Orthopaedic physical therapy secrets 2nd ed

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ORTHOPAEDIC PHYSICAL THERAPY SECRETS
ISBN-13: 978-1-56053-708-3
Copyright © 2006, 2001 by Elsevier Inc.
ISBN-10: 1-56053-708-6
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Notice
Knowledge and best practice in this field are constantly changing. As new research and experience
broaden our knowledge, changes in practice, treatment and drug therapy may become necessary
or appropriate. Readers are advised to check the most current information provided (i) on
procedures featured or (ii) by the manufacturer of each product to be administered, to verify
the recommended dose or formula, the method and duration of administration, and
contraindications. It is the responsibility of the practitioner, relying on their own experience and
knowledge of the patient, to make diagnoses, to determine dosages and the best treatment for each
individual patient, and to take all appropriate safety precautions. To the fullest extent of the law,
neither the Publisher nor the Editors assumes any liability for any injury and/or damage to persons
or property arising out or related to any use of the material contained in this book.

Previous edition copyrighted 2001
ISBN-13: 978-1-56053-708-3

ISBN-10: 1-56053-708-6
Acquisition Editor: Kathy Falk
Publishing Services Manager: Patricia Tannian
Project Manager: Jonathan M. Taylor
Design Direction: Bill Drone

Printed in the United States of America
Last digit is the print number: 9 8 7 6 5 4 3 2 1


To my wife, Laura, my best friend, my soul mate, my rock, my inspiration. To
my three angels, Alexis, Bailey, and Lily, my life’s true joy, my deepest love,
my serenity, my peace.
JDP

To my mother and father, for instilling in me a strong work ethic. To my wife,
Marcia Boyce, and my children, Elizabeth, Emily, and Cole, for your constant
love and support. Finally, to my students and patients—thank you for
teaching me so much over the years.
DAB

In loving memory of Dr. Edward G. Tracy (November 2, 1941 March 3, 2004) who devoted himself to educating health professionals for
three decades. It is hoped that the presentation of his contribution to this
book provides a window into his humor, kindness, compassion, and
enthusiasm. Dr. Tracy brought joy into his classroom and made a heavy
burden seem light. Generations of students remember him in the same way
they remember the material he taught—with affection.


Contributors

JEFFREY E. BALAZSY, MD
Attending Trauma Surgeon
Department of Orthopaedic Surgery
William Beaumont Hospital
Royal Oak, Michigan

KATHLEEN A. BRINDLE, MD
Chief, Musculoskeletal Radiology
Assistant Professor of Radiology
George Washington University
Washington, D.C.

JUDITH L. BATEMAN, MD
Oakland Arthritis Center
Bingham Farms, Michigan

TIMOTHY J. BRINDLE, PT, PHD, ATC
Post Doctoral Research Physical Therapist
Physical Disabilities Branch
National Institutes of Health
Bethesda, Maryland

TURNER A. “TAB” BLACKBURN, JR.,
PT, MED, ATC
Vice President, Corporate Development
Clemson Sports Medicine and
Rehabilitation
Seneca, South Carolina
Clinical Director

SportsPlus Physical Therapy of Manchester
Manchester, Georgia
Adjunct Assistant Professor
Physical Therapy School
Belmont University
Nashville, Tennessee
DAVID A. BOYCE, PT, EDD, OCS, ECS
Assistant Professor
Bellarmine University Physical Therapy
Program
Owner, Physical Therapy Plus
Louisville, Kentucky
DOUGLAS BOYCE, MD, RPH
Associate Clinical Professor
Wayne State University
Detroit, Michigan

JOSEPH A. BROSKY, JR., PT, MS, SCS
Associate Professor
Bellarmine University Physical Therapy
Program
Louisville, Kentucky
JUDITH M. BURNFIELD, PT, PHD
Director, Movement Sciences Center
Clifton Chair in Physical Therapy and
Movement Science
Institute for Rehabilitation Science and
Engineering
Madonna Rehabilitation Hospital
Lincoln, Nebraska

MARK A. CACKO, PT, MPT, OCS
Physical Therapy Specialists, PC
Troy, Michigan
CHARLES D. CICCONE, PT, PHD
Professor
Department of Physical Therapy
Ithaca College
Ithaca, New York
vii


viii

Contributors

GEORGE J. DAVIES, PT, DPT, MED, SCS,
ATC, LAT, CSCS, FAPTA
Professor
Armstrong Atlantic State University
Department of Physical Therapy
Savannah, Georgia
MICHAEL DOHM, MD, FAAOS
Rocky Mountain Orthopaedic Associates
Grand Junction, Colorado
SUSAN DUNN, PT
Dunn & Associates Physical Therapy, PLLC
Lecturer, Bellarmine University
Louisville, Kentucky
CHRISTOPHER J. DURALL, PT, DPT, MS,
LAT, SCS, CSCS

Clinical Research Director
Director of Physical Therapy
Student Health Center
University of Wisconsin–La Crosse
La Crosse, Wisconsin
BETH ENNIS, PT, EDD, PCS
Assistant Professor
Bellarmine University Physical Therapy
Program
Louisville, Kentucky
JOHN L. ECHTERNACH, PT, DPT, EDD,
ECS, FAPTA
Professor and Eminent Scholar
School of Community Health Professions
and Physical Therapy
Old Dominion University
Norfolk, Virginia
RICHARD ERHARD, PT, DC
Assistant Professor
Department of Physical Therapy
University of Pittsburgh
Pittsburgh, Pennsylvania
SEAN P. FLANAGAN, PHD, ATC, CSCS
Assistant Professor
Department of Kinesiology
California State University Northridge
Northridge, California

TRACEY M. FLECK, PT, MPT
Instructional Assistant

Department of Physical Therapy
Wayne State University
Detroit, Michigan
Physical Therapist
Maines and Dean Physical Therapy
Howell, Michigan
TIMOTHY W. FLYNN, PT, PHD, OCS,
FAAOMPT
Associate Professor
Department of Physical Therapy
Regis University
Denver, Colorado
JULIE M. FRITZ, PT, PHD, ATC
Assistant Professor
Division of Physical Therapy
University of Utah
Salt Lake City, Utah
KATHLEEN GALLOWAY, PT, MPT,
DSC, ECS
Assistant Professor
Department of Physical Therapy
Oakland University
Rochester, Michigan
TERI L. GIBBONS, PT, MPT, OCS
Physical Therapy Specialists, PC
Troy, Michigan
PATRICIA DOUGLAS GILLETTE, PT, PHD
Associate Professor
Bellarmine University Physical Therapy
Program

Louisville, Kentucky
DAVID G. GREATHOUSE, PT, PHD, ECS
Director, Clinical Electrophysiology
Services
Texas Physical Therapy Specialists
New Braunfels, Texas
Adjunct Professor
U.S. Army–Baylor University Doctoral
Program in Physical Therapy
Fort Sam Houston, Texas


Contributors

DARREN GUSTITUS, OTR, CHT
Director of Rehabilitation Services
Michigan Hand and Wrist Rehabilitation
Center
Novi, Michigan

TODD R. HOCKENBURY, MD
Assistant Clinical Professor of Orthopedic
Surgery
University of Louisville
Bluegrass Orthopedic Group
Louisville, Kentucky

ROBERT “CLIFF” HALL, PT, MS, SCS, ATC
Deputy Director of Health and Fitness
National Defense University

Washington, D.C.

SUSAN J. ISERNHAGEN, PT
DSI Work Solutions
Duluth, Minnesota

JOHN S. HALLE, PT, PHD
Associate Professor
School of Physical Therapy
Belmont University
Nashville, Tennessee

JAY D. KEENER, MD, PT
Assistant Professor
Department of Orthopaedic Surgery
University of North Carolina
Chapel Hill, North Carolina

CRAIG T. HARTRICK, MD, DABPM
Director, Anesthesiology Research
Department of Anesthesiology and
Perioperative Medicine
William Beaumont Hospital
Royal Oak, Michigan

MATTHEW A. KIPPE, MD
Department of Orthopedic Surgery
William Beaumont Hospital
Royal Oak, Michigan

HARRY N. HERKOWITZ, MD
Chairman, Department of Orthopaedic
Surgery
William Beaumont Hospital
Royal Oak, Michigan
JAMES ROBIN HINKEBEIN, PT, OCS, ATC
Director, Bardstown Rehab Services
Kentucky Orthopedic Rehab Team
Bardstown, Kentucky
SALLY HO, PT, DPT, MS
Adjunct Assistant Professor
Department of Biokinesiology and
Physical Therapy
University of Southern California
Los Angeles, California
Owner and Director
Ho Physical Therapy
Beverly Hills, California

ix

PATRICK H. KITZMAN, PT, PHD
Department of Rehabilitation Sciences
Division of Physical Therapy and the
Rehabilitation Sciences Doctoral Program
University of Kentucky
Lexington, Kentucky
JOHN R. KRAUSS, PT, PHD, OCS, FAAOMPT
Assistant Professor
School of Health Sciences

Program in Physical Therapy
Assistant Professor
OMPT Program Coordinator
Oakland University
Rochester, Michigan
KORNELIA KULIG, PT, PHD
Associate Professor of Clinical Physical
Therapy
Department of Biokinesiology and
Physical Therapy
University of Southern California
Los Angeles, California


x

Contributors

EDWARD M. LICHTEN, MD, FACS, FACOG
Department of Obstetrics and Gynecology
Providence Hospital
Southfield, Michigan
(Retired)
M. ELAINE LONNEMANN, PT, DPT, MSC,
OCS, MTC, FAAOMPT
Assistant Professor
Bellarmine University Physical Therapy
Program
Louisville, Kentucky
Instructor

University of St. Augustine
St. Augustine, Florida
JANICE K. LOUDON, PT, PHD, ATC
Department of Physical Therapy
Education and Rehabilitation Sciences
University of Kansas
Kansas City, Kansas
TERRY R. MALONE, PT, EDD, ATC, FAPTA
Professor and Director
Division of Physical Therapy
University of Kentucky
Lexington, Kentucky
JAMES W. MATHESON, PT, MS, SCS, CSCS
Clinical Research Director
Therapy Partners, Inc.
Maplewood, Minnesota
Staff Physical Therapist
Minnesota Sport and Spine Rehabilitation
Burnsville, Minnesota
JOSEPH M. MCCULLOCH, PT, PHD, CWS,
FAPTA, FCCWS
Dean, School of Allied Health Professions
Louisiana State University Health
Sciences Center
Shreveport, Louisiana
ANDREA LYNN MILAM, PT, MSED
Assistant Professor
Division of Physical Therapy
University of Kentucky
Lexington, Kentucky

ARTHUR J. NITZ, PT, PHD, ECS, OCS
Professor
Division of Physical Therapy
Department of Rehabilitation Sciences
College of Health Sciences
University of Kentucky
Lexington, Kentucky
JOHN NYLAND, PT, EDD, SCS, ATC, CSCS,
FACSM
Assistant Professor
Division of Sports Medicine
Department of Orthopaedic Surgery
University of Louisville
Adjunct Professor
School of Physical Therapy
Bellarmine University
Louisville, Kentucky
BRIAN T. PAGETT, PT, MPT
Physical Therapy Specialists, PC
Troy, Michigan
JOHN J. PALAZZO, PT, DSC, ECS
Director, Neurolabs
Waterford, Michigan
STANLEY V. PARIS, PT, PHD
President and Professor
Department of Physical Therapy
University of St. Augustine
St. Augustine, Florida
SARA R. PIVA, PT, MS, OCS, FAAOMPT

Department of Physical Therapy
School of Health and Rehabilitation
Sciences
University of Pittsburgh
Pittsburgh, Pennsylvania
JEFFREY D. PLACZEK, MD, PT
Hand and Upper Extremity Surgery
Michigan Hand & Wrist, PC
Novi, Michigan
Providence Park Medical Center
Novi, Michigan
Associate Clinical Professor
Department of Physical Therapy
Oakland University
Rochester, Michigan


Contributors

FREDRICK D. POCIASK, PT, PHD, OCS,
FAAOMPT
Assistant Professor
Physical Therapy Program
College of Pharmacy and Health
Sciences
Wayne State University
Detroit, Michigan
CHRISTOPHER M. POWERS, PT, PHD
Associate Professor
Department of Biokinesiology and

Physical Therapy
Co-Director
Musculoskeletal Biomechanics Research
Laboratory
University of Southern California
Los Angeles, California
MICHAEL QUINN, MD
Bloomfield Hand Specialists
Bloomfield Hills, Michigan
STEPHEN F. REISCHL, PT, DPT, OCS
Adjunct Assistant Professor of Clinical
Physical Therapy
Department of Biokinesiology and
Physical Therapy
University of Southern California
Los Angeles, California
SUSAN MAIS REQUEJO, PT, DPT
Department of Physical Therapy
Mount St. Mary’s College
Assistant Adjunct Professor of Clinical
Physical Therapy
University of Southern California
Los Angeles, California
ROBERT C. RINKE, PT, DC, FAAOMPT
Puget Orthopedic Rehabilitation
Everett, Washington
T. KEVIN ROBINSON, PT, DSC, OCS
Associate Professor
School of Physical Therapy
Belmont University

Nashville, Tennessee

xi

MATTHEW G. ROMAN, PT, OMPT
Senior Physical Therapist, Department of
Physical and Occupational Therapy
Duke University Medical Center
Durham, North Carolina
PAUL J. ROUBAL, PT, PHD
Owner and Director
Physical Therapy Specialists, PC
Troy, Michigan
ROBIN SAUNDERS RYAN, PT, MS
Chief Operating Officer
The Saunders Group, Inc.
Chaska, Minnesota
H. DUANE SAUNDERS, PT, MS
Chief Executive Officer and President
The Saunders Group, Inc.
Chaska, Minnesota
EDWARD SCHRANK, MPT, DSC, ECS
Assistant Professor of Physical Therapy
Shenandoah University
Winchester, Virginia
Physical Therapist in Private Practice
Colorado Springs, Colorado
ROBERT A. SELLIN, PT, DSC, ECS
Director
Electrophysiologic Testing

Professional Rehabilitation Associates
Lexington, Kentucky
AMANDA L. SIMIC, MS, OTR, CHT
Milliken Hand Center
Barnes-Jewish Hospital
St. Louis, Missouri
PAUL SIMIC, MD
Southern California Orthopedic
Institute
Van Nuys, California
BRITT SMITH PT, MSPT, OCS,
FAAOMPT
S.O.A.R. Physical Therapy
Grand Junction, Colorado


xii

Contributors

LEANN SNOW, MD, PHD
Assistant Professor
Department of Physical Medicine and
Rehabilitation
University of Minnesota
Minneapolis, Minnesota
TRACY SPIGELMAN, MED, ATC
Division of Athletic Training
University of Kentucky
Lexington, Kentucky

SUSAN W. STRALKA, PT, MS
Baptist Rehabilitation Hospital
Germantown, Tennessee
LADORA V. THOMPSON, PT, PHD
Associate Professor
Program in Physical Therapy
Department of Physical Medicine and
Rehabilitation
University of Minnesota
Minneapolis, Minnesota
DAVID TIBERIO, PT, PHD, OCS
Associate Professor
Department of Physical Therapy
University of Connecticut
Storrs, Connecticut
†

EDWARD G. TRACY, PHD

EERIC TRUUMEES, MD
Attending Spine Surgeon
Department of Orthopaedic Surgery
William Beaumont Hospital
Royal Oak, Michigan
Orthopaedic Director
Harold W. Gehring Center for
Biomechanical Research
Adjunct Faculty
Bioengineering Center
Wayne State University

Detroit, Michigan

†

Deceased

TIM L. UHL, PT, PHD, ATC
Associate Professor
Division of Athletic Training
Director of Musculoskeletal Laboratory
College of Health Sciences
University of Kentucky
Lexington, Kentucky
FRANK B. UNDERWOOD, PT, PHD, ECS
Professor of Physical Therapy
Department of Physical Therapy
University of Evansville
Evansville, Indiana
VICTORIA L. VEIGL, PT, PHD
Assistant Professor
Division of Natural Science and Math
Jefferson Community and Technical
College, Downtown Campus
Louisville, Kentucky
BRADY VIBERT, MD
Fellow in Spine Surgery
UCSD Medical Center
University of California–San Diego
San Diego, California
MICHAEL L. VOIGHT, PT, DHSC, OCS,

SCS, ATC
Associate Professor
School of Physical Therapy
Belmont University
Nashville, Tennessee
BARRY L. WHITE, PT, MS, ECS, CNIM,
DABNM
Director of Neurophysiological Services
Human Performance and Rehabilitation
Centers, Inc.
Columbus, Georgia
(Retired)
J. MICHAEL WIATER, MD
Attending Shoulder and Elbow Surgeon
Department of Orthopaedic Surgery
William Beaumont Hospital
Royal Oak, Michigan
Beverly Hills Orthopaedic Surgery
Beverly Hills, Michigan


Contributors

MARK WIEGAND, PT, PHD
Program Director/Department Chairperson
Bellarmine University Physical Therapy
Program
Louisville, Kentucky
PATRICIA WILDER, PT, PHD
Professor Emeritus

Department of Health Professions
Program in Physical Therapy
University of Wisconsin–La Crosse
La Crosse, Wisconsin

xiii

ERIC WINT, PT, OCS
Regional Director
Physical Therapy Plus Orthopedic Clinic
Prospect, Kentucky
Lecturer in Orthopedics
Bellarmine University
Louisville, Kentucky


Preface

We are pleased that the first edition of Orthopaedic Physical Therapy Secrets has become
a standard study guide for the orthopaedic certification specialty examination. This text
provides condensed, high-quality, preprocessed information that gets to the heart of
orthopaedic examination, intervention, and outcomes. Orthopaedic Physical Therapy
Secrets promotes the concept of efficient and effective practice and thus has also become
a widely used, quick, and well-organized clinical resource guide.
We have included new, extremely detailed chapters covering differential diagnosis
and radiology. These chapters are a direct reflection of the direction in which contemporary physical therapy practice is moving. Likewise, we have added significant detail to
the chapters covering anatomy, orthopaedic neurology, pharmacology, and the evaluation
of medical laboratory tests. As always, we have emphasized questions founded on sound
outcome-based and evidence-based research.
Orthopaedic Physical Therapy Secrets has gathered experts from a wide variety of

disciplines, including orthopaedic physical therapy, occupational therapy, orthopaedic
surgery, radiology, rheumatology, spine surgery, sports medicine, exercise physiology,
anesthesiology, and obstetrics/gynecology. This vast array of experts has made this text
an exceptional, well-rounded quick reference and study guide for not only physical
therapists, but also occupational therapists, athletic trainers, and primary care physicians.
We hope this text provides its readers insight into the rapidly advancing field of
orthopaedic physical therapy, and ultimately, benefits and improves the quality of life in
those so important to us . . . our patients.
Jeffrey D. Placzek, MD, PT
David A. Boyce, PT, EdD, ECS, OCS


C h a p t e r

1

Muscle Structure and Function
LeAnn Snow, MD, PhD, and
LaDora V. Thompson, PT, PhD
1. What is the organizational hierarchy of skeletal muscle?
• Muscle fascicles
• Muscle fibers or cells
• Myofibrils (arranged in parallel)
• Sarcomeres (arranged in series)

2. Describe the characteristics of a sarcomere.
• In the middle of the sarcomere, the areas that appear dark are termed anisotropic. This portion
of the sarcomere is known as the A band.
• Areas at the outer ends of each sarcomere appear light and are known as I bands because they
are isotropic with respect to their birefringent properties.

• The H band is in the central region of the A band, where there is no myosin and actin filament
overlap.
• The H band is bisected by the M line, which consists of proteins that keep the sarcomere in
proper spatial orientation as it lengthens and shortens.
• At the ends of each sarcomere are the Z disks. The sarcomere length is the distance from one Z
disk to the next.
• Optimal sarcomere length in mammalian muscle is 2.4 to 2.5 µm. The length of a sarcomere
relative to its optimal length is of fundamental importance to the capacity for force generation.

3. What are the contractile and regulatory proteins?
The most prominent protein making up the myofibrillar fraction of skeletal muscle is myosin,
which constitutes approximately one half of the total myofibrillar protein. The other contractile
protein, actin, comprises about one fifth of the myofibrillar protein fraction. Other myofibrillar
proteins include the regulatory proteins tropomyosin and troponin complex.

4. Name the structural proteins in skeletal muscle.
• C protein—part of the thick filament; involved in holding the tails of myosin in their correct
spatial arrangement
• Titin—links the end of the thick filament to the Z disk
• M line protein—also known as myomesin; functions to keep the thick and thin filaments in
their correct spatial arrangement
• α-Actinin—attaches actin filaments together at the Z disk
• Desmin—links Z disks of adjacent myofibrils together
• Spectrin and dystrophin—have structural and perhaps functional roles as sarcolemmal
membrane proteins

3


4

Basic Science

A
Muscle
B

Muscle fasciculus
C

Muscle fiber
H
Z
A
I
Band Disc Band Band

D
Myofibril

Z Sarcomere Z
H

E

G-Actin molecules
J

Myofilaments
K

F-Actin filament
Z

Z

L
Myosin filament
Myosin molecule

F

G

H

I

M
N
Light
Heavy
meromyosin meromyosin

Organization of skeletal muscle, from the gross to the molecular level. F, G, H, and I are cross-sections at the levels
indicated. (Drawing by Sylvia Colard Keene. Modified from Bloom W, Fawcett DW: A textbook of histology, Philadelphia, 1986,
WB Saunders.)

5. What are the characteristics of myosin?
Myosin is of key importance for the development of muscular force and velocity of contraction. A
myosin molecule is a relatively large protein (approximately 470 to 500 kD) composed of two

identical myosin heavy chains (MHCs) (approximately 200 kD each) and four myosin light chains
(MLCs) (16 to 20 kD each). In different muscle fibers, MHCs and MLCs are found in slightly
different forms, called isoforms. The isoforms have small differences in some aspects of their
structure that markedly influence the velocity of muscle contraction.

6. Describe the components of myosin.
Light-meromyosin (LMM) is the tail or backbone portion of the molecule, which intertwines with
the tails of other myosin molecules to form a thick filament. Heavy-meromyosin (HMM) consists
of two subfragments: S-1 and S-2. The S-2 portion of HMM projects out at an angle from LMM,
and the S-1 portion is the globular head that can bind to actin. S-1 and S-2 together are also termed


Muscle Structure and Function

5

a myosin cross-bridge. There are approximately 300 molecules of myosin in 1 myofilament or
thick filament. Approximately one half of the MHCs combine with their HMM at one end of the
thick filament; the other half have their HMM toward the opposite end of the thick filament—a
tail-to-tail arrangement. When molecules combine, they are rotated 60 degrees relative to the
adjacent molecules and are offset slightly in the longitudinal plane. As a consequence of these
three-dimensional structural factors, myosin has a characteristic bottlebrush appearance, with
HMM projecting out along most of the filament.

7. Explain the role of the enzyme myosin adenosinetriphosphatase (ATPase).
A specialized portion of the MHC provides the primary molecular basis for the speed of muscular
contraction. The enzyme myosin ATPase is located on the S-1 subfragment. In different fibers, the
myosin ATPase can be one of several isoforms that range along a functional continuum from slow
to fast. The predominant isoforms of MHC are the slow type I and the fast types IIa, IIx, and IIb.

8. What are the characteristics of actin?
Actin consists of approximately 350 monomers and 50 molecules of each of the regulatory
proteins—tropomyosin and troponin. The actin monomers are termed G-actin because they are
globular and have molecular weights of approximately 42 kD. G-actin normally is polymerized to
F-actin (i.e., filamentous actin), which is arranged in a double helix. The polymerization from Gactin to F-actin involves the hydrolysis of ATP and the binding of adenosine diphosphate (ADP)
to actin; 90% of ADP in skeletal muscle is bound to actin. The actin protein has a binding site that,
when exposed, attaches to the myosin cross-bridge. The subsequent cycling of cross-bridges causes
the development of muscular force. The actin filaments also join together to form the boundary
between two sarcomeres in the area of the A band. ␣-Actinin is the protein that holds the actin
filaments in the appropriate three-dimensional array.

9. Explain the sliding filament theory of muscle contraction.
A muscle shortens or lengthens because the myosin and actin myofilaments slide past each other
without the filaments themselves changing length. The myosin cross-bridge projects out from the
myosin tail and attaches to an actin monomer in the thin filament. The cross-bridges then move as
ratchets, forcing the thin filaments toward the M line and causing a small amount of sarcomere
shortening. The major structural rearrangement during contraction occurs in the region of the I
band, which decreases markedly in size.

10. How is the hierarchical organization of skeletal muscle achieved?
The connective tissue that surrounds an entire muscle is called the epimysium; the membrane that
binds fibers into fascicles is called the perimysium. Two separate membranes surround individual
muscle fibers. The outer membrane of fibers has three names that are interchangeable: basement
membrane, endomysium, or basal lamina. An additional, thin elastic membrane is found just
beneath the basement membrane and is termed the plasma membrane or sarcolemma.

11. List the functions of myonuclei and satellite cells.
• Growth and development of muscle
• Adaptive capacity of skeletal muscle to various forms of training or disuse
• Recovery from exercise-induced or traumatic injury

12. What percentages of the nuclear material are myonuclei and satellite cells?
True myonuclei (located inside the plasma membrane) compose 85% to 95% of nuclear material
with satellite cells (located between the basal lamina and plasma membrane) accounting for the
remaining 5% to 15% of nuclear material.


6

Basic Science

13. How many nuclei are found in the skeletal muscle fiber?
There are approximately 200 to 3000 nuclei per millimeter of fiber length. This is in contrast to
many other cells in the human body that have only a single nucleus.

14. What is the range of muscle fiber lengths?
Muscle fiber lengths range from a few millimeters in the intraocular muscles of the eye to >45 cm
in the sartorius muscle.

15. Discuss the role of satellite cells in the formation of a new muscle fiber.
Satellite cells are normally dormant, but under conditions of stress or injury, they are essential for
the regenerative growth of new fibers. Satellite cells have chemotactic properties, which means they
migrate from one location to another area of higher need within a muscle fiber, and then undergo
the normal process of developing a new muscle fiber. The process of new fiber formation begins
with satellite cells entering a mitotic phase to produce additional satellite cells. These cells then
migrate across the plasma membrane into the cytosol, where they recognize each other, align, and
fuse into a myotube, an immature form of a muscle fiber. The multinucleated myotube then
differentiates into a mature fiber.

16. Identify and define or describe muscle growth factors.

Muscle growth factors are proteins that either promote muscle growth and repair or inhibit muscle
protein breakdown. Examples include insulin-like growth factors, fibroblast growth factor,
hepatocyte growth factor, and transforming growth factors.

17. What are the characteristics of myofibrils?
Individual myofibrils are approximately 1 µm in diameter and comprise approximately 80% of the
volume of a whole muscle. The number of myofibrils is a regulated variable during the
hypertrophy of muscle fibers associated with growth; for example, the number of myofibrils ranges
from 50 per muscle fiber in the muscles of a fetus to approximately 2000 per fiber in the muscles
of an untrained adult. The hypertrophy and atrophy of adult skeletal muscle are associated with
certain types of training and disuse and result from the regulation of the number of myofibrils per
fiber. Training and disuse have negligible effects on the number of fibers in mammals.

18. Describe the characteristics of individual muscle fibers.
The cross-sectional area of an individual muscle fiber ranges from approximately 2000 to
7500 µm2, with the mean and median in the 3000- to 4000-µm2 range. Muscle fiber and muscle
lengths vary considerably. For example, the length of the medial gastrocnemius muscle is
approximately 250 mm, with fiber lengths of 35 mm, whereas the sartorius muscle is
approximately 500 mm, with fiber lengths of 450 mm. The number of fibers ranges from several
hundred in small muscles to >1 million in large muscles, such as those involved in hip flexion and
knee extension.

19. Discuss the relationship between the size of the cell and diffusion of
important nutrients.
The radius of muscle cells (typically 25 to 50 µm) is an important variable for sustained muscular
performance because it affects the diffusion distance from the capillary network (which is exterior
to the muscle cell) to the cell’s interior. As the radius of muscle cells increases, the distance through
which gases, such as oxygen, must travel to diffuse from the capillary blood to the center of the
muscle cell increases. This can be a problem, limiting the muscle’s ability to sustain endurance

Muscle Structure and Function

7

exercise, because sufficient oxygen delivery is needed for the mitochondria, where most energy for
muscle contraction is produced.

20. What is a strap or fusiform muscle?
Muscles that have a parallel-fiber arrangement are strap or fusiform muscles. In a parallel-fiber
muscle, the muscle fibers are arranged essentially in parallel with the longitudinal axis of the
muscle itself. Muscles with a parallel-fiber arrangement generally produce a greater range of
motion (ROM) and greater joint velocity than muscles with the same cross-sectional area but with
a different fiber arrangement.

21. List examples of fusiform muscles.
• Sartorius
• Biceps brachii
• Sternohyoid

22. Explain the role of pennation in force production.
When muscles are designed with angles of pennation, which is the most common architecture,
more sarcomeres can be packed in parallel between the origin and insertion of the muscle. By
packing more sarcomeres in a muscle, more force can be developed. As the angle of pennation
increases, an increasing portion of the force developed by sarcomeres is displaced away from the
tendons. As long as the angle of pennation is <30 degrees, the force lost as a result of the angle of
pennation is more than compensated for by the increased packing of sarcomeres in parallel,
producing an overall benefit to the force-producing capacity of muscle.

23. Describe the differences among unipennate, bipennate, and multipennate

muscles.
• In unipennate muscles, such as the flexor pollicis longus, the obliquely set fasciculi fan out on
only one side of a central muscle tendon.
• In a bipennate muscle, such as the gastrocnemius, the fibers are obliquely set on both sides of a
central tendon.
• In a multipennate muscle, such as the deltoid, the fibers converge on several tendons.

24. Define the force-velocity relationship.
The muscle shortens at different velocities depending on the load placed on the muscle. As the load
is increased, the velocity decreases. When the load exceeds the maximal force capable of being
developed by the muscle, a lengthening contraction ensues. The force developed during a
shortening contraction is less than the isometric force. The force developed during a lengthening
contraction exceeds the isometric force by 50% to 100% because of the increased extension of the
attached cross-bridges.

25. Describe additional factors influencing muscle strength.
Myosin structural state, the ratio of strong binding and weak binding cross-bridges to actin, muscle
innervation, motor unit recruitment, and synchronization are all factors influencing muscle
strength.

26. What is active insufficiency at the sarcomere level?
Active insufficiency is the diminished ability of a muscle to produce or maintain active tension
when a muscle is elongated to a point at which there is no overlap between myosin and actin or
when the muscle is excessively shortened.


8

Basic Science

27. What is active insufficiency at the muscle level?
This type of insufficiency is most commonly encountered when the full ROM is attempted
simultaneously at all joints crossed by a two-joint or multijoint muscle. During active shortening, a
two-joint muscle becomes actively insufficient at a point before the end of a joint range, when full
ROM at all joints occurs simultaneously. Active insufficiency also may occur in one-joint muscles
but is not common.

28. Define excitation-contraction coupling.
Excitation-contraction coupling is the physiologic mechanism whereby an electric discharge at the
muscle initiates the chemical events that lead to contraction.

29. Summarize how excitation-contraction coupling occurs in skeletal muscle.
1. Action potentials in the alpha motor neuron propagate down the axon to the axon terminals.
2. Acetylcholine, the neurotransmitter at the neuromuscular junction, is released from the axon
terminals.
3. Acetylcholine diffuses across the neuromuscular junction and binds with acetylcholine
receptors on the sarcolemma of the muscle.
4. A muscle action potential is generated at the motor end plate.
5. The muscle action potential travels along the sarcolemma and into the depths of the transverse
tubules, which are continuous with the sarcolemma.
6. The action potential (voltage change) is sensed by the dihydropyridine receptors in the
transverse tubules.
7. The dihydropyridine receptors communicate with the ryanodine receptors of the
sarcoplasmic reticulum, a mechanism poorly understood.
8. Calcium is released from the sarcoplasmic reticulum through the ryanodine receptors.
9. Calcium binds to the regulatory protein troponin C, and the interaction between actin and
myosin can occur.
10. Myosin cross-bridges, previously activated by the hydrolysis of ATP, attach to actin.
11. The myosin cross-bridges move into a strong binding state, and force production occurs.

30. What are the characteristics of the different skeletal muscle fiber types?
31. Define type IIx myosin heavy chain in human fibers.
The type IIx myosin heavy chain was first described in animals (rat, mouse). Type IIx myofibers
have maximal shortening velocity and maximal isometric tension that are intermediate between
types IIa and IIb. The fiber type IIb in animals is not found in humans. Rather, the type IIb that is
described in humans has a myosin composition very similar to that of type IIx.

32. Define muscle spindles and their function in muscular dynamics and limb
movement.
Muscle spindles provide sensory information concerning changes in the length and tension of the
muscle fibers. Their main function is to respond to stretch of a muscle and, through reflex action,
to produce a stronger contraction to reduce the stretch.

33. Describe the appearance of the muscle spindle.
The spindle is fusiform in shape and is attached in parallel to the regular or extrafusal fibers of the
muscle. Consequently, when the muscle is stretched, so is the spindle. There are more spindles in
muscles that perform complex movements. There are two specialized cells within the spindle,
called intrafusal fibers. There are two sensory afferents and one motor efferent innervating the


Muscle Structure and Function

9

intrafusal fibers. The gamma efferent innervates the contractile portion—the striated ends of the
spindle. These fibers, activated by higher cortex levels, provide the mechanism for maintaining the
spindle at peak operation at all muscle lengths.

34. Discuss the function of the Golgi tendon organs.
Connected in series to 25 extrafusal fibers, these sensory receptors also are located in the ligaments

of joints and are primarily responsible for detecting differences in muscle tension. The Golgi
tendon organs respond as a feedback monitor to discharge impulses under one of two conditions:
(1) in response to tension created in the muscle when it shortens and (2) in response to tension
when the muscle is passively stretched. Excessive tension or stretch on a muscle activates the
tendon’s Golgi receptors. This causes a reflex inhibition of the muscles they supply. The Golgi
tendon organ functions as a protective sensory mechanism to detect and inhibit subsequently
undue strain within the muscle-tendon structure.

35. Describe the adaptations in muscle structure with progressive resistance
exercises.
The major adaptation is an increase in the cross-sectional area of muscle, which is termed
hypertrophy. The number of muscle fibers is minimally affected. Progressive resistive exercise
involves 10 repetitions a day at 60% to 90% of maximal capacity; this results in an increase in
strength by 0.5% to 1.0% per day over a period of several weeks. The fast-twitch type II fibers are
more responsive to progressive resistance exercise than slow-twitch type I fibers. There are increases
in the amounts of transverse tubular and sarcoplasmic reticulum membranes as well. There are
neural adaptations, which result in an increased ability to recruit high-threshold motor units. The
functional significance of the morphologic change is primarily a greater capacity for strength and
power development.

Motor Unit Type and Muscle Fiber Types in the Motor Unit

Property

I
(S)
(SO)

IIa
(FR)

(FOG)

IIb
(FF)
(FG)

Contraction speed
Force production
Fatigue resistance
Fiber diameter
Red color
Myoglobin
Capillary supply
Respiration type
Mitochondria
Z line thickness
Glycogen content
Alkaline ATPase
Acid ATPase
Oxidative capacity
Glycolytic ability

Slow
Small
High
Small
Dark
High
Rich
Aerobic

Many
Intermediate (wide)
Low
Low
High
High
Low

Fast
Intermediate
High (intermediate)
Intermediate
Dark
High
Rich
Aerobic
Many
Wide (intermediate)
High (intermediate)
High
Low
Medium-high
High

Fast
Large
Low
Large
Pale
Low

Poor
Anaerobic
Few
Narrow
High
High
Moderate
Low
High


10

Basic Science

36. List the effects of progressive resistance exercise.
• Increased mass and strength
• Increased cross-sectional area of muscle (increased number of myofibrils, leading to
hypertrophy)
• Increased type I and type II fiber area
• Decreased mitochondrial density per fiber and oxidative capacity
• Increased intracellular lipids and capacity to use lipids as fuel
• Increased intracellular glycogen and glycolytic capacity
• Increased intramuscular high-energy phosphate pool and improved phosphagen metabolism

37. Describe the adaptations in muscle structure with endurance exercises.
Endurance exercise has minimal impact on the cross-sectional area of muscle and muscle fibers.
The smaller cross-sectional area allows better diffusion of metabolites and nutrients between the
contractile filaments and the cytoplasm and between the cytoplasm and the interstitial fluid. There
is a decrease in fatigability. The number of capillaries increases around each fiber, and there is an

increase in mitochondria, especially in the type I fibers. The increased mitochondria can provide
a good supply of ATP during exercise. The more extensive capillary bed improves the delivery of
oxygen and circulating energy sources to the fibers, whereas the products of muscle activity are
removed more efficiently. The functional significance of these changes is observed during
sustained exercise, in which there is a delay in the onset of fatigue.

38. List the effects of endurance exercise.
•
•
•
•
•
•
•
•
•
•

Improved ability to obtain ATP from oxidative phosphorylation
Increased size and number of mitochondria
Less lactic acid produced per given amount of exercise
Increased myoglobin content
Increased intramuscular triglyceride content
Increased lipoprotein lipase (enzyme needed to use lipids from blood)
Increased proportion of energy derived from fat; less from carbohydrates
Lower rate of glycogen depletion during exercise
Improved efficiency in extracting oxygen from blood
Decreased number of type IIb fibers; increased number of type IIa fibers

39. What are the consequences of muscle disuse?

• The most striking consequence is atrophy—a reduction in muscle and muscle fiber crosssectional area.
• The slow type I fibers show greater atrophy with disuse than the fast type II fibers.
• A few fibers undergo necrosis, and there is an increase in the endomysial and perimysial
connective tissue.
• The muscles develop smaller twitch and tetanic tensions, beyond those expected on the basis of
fiber atrophy.
• There is an increase in fatigability.
• There is a tendency for slow-twitch fibers to be transformed into fast-twitch fibers, with changes
in the isoforms of the myofibrillar proteins.
• In the sarcolemma, there is a spread of acetylcholine receptors beyond the neuromuscular
junction, and the resting membrane potential is diminished.
• The motor nerve terminals are abnormal in showing signs of degeneration in some places and
evidence of sprouting in others.
• There is a loss of motor drive, such that the motor units cannot be recruited fully.


Muscle Structure and Function

11

40. What physiologic adaptations occur if muscles are immobilized in a shortened
position?
•
•
•
•
•
•

Decrease in the number of sarcomeres

Increase in the amount of perimysium
Thickening of endomysium
Increase in ratio of collagen concentration
Increase in ratio of connective tissue to muscle fiber tissue
Atrophy

41. List the changes that result from muscles being immobilized in a shortened
position.
• Altered strength
• Increased stiffness to passive stretch
• Increased fatigability

42. What occurs as a result of lengthening the muscles?
Sarcomeres are added.

43. Does muscle splitting occur, or can there be an increase in the number of
cells (hyperplasia)?
Hyperplasia, defined as an increase in fiber number, generally does not occur. Individual fiber
splitting may occur in specific pathologic conditions, such as neuromuscular diseases.

44. Define disease-associated muscle atrophy, such as cachexia.
Disease-associated muscle atrophy is due to accelerated proteolysis. This form of skeletal muscle
atrophy is systemic and associated with metabolic and/or inflammatory factors.

45. Differentiate apoptosis from necrosis as applied to skeletal muscle.
Apoptosis, or programmed cell death, is a regulated physiologic process critical to cellular
homeostasis, which can become dysregulated, leading to disease states including muscle disease or
dysfunction. Apoptosis results in cell shrinkage, DNA fragmentation, membrane blebbing, and
disassembly into apoptotic bodies (membrane-bound cell fragments). Necrosis is a pathologic
process caused by the progressive degradative action of enzymes that is generally associated with

severe cellular trauma in muscles, leading to cell death.

46. Can changes in muscle temperature be beneficial?
Changes can be advantageous as well as deleterious to individuals. Before starting an exercise
program, the warming-up period can have several beneficial effects. When a muscle warms up, it
takes advantage of the local Q10 effect. Q10 is the ratio of the rate of a physiologic process at a
particular temperature to the rate at a temperature 10° C lower, when the logarithm of the rate is
an approximately linear function of temperature. Physiologically, the warming-up period can
increase the speed of particular enzymatic processes in muscles through the Q10 effect.
Temperatures >40° C have been observed to decrease the efficiency of oxygen use in muscle.

Bibliography
Bagshaw CR: Muscle contraction, ed 2, London, 1993, Chapman & Hall.
Brooks S: Current topics for teaching skeletal muscle physiology, Adv Physiol Educ 27:171-182, 2003.
Enoka RM: Neuromechanics of human movement, ed 3, Champaign, Ill, 2002, Human Kinetics Publishers.


12

Basic Science

Franzini-Armstrong C, Engel A: Myology, ed 3, New York, 2004, McGraw-Hill.
Hawke TJ: Muscle stem cells and exercise training, Exercise Sport Sci Rev 33:63-68, 2005.
Jones DA, Round JM, deHaan A: Skeletal muscle from molecules to movement, Edinburgh, 2004, Churchill
Livingstone.
Lieber RL: Skeletal muscle structure, function, & plasticity: The physiological basis of rehabilitation, ed 2,
Baltimore, 2002, Lippincott Williams & Wilkins.
McArdle WD, Katch FI, Katch VL: Exercise physiology: Energy, nutrition and human performance, ed 5,
Baltimore, 2001, Lippincott Williams & Wilkins.
Schiaffino S, Reggiani C: Molecular diversity of myofibrillar proteins: Gene regulation and functional

significance, Physiol Rev 76:371-423, 1996.

C h a p t e r

2

Biomechanics
Sean P. Flanagan, PhD, ATC, CSCS, and
Kornelia Kulig, PT, PhD
1. Define the terms biomechanics and kinesiology.
Biomechanics is the study of the structure and function of biological systems by the methods of
mechanics. Mechanics is a branch of physics that is concerned with the analysis of the action of
forces on matter or material systems.
The term kinesiology combines two Greek words—kinein, which means to move, and
logos, which means to discourse. Therefore kinesiology is the discourse of movement or the
science of movement of the body. Because human movement is an expression of complex
musculoskeletal, neural, and cardiovascular biological systems, kinesiology encompasses the
sciences underlying the study of those systems.

2. Define the term kinematics.
Kinematics is the study of the geometry of motion without reference to the cause of motion.
Kinematics is the analytical and mathematical description of motion (e.g., position, displacement,
velocity, acceleration, and time). Displacement, velocity, and acceleration are vector quantities
(they have magnitude and direction) and can be linear or angular in nature.

3. What is the difference between osteokinematics and arthrokinematics?
Osteokinematics describes the motion of bones around an axis. By convention, the motion is
referenced relative to sagittal, frontal, and/or transverse planes. Terms such as flexion, extension,
abduction, adduction, internal rotation, and external rotation are used to describe osteokinematics.
Arthrokinematics describes the motion that occurs between the articular surfaces of the two bones

of a joint. Terms such as spin, roll, and glide are used to describe arthrokinematics.


12

Basic Science

Franzini-Armstrong C, Engel A: Myology, ed 3, New York, 2004, McGraw-Hill.
Hawke TJ: Muscle stem cells and exercise training, Exercise Sport Sci Rev 33:63-68, 2005.
Jones DA, Round JM, deHaan A: Skeletal muscle from molecules to movement, Edinburgh, 2004, Churchill
Livingstone.
Lieber RL: Skeletal muscle structure, function, & plasticity: The physiological basis of rehabilitation, ed 2,
Baltimore, 2002, Lippincott Williams & Wilkins.
McArdle WD, Katch FI, Katch VL: Exercise physiology: Energy, nutrition and human performance, ed 5,
Baltimore, 2001, Lippincott Williams & Wilkins.
Schiaffino S, Reggiani C: Molecular diversity of myofibrillar proteins: Gene regulation and functional
significance, Physiol Rev 76:371-423, 1996.

C h a p t e r

2

Biomechanics
Sean P. Flanagan, PhD, ATC, CSCS, and
Kornelia Kulig, PT, PhD
1. Define the terms biomechanics and kinesiology.
Biomechanics is the study of the structure and function of biological systems by the methods of
mechanics. Mechanics is a branch of physics that is concerned with the analysis of the action of
forces on matter or material systems.
The term kinesiology combines two Greek words—kinein, which means to move, and

logos, which means to discourse. Therefore kinesiology is the discourse of movement or the
science of movement of the body. Because human movement is an expression of complex
musculoskeletal, neural, and cardiovascular biological systems, kinesiology encompasses the
sciences underlying the study of those systems.

2. Define the term kinematics.
Kinematics is the study of the geometry of motion without reference to the cause of motion.
Kinematics is the analytical and mathematical description of motion (e.g., position, displacement,
velocity, acceleration, and time). Displacement, velocity, and acceleration are vector quantities
(they have magnitude and direction) and can be linear or angular in nature.

3. What is the difference between osteokinematics and arthrokinematics?
Osteokinematics describes the motion of bones around an axis. By convention, the motion is
referenced relative to sagittal, frontal, and/or transverse planes. Terms such as flexion, extension,
abduction, adduction, internal rotation, and external rotation are used to describe osteokinematics.
Arthrokinematics describes the motion that occurs between the articular surfaces of the two bones
of a joint. Terms such as spin, roll, and glide are used to describe arthrokinematics.


Biomechanics

13

4. What are the various types of levers?
A class 1 lever has the axis of rotation between the resistance and effort (e.g., seesaw or scissors),
and a class 2 lever has the resistance between the axis and effort (e.g., bottle opener or wheelbarrow). An example of a class 1 lever in the body is the head on the spinal column, and it is
questionable whether there are any class 2 levers in the body (possibly the gastrocnemius/soleus
attachment onto the calcaneus). A class 3 lever is one in which the effort is between the axis of
rotation and the resistance to overcome (e.g., elbow [axis], biceps [effort], and weight [resistance]
in a curl). This configuration provides us with the ability to move a resistance through a larger

range of motion (moving through a greater range allows for greater speed of movement) but at the
expense of using a greater force than the resistance we are overcoming.

5. What is the relation between the linear motion at the joint surface and the
angular motion of a bone around the joint axis?
A theoretical construct, developed to describe this relation and advocated by Kaltenborn, is known
as the convex-concave rule. In brief, if the convex surface of one bone is moving on the fixed
concave surface of another bone, rotation and translation will occur in opposite directions.
Additionally, if the concave surface of one bone is moving on the fixed convex surface of another
bone, rotation and translation occur in the same direction. This rule should be appreciated when
joint mobilizations are performed. It is proposed that in order to restore rotational motion at a
joint, a linear mobilization is performed in relation to the treatment plane (in the concave joint
surface) and in accordance with the convex-concave rule.

6. Has the convex-concave rule been experimentally verified?
No, at least not for all joints. For example, it has been demonstrated that the glenohumeral joint
contradicts the convex-concave rule during external rotation when the humerus is abducted to
90 degrees, and there is no clear consensus that the femur translates anteriorly when the knee is
flexing in a weight-bearing position. However, these findings may not violate the convex-concave
rule if the amount of translation in the direction of rolling is less than what the curvature of the
convex segment would predict. The amount of rolling in one direction may be greater than the
sliding in the opposite direction. Furthermore, pathologic joints (e.g., ACL-deficient knees) have
different arthrokinematics than normal joints. Further research is necessary, and the rationale for
manual therapy techniques may have to be modified, for different joints, different motions of the
same joint, and/or pathologic joints.

7. Where is the location of the joint axis of rotation?
The axis of rotation (AOR) must be determined experimentally, because the AOR may be located
within the joint or outside the two bones composing a joint. In a nonpathologic joint, the AOR is
generally within the convex joint member and may stay in the same location (fixed AOR). A

degenerated joint may lose its integrity and the AOR may change its location throughout the range
of motion. To reflect that change, the axis (or center) of rotation is called the instantaneous axis
(or center) of rotation.

8. Why is it important to know the axis of rotation?
Knowing the location of the AOR is important for at least three reasons. First, motion will occur
in a cardinal plane only if the AOR is perpendicular to that plane; otherwise, motion will occur in
two or all three planes of motion. Second, a muscle’s function is governed by the orientation of its
line of pull with respect to the AOR of a joint. Third, when quantifying joint range of motion, the
AOR of the goniometer should be aligned with the AOR of the joint.


14

Basic Science

9. What is the difference between an absolute and a relative joint angle?
An absolute angle is the angle that the distal point of a segment (e.g., foot, shank, thigh) makes
with respect to some reference line (such as the horizontal for sagittal plane movements). A relative
angle is the joint angle made by two segments (e.g., the knee angle is the angle between the shank
and thigh). Relative angles can be stated as either internal (included) or external (anatomic) angles.
An internal angle is the angle between the longitudinal axes of the two segments comprising a
joint, while the external angle is the angular displacement from the anatomic position. For
example, in the anatomic position, the internal knee angle is 180 degrees, while the external angle
is 0 degrees. If this angle were decreased by 30 degrees, the internal angle would be 150 degrees
while the external angle would be 30 degrees (see figure).

a

b

c
A graphic depiction of the three types of angles: a, absolute angle from the horizontal; b, relative, internal angle; c, relative,
external angle.

It is important to understand the distinction between these three measures and to be
consistent in their use. In observational gait analysis, for example, ankle and knee measures are
usually external, relative angles while the thigh is usually an absolute angle with respect to the
vertical; many motion capture systems, on the other hand, report internal angles for all three
joints.

10. How are force and strength related? Define commonly used biomechanical
terms and equations.
Force is a push or pull of one object on another. Force is a vector quantity, having both a
magnitude and a direction. Strength may be thought of as the ability to produce or absorb force.

11. Does the amplitude of the electromyography (EMG) signal quantify a muscle’s
force-producing (absorbing) capability?
No. A muscle’s force-producing (absorbing) capability is primarily determined by the:
• Type of muscle action (concentric, eccentric, isometric)
• Length of muscle (force-velocity relation)
• Physiologic cross-sectional area of the muscle
• Number of motor units within a muscle that are activated (intramuscular coordination)
• Rate of motor unit activation (rate-coding)
• Intrinsic force-generating capability of the muscle (specific tension)
• Contractile history of the muscle (e.g., prestretch)


Biomechanics

15

Common Biomechanical Terms and Equations
Equation

Term
(Linear; Angular)
Displacement
(∆x; ∆θ)
Velocity
(ν; ω)

Acceleration
(a; α)
Force; Moment
(F; M)
Momentum
(H; L)
Impulse
(I)
Work
(W)
Gravitational
potential energy
Elastic potential
energy
Kinetic energy
Power
(P)
Stress

(Pressure)
σ
Strain

Physical Meaning

Linear

Angular

A change in position
A change in
displacement with
respect to a change in
time
A change in velocity
with respect to a
change in time
A push or pull by one
object on another object
Resistance to change
in velocity
Effect of a force during
the time the force acts
A change in energy

x2 − x1
∆x/∆t

θ2 − θ1

∆θ/∆t

∆ν/∆t

∆ω/∆t

Energy caused by
position
Energy caused by
deformation
Energy caused by
motion
Time rate of doing work

ΣF = ma ΣM = Iα
H = mν

L = Iω

∫F dt

∫M dt

∫F dx

∫M dθ

mgh
1

⁄2ks2

1

⁄2mν2

∆W/∆t

Magnitude of force
dispersed over an area

F/A

Amount of deformation

∆L/Lo

Units

Linear
(Metric,
English)

Angular
(Metric,
English)

m
ft
m/sec

ft/sec

deg
rad
deg/sec
rad/sec

m/sec2
ft/sec2

deg/sec2
rad/sec2

N
lb
kg•m/sec

N-m
lb-ft
kg•m2/sec

N-s
lb-sec
J
ft-lb
J

N-m-sec
lb-ft-sec

J
1

⁄2Iω2

J
W
hp
N/m2
lb/in2
Unitless measure

The EMG signal quantifies the number of motor units and their rate of activation within the electrode
field. In addition, because electrode placement can affect the number of motor units within the
field, it is important to compare relative values (usually normalized to a maximum voluntary
isometric contraction) rather an absolute values when comparing differences in EMG signals.

12. Explain why it is useful to identify the components of a force.
Just as forces can be combined together to determine a resultant, they can also be broken into their
components. The components are useful in identifying the different effects of a force on a joint.
For example, a muscle force can be divided into the component that is perpendicular to the bone