Kinematic, muscular, and metabolic responses during exoskeletal-, elliptical-, or therapist-assisted stepping in people with incomplete spinal cord injury

Abstract

Background: Robotic-assisted locomotor training has demonstrated some efficacy in individuals with neurological injury and is slowly gaining clinical acceptance. Both exoskeletal devices, which control individual joint movements, and elliptical devices, which control endpoint trajectories, have been utilized with specific patient populations and are available commercially. No studies have directly compared training efficacy or patient performance during stepping between devices.

Objective: The purpose of this study was to evaluate kinematic, electromyographic (EMG), and metabolic responses during elliptical- and exoskeletal-assisted stepping in individuals with incomplete spinal cord injury (SCI) compared with therapist-assisted stepping. Design A prospective, cross-sectional, repeated-measures design was used.

Methods: Participants with incomplete SCI (n=11) performed 3 separate bouts of exoskeletal-, elliptical-, or therapist-assisted stepping. Unilateral hip and knee sagittal-plane kinematics, lower-limb EMG recordings, and oxygen consumption were compared across stepping conditions and with control participants (n=10) during treadmill stepping.

Results: Exoskeletal stepping kinematics closely approximated normal gait patterns, whereas significantly greater hip and knee flexion postures were observed during elliptical-assisted stepping. Measures of kinematic variability indicated consistent patterns in control participants and during exoskeletal-assisted stepping, whereas therapist- and elliptical-assisted stepping kinematics were more variable. Despite specific differences, EMG patterns generally were similar across stepping conditions in the participants with SCI. In contrast, oxygen consumption was consistently greater during therapist-assisted stepping. Limitations Limitations included a small sample size, lack of ability to evaluate kinetics during stepping, unilateral EMG recordings, and sagittal-plane kinematics.

Conclusions: Despite specific differences in kinematics and EMG activity, metabolic activity was similar during stepping in each robotic device. Understanding potential differences and similarities in stepping performance with robotic assistance may be important in delivery of repeated locomotor training using robotic or therapist assistance and for consumers of robotic devices.

Figure 1.

Experimental setup for kinematic, electromyographic, and metabolic data collection during therapist-assisted stepping (A), exoskeletal-assisted stepping (B), and elliptical-assisted stepping (C).

Figure 2.

Single-subject sagittal-plane hip (A) and knee (B) kinematics during therapist-assisted stepping (blue), exoskeletal-assisted stepping (black), and elliptical-assisted stepping (red) averaged over more than 20 gait cycles and normalized to percentage of the gait cycle. Normative data provided in dark gray, with standard deviation in light shaded gray. Average angular excursions for hip (C) and knee (D) kinematics are provided (error bars=standard errors), with asterisk indicating significant post hoc Tukey-Kramer differences. Single-subject hip-knee angle-angle plots during therapist-, exoskeletal-, and ellipitical-assisted stepping (E), with average coefficient of correlation (ACC) values (F) provided (significance indicated by asterisk).

Figure 3.

Rectified, filtered, single-subject electromyographic (EMG) activity for the (A) tibialis anterior (TA), (B) medial gastrocnemius (MG), (C) soleus (SOL), (D) rectus femoris (RF), (E) vastus lateralis (VL), and (F) medial hamstring (MH) muscles recorded during therapist-assisted stepping (blue), exoskeletal-assisted stepping (black), and elliptical-assisted stepping (red). Data were averaged over more than 20 gait cycles and normalized to percentage of the gait cycle. Shaded areas indicate periods of normative EMG activity evaluated in 10 participants without neurological injury.

Figure 4.

Grouped averages of oxygen consumption (V̇o₂) during each 6-minute bout of therapist-assisted stepping (blue), exoskeletal-assisted stepping (black), and elliptical-assisted stepping (red). Data were averaged over each minute. Asterisk indicated significant post hoc Tukey-Kramer differences.

Figure 5.

Associations between Lower Extremity Motor Score (LEMS) and (A) peak hip flexion (P=.48 for exoskeletal-assisted stepping, P=.65 for elliptical-assisted stepping), (B) peak knee extension (P=.14 for exoskeletal-assisted stepping, P=.11 for elliptical-assisted stepping), (C) rectus femoris muscle (RF) electroyographic (EMG) activity during “on” period (P=.42 for exoskeletal-assisted stepping, P<.01 for elliptical-assisted stepping), and (D) oxygen consumption (V̇o₂) (P=.13 for exoskeletal-assisted stepping, P=.02 for elliptical-assisted stepping). Black=therapist-assisted stepping minus exoskeletal-assisted stepping, red=therapist-assisted stepping minus elliptical-assisted stepping