Chapter 17: Moving Objects: Pushing and Pulling

1. Chapter 17:Moving Objects:Pushing and Pulling KINESIOLOGY Scientific Basis of Human Motion, 11th edition Hamilton, Weimar & Luttgens Presentation Created by TK Koesterer, Ph.D., ATC Humboldt State University Revised by Hamilton & Weimar

2. Objectives • Classify activity involving push or pull patterns to the nature of the force application. • Name and discuss anatomical and mechanical factors and principles that apply to representative push or pull activities. • Analyze the performance of someone performing a push-pull skill under each of these force application conditions: momentary contact, projection, or continuous application.

3. PUSHING AND PULLINGJoint Action Patterns • The basic joint actions are flexion and extension in one or more of the extremities. • These joint motions produce a rectilinear path of motion at the distal end point of the segments involved. • Rectilinear path: all forces are applied directly to the object in the direction of motion. • Force may be applied directly or indirectly to an object.

4. Nature of Force ApplicationMomentary Contact • Striking and hitting. • Contact made with an object by moving part of body or implement. • Object may be stationary or moving. Fig 17.1

5. Projection • Development of kinetic energy in a movable object held in the hand. • Followed by the release of the object. Fig 17.2

6. Continuous Application • Continuous application of force, usually by hand. • Moving a large resistance. Fig 17.3

7. PRINCIPLES OF PUSHING AND PULLING MOTIONS • Motion involves imparting a force, described in terms of its magnitude, direction, and point of application. • These aspects of force provide the basis of the principles that apply to giving motion to objects or bodies through pushing and pulling.

8. Principles Relating to the Magnitude of Force • The object will move only if the force is of sufficient magnitude to overcome the object’s inertia.The force must overcome not only the mass of the object, but also; • friction between object and supporting surface. • resistance to surrounding medium. • internal resistance.

9. Principles Relating to the Magnitude of Force • Force exerted by the body will be transferred to an external object in proportion to the effectiveness of the counterforce of the feet against the ground. • Optimum summation of internal force is needed if maximum force is to be applied to move an object. (Maximum number of segments moved through largest ROM.)

10. Principles Relating to the Magnitude of Force • For maximum accuracy, the smallest possible number of segments should be used through the smallest possible ROM. • For a change in momentum to occur, force must be applied over time.

11. Principles Relating to the Direction of Force • The direction in which the object moves is determined by the direction of the force applied to it. • If an object is forced to move only along a predetermined pathway, any component of force not in the direction of this pathway is wasted and may serve to increase friction. • When optimum force production is the purpose, those segments involved should be aligned with the direction of intended force production.

12. Principles Relating to the Point at Which the Force is Applied • Force applied in line with an object’s center of gravity will result in linear motion. • Force applied not in line with an object’s center of gravity will result in rotary motion. • If the free motion of an object is interfered with by friction or by the presence of an obstacle, rotary motion may result, even though the force is applied in line with the object’s center of gravity.

13. PUSH-PULL APPLICATIONSPushing and Pulling • The magnitude of force used in pushing, pulling, and lifting can be increased in two ways: • Using the lower extremities. • Using body weight to supplement the force provided by the upper extremities. • Economy of effort is when force is applied in line with object’s center of gravity and in the direction of motion.

14. Pushing an Object • The horizontal push should be applied close to the object’s center of gravity at a point found by experimentation. Fig 17.4

15. Pulling an Object • It may be advantageous to pull in a slightly upward direction because lifting effect would help to reduce friction.

16. Lifting • Is a form of pulling. • Minimizing the resistance arm will reduce the amount of effort needed to lift object. Fig 17.5

17. Lifting • Several factors must be considered for safe, efficient lifting: • Reduce load mass as much as possible. • Avoid loads at floor level to reduce trunk bending. • The farther the load is from the involved joints, the greater the resistance arm. Keep loads close to the body. • Maintain a neutral posture of the spine. • Avoid trunk rotation & lateral flexion while lifting to reduce stress on the spine. • Maintain constant lift velocity to avoid acceleration forces.

18. Holding and Carrying • Holding: effort can be minimized by supporting the object from underneath, with only enough force applied to counteract the downward pull of gravity. • Carrying: most efficient manner is that which requires the least accommodation of the body’s center of gravity.

19. Weight Lifting • Depending on lift, either a push or a pull pattern may be used. • The key to safe and successful weight lifting is in arranging the various levers involved in such a way as to minimize the torque produced by the external resistance while maximizing the available muscle torques.

20. Punching • Simultaneous push pattern motions. • Usually directed horizontally. • Usually terminates with contact. • Since momentum is to be transferred to the opponent, it is desirable for punch velocity to be high. • Simultaneous nature allows for maximum force production with a straight-line motion.

21. Working with Long-Handled Implements • Involves a combination of pushing, pulling, and, in some instances, lifting. • Back and forth motion: tendency to lean forward. • Although implement is light, the forward position means a long resistance arm and added resistance on back muscles. • When shoveling, slide one hand down the shaft to reduce lever arm.

22. ANALYSIS OF ERGOMETER ROWING • The motion is a combination of leg push and arm pull in a continuous cycle. • Two primary phases; • Drive phase • Recovery phase

23. Drive Phase • Rower starts with slide in forward position. • Starting position: knees and hips fully flexed, shoulders flexed, and elbows in extension. • Initiated through extension of legs, pushing body backward. • As legs near full extension, spine begins extension to maintain smooth, continuous motion. • Arms now begin motion, pulling arms in.

24. Recovery Phase • Leg flexion is produced by a fairly moderate concentric contraction of flexor muscles. • The forward reach of the upper extremity is produced by similar contraction of appropriate muscles.

25. Mechanical Analysis • Primary objective is to produce maximum power. • Generate the highest possible velocity through a combination of stroke length and stroke rate. • Effective performance is when force can be applied through the full ROM and at the fastest possible stroke rate.

26. Chapter 17:Moving Objects:Pushing and Pulling