The effect of handle friction and inward or outward torque on maximum axial push force.
OBJECTIVE
To investigate the relationship among friction, applied torque, and axial push force on cylindrical handles.


BACKGROUND
We have earlier demonstrated that participants can exert greater contact force and torque in an "inward" movement of the hand about the long axis of a gripped cylinder (wrist flexion/forearm supination) than they can in an "outward" hand movement.


METHODS
Twelve healthy participants exerted anteriorly directed maximum push forces along the long axis of aluminum and rubber handles while applying deliberate inward or outward torques, no torque (straight), and an unspecified (preferred) torque.


RESULTS
Axial push force was 12% greater for the rubber handle than for the aluminum handle. Participants exerted mean torques of 1.1, 0.3, 2.5, and -2.0 Nm and axial push forces of 94, 85, 75, and 65 N for the preferred, straight, inward, and outward trials, respectively. Left to decide for themselves, participants tended to apply inward torques, which were associated with increased axial push forces.


CONCLUSIONS
Axial push force was limited by hand-handle coupling--not the whole body's push strength. Participants appeared to intuitively know that the application of an inward torque would improve their maximum axial push force. Axial push forces were least when a deliberate torque was requested, probably because high levels of torque exertions interfered with the push.


CONCLUSIONS
A low-friction handle decreases maximum axial push force. It should be anticipated that people will apply inward torque during maximum axial push.
University of Michigan, Ann Arbor, Michigan, USA. n-seo@northwestern.edu
Na Jin
NJ
Seo
Thomas J
TJ
Armstrong
Don B
DB
Chaffin
James A
JA
Ashton-Miller
D000328:Adult; D000367:Age Factors; D000535:Aluminum; D000704:Analysis of Variance; D004576:Electromyography; D006804:Ergonomics; D005260:Female; D017276:Friction; D006225:Hand / Q000502:physiology*; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D007258:Informed Consent; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D012408:Rubber; D012737:Sex Factors; D019415:Torque; D014955:Wrist Joint / Q000502:physiology
D012408:Rubber; D000535:Aluminum