Musculoskeletal Biomechanics. Biomechanics in its broadest sense is mechanics (that is the study of loads, motion, stress, and strain of solids and fluids) applied to biological systems. Musculoskeletal Biomechanics is a branch of biomechanics specifically focussing on the musculoskeletal system.

1. BIOMECHANICS OF SKELETAL MUSCLES
BY
OBAJE Godwin Sunday
Department of Anatomy
Alex Ekwueme Federal University Ndufu
Alike
obaje199@gmail.com, +2348068638121
2018/5/17obaje et al. 1

2.  Bone is a living tissue as well as a structural
material, and as such it is susceptible to the
effects of age, disease and injury.
 It is important to study the range of factors
that can affect the mechanical competence of
the skeletal system. By employing
micromechanical, imaging, modeling and
non-destructive techniques.
 The biological and mechanical factors that
affect skeletal integrity can be investigated.
2018/5/17obaje et al. 2
General Introduction

3.  A better understanding of the mechanisms
that provide bone with its mechanical
competence can be largely utilized in the
development of more accurate diagnostic
techniques.
 Treatment modalities for diseases associated
with skeletal fragility and in the design of
orthopaedic implants and biometic materials.
2018/5/17obaje et al. 3
Importance of mechanics to musculoskeletal systems

4.  In addition to isolated tissue studies, the
interaction of structures within the
musculoskeletal system (muscles, bones,
joints, etc.) can lend substantial insight into the
physiology and biomechanics of this complex
system.
 High speed radiographic techniques can be
used to investigate the motion and interaction
of bony and soft tissue structures in order to
obtain information for in vivo environment.
2018/5/17obaje et al. 4
Importance of mechanics to musculoskeletal systems

5. 2018/5/17obaje et al. 5
Proper

6.  The mechanical behavior of a single muscle:
from Sarcomere to entire muscle.
 Skeletal muscle is a biological motor that
exert force and produce mechanical work.
 Also act as force transmitters and shock
absorbers.
 Above are kinetic functions, skeletal muscles
produce heat and assist thermoregulations.
2018/5/17obaje et al. 6
Muscle Architecture

7.  Maintaining a
constant length
 Shortening by
action
 Lengthening by
action of the
muscle
 Static or isometric
action
 Concentric or
miometric action
 Eccentric or
plyometric action
2018/5/17obaje et al. 7

8.  Made up of bundles of
fibres running
alongside each other.
 Individual fibre is
enclosed by
sarcolemma.
 Surrounded by sheath
of
collagen(endomysium).
 Fascicle made up of
bundles
2018/5/17obaje et al. 8

9.  Thin filaments are
composed of action
molecules arranged
alongside nebulin,
making filament
inelastic.
 Thin filament
attached to Z-
membrane.
 Thick+Thin=Attache
d by Z-membrane
2018/5/17obaje et al. 9

10.  In situ
 In vitro
 In vivo
 In the biological
location but with
partial isolation
 Isolated from the
living and attificially
maintained
 Within a living body
2018/5/17obaje et al. 10
Muscle mechanics
can best be studied
in this way. Although,
there are challenges
of technical hitches
and ethics.

11.  It is difficult to maintain muscles biological
life when isolated from the body for long
period of time. Hence, experiment in
individual muscles can be done on nonhuman
mammals like frog and toads.
 Frog sartorius muscle being the most popular
object of research.
2018/5/17obaje et al. 11

12.  Muscles or fascicles attached to tendon at an
angle. There are like feathers. Fibers lie at an
angle to line of action of entire muscle. Here,
directions of fiber shortening and tendon
movement are different.
 There are like parallel and fusiform muscles.
 Pennates have both mechanical advantages and
disadvantages.
 More fibres can be filled into a given volume of
muscle (Advantages) and maximum
displacements and velocities are smaller
(Disadvantage).
2018/5/17obaje et al. 12
General Characteristics

13. 2018/5/17obaje et al. 13
Pennate muscles are
greater in
bodybuilders.
Muscle-fibers
pennation angles are
measured using
Ultrasonography.

14.  Is a collection of muscle fibers innervated by the
same motoneurons, a neural cell in the ventral part
of spinal cord or in the brain (incase of facial
muscles).
 Motoneurons activity excites all fibers in the MU
 Motor units differ in their properties
 It can be slow, high, slow-twitch, fast, fast-twitch
 Presence of axon, dendrites, cells and sheath
 More detailed classification are type l (slow), typell
A (fast but fatique resistant), typellX (fast but low
resistance)
2018/5/17obaje et al. 14

15.  To better control muscle force, the central
nervous system activates the MU. It is
according to size of their motoneurons.
 It is called the "size principle". Small motor
neurons innervate slow-twitch fibers whereas
large motor neurons innervate fast-twitch
fibers.
 This principle is unique as, at low forces only
slow muscle fibers are active by firing rate.
2018/5/17obaje et al. 15

16.  Muscle mechanics have variables such as:
muscle length, speed of muscle (shortening
or lengthening), force exerted and muscle
movement arm. The knowledge of this gives
clear picture of forces exerted by muscles
and transmission from one attachment site to
another.
 Classification based on muscle path are:
muscle with straight line and curved muscles.
2018/5/17obaje et al. 16

17.  The use of muscle path generated by a muscle
lies along a straight line connecting centers of
pelvis and femur. The straight line method
today is used in biomechanics because it is
simple and easy.
 Centroids used to determine the muscle
transverse cross-sections of the locus in
geometric centers.
 Centroids allow a more realistic representations
of muscle line of action than does the straight-
line model.
2018/5/17obaje et al. 17

18. Straight-line and Centroid forms
 Line of actions of the psoas muscle
major muscle in sagittal view
 The centroid line of action (thick
line) is compared with straight lines
of action(thin line)
 Centroid path yields larger
compression forces and increasing
shear forces from upper to lower
lumbar level
2018/5/17obaje et al. 18

19. 2018/5/17obaje et al. 19
Straight-line and Centroid forms

20. 2018/5/17obaje et al. 20