Page 176 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

CHAPTER 7

BIOMECHANICS OF THE

MUSCULOSKELETAL
SYSTEM

Marcus G. Pandy
University of Melbourne, Victoria, Australia

Jonathan S. Merritt
University of Melbourne, Melbourne, Australia

Ronald E. Barr
University of Texas at Austin, Austin, Texas

7.1 INTRODUCTION 153 7.5 MUSCLE ACTIVATION AND
7.2 MECHANICAL PROPERTIES OF SOFT CONTRACTION DYNAMICS 170
TISSUE 155 7.6 DETERMINING MUSCLE FORCE 177
7.3 BODY-SEGMENTAL DYNAMICS 162 7.7 MUSCLE, LIGAMENT, AND
7.4 MUSCULOSKELETAL JOINT-CONTACT FORCES 181
GEOMETRY 164 7.8 REFERENCES 190

7.1 INTRODUCTION

As the nervous system plans and regulates movement, it does so by taking into account the mechan-
ical properties of the muscles, the mass and inertial properties of the body segments, and the exter-
nal forces arising from contact with the environment. These interactions can be represented
schematically as in Fig. 7.1, which suggests that the various elements of the neuromusculoskeletal
system can be compartmentalized and modeled independently.
Muscles provide the forces needed to make movement possible; they transmit their forces to ten-
dons, whose forces in turn cause rotation of the bones about the joints. Muscles, however, are not
simple force generators: the force developed by a muscle depends not only on the level of neural
excitation provided by the central nervous system (CNS), but also on the length and speed at which
the muscle is contracting. Thus, muscles are the interface between the neuromuscular and muscu-
loskeletal systems, and knowledge of their force-producing properties is crucial for understanding
how these two systems interact to produce coordinated movement.
In this chapter, we review the structure and properties of the neuromusculoskeletal system, and
show how the various components of this system can be idealized and described in mathematical terms.

153