KINE 3301
Biomechanics of Human Movement
Effects of Exercise on Biological Tissues
Chapter 15
Structure of
Bone
Osteocytes in cortical bone
are encased in lamellar
layers.
Several layers wrap around
each other to form an
osteon or Haversian
system.
The Haversian system in
the center of the osteon
contains blood vessels and
nerve fibers.
Volkmann’s canal forms
interconnections between
adjacent osteons.
Osteons in Cortical Bone
From: Gardinier JD, et al. In situ permeability measurement of the mammalian lacunar-canalicular system. Bone, 46: 1075-1081. Used
with permission from Elsevier.
Relation between Load and Structural Alignment
The alignment of cortical
and cancellous bone
tissue is arranged to
withstand typical daily
loads.
Femoral image courtesy of Bartleby.com Inc.
Stress – Strain for a Viscoelastic Material
Stress – Strain for a Viscoelastic Material
From: Stolken JS, Kinney JH. On the importance of geometric nonlinearity in finite-element simulations of trabecular bone failure.
Bone, 33: 494-504, 2003. Used with permission from Elsevier
Canaliculi Form Intercellular Communication Network
From: Tanaka-Kamioka K, et al. In situ permeability measurement of the mammalian lacunar-canalicular system. J Bone Min Res, 13: 15551568, 1988. Used with permission from Blackwell Science, Inc.
Stress – Strain for a Viscoelastic Material
Osteocytes are
embedded in osteons
which are arranged
around a central
Haversian canal.
Mechanical loading of
bone generates fluid
flow in the cannicular
space, eliciting
biochemical responses
from the osteocytes to
the imposed loads.
Material Testing System
Images courtesy of Instron
Strain Units & Physiological Strain
Microstrain (με) Units
% Change in Length
1,000 microstrain
1,000 με
0.1%
10,000 microstrain
10,000 με
1.0%
25,000 microstrain
25,000 με
2.5%
Physiological Strain Ranges for Long Bones
400 – 3,000
microstrain
Seldom above 1,000
microstrain
400 – 3,000 με
0.04 – 0.3%
1,000 με
0.1%
Comparison of Stress – Strain for Cortical & Cancellous
Effects of Rate of Loading on Mechanical Response
Viscoelastic tissues
are stronger when
loaded fast.
The increased
stiffness is
attributed to the
resistance of
movement of fluid.
Relationship between Load and Fracture
Relationship between Load and Fracture
Objective of Adaptive Bone Remodeling
• How does a region of bone cells determine the
required strength for a region on bone?
• During walking peak strains are less than 1000 με.
• Strains in vigorous activities (landing, plyometrics)
are 2000 – 3200 με (Fritton, 2000).
• The objective of adaptive remodeling is to maintain
bone cell alignment and structural density so that
typical daily loads produce strains of 400 – 1000 με.
Osteocytes
Osteocytes are
thought to inhibit
osteoclasts from
absorbing bone
tissue.
When a crack occurs
the osteocyte
network is no longer
able to inhibit
osteoclasts
What is the Advantage of Curved Bones?
• A curved bone deforms
in a predictable
direction.
• Increasing the
magnitude of loading
causes an increase in
the osteogenic
stimulus.
Measuring Bone Density with
Dual-Energy X-Ray Absorptiometry (DEXA)
Example DEXA Measurement
Understanding DEXA Results
For BMD the DEXA reports T and Z Scores
T Score: This number compares the amount of bone you have
to a young adult of the same sex with peak bone mass.
The T score is used to define osteoporosis:
T −1 (T minus 1) or higher is normal
T − 2.5 to -1 is considered osteopenia
T − 2.5 and below is a diagnosis of osteoporosis
The T score can be used to estimate fracture risk:
T − 0 means your risk is the same as a normal 40 year old
T − 1 means your risk is twice as likely
T − 2 means your risk is four times as likely
T − 3 means your risk is eight times as likely
Z Score
This number compares the amount of bone you have to a
person in your age group of the same sex and size.
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T-Score Compares BMD with a 40 Year Old
21
Trabecular Bone Thinning with Osteoporosis
From Mosekilde L. Age-related changes in bone mass, structure, and strength – effects of loading . Z Rheumatol, 59 (Suppl 1):1-9, 2000.
Used with permission from Steinkopff Verlag.
Articular Cartilage
From: Herzog et al. The role of muscles in joint degeneration and osteoarthritis J Biomech, 40 S1: S54-S63
Impact
Loading &
Osteoarthritis
The rabbit’s leg was
impacted with a force of
1.5 BW that reached a
peak in 50 ms.
One hour of impacts
were delivered each day.
In 36 days:
Cortical bone on the
ends of the bone
thickened, cancellous
bone became brittle,
cartilage was thin or
non-existent.
From Radin EL, et al. Response of joints to impact loading – III. J Biomech, 6:51-57, 1973. Used with permission from Elsevier.
Radin’s Sheep
• Adult sheep were subjected to prolonged activity on
hard surfaces by walking them daily on concrete and
housing them on tarmac.
• Control sheep were walked on compliant wood chip
surfaces and pastured.
Femoral condyle of sheep
that walked on concrete
• After 9 months the sheep exposed only to concrete
walked with a limp.
• After 2 ½ years significant changes occurred:
Femoral condyle of sheep
that walked on compliant
wood chips
1.
Articular cartilage thinned or was non-existent.
2.
Subchondral cortical bone thickened.
3.
Trabecular pattern of cancellous bone was altered.
4.
The increased cortical thickness and altered
trabecular alignment stiffened the bone.
Radin EL, Orr RB, Kelman JL, Igor LP, Rose RM. Effect of prolonged walking on concrete
26
on the knees of sheep. J Biomech. 15:487-492, 1982.
Osteoarthritis
Knee Arthroscopy
Articular Cartilage
From: Herzog et al. The role of muscles in joint degeneration and osteoarthritis J Biomech, 40 S1: S54-S63
Subchondral Bone Stiffening
Cracks in articular cartilage are one of the first visible signs of the
development of osteoarthritis. Radin & coworkers have suggested
that subchondral bone stiffening may occur prior to any visible sign
of the development of osteoarthritis.
From: Herzog et al. The role of muscles in joint degeneration and osteoarthritis J Biomech, 40 S1: S54-S63
Principles of Health Bone Loading for Physical Education
• Physical educators can optimize the osteogenic effect of exercise by
incorporating exercises designed to stimulate healthy bone loading
(McKay, et al. 2005).
• Physical educators should follow these principles to optimize
healthy bone loading:
1. Children should perform 120 – 200 jumps / day, for 5 days/week.
2. Different types of jumps should be performed each day or each week.
For example: week 1 – jumping rope, week 2 – hopping…., week 3 –
shuttle run…
3. Static loads are not as effective as dynamic loads.
4. Spreading the activity over 3 – 5 days is far more effective than doing
the jumping/hopping activity all in one day.
Adapted from: McKay HA et al. “Bounce at the Bell”: a novel program of short bouts of exercise improves
proximal femur bone mass in early pubertal children. Br J Sports Med, 39(8): 521 – 526, 2005.
Blood Vessels Invade Articular Cartilage
Yield Point for Ligaments & Tendons
Effects of Exercise on Ligaments & Tendons
Biomechanical Descriptors of the Mechanisms of Injury
• Minimum time for neuromuscular system to respond
to a stimulus.
• Magnitude of force.
• Rate of force application.
• Point of force application.
• Direction of force application.
• Number of repetitions of loading.
• State of training (de-trained, immobilized, overtrained).
• Critical limits of the tissue (warm-up, previous injury).
• Magnitude of muscular preactivation.
Reflex Responses
The minimum time of the
neuromuscular system to
respond to a stimulus is
80 – 200 ms.
What happens when you go
down a flight of stairs in the
dark and you think you are at
the bottom, but there is one
more stair?
This scenario illustrates the
limitations of the
neuromuscular system to
respond to a stimulus.
Reflex Responses
• The minimum time of the
neuromuscular system to
respond to a stimulus is 80 –
200 ms.
• 30-120 ms from sensor
(muscle spindle, GTO ..) to
initiation of muscle tension
• 50-300 ms for muscle to
develop peak tension.
• Additional time will be
necessary to overcome the
momentum of the body:
 Ft  mV
f
 mVi
The Role In Muscles In Preventing Injury
• Does strength
training protect
joints from injury?
• Yes, but it depends
upon the rate of
loading and the
magnitude of
preactivation of
the muscles.
[Pope #226]
38
Critical Limits of the Tissue
The Antero-Talofibular Ligament can withstand
approximately 139 N. [Nordin & Frankel, p 247 3Ed]
39
40
Prior to ground contact the knee extensors are preactivated to prepare for the collision with the ground.
Muscular Preactivation
41
Muscular Preactivation
EMG activity during landing from a drop height of 0.2 m with and without vision
The rectified EMG recordings from the tibialis anterior, soleus, rectus femoris and biceps femoris muscles (TA,
SO, RF and BF, respectively) during landings from a 0.2 m drop height are shown for ‘no vision’ and ‘vision’
conditions (left and right column, respectively). The traces are averages of five landings (subject 3). Dashed
and continuous lines indicate take-off and touchdown, respectively. Calibration bars, expressed as a
percentage of the EMG amplitude recorded during maximal voluntary contraction, apply to both landing
conditions.
From: Santello et al, Visual and non-visual control of landing movements in humans. J Physiol. 537 (Pt 1): 313-237, 2001.
Muscular Preactivation
EMG activity during landing from a drop height of 0.8 m with and without vision
Rectified EMG recordings from the TA, SO, RF and BF muscles during landings from a 0.8 m drop height are
shown for ‘no vision’ and ‘vision’ conditions (left and right column, respectively). The traces are averages of
five landings (subject 3). Dashed and continuous lines indicate take-off and touchdown, respectively.
Calibration bars, expressed as a percentage of the EMG amplitude recorded during maximal voluntary
contraction, apply to both landing conditions.
From: Santello et al, Visual and non-visual control of landing movements in humans. J Physiol. 537 (Pt 1): 313-237, 2001.
Muscular
Preactivaton
Soleus
preactivation 100
ms prior to ground
contact.
Tibialis anterior
preactivation 100
ms prior to ground
contact.
From: Santello et al, The control of
timing and amplitude of EMG activity
in landing movements in humans.
Exp Physiol. 83: 857-874, 1998.
Effects of Drop Height on Preactivation
From: Santello et al., The control of timing and amplitude of EMG activity in landing movements in humans. Exp
Physiol. 83: 857-874, 1998.
Muscular Preactivation in
Running
Runner increases
muscular
preactivation with
increasing
running speed.
46
Direction & Point of Force Application
Magnitude of Force & Repetitions