What is Biomechanics
Biomechanics is a branch of science which employs
mechanical and engineering principles to study
biological systems
The objectives of Biomechanics are:
• To understand human physical performance: how
do we perform movement and apply forces? how is
human motion controlled and how can it be refined;
• To understand how the biological tissues (materials)
such as muscles, bones, cartilage, tendons and other
soft tissues participate in such performance;
Objectives of Biomechanics Cont.
• To determine what kind of forces are acting on
musculoskeletal tissue elements during physical
• To find out what are the mechanical properties of the
relevant biological tissues; how do they deform and
endure the application of forces and how do they
• To understand the mechanisms of injury; what kind
of loads cause tissues to fail (lose their structural
Examples of Questions that
Biomechanics can Answer
• Truck drivers are known to develop chronic lower
back pain. Is there a critical vibration spectrum
which will cause injury?
• Running can produce injuries to the joints of the
lower limbs. Can athletic shoes help prevent injury
by improving dynamic foot-ground interaction?
• Leg amputation and a continuous use of prosthesis
is likely to produce lower back pain in later life.
Can such arthritic development be prevented via
control of the limb structural parameters?
Examples of Biomechanical Applications
 Plastic surgeon needs to perform skin graft to cover
an affected area of burned skin. What is the best
way to prepare skin for grafting?
 Plastic surgeon needs to perform reconstructive
surgery by transplanting cartilage from the sternum
to the nose. How can he prevent stress related
 How does one control an overuse syndrome in
articular cartilage such as in osteoarthritis of the
knee or hip;
Examples Cont.
• An orthopedic surgeon is presented with
a case of a child where the hip joint is
abnormally overloaded such that it
causes degeneration of the joint cartilage.
What kind of solution can be applied and
what are the consequences;
• Degenerative changes in a joint (Ankle,
knee, hip, spine) may cause unbearable
pain. The surgeon may consider fusion of
the bony elements of the joint. What are
the benefits and the shortcomings of the
Examples Cont.
• An alternative solution to the same problem
could be to resurface the joint with prosthetic
components, what kind of loads need to be
considered? how should the prosthetic
component be interfaced to the bony tissue? what
kind of geometry need to be reproduced?
• Runners often suffer joint injuries as a result of
the frequent and extensive loading. Are shoes
contributory to the alleviation of such stresses?
Which shoe characteristics need to be
• A child broke his tibia. Is plaster
casting a good solution?
Examples Cont.
• In the design of high acceleration equipment, such as:
airplanes, space rockets, roller coasters and road vehicles,
how does one decide what kind of accelerations can the
body sustain without being injured?
• In the design of off road equipment and vehicles, exposure
to vibrations considers: frequencies; amplitudes; duty
cycle; exposure time, etc.?
• In the design of seat belts for automotive application, what
would be an optimal configuration to prevent rib fractures?
Human Performance Biomech.
• Biomechanics in Rehabilitation
• Biomechanics in Sport
• Occupational Biomechanics
Performance of Movement
1. How do we perform movement and/or apply forces;
The Musculoskeletal System
Musculoskeletal Biomechanics
• Modeling of the MSK system
with the objective of identifying
forces exerted/acting on the
Bones, Joints, Muscles and
other soft tissues;
• Application to Trauma,
Prosthetics and Orthopedic
Implant Design.
Tissue Biomechanics
• The study of the mechanical behavior of
biological tissues
Growth and Remodeling
Bone Mechanics &
Knowledge Required to deal with
Biomechanical Problems
• Anatomy: understanding body structural
• Physiology: understanding the body operational
• Applied Engineering-Mechanics: The modeling
The Principles of Biomechanical Analysis
• We approach the biomechanical analysis
similarly to the mechanical analysis:
Determine the external forces either by static
modeling or by dynamic modeling
Determine the internal forces via fragmentation
and free body diagrams
Attribute the internal forces and moments to the
corresponding tissues
Perform Tissue Mechanics analysis
Performance Analysis is the way to
Determine the External Loading
Document the motion (kinematics);
Measure the applied forces;
Assess muscular activity (EMG);
Analyze trajectories of motion;
Develop a dynamic model to determine the forces;
Suggest ways to ptimize the performance;
Alternatively, analyze the motions of an elite athlete
and adopt his/her criteria;
A Typical Protocol For Tissue Mechanics Study
• Determine the performance characteristics
– Motion, External Forces (measurable);
• Focus on a particular body part/tissue of interest
and determine the forces acting on it
– Typically a model is required;
• Subject the specific part/tissue to the applied
forces and obtain its mechanical behavior
comparing loads and deformations;
• Compare the forces to the tissue endurance
1. Document the motion (kinematics)
2. Measure the applied forces
Ground Forces acting during locomotion
Analyze Trajectories of Motion
Determine velocities and

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