Effects of intramuscular trunk stimulation on manual wheelchair propulsion mechanics in 6 subjects with spinal cord injury.

OBJECTIVE

To quantify the effects of stabilizing the paralyzed trunk and pelvis with electrical stimulation on manual wheelchair propulsion.

DESIGN

Single-subject design case series with subjects acting as their own concurrent controls.

SETTING

Hospital-based clinical biomechanics laboratory.

PARTICIPANTS

Individuals (N=6; 4 men, 2 women; mean age ± SD, 46 ± 10.8y) who were long-time users (6.1 ± 3.9y) of implanted neuroprostheses for lower extremity function and had chronic (8.6 ± 2.8y) midcervical- or thoracic-level injuries (C6-T10).

INTERVENTIONS

Continuous low-level stimulation to the hip (gluteus maximus, posterior adductor, or hamstrings) and trunk extensor (lumbar erector spinae and/or quadratus lumborum) muscles with implanted intramuscular electrodes.

MAIN OUTCOME MEASURES

Pushrim kinetics (peak resultant force, fraction effective force), kinematics (cadence, stroke length, maximum forward lean), and peak shoulder moment at preferred speed over 10-m level surface; speed, pushrim kinetics, and subjective ratings of effort for level 100-m sprints and up a 30.5-m ramp of approximately 5% grade.

RESULTS

Three of 5 subjects demonstrated reduced peak resultant pushrim forces (P≤.014) and improved efficiency (P≤.048) with stimulation during self-paced level propulsion. Peak sagittal shoulder moment remained unchanged in 3 subjects and increased in 2 others (P<.001). Maximal forward trunk lean also increased by 19% to 26% (P<.001) with stimulation in these 3 subjects. Stroke lengths were unchanged by stimulation in all subjects, and 2 showed extremely small (5%) but statistically significant increases in cadence (P≤.021). Performance measures for sprints and inclines were generally unchanged with stimulation; however, subjects consistently rated propulsion with stimulation to be easier for both surfaces.

CONCLUSIONS

Stabilizing the pelvis and trunk with low levels of continuous electrical stimulation to the lumbar trunk and hip extensors can positively impact the mechanics of manual wheelchair propulsion and reduce both perceived and physical measures of effort.