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. 2013 Jul;36(4):313-21.
doi: 10.1179/2045772313Y.0000000126.

Vertical ground reaction force-based analysis of powered exoskeleton-assisted walking in persons with motor-complete paraplegia

Drew B Fineberg  1 , Pierre Asselin, Noam Y Harel, Irina Agranova-Breyter, Stephen D Kornfeld, William A Bauman, Ann M Spungen
Affiliations

Vertical ground reaction force-based analysis of powered exoskeleton-assisted walking in persons with motor-complete paraplegia

Drew B Fineberg et al. J Spinal Cord Med. 2013 Jul.

Abstract

Objective: To use vertical ground reaction force (vGRF) to show the magnitude and pattern of mechanical loading in persons with spinal cord injury (SCI) during powered exoskeleton-assisted walking.

Research design: A cross-sectional study was performed to analyze vGRF during powered exoskeleton-assisted walking (ReWalk™: Argo Medical Technologies, Inc, Marlborough, MA, USA) compared with vGRF of able-bodied gait.

Setting: Veterans Affairs Medical Center.

Participants: Six persons with thoracic motor-complete SCI (T1-T11 AIS A/B) and three age-, height-, weight- and gender-matched able-bodied volunteers participated.

Interventions: SCI participants were trained to ambulate over ground using a ReWalk™. vGRF was recorded using the F-Scan™ system (TekScan, Boston, MA, USA).

Outcome measures: Peak stance average (PSA) was computed from vGRF and normalized across all participants by percent body weight. Peak vGRF was determined for heel strike, mid-stance, and toe-off. Relative linear impulse and harmonic analysis provided quantitative support for analysis of powered exoskeletal gait.

Results: Participants with motor-complete SCI, ambulating independently with a ReWalk™, demonstrated mechanical loading magnitudes and patterns similar to able-bodied gait. Harmonic analysis of PSA profile by Fourier transform contrasted frequency of stance phase gait components between able-bodied and powered exoskeleton-assisted walking.

Conclusion: Powered exoskeleton-assisted walking in persons with motor-complete SCI generated vGRF similar in magnitude and pattern to that of able-bodied walking. This suggests the potential for powered exoskeleton-assisted walking to provide a mechanism for mechanical loading to the lower extremities. vGRF profile can be used to examine both magnitude of loading and gait mechanics of powered exoskeleton-assisted walking among participants of different weight, gait speed, and level of assist.

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Figures

Figure 1
Figure 1
Using F-Scan™ Sensors with the ReWalk™. (A) Participant using the ReWalk™ exoskeletal device; (B) participant wearing F-Scan™ incorporated into the ReWalk™ setup; and (C) F-Scan™ in-shoe pressure sensors placed above the insole below the surface of the foot. The footplate of the ReWalk™ powered exoskeleton sits below the insole of the shoe; the weight of the ReWalk™ is not transferred onto the force sensor. Note: The heel strike as the participant takes a step in the ReWalk™.
Figure 2
Figure 2
vGRF of stance phase component by group. Variability bars represent the 95% confidence intervals. Body weight of the SCI groups is adjusted by subtracting the backpack and remote watch weight. *SCI min-assist vs. AB control: P = 0.0034. ‡SCI min-assist vs. SCI no-assist: P = 0.0095 and 0.0457, respectively.
Figure 3
Figure 3
PSA of vGRF with error bars at 95% confidence intervals. Able-bodied controls are shown in black, participants with SCI walking in the ReWalk™ with no-assist are shown in blue, and those with min-assist are shown in red. PSA, peak stance average; GRF, ground reaction force.
Figure 4
Figure 4
PSA indexed for vGRF minimum/maximum peaks. Peak stance average is shown for all groups by stance phase with error bars removed for clarity. Peak vertical ground reaction force are indexed: heel strike vertical ground reaction force, mid-stance vertical ground reaction force, and toe-off vertical ground reaction force (vGRFTOAB, and vGRFTOSCI). vGRFTO is indexed sepearately for able-bodied control group and SCI groups, as peak toe-off force occurs later in the exoskeletal gait cycle.
Figure 5
Figure 5
Harmonic analysis of PSA. Fourier transform is shown for all groups for first eight harmonics. Able-bodied control group has greater representation in the second harmonic (black) whereas SCI groups have greater representation in the first harmonic. Harmonic analysis appears to permit sufficient sensitivity to differentiate level of assistance between SCI groups of min-assist and no-assist.
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