Biomechanics, NTUPT 2003

Pushing and Pulling

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Push-and-Pull Motions
Force Imparting
Biomechanics of Pushing a Cart

Hamilton, N., & Luttgens, K. 2002. Kinesiology, Scientific Basis of Human Motion, 10^thed. Boston: McGraw-Hill. Chapter 17, pp. 435-449.

Chaffin, D.B, & Andersson G.B.J., 1999. Occupational Biomechanics, 2^nd ed.

Objectives: After studying this topic, the students will be able to

define push and pull patterns of motion
identify the the activities that involves push and pull patterns and give examples
analyze mechanical factors that affecting to push-and-pull activities

Push-and-Pull Motions

Definition

broad definition： a segment motion that involves moving an object, either directly by part of the body or by means of implement, in pushing and pulling pattern (Hamilton & Luttgens 2002, p.436)

a pitcher throws a baseball

a tennis player serves a tennis

a worker lifts a box from the floor onto an overhead rack

an archer shoots an arrow from a bow

limited definition： a segmental motion that all forces are continuously applied onto an external object (continuous application pattern of sequential movement)

an individual pushes a desk across the room

a traveler pulls his suitcase

Joint Action Patterns

simultaneous and opposite movement pattern in the upper extremity

flexion in elbow with extension in shoulder

extension in elbow with flexion in shoulder

simultaneous movement pattern in the lower extremity

simultaneous extension in the hip, knee, and ankle joints

simultaneous flexion in the hip, knee, and ankle joints

at the distal end of the movement chain, a rectilinear path of motion is present.

All forces produced by segmental motion are applied directly to the object and applied in the direction of motion. (Hamilton & Luttgens 2002, p.436)

results： maximum forces and/or maximum accuracy but no tangential forces

trade-off in velocity and accuracy

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Force Imparting

Mechanical Factors to be Considered

source of force

by hand

by foot

by head

by trunk

by implement

force

magnitude of force

direction of force

point of force application

stability of the body at the moment of giving motion

the interaction between the body and the surface that supports it

characteristics of the moving object

Magnitude of Force

The force to move an object must be greater enough to overcome the resultant of the following forces

internal resistance (moment of inertia)

friction between the object and the supporting surface

resistance of the surrounding medium, such as air or water

For maximum force production, the maximum number of segments should be used through the largest safe range of motion.

For maximum force accuracy, the minimum number of segments should be used through the smallest possible range of motion.

Direction of Force

The direction the object moves is determined by the direction of the resultant of all forces imparting on it

For maximum force production, the segments involved should be aligned with the intended direction.

If the object is subject to move along a preset path (e.g. a sliding door), any component of force not in this direction will be wasted and may act to increase resistance. If that force is greater enough, then some destructions will occur.

Point of Force Application

Force applied in line with the COM of an object will result in linear motion of that object, provided the object is freely movable; otherwise, it will result in rotary motion.

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Biomechanics of Pushing a Cart

Economy of Effort

use lower extremities ( friction)

force applied in line with the object’s COM and in desired direction

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