locomotion

Impaired foot-force direction regulation during postural-loaded locomotion in individuals post-stroke

Submitted by Jing Nong Liang

In our earlier experiment, we observed intact force-control capabilities in individuals post-stroke during locomotion without postural influence. We sought to better understand the mechanisms underlying the interaction of locomotor and postural control and the role of postural control as an interactive mechanism that might interfere with appropriate foot-force generation. We designed an experiment in which subjects performed biomechanically-controlled locomotion, under posturally challenged pedaling while generating force outputs comparable to pedaling without postural challenge, thus allowing us to monitor the different strategies by the nervous system when postural conditions were manipulated. We hypothesized that with postural influence, individuals post-stroke will generate inappropriate shear forces accompanied by inappropriate coupling of muscle activity, and will be exaggerated with increased postural loading. Methods: Post-stroke (n=11) and non-impaired (n=5) individuals pedaled on a cycle ergometer under (1)seated, and (2)non-seated postural-loaded conditions, generating matched pedal normal force, with the motor-driven crank moving at 40rpm. Forces and EMG were recorded and analyzed offline. Results: During seated pedaling, we observed comparable shear pedal forces in both groups. During non-seated postural-loaded pedaling, we observed greater forward-directed shear forces in individuals post-stroke, but not in controls, which were exaggerated with increased postural loading. With postural influence, individuals post-stroke showed increased SOL and RF activities, whereas, in non-impaired controls we observed decreased VM, RF and BF activity. Conclusion: Reduced force-control capabilities during locomotion only when postural mechanisms were involved, suggests impaired interaction between locomotion and posture in the post-stroke nervous system. This inability to regulate postural loads may compromise the ability to adapt and react to changes in environmental conditions during walking, and could result in slips and falls.


Listed In: Neuroscience, Other 




  

    			
Touching Ground: Inertial Sensors.  Accuracy and precision of spatiotemporal characteristics from fetlock mounted inertial 
measurement units compared to motion capture in horses during over ground walk 

		    
        

      Submitted by Emil Olsen
    

    
        	

    		
    		

    			    			    		

    		

    			
Accurate distal limb spatiotemporal characteristics are useful parameters for a mobile kinematic system to quantify lameness and ataxia in horses. The objective was to compare spatial (position estimates) and temporal characteristics (hoof-on/off and stance time) from fetlock mounted inertial measurement units (IMUs) to motion capture and force plates during walk. Seven horses were walked across a 25 m runway with a central 4.8 m data collection area. We used IMUs (sampling at 200 Hz) that were placed proximal to all four fetlock joints and synchronized to a 12 camera motion capture system sampling at 200 Hz and eight force plates sampling at 500 Hz. We found the temporal characteristics were obtained with an accuracy of -0.02 to -7.38 ms and spatial characteristics with an accuracy of 0.9 to -29.79 mm with good precision for spatial and temporal characteristics, showing the potential for a reliable portable kinematic system based on IMUs.



    			Listed In: Biomechanics, Gait
    		

    	

        
      









  

    			
Touching Ground: Inertial Sensors.  Accuracy and precision of spatiotemporal characteristics from fetlock mounted inertial 
measurement units compared to motion capture in horses during over ground walk 

		    
        

      Submitted by Emil Olsen
    

    
        	

    		
    		

    			    			    		

    		

    			Accurate distal limb spatiotemporal characteristics are useful parameters for a mobile kinematic system to quantify lameness and ataxia in horses. The objective was to compare spatial (position estimates) and temporal characteristics (hoof-on/off and stance time) from fetlock mounted inertial measurement units (IMUs) to motion capture and force plates during walk. Seven horses were walked across a 25 m runway with a central 4.8 m data collection area. We used IMUs (sampling at 200 Hz) that were placed proximal to all four fetlock joints and synchronized to a 12 camera motion capture system sampling at 200 Hz and eight force plates sampling at 500 Hz. We found the temporal characteristics were obtained with an accuracy of -0.02 to -7.38 ms and spatial characteristics with an accuracy of 0.9 to -29.79 mm with good precision for spatial and temporal characteristics, showing the potential for a reliable portable kinematic system based on IMUs.

    			Listed In: Biomechanics, Gait
    		

    	

        
      









  

    			
Dissociation of normal vs shear surface force generation during locomotion in people post-stroke

		    
        

      Submitted by Jing Nong Liang
    

    
        	

    		
    		

    			    			    		

    		

    			During bipedal locomotion, execution of a functional and coordinated gait pattern requires appropriate muscle activity phasing that adapts to varying environments.  Individuals post-stroke are at a high risk for falls, particularly on slippery surfaces, potentially resulting from an inability to dissociate forces in the shear vs. normal directions.  Our purpose was to test if the post-stroke nervous system can appropriately dissociate normal from shear surface force to interact with slippery surfaces. 
Non-impaired (NI) (N=8;Age=61±12yrs) and chronic post-stroke individuals (N=8;Age=61±12yrs) were positioned on a custom-designed, motorized cycle ergometer.  Subjects achieved a target normal pedal force of 40% maximum effort given visual feedback, while simultaneously assuming various pedal angle orientations during stationary and pedaling conditions, therefore causing magnitude and direction of shear force outputs to change.  EMG and pedal forces were collected. 
The paretic leg generates less force during both conditions.  The pedal angle positions and shear forces in individuals post-stroke are similar to NI except in a few cases.  The paretic ankle generated limited range of pedal angle positions and shear force.  In contrast to NI, pedal angle alone did not fully account for variability in normalized shear forces in individuals post-stroke, thigh muscle activity accounted for the remaining variability.
Individuals post-stroke are less capable of generating a high range of surface shear forces. In addition, they utilized different muscle activity combinations in order to vary surface shear forces.  These results demonstrate that, when interacting with slippery surfaces, post-stroke individuals have less range and muscle activity activation flexibility to prevent high shear forces from resulting in a slip.


    			Listed In: Neuroscience
    		

    	

        
      









  

    			
Gait in Patients with COPD is Mainly Affected in Proximal Musculature

		    
        

      Submitted by Jennifer Yentes
    

    
        	

    		
    		

    			    			    		

    		

    			The effects of chronic obstructive pulmonary disease (COPD) are not limited to the lung. Patients with COPD exhibit abnormalities in structure and function of skeletal muscle tissue. We hypothesized that the abnormalities in skeletal muscle tissue lead to changes in gait patterns in patients with COPD. Twenty subjects walked at their self-selected pace while kinematics and kinetics were recorded. All subjects underwent a rest condition, a minimum of one minute rest between each trial. Patients with COPD then underwent a treadmill protocol to induce fatigue. Subjects repeated walkover trials with no rest between trials. Group means were compared using independent and dependent t-tests. Peak hip extension moment was significantly increased in patients with COPD as compared to healthy controls in the rest condition. Hip extension moment was significantly increased in patients with COPD as compared to healthy controls in the fatigue condition. No significant differences were found for the rest vs. fatigue condition. The peak hip extension moment was the only parameter to demonstrate significant differences. This may not be due to the changes in skeletal muscle structure and function. It is possible that the subjects with COPD walked with a forward trunk inclination as compared to controls. The peak hip extension moment was not significantly different within the patients with COPD from rest to fatigue condition. The gait abnormalities in patients with COPD are present even when the subject is well rested. Another reason for lack of significant differences between the two conditions could have been our fatigue protocol. 

    			Listed In: Biomechanics, Gait
    		

    	

        
      









  

    			
The Mechanics of Uphill and Downhill Walking: Mechanical Work Performed by the Individual Legs

		    
        

      Submitted by Jason Franz
    

    
        	

    		
    		

    			    			    		

    		

    			

	Previous studies of the mechanical work performed during uphill and downhill walking have neglected the simultaneous positive and negative work performed by the trailing and leading legs during double support. Our goal was to quantify the mechanical work performed by the individual legs across a range of uphill and downhill grades. We hypothesized that 1) with steeper uphill grade, the negative work performed by the leading leg would become negligible and the trailing leg would perform progressively greater positive work to raise the center of mass (CoM), and 2) with steeper downhill grade, the positive work performed by the trailing leg would become negligible and the leading leg would perform progressively greater negative work to lower the CoM. 11 healthy young adults (6M/5F, 71.0 ± 12.3 kg) walked at 1.25 m/s on a dual-belt force-measuring treadmill at seven grades (0, ±3, 6, 9°). We collected three-dimensional ground reaction forces (GRFs) and used the individual limbs method to calculate the mechanical work performed by the individual legs. As hypothesized, the trailing leg performed progressively greater positive work with steeper uphill grade, and the leading leg performed progressively greater negative work with steeper downhill grade (p<0.005). However, unlike during level-ground walking, the leading leg performed considerable positive work when walking uphill, and the trailing leg performed considerable negative work when walking downhill (p<0.005). Our findings reveal important biomechanical aspects of individual leg function during uphill and downhill walking that may help guide the improvement of rehabilitation techniques and prosthetic design.



    			Listed In: Biomechanics, Gait