The Importance of Using an Appropriate
Body Weight Support System
in Locomotor Training

K.E. Gordon1; D.P. Ferris1; M.Roberton1,3; J.A. Beres1; S.J. Harkema1,2
1. Neurology, 2. Brain Research Institute and 3. Biomed. Eng., University of California at Los Angeles, Los Angeles, CA, USA

 
Table of Contents
::Home
::Introduction
::Methods
::Results
::Conclusions
::References
::Acknowledgments

::Introduction
Locomotor training using body weight support (BWS) on a treadmill and manual assistance has emerged as a potential rehabilitation intervention for the recovery of walking following spinal cord injury (SCI)(2). The success of this approach is dependent on providing appropriate sensory cues to the spinal cord by simulating the kinetics and kinematics of over-ground walking(2,6). Several different BWS systems have been used to accomplish the unweighting component of this training (i.e., a winched rope(1,6,8), a pneumatic lift(4), stretched springs(5) or counter-balanced weights(3)). The type of BWS system used in locomotor training may affect ground reaction forces (GRF) and center of mass (COM) movement during gait which in turn could modulate afferent information. The purpose of this study was to compare the effects of two BWS systems, a position control system and a open - loop force control system, on limb loading, (COM) movement and motor control during locomotor training.

 

::Methods
A. Subjects
Two non-disabled (ND) and two clinically complete(7) SCI subjects participated in the study. Informed consent was obtained from all subjects and the experiments were approved by the U.C.L.A. Human Subjects Protection Committee.


B. Equipment
Ground reaction forces (GRF) were collected during stepping using pressure sensing insoles (Novel, St. Paul, MN). BWS force was collected from a force transducer placed in series with the BWS system cable. Center of mass (COM) movement was estimated from 6 dimensional recordings of pelvis movement (Skill Technologies, Phoenix, AZ). Three different BWS systems were used to support the subject’s body weight during locomotion: 1)Position Control System (Cal South Equipment, Long Beach, CA), 2) Open - Loop Force Control System (Vigor Equipment, Stevensville, MI), 3)Closed - Loop Force Control System (Vigor Equipment, Stevensville, MI). EMG data was collected from lower limb muscles (Kongisberg Instruments, Pasadena, CA).

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C. Procedure
All subjects stepped on a treadmill at a range of speeds (0.5 - 1.34 m/s) and levels of BWS (0 - 100% body weight) on both the position control system and the open - loop force control system. We provided SCI subjects with manual assistance as needed. COM movement, GRF, BWS force and EMG were analyzed. Following the analysis, a dynamic force control BWS system was designed to minimize any fluctuations in BWS force during locomotion. One of the ND subjects repeated the procedure on the closed - loop force control system.

 

::Results
click thumbnails for actual size

Normal center of mass movement and ground reaction forces during walking.


Figure 2. ND-1 walking at 100% mean body weight load (BWL). Region between lines represents +1 SD of mean

Comparison of BWS force, vertical movement of the COM and GRF in a ND and SCI during locomotion on the Position Control System and the Open - Loop Force Control System.


Figure 3. ND-1 walking at various loads and speeds on both the Position Control system and the Open - Loop Force Control system


Figure 4. SCI-1 walking at various loads and speeds on both the Position Control system and the Open - Loop Force Control system.



*Figure 5. Summary graphs for all subjects of mean peak GRF (+1 SD) for Heel Strike and Toe Off, mean GRF during stance, and mean load during the step cycle calculated as body weight (100) - BWS.


Figure 6. Summary graphs for ND-1 and SCI-1 of mean vertical diplacement of COM (+1 SD) during step cycle. * Difference between Position Control and Open - Loop Force Control System (p <0.01, student t-test).

Comparison of EMG activity during stepping on the Position and Open - Loop Force Control Systems.



Figure 7. Mean EMG activity and GRF (lowpass filtered at 6Hz) (+1 SD) from 8 steps normalized to mean step cycle duration.

2. BWS force, vertical movement of the COM and GRF in a ND during locomotion on the Closed - Loop Force Control BWS


Figure 8. ND-1 walking at various loads on the Closed - Loop Force Control BWS System.

 

::Conclusion
1) Position Control BWS System


2) Open
  • Loop Force Control BWS System
  • Allows vertical COM movement similar to over-ground locomotion
  • BWS force fluctuates with COM movement
  • GRF had both heel strike and toe-off peaks, however heel strike peaks were higher and toe-off peaks were lower than expected

3) Closed
  • Loop Force Control BWS System
  • Allows vertical COM movement similar to over-ground locomotion
  • Of the three systems it showed the smallest fluctuations in BWS force during locomotion
  • GRF showed distinct heel strike peak, toe-off peak, and unloading at midstance. Amplitude of all three of these components were comparable to over ground gait adjusted for BWS

4) The interaction between the BWS systems and COM movement / GRF occur for both the ND and SCI subjects.
5) Kinetics and kinematics during locomotor training become more comparable to over-ground walking as deviations in BWS force during gait are controlled and minimized. (Closed - loop force control system)
6) The BWS system used in locomotor training effects both COM movement and GRF which modulates efferent motor output.

 

::References
1) Barbeau, H., Wainberg, M., Finch, L. Description and application of a system for locomotor rehabiliation. Med Biol Eng Comput. 25:341-344, 1987.
2) Behrman, A.L., Harkema, S.J. Locomotor training after human spinal cord injury: a series of case studies. Phys Ther. 80:688 -700. 2000.
3) Dietz, V., Nakazawa, K., Wirw, M., Erni, Th. Level of spinal cord lesion determines locomotor activity in spinal man. Exp. Brain Res. 128:405-409, 1999.
4) Flynn T.W., Canavan, P.K., Cavanagh, P.R., Chiang, J-H. Plantar pressure reduction in an incremental weight-bearing system. Phys Ther. 77:410-416, 1997.
5) Griffin, T.M., Tolani, N.A., Kram, R. Walking in simulated reduced gravity: mechanical energy fluctuations and exchange. J. Appl. Physiol. 86(1): 383-390, 1999.
6) Harkema, S.J., Hurley, S.L., Patel, U.K., Requejo, P.S., Dobkin, B.H., Edgerton, V.R. Human lumbosacral spinal cord interprets loading during stepping. J. Neurophysiol. 77: 797-811, 1997.
7) Maynard, F.M., Bracken, M.B. Creasey, G., et. al. International standards for neurological and functional classification of spinal cord injury. American Spinal Injury Association. Spinal Cord. 35:266-274, 1997.
8) Wernig, A., Muller, S. Laufband locomotion with body weight support improved walking in persons with severe spinal cord injuries. Paraplegia 30:229-238, 1992.

 

:: Acknowledgements
This work was supported by: NIH NS36854, NS16333, RR00865.