title: In vivo measurement of dynamic rectus femoris function at postures representative of early swing phase.
abstract: Forward dynamic models suggest that muscle-induced joint motions depend on dynamic coupling between body segments. As a result, biarticular muscles may exhibit non-intuitive behavior in which the induced joint motion is opposite to that assumed based on anatomy. Empirical validation of such predictions is important for models to be relied upon to characterize muscle function. In this study, we measured, in vivo, the hip and knee accelerations induced by electrical stimulation of the rectus femoris (RF) and the vastus medialis (VM) at postures representatives of the toe-off and early swing phases of the gait cycle. Seven healthy young subjects were positioned side-lying with their lower limb supported on air bearings while a 90 ms pulse train stimulated each muscle separately or simultaneously. Lower limb kinematics were measured and compared to predictions from a similarly configured dynamic model of the lower limb. We found that both RF and VM, when stimulated independently, accelerated the hip and knee into extension at these postures, consistent with model predictions. Predicted ratios of hip acceleration to knee acceleration were generally within 1 s.d. of average values. In addition, measured responses to simultaneous RF and VM stimulation were within 13% of predictions based on the assumption that joint accelerations induced by activating two muscles simultaneously can be found by adding the joint accelerations induced by activating the same muscles independently. These results provide empirical evidence of the importance of considering dynamic effects when interpreting the role of muscles in generating movement.
authors: Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, WI, USA.
authors: Antonio
authors: A
authors: Hernández
authors: Yasin
authors: Y
authors: Dhaher
authors: Darryl G
authors: DG
authors: Thelen
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006615:Hip / Q000502:physiology; D006801:Humans; D007717:Knee / Q000502:physiology; D035002:Lower Extremity / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D009068:Movement / Q000502:physiology*; D011187:Posture; D052097:Quadriceps Muscle / Q000502:physiology*
references: Dev Med Child Neurol. 1997 Feb;39(2):99-105
references: 9062424
references: J Biomech. 1989;22(1):1-10
references: 2914967
references: J Neuroeng Rehabil. 2006 Mar 06;3:5
references: 16519796
references: J Biomech. 2005 Nov;38(11):2181-9
references: 16154404
references: Gait Posture. 2003 Feb;17(1):1-17
references: 12535721
references: J Biomech. 1998 Sep;31(9):835-40
references: 9802784
references: J Biomech. 2004 Jan;37(1):99-110
references: 14672573
references: Exerc Sport Sci Rev. 1989;17:187-230
references: 2676547
references: J Biomech. 2000 Feb;33(2):219-24
references: 10653036
references: J Biomech. 2000 Feb;33(2):145-54
references: 10653027
references: Gait Posture. 2002 Dec;16(3):215-32
references: 12443946
references: Comput Methods Biomech Biomed Engin. 1999;2(3):201-231
references: 11264828
references: J Biomech. 2004 Aug;37(8):1189-96
references: 15212924
references: J Biomech. 1996 Jun;29(6):723-33
references: 9147969
references: Gait Posture. 2006 Feb;23(2):211-21
references: 16399518
references: IEEE Trans Rehabil Eng. 1999 Dec;7(4):420-6
references: 10609629
references: Gait Posture. 2003 Apr;17(2):159-69
references: 12633777
references: J Biomech. 2001 Nov;34(11):1387-98
references: 11672713
references: J Biomech. 1996 Sep;29(9):1223-30
references: 8872282
references: IEEE Trans Biomed Eng. 1990 Aug;37(8):757-67
references: 2210784