This document discusses working postures and movements related to reaching. It defines key concepts like postural space, which refers to all postures the body can adopt given physical limitations, and postural strategy, which is a systematic relationship between determinants and posture. Postural strategy aims to minimize factors like movement, discomfort and work. Reach direction and distance are also discussed, with reach direction defined as the arm angle relative to the body and reach distance as the arm length. Studies show that reach distance affects trunk and arm movements, with the pelvis and proximal segments tending to remain neutral.

1. Motor Behavior
Working Postures and Movements 1

2. CONTENTS
Introduction
Postural Space
Postural Strategy
Reaching
Reach Direction
Reach Distance
2

3. Introduction
working posture is how a
person positions their
body while performing a
task
Working posture is determined by
the characteristics of
workstation
operation
w
orker
sense systems
motor systems
level of skill
psychosocial factors such as stress,
boredom
1.
2.
3.
two concepts that are
related to working posture:
postural space and
postural strategy
3

4. Postural Space
all working postures that can be adopted voluntarily and
momentarily, given a set of physical limitations
4

5. The postural space depends on several factors:
- ranges of motion of body joints
- visual acuity
- Dimensions, spatial position, and orientation of a workstation and a
worker
- The operation may pose demands on vision, control, and stability
5

6. Stability: balanced and stable posture of their whole body and
the body segments, enough support from the workstation.
factors can influence the postural space by operation:
Vision: requires a minimum angle between the line of sight
(gaze direction) and the surface of a visual target
Control: require a certain type and orientation of grip/contact
6

7. 7

8. Postural Strategy
A postural strategy is defined as a systematic relationship disclosed
between the determinant in question and the working posture
Some of the postural strategies are based on minimizing movement,
deviation, discomfort, work, or error. For example, Evershed's states
that a body segment will be moved only if a target cannot be reached
by movement of more distal segments
8

9. Some of the postural strategies are based on neutral posture .
for example Hsiao and Keyserling hypothesize that a proximal
segment (i.e., one closer to the buttocks) would show a greater
tendency to stay close to a neutral posture than a distal segment,
whenever movement of segments was necessary to view or reach
a target.
Some of the postural strategies are based on optimization. Jung
et al. incorporates an optimization algorithm. The model predicts
that in reality the upper body posture with the lowest total score
will be chosen by subjects
9

10. Reaching
For manual operations the hand is directed toward a target by
reorienting one or more body segments (e.g., forearm, upper
arm, shoulder girdle, chest, and pelvis).
the position of a target is described with respect to the upper
body in terms of spherical coordinates by a reach direction and a
reach distance. 10

11. Reach Direction
angle of the arm relative to the body when reaching for a target
depending on the target position, a plane or a curved surface
Listing's law, Fick's law: They describe how the arm avoids
unnecessary rotations and maintains a stable orientation
Listing's law :arm changes its direction by rotating around axes that
all lie in one plane( Listing's plane) for small target positions
For more eccentric targets, the arm rotates around axes that lie on
a curved surface instead of a plane. This surface is called the Fick's
surface
11

12. 12

13. Reach distance is the length of the arm when reaching
for a target
Reach distance influences how these joints move and
how much they contribute to reaching
Hepp et al. (1992)
Fischer et al. (1997) quantified the travel costs in the
model by Rosenbaum (1995)
13

14. Hsiao and Keyserling studied the movements of the upper
extremity, chest, and pelvis when reaching for different targets in
front of them.
A neutral posture is a posture that minimizes stress and strain on
the muscles and joints.
Jung et al. (1992, 1995) agreed that trunk twisting and lateral
bending were the least likely options to be used by subjects to
reach a target.
posture behavior of seated subjects during reaching tasks
Posture behavior
14

15. Several researchers have studied the effects of reach distance on upper
body posture
Hsiao and Keyserling
the pelvis shifts when a target location is too far away
Snyder et al
the upper arm elevation and trunk inclination change at different rates
when moving the elbow forward
the contribution of the trunk is smaller during standing than during sitting
the reach distance affects trunk flexion, shoulder flexion, elbow flexion, and
pelvis-shifting
Reach Distance
15

16. Summary A hand position and a gaze direction may be realized by
many combinations of orientations of body segments and
eyes.
(1) a body segment will be moved only if a target cannot
be reached by the segments located more distally
(2) a proximal segment will show a greater tendency to
stay close to its neutral joint position than distal segment,
to minimize discomfort
(3) segments will be moved in such a way that the amount
of work done is minimized
16