Nature's Machines

An Introduction to Organismal Biomechanics

David E. Alexander

• Publisher: Academic Press
• Year: 2017
• ISBN:
  9780128498972
• Topic: Biological Sciences
• Subtopic: Evolution
• Index: Biological Sciences

Nature's Machines: An Introduction to Organismal Biomechanics presents the fundamental principles of biomechanics in a concise, accessible way while maintaining necessary rigor. It covers the central principles of whole-organism biomechanics as they apply across the animal and plant kingdoms, featuring brief, tightly-focused coverage that does for biologists what H. M. Frost's 1967 Introduction to Biomechanics did for physicians. Frequently encountered, basic concepts such as stress and strain, Young's modulus, force coefficients, viscosity, and Reynolds number are introduced in early chapters in a self-contained format, making them quickly available for learning and as a refresher.

More sophisticated, integrative concepts such as viscoelasticity or properties of hydrostats are covered in the later chapters, where they draw on information from multiple earlier sections of the book. Animal and plant biomechanics is now a common research area widely acknowledged by organismal biologists to have broad relevance. Most of the day-to-day activities of an animal involve mechanical processes, and to the extent that organisms are shaped by adaptive evolution, many of those adaptations are constrained and channelized by mechanical properties. The similarity in body shape of a porpoise and a tuna is no coincidence.

Many may feel that they have an intuitive understanding of many of the mechanical processes that affect animals and plants, but careful biomechanical analyses often yield counterintuitive results: soft, squishy kelp may be better at withstanding pounding waves during storms than hard-shelled mollusks; really small swimmers might benefit from being spherical rather than streamlined; our bones can operate without breaking for decades, whereas steel surgical implants exhibit fatigue failures in a few months if not fully supported by bone.

• Offers organismal biologists and biologists in other areas a background in biomechanics to better understand the research literature and to explore the possibility of using biomechanics approaches in their own work
• Provides an introductory presentation of the everyday mechanical challenges faced by animals and plants
• Functions as recommended or required reading for advanced undergraduate biology majors taking courses in biomechanics, supplemental reading in a general organismal biology course, or background reading for a biomechanics seminar course

Chapter 1

Introduction and Physics Review

Abstract

This chapter opens with a general definition of biomechanics and then compares the various applied biomechanics subdisciplines—clinical biomechanics, biomedical engineering, sports biomechanics—with the main subject of this book, organismal biomechanics. It then looks briefly at the early history of biomechanics in general. This is followed by a description of pioneering early work in organismal biomechanics in the 1950s. Next is a sampling of the researchers and their topics during the great expansion of organismal biomechanics in the 1960s through the 1980s, including a list of several influential books those researchers published during this period. The second section reviews basic Newtonian mechanics, which is the branch of physics of relevance to biomechanics. The review includes topics such as vectors and scalars, work and energy, Newton's three laws of motion, forces and accelerations and related quantities, and mass versus weight (and why the distinction matters). It concludes with a brief discussion of the importance of proper units.

Keywords

Biomechanics history; Comparative biomechanics; Mass units; Newtonian mechanics; Newton's laws; Physics review; SI units; Weight units

1.1. What Is Biomechanics?

A dictionary might define biomechanics as “the mechanics of biological activity” (Mish, 1983). Most scientists who actually perform biomechanics research tend to describe biomechanics as something like engineering in reverse: engineers are given a task and they design a device to carry out the task, whereas biomechanics researchers have the “device” (an organism) and they seek to understand its mechanical properties and constraints, and how it operates. Nowadays, at least for nonhuman organisms, this is usually put in an evolutionary framework—what are the benefits that might have selected for a given mechanical arrangement, and how does that arrangement compare to those of the organism's relatives? Traditionally, biomechanists have said that they take engineering approaches and techniques and apply them to help understand how organisms work. In recent decades, many biomechanics researchers have actually moved beyond standard engineering approaches and developed new methods better suited to biological subjects, as we will see in later chapters.

Under the subject listing of “biomechanics,” the catalog of a typical university library will group together books in several areas. One of these areas will be clinical or medical biomechanics; the wonderfully concise book Introduction to Biomechanics by Frost (1967) in this area was part of the inspiration for this book. Clinical biomechanics focuses on humans, only involving nonhumans to the extent that they help understand human mechanics. This area was originally developed by and for surgeons, who needed to know how their surgical interventions affected a patient's ability to function mechanically. As artificial joints and other musculoskeletal repairs and implants came into use, the focus of clinical biomechanics shifted toward orthopedic medicine, as well as analyzing normal body structure and movements, and the mechanical consequences of pathological conditions.

Clinical biomechanics overlaps considerably with biomedical engineering; many books on the latter will also be found under the “biomechanics” subject heading. Biomedical engineers design medical equipment, including prosthetics, implantable devices, surgical equipment and processes, ultrasonic and other imaging systems, and devices for treatment and rehabilitation such as dialysis machines and physical therapy equipment, among many other things. Biomedical engineers also perform the same sorts of analyses on body structure and movement as do clinical biomechanics researchers, but with a more engineering-oriented perspective. Biomedical engineers and clinical biomechanists often form part of a research team, bringing a variety of approaches to a research problem.

Another large cluster of books under the “biomechanics” heading in the library catalog consists of those aimed at sports, athletic performance and training, and general human fitness. Sports biomechanics is largely focused on improving athletic performance or reducing sports injuries. For example, research on the mechanics of running led to improvements in both running shoes and resilient running tracks. Part of the goal was to try to increase running speeds, but what was originally a side benefit of reducing running-related injuries has now become a major priority. Sports biomechanics has focused heavily on running and swimming, but it has also produced some fascinating results in areas such as the sensory tasks involved in batting and catching high fly balls in baseball (e.g., Cross, 2011; Higuchi et al., 2016).

Taken together, these three human-oriented areas—clinical biomechanics, sports biomechanics, and biomedical engineering—make up applied biomechanics. Each area has its own specialist practitioners and its own types of problems, but they overlap a fair amount. Sports biomechanics encompasses some of the same topics as clinical biomechanics, especially in the area of normal locomotion mechanics. Understanding the mechanics of human locomotion may be just as important for researchers designing prosthetic limbs as for those working on improved athletic shoes. Indeed, sports and clinical biomechanics merge in physical therapy and rehabilitation research.

Perhaps the smallest cluster of “biomechanics” books in the university library consists of those books on the biomechanics of nonhuman organisms. This discipline was originally called “comparative biomechanics” to distinguish it from applied biomechanics, just as “comparative physiology” traditionally referred to physiology of nonhuman animals. More recently, some systematists^a co-opted “comparative” as used in the phrase “the comparative method” to describe a particular phylogenetic approach to biological research (Felsenstein, 1985), quite unrelated to the traditional “comparative” versus “applied” meaning. To avoid any confusion, I prefer the term organismal biomechanics. As generally understood by scientists, comparative or organismal biomechanics focuses on macroscopic organisms, essentially macroscopic animals and plants. Certainly microscopic organisms experience mechanical processes and possess mechanical properties, but those processes and properties are so different from the mechanics of macroscopic organisms that they represent a completely different subset of mechanics. So this book will focus on the mechanics of macroscopic animals and plants.

The dictionary definition of “biophysics” is “the application of physical principles and methods to biological problems” (Mish, 1983). In spite of this definition, biomechanics in practice is not a subdiscipline of biophysics. Re...

Table of contents

• Cover image
• Title page
• Table of Contents
• Dedication
• Copyright
• Preface
• Chapter 1. Introduction and Physics Review
• Chapter 2. Solid Materials
• Chapter 3. Fluid Biomechanics
• Chapter 4. Biological Materials Blur Boundaries
• Chapter 5. Systems and Scaling
• Chapter 6. Organismal Versus Technological Design
• Bibliography
• Index