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By counteracting gravity, triceps surae sets both kinematics and kinetics of gait.
MedLine Citation:
PMID:  24744898     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Abstract/OtherAbstract:
In the single-stance phase of gait, gravity acting on the center of mass (CoM) causes a disequilibrium torque, which generates propulsive force. Triceps surae activity resists gravity by restraining forward tibial rotation thereby tuning CoM momentum. We hypothesized that time and amplitude modulation of triceps surae activity determines the kinematics (step length and cadence) and kinetics of gait. Nineteen young subjects participated in two experiments. In the gait initiation (GI) protocol, subjects deliberately initiated walking at different velocities for the same step length. In the balance-recovery (BR) protocol, subjects executed steps of different length after being unexpectedly released from an inclined posture. Ground reaction force was recorded by a large force platform and electromyography of soleus, gastrocnemius medialis and lateralis, and tibialis anterior muscles was collected by wireless surface electrodes. In both protocols, the duration of triceps activity was highly correlated with single-stance duration (GI, R (2) = 0.68; BR, R (2) = 0.91). In turn, step length was highly correlated with single-stance duration (BR, R (2) = 0.70). Control of CoM momentum was obtained by decelerating the CoM fall via modulation of amplitude of triceps activity. By modulation of triceps activity, the central nervous system (CNS) varied the position of CoM with respect to the center of pressure (CoP). The CoM-CoP gap in the sagittal plane was determinant for setting the disequilibrium torque and thus walking velocity. Thus, by controlling the gap, CNS-modified walking velocity (GI, R (2) = 0.86; BR, R (2) = 0.92). This study is the first to highlight that by merely counteracting gravity, triceps activity sets the kinematics and kinetics of gait. It also provides evidence that the surge in triceps activity during fast walking is due to the increased requirement of braking the fall of CoM in late stance in order to perform a smoother step-to-step transition.
Authors:
Jean-Louis Honeine; Marco Schieppati; Oliver Gagey; Manh-Cuong Do
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Publication Detail:
Type:  Journal Article     Date:  2014-02-10
Journal Detail:
Title:  Physiological reports     Volume:  2     ISSN:  2051-817X     ISO Abbreviation:  Physiol Rep     Publication Date:  2014 Feb 
Date Detail:
Created Date:  2014-04-18     Completed Date:  2014-04-18     Revised Date:  2014-04-21    
Medline Journal Info:
Nlm Unique ID:  101607800     Medline TA:  Physiol Rep     Country:  United States    
Other Details:
Languages:  eng     Pagination:  e00229     Citation Subset:  -    
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