Biomechanics of Human Movement

Introduction

In recent years, the discipline of biomechanics has undergone significant growth. Technological advancements in microcomputers, video analysis and laboratory data acquisition hardware have provided tools for improved biomechanical research and instructional programs (Figure 1-1). These tools can be applied to the study of human movement in a wide range of settings – from the detailed analysis of Olympic athletes to the qualitative inspection of a child’s gait. The high tech tools themselves allow biomechanists to make better and better measurements of human motion. In the end however, the meaning of the data must be interpreted and evaluated. Thus, while tools for analysis are improving, they do not, by themselves, answer our questions. Skilled practitioners must perform the last and most critical step in the analysis. The ability to interpret data and create improved programs for instruction, training and rehabilitation hinges upon our ability to apply theoretical positions in the solution of practical problems.

We will see in this course that the mechanical constraints that influence human movement can sometimes be reduced to discrete mathematical relationships. Under these circumstances, it will be possible to generate specific answers to clear-cut questions. In other instances, we will see that the biomechanical analysis of movement leads us to only partial answers for movement problems. We will find that most movement problems do not lend themselves to a complete mathematical solution. Instead, we will need to understand how a broad variety of biomechanical principles can be integrated with information from other fields of study to produce a better understanding of realistic movement problems.

Figure 1-1. A digital video camcorder, video capture notebook PC and analysis software.

Definitions of Biomechanics

Our work in Biomechanics will focus upon the application of mechanical principles to the analysis of human motion. At a more general level, biomechanics can be defined as “the science involving the study of biological systems from a mechanical perspective.” (Nelson, 1980). Under this definition, the mechanical principles that influence motion are seen to apply to any organism or the systems within an organism, such as the fluid mechanics of blood flow. Hay (1993) provides a more human-centric definition of biomechanics: 

 “Biomechanics is the science concerned with the internal and external forces acting on the human body and the effects produced by these forces.”

Figure 1-2. Biomechanical measures for a skillful runner. The ground reaction forces (external forces) are labeled as GRFx and GRFy. The joint reaction forces (internal forces) are shown acting at the proximal and distal ends of the shank and foot segments.

This definition reflects the organization of materials in this book. The forces acting on the human body will be studied in our chapters on kinetics (Chapters 10-13, Linear Kinetics, Chapters 20-23, Angular Kinetics and Chapters 24-25 Fluid Mechanics), and the effects produced by forces applied to the body will be studied in our chapters on kinematics (Chapters 4-9, Linear Kinematics and Chapters 14-19, Angular Kinematics).

While we will focus on mechanical principles in this course, it will be very important for us to see the role of biomechanics within the larger area of study in kinesiology. In particular, we should understand the interrelationships between biomechanics and other areas in kinesiology, such as exercise physiology and motor learning.