available, are highlighted.

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