TY - JOUR
T1 - Multivariable static ankle mechanical impedance with relaxed muscles
AU - Lee, Hyunglae
AU - Ho, Patrick
AU - Rastgaar, Mohammad A.
AU - Krebs, Hermano I.
AU - Hogan, Neville
N1 - Funding Information:
This work was funded by Toyota Motor Corporation's Partner Robot Division. H. Lee was supported by a Samsung Scholarship. Drs. N. Hogan and H. I. Krebs are co-inventors of the MIT patents for the robotic devices used in this study. They hold equity positions in Interactive Motion Technologies, Inc., the company that manufactures this type of technology under license to MIT.
PY - 2011/7/7
Y1 - 2011/7/7
N2 - Quantitative characterization of ankle mechanical impedance is important to understand how the ankle supports lower-extremity functions during interaction with the environment. This paper reports a novel procedure to characterize static multivariable ankle mechanical impedance. An experimental protocol using a wearable therapeutic robot, Anklebot, enabled reliable measurement of torque and angle data in multiple degrees of freedom simultaneously, a combination of inversion-eversion and dorsiflexion-plantarflexion. The measured multivariable torque-angle relation was represented as a vector field, and approximated using a method based on thin-plate spline smoothing with generalized cross validation. The vector field enabled assessment of several important characteristics of static ankle mechanical impedance, which are not available from prior single degree of freedom studies: the directional variation of ankle mechanical impedance, the extent to which the ankle behaves as a spring, and evidence of uniquely neural contributions. The method was validated by testing a simple physical "mock-up" consisting of passive elements. Experiments with young unimpaired subjects quantified the behavior of the maximally relaxed human ankle, showing that ankle mechanical impedance is spring-like but strongly direction-dependent, being weakest in inversion. Remarkably, the analysis was sufficiently sensitive to detect a subtle but statistically significant deviation from spring-like behavior if subjects were not fully relaxed. This method may provide new insight about the function of the ankle, both unimpaired and after biomechanical or neurological injury.
AB - Quantitative characterization of ankle mechanical impedance is important to understand how the ankle supports lower-extremity functions during interaction with the environment. This paper reports a novel procedure to characterize static multivariable ankle mechanical impedance. An experimental protocol using a wearable therapeutic robot, Anklebot, enabled reliable measurement of torque and angle data in multiple degrees of freedom simultaneously, a combination of inversion-eversion and dorsiflexion-plantarflexion. The measured multivariable torque-angle relation was represented as a vector field, and approximated using a method based on thin-plate spline smoothing with generalized cross validation. The vector field enabled assessment of several important characteristics of static ankle mechanical impedance, which are not available from prior single degree of freedom studies: the directional variation of ankle mechanical impedance, the extent to which the ankle behaves as a spring, and evidence of uniquely neural contributions. The method was validated by testing a simple physical "mock-up" consisting of passive elements. Experiments with young unimpaired subjects quantified the behavior of the maximally relaxed human ankle, showing that ankle mechanical impedance is spring-like but strongly direction-dependent, being weakest in inversion. Remarkably, the analysis was sufficiently sensitive to detect a subtle but statistically significant deviation from spring-like behavior if subjects were not fully relaxed. This method may provide new insight about the function of the ankle, both unimpaired and after biomechanical or neurological injury.
KW - Ankle joint
KW - Ankle joint stiffness
KW - Ankle mechanical impedance
KW - Human ankle
KW - Multivariable stiffness
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U2 - 10.1016/j.jbiomech.2011.04.028
DO - 10.1016/j.jbiomech.2011.04.028
M3 - Article
C2 - 21571278
AN - SCOPUS:79959515261
SN - 0021-9290
VL - 44
SP - 1901
EP - 1908
JO - Journal of Biomechanics
JF - Journal of Biomechanics
IS - 10
ER -