TY - JOUR
T1 - In vivo measurement of dynamic rectus femoris function at postures representative of early swing phase
AU - Hernández, Antonio
AU - Dhaher, Yasin
AU - Thelen, Darryl G.
N1 - Funding Information:
Antonio Hernández was supported by NIH Training Grant T32 AG20013 (Institute on Aging, Sanjay Asthana, PI) and the Graduate Engineering Research Scholars at the University of Wisconsin-Madison. Funding was also received from NIH AG24276 and the Midwest Rehabilitation Research Network. The authors gratefully acknowledge the contributions of Dr. Deborah McLeish, Dr. James Leonard, Betsy Hunter, Amy Silder, Yomary Muñoz and Andrew Sterling.
PY - 2008
Y1 - 2008
N2 - 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.
AB - 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.
KW - Biarticular muscle
KW - Electrical stimulation
KW - Forward dynamic simulation
KW - Induced acceleration
KW - Musculoskeletal model
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U2 - 10.1016/j.jbiomech.2007.07.011
DO - 10.1016/j.jbiomech.2007.07.011
M3 - Article
C2 - 17707384
AN - SCOPUS:37249044654
SN - 0021-9290
VL - 41
SP - 137
EP - 144
JO - Journal of Biomechanics
JF - Journal of Biomechanics
IS - 1
ER -