This document discusses biomechanics and activities of daily living. It defines biomechanics as the study of mechanics in the human body. Functional biomechanics looks at the link between the human body and its environment. Biomechanics consists of kinematics, the description of motion, and kinetics, the forces producing motion. Common activities like running, lifting, and walking are analyzed in terms of joint motion and ground reaction forces. Proper form and muscle engagement can reduce stresses, as seen in squat lifting versus stoop lifting.

1. BIOMECHANICS OF
ACTIVITIES OF DAILY
LIFE
PART-I
Radhika Chintamani03/30/20
Activities 1

2. Definition of biomechanics and
Functional Biomechanics
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 Biomechanics: The study of
mechanics in the human body is
referred to as biomechanics.
 Functional Biomechanics: It is the link
between human body and environment
which dictates human function.
 Usually human functions are 3
dimensional.

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Biomechanics Consists of: kinematics and
kinetics.
 Kinematics is the area of biomechanics that
includes descriptions of motion without regard for
the forces producing the motion.
 Kinetics is the area of biomechanics concerned
with the forces producing motion or maintaining
equilibrium.

4. Kinematics
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Kinematics variables for a given movement may
include
 The type of motion that is occurring
 The location of the movement
 The direction of the motion
 The magnitude of the motion, and
 The rate or duration of motion

5. Type of Functional Motion
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 In human body one can describe the path
taken by the body as a whole, or describe
the path taken by one or more of its
component levers.
 Types are:
1. Running
2. Lifting
3. Sit-to-stand
4. Throwing
5. Walking

6. Movements are always described
on the basis of axis and planes
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 A sagittal axis lies parallel to the sagittal suture
of the skull i.e. anterior-posterior direction.
Movement about this axis is in a frontal plane.
 A frontal axis lies parallel to the transverse
suture of the skull. Movement about a frontal
axis is in a sagittal plane.
 A vertical axis lies parallel to the line of gravity
and movement is in a horizontal plane

7. KINETICS
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 Forces- is that which alters the sate of rest of a
body or its uniform motion in a straight line.
Application of a force to a body is specified by
-direction of the force
-magnitude of the force

8. Running
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 Running is defined as:
 As running Velocity increases, there is an initial increase in
step length, followed by increased cadence
 Stride length is limited by runner’s leg length, height, and
ability; generally the longer the stride, the higher the velocity
 When optimum stride length is attained; further velocity
increases will come from increased cade
 Step length – IC of one foot to IC of the 2nd foot
 Stride length – IC of 1st foot to IC of the same foot
 Cadence – number of steps in a given time; on average about
100-122 steps/min with females averaging about 6-9 s/m
higher

9. Running vs Walking Cycle
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 The Running Gait Cycle has a temporal reversal of
Stance: Swing phases (40:60) as compared to
Walking Gait Cycle (60:40); the stance phase during
sprinting may be as low as 22% of cycle
Stance Phase: Absorption – (Mid stance) – Propulsion
Swing Phase: ISW (75%) – (MSW) - TSW (25%)
Running Gait – two periods of double float in swing;
refers to when neither foot is in contact w/ the ground;
at the beginning and at the end of each running swing
phase
Walking Gait – two double support periods in stance

10. Knee Kinematics of Running
 The knee demonstrates increased flexion with increasing velocity.
 Absorption phase of the stance phase sees knee flexion to accommodate
ground reactive forces; (walking only requires about 10 deg of flexion
vs.35 during running)
 Max knee flexion occurs at Mid Stance, after IC, during the absorption
phase;
 This is followed sequentially by knee extension; max knee flexion during
walking occurs just after Toe Off
 Avg. Knee ROM is 63 deg during Running and 60 deg during walking

11. Hip Kinematics of Running
 Degree of Flexion of the hip increases and
extension of the hip decreases with increasing
velocity.
 Maximum hip extension occurs at Toe Off
 Maximum hip flexion occurs at TSW

12. Ankle and Foot Kinematics
 There are various joints in ankle and foot complex.
Following are the movements occurring in that
complex;
 Ankle joint – primary plantar/dorsiflexion
 Foot joints – including subtalar, oblique midtarsal,
longitudinal midtarsal and 5th ray= for tri-planar
pronation/supination
 Pronation – dorsiflexion/eversion/abduction
 Supination – plantarflexion/inversion/adduction
 Metatarsophalangeal joints (MTP) are biplanar –
mostly dorsiflexion/plantarflexion w/ some
abduction/adduction

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 Running: Ankle ROM accumulates up
to 50 degrees
 During Initial Contact: ankle undergoes
rapid dorsiflexion
 Supination is limited due to diminished
time of plantarflexion
 Sudden pronation may lead to excessive
pronation injuries
Running shoes or orthotics may limit this
excessive pronation, and allow for more
supination, and thus a more rigid foot for
propulsion
A pronated subtalar joint allows the foot
to become the “mobile adapter”; whereas
a supinated subtalar joint serves to lock
the midtarsal joints, creating a rigid lever
to better serve propulsion
Overpronation

14. Windlass Mechanism
The plantar fascia and the intrinsic foot muscles increases the
efficiency of propulsion by providing “spring-like” support to the
medial arch of the foot, which helps to undergo supination, thus
contributing an elastic tension.

15. Hip-Knee and Ankle mechanism of
Running
 At Initial Contact: the pelvis, femur and tibia
begin to internally rotate; int. rotation lasts
through Loading Response until Mid Stance
causing eversion of the foot complex (mid-foot
unlocking).
 External Rotation of the pelvis, femur and tibia
begin during Mid Stance, causing inversion
(mid-foot locking)

16. Kinetics
 As compared to walking, running increases muscle
activity in all muscles
 Vertical reactive forces are the most significant in
running
 In rearfoot or heel strikers (80% of runners), there is
a “two-bump” force plate appearance with one
occurring in the rearfoot during loading response
and one in the forefoot during propulsion suggesting
maximum weight bearing during loading response
and propulsion.
 Thus; Running produces GRF of 3-4x body weight

17. Lifting
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 There are various types of lifting positions. Two
basic types are;
a. With lumbar flexion =Stoop lift: extensor of back
contribute to most of the work. (Lumbo-pelvic
rhythm)
b. With neutral position of lumbar= Squat lift:
extensor of hip contribute to most of the work.
(Reverse Lumbo-pelvic rhythm)
 With regard to lifting postures, the load on lumbar
region increases as inclination of trunk increases.

18. Factors influencing the loads on
spine during lifting
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 The position of the object relative to the COM in the
spine: nearer the object to the human body, lesser
the trunk flexion (less load on Lx spine) and farther
the object greater the trunk flexion (more load on Lx
spine).
 Velocity of lifting= greater the velocity: greater the
load on Lx spine. (the Maximum peak amplitude
increases as the velocity increase, suggesting the
greater number of motor unit recruitment)
 The degree of flexion of the spine: greater the
flexion degree, greater the load imposed on the
spine.
 The size, shape, weight, and density of the object.

19. Importance of Squat lifting
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 During squat lifting the entire core muscles are
engaged to support the lumbar spine as one cylinder.
 The important muscle among core to engage the spine
is transversus abdominis. It is known as abdominal
binder which binds the rectus abdominis (trunk flexor)
with multifidus and erector spinae(back extensor).
 Thus, weakness of transversus abdominis lead to weak
core and maximum load on Lx spine during lifting.
 During stoop lifting the transversus abdominis remain
slightly relaxed, thus Lx experiences maximum load.

20. References
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 Oatis C. Kinesiology-Mechanics and
Pathomechanics of Human Movement
 Gardiner D. The principles of Exercise
Therapy
 Levangie P and Norkin C. Joint Structure and
Function