Introduction to Biomechanics

Marcos Duarte
Laboratory of Biomechanics and Motor Control (http://demotu.org/)
Federal University of ABC, Brazil

Biomechanics

Biomechanics is the study of the structure and function of biological systems by means of the methods of mechanics.
(Herbert Hatze, 1974)

Biomechanics is fundamental for all fields of science and technology related to biology and health and it's also relevant for the development of synthetic systems inspired on biological systems, e.g., in robotics.

Branches of Mechanics (ergo, add bio- for biomechanics)

Mechanics is a branch of the physical sciences that is concerned with the state of rest or motion of bodies that are subjected to the action of forces. In general, this subject can be subdivided into three branches: rigid-body mechanics, deformable-body mechanics, and fluid mechanics (Hibbeler, 2012).
In fact, only a subset of Mechanics matters to Biomechanics, the Classical Mechanics subset, the domain of mechanics for bodies with moderate speeds $(\ll 3.10^8 m/s!)$ and not very small $(\gg 3.10^{-9} m!)$ as shown in the following diagram:

Domains of mechanics
Figure. Domain of validity for Classical Mechanics (image from Wikipedia).

Biomechanics and the Biomedical Engineering at UFABC (2016)

At the university level, the study of Mechanics is typically done in the disciplines Statics and Dynamics (rigid-body mechanics), Strength of Materials (deformable-body mechanics), and Mechanics of Fluids (fluid mechanics). Consequently, the study on Biomechanics must also cover these topics for a greater understanding of the structure and function of biological systems.

The Biomedical Engineering degree at UFABC covers these topics for the study of biological systems in different courses: Ciência dos Materiais Biocompatíveis, Modelagem e Simulação de Sistemas Biomédicos, Métodos de Elementos Finitos aplicados a Sistemas Biomédicos, Mecânica dos Fluidos, Caracterização de Biomateriais, Sistemas Biológicos, and last but not least, Princípios e Aplicações de Biomecânica.
How much of biological systems is in fact studied in these disciplines varies a lot. Anyway, none of these courses cover the study of human motion with implications to health, rehabilitation, and sports, except the last course. This is the reason why the course Princípios e Aplicações de Biomecânica focuses on the analysis of the human movement.

Biomechanics & (Human) Movement Science

Movement science will be one of the most important and most recognized science fields in the twenty-first century... The future discipline of movement science has a unique opportunity to become an important contributor to the well-being of mankind.
Nigg BM (1993) Sport science in the twenty-first century. Journal of Sports Sciences, 77, 343-347.

On the branches of Mechanics and Biomechanics

Nowadays, (Classical) Mechanics is typically partitioned in Statics and Dynamics. In turn, Dynamics is divided in Kinematics and Kinetics. This classification is clear; dynamics is the study of the motions of bodies and Statics is the study of forces in the absence of changes in motion. Kinematics is the study of motion without considering its possible causes (forces) and Kinetics is the study of the possible causes of motion.

Nevertheless, it's common in Biomechanics to adopt a slightly different classification: to partition it between Kinematics and Kinetics, and then Kinetics into Statics and Dynamics (David Winter, Nigg & Herzog, and Vladimir Zatsiorsky, among others, use this classification in their books). The rationale is that we first separate the study of motion considering or not its causes (forces). The partition of (Bio)Mechanics in this way is useful because is simpler to study and describe (measure) the kinematics of human motion and then go to the more complicated issue of understanding the forces related to the human motion.

Anyway, these different classifications reveal a certain contradiction between Mechanics (particularly from an engineering point of view) and Biomechanics; some scholars will say that the naming in Biomechanics is simply wrong and it should be corrected to align with the Mechanics. Be aware.

More on Biomechanics

The Wikipedia page on biomechanics is a good place to start:

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See these introductory videos about biomechanics:

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History of biomechanics

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IFrame('http://courses.washington.edu/bioen520/notes/History_of_Biomechanics_(Martin_1999).pdf',
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The International Society of Biomechanics

The biomechanics community has an official scientific society, the International Society of Biomechanics, with a journal, the Journal of Biomechanics, and an e-mail list:

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Topics covered in the Journal of Biomechanics

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Some examples in Biomechanics

The possibilities of applying Biomechanics to the understanding of living systems are endless.
Let me show a few examples I've been involved with.

Biomechanics of walking in shallow water

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YouTubeVideo('ahmJeCJX3F8', width=640, height=360, rel=0)
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IFrame('http://ebm.ufabc.edu.br/publications/md/JB11b.pdf', width='100%', height=400)
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Biomechanics of the bicycle kick in football

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IFrame('http://demotu.org/x/pele/', width='100%', height=400)
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IFrame('http://demotu.org/pubs/CH14.pdf', width='100%', height=400)
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Problems

  1. Go to Biomechanics Classes on the Web to visit websites of biomechanics classes around the world and find out how biomechanics is studied in different fields.
  2. Find three more examples of applications of biomechanics in different areas.
  3. Watch the video The Weird World of Eadweard Muybridge to learn about Eadweard Muybridge, an important person to the development of instrumentation for biomechanics.
  4. Think about practical problems in nature that can be studied in biomechanics with simple approaches (simple modeling and low-tech methods) or very complicated approaches (complex modeling and high-tech methods).
  5. What the study in the biomechanics of athletes, children, elderlies, persons with disabilities, other animals, and computer animation for the cinema industry may have in common and different?
  6. Is there anything in biomechanics that interests you? How could you pursue this interest?

References