Biomechanics
Zhang Ming,ST408
Tel: 2766 4939
Muscle Mechanics
Lecture Outline /Keywords:
Compositions of Skeletal Muscle
Myofilament Sliding mechanism
Fast/slow fibers
Motor unit
Series/parallel elastic elements
Force-length relationship
Force-velocity relationship, Hill’s
equation
Force-time relationship
References:
Biomechanics of skeletal
muscle, Chapter 5, pp89110, in: Basic
Biomechanics of the
Musculoskeletal System,
Nordin M and Frankel
VH.
Types of Muscle Work and Contraction
Isometric: constant length
Isokinetic: constant velocity
Isoinertial: constant exteral load (resistance)
Isotonic: constant force
Compositions of
Skeletal Muscle
3D reconstruction of skeletal muscle to show organization of
myofibrils, mitochondria and membrane systems.
Muscle
Myofilament Sliding mechanism
Myosin
Actin-myosin
Group of muscle fibres
Myofibril
Myofilaments
Myosin
Sarcomere
Actin
Actin
Motor Unit - twitch and summation
Twitch: the mechanical response of a single stimulus of motor nerve
Two Types of Muscle Fibers
Properties
FAST
SLOW
Color
Mitochondria
Vascularization
Energy source
pale
few
poor
glycolysis
(anaerobic)
fast
wide
high
high intensity
short duration
red
many
rich
oxidative
(aerobic)
slow
narrow
low
long-term
contraction
Kinetics
Range of tensions
Fatiguability
Function
Force-length relationship
Actin-myosin
The length–tension curve of a whole muscle. The
length–tension curve of a whole muscle
demonstrates how muscle length affects the force
production of the whole muscle. The contractile,
or active, component; the passive component
primarily due to the connective tissue; and the
total muscle tension all are affected by the stretch
of the muscle.
Muscle Model
A mechanical model of the contractile and elastic components of
a muscle. A muscle’s contractile (actin and myosin) and elastic
(connective tissue) components are often modeled mechanically
as a combination of a contractile element (CE) with springs that
represent the elastic elements that are both in series (SE) and in
parallel (PE) with the contractile component.
Force-velocity relationship
Hill’s Equation:
V= b(F0-F)/(F+a)
V - velocity
F - instantaneous force
F0 – maximum force at zero velocity
a, b, constants