title: A novel shoulder-elbow mechanism for increasing speed in a multijoint arm movement.
abstract: The speed of arm movements is normally increased by increasing agonist muscle activity, but in overarm throwing, an additional effect on speed may come from exploitation of interaction torques (a passive torque associated with motion at adjacent joints). We investigated how the central nervous system (CNS) controls interaction torques at the shoulder and elbow to increase speed in 2-D overarm throwing. Twelve experienced throwers made slow, medium, and fast 2-D throws in a parasagittal plane. Joint motions were computed from recordings made with search coils; joint torques were calculated using inverse dynamics. For slow and medium-speed throws, elbow extension was primarily produced by elbow muscle torque. For fast throws, there was an additional late-occurring elbow extensor interaction torque. Parceling out this elbow extension interaction torque revealed that it primarily arose from shoulder extension deceleration. Surprisingly, shoulder deceleration before ball release was not caused by shoulder flexor (antagonist) muscle torque. Rather, shoulder deceleration was produced by passive elbow-to-shoulder interaction torques that were primarily associated with elbow extension acceleration and velocity. It is concluded that when generating fast 2-D throws, the CNS utilized the arm's biomechanical properties to increase ball speed. It did this by coordinating shoulder and elbow motions such that an instantaneous mechanical positive feedback occurred of interaction torques between shoulder and elbow before ball release. To what extent this mechanism is utilized in other fast multijoint arm movements remains to be determined.
authors.affiliation: Department of Physiology and Pharmacology, The University of Western Ontario, Medical Science Bldg, London, ON, N6A 5C1, Canada.
authors.forename: Derek B
authors.initials: DB
authors.lastname: Debicki
authors.forename: Sherry
authors.initials: S
authors.lastname: Watts
authors.forename: Paul L
authors.initials: PL
authors.lastname: Gribble
authors.forename: Jon
authors.initials: J
authors.lastname: Hore
mesh_terms: D000704:Analysis of Variance; D001132:Arm / Q000502:physiology*; D001696:Biomechanical Phenomena; D001921:Brain / Q000502:physiology; D004550:Elbow / Q000502:physiology*; D004551:Elbow Joint / Q000502:physiology; D025461:Feedback, Physiological; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D012782:Shoulder / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology; D019415:Torque; D055815:Young Adult
references.citation: Exp Brain Res. 2004 May;156(1):39-54
references.pmid: 14689134
references.citation: J Biomech. 1993;26 Suppl 1:125-35
references.pmid: 8505347
references.citation: Exp Brain Res. 2002 Jan;142(2):163-80
references.pmid: 11807572
references.citation: Med Sci Sports Exerc. 1991 Jan;23(1):130-44
references.pmid: 1997807
references.citation: J Neurophysiol. 1999 Jul;82(1):103-14
references.pmid: 10400939
references.citation: J Theor Biol. 2001 Jul 7;211(1):39-53
references.pmid: 11407890
references.citation: J Neurophysiol. 1996 Apr;75(4):1760-4
references.pmid: 8727412
references.citation: Exp Brain Res. 2004 Feb;154(3):382-94
references.pmid: 14598003
references.citation: Exp Brain Res. 2002 Sep;146(1):11-25
references.pmid: 12192573
references.citation: Exp Brain Res. 1995;103(3):451-9
references.pmid: 7789451
references.citation: Vision Res. 1990;30(1):97-110
references.pmid: 2321369
references.citation: Exp Brain Res. 1998 Aug;121(3):239-54
references.pmid: 9746130
references.citation: J Neurophysiol. 1995 Oct;74(4):1374-81
references.pmid: 8989378
references.citation: J Biomech. 1989;22(8-9):805-17
references.pmid: 2613716
references.citation: J Neurophysiol. 1996 Jul;76(1):492-509
references.pmid: 8836239
references.citation: Biol Cybern. 1982;44(1):67-77
references.pmid: 7093370
references.citation: J Neurophysiol. 1999 Nov;82(5):2310-26
references.pmid: 10561408
references.citation: J Neurophysiol. 2000 Oct;84(4):1988-2000
references.pmid: 11024092
references.citation: Cerebellum. 2008;7(3):366-78
references.pmid: 18597149
references.citation: J Neurophysiol. 2007 Sep;98(3):1240-52
references.pmid: 17625062
references.citation: J Biomech. 1986;19(10):867-77
references.pmid: 3782169
references.citation: J Neurophysiol. 2004 Aug;92(2):754-65
references.pmid: 15056688
references.citation: Exp Brain Res. 2005 May;163(2):252-7
references.pmid: 15754174
references.citation: J Biomech. 1992 Oct;25(10):1173-84
references.pmid: 1400517
references.citation: Exp Brain Res. 2005 Sep;166(1):1-16
references.pmid: 16132966
references.citation: J Biomech. 1983;16(6):411-7
references.pmid: 6619157
references.citation: Exp Brain Res. 2001 Dec;141(4):471-84
references.pmid: 11810141
references.citation: J Neurophysiol. 2007 Jan;97(1):680-91
references.pmid: 17079349
references.citation: J Neurophysiol. 1985 Nov;54(5):1282-94
references.pmid: 4078617
references.citation: J Sports Sci. 2006 Nov;24(11):1183-94
references.pmid: 17175616
references.citation: J Neurophysiol. 2000 May;83(5):3019-30
references.pmid: 10805697
references.citation: Exp Brain Res. 2005 Jul;164(3):365-75
references.pmid: 15883810
references.citation: J Neurophysiol. 1999 Sep;82(3):1187-97
references.pmid: 10482738
references.citation: J Neurophysiol. 2003 Apr;89(4):1784-96
references.pmid: 12611996
references.citation: J Neurophysiol. 2005 Jun;93(6):3189-99
references.pmid: 15911892
references.citation: J Sports Sci. 1996 Dec;14(6):483-95
references.pmid: 8981287
references.citation: J Neurophysiol. 1996 Mar;75(3):1013-25
references.pmid: 8867114
references.citation: J Neurophysiol. 1985 Nov;54(5):1271-81
references.pmid: 4078616