Leg Cycling Dynamics Of Individuals With Spinal Cord Injury During Stationary Leg Cycle Ergometry

Abstract

Functional electrical stimulation leg cycle ergometry (FES-LCE) is used clinically as a therapeutic exercise for individuals with spinal cord injury (SCI). However, studies argue that FES-LCE control algorithms used to adjust muscle stimulation levels pose significant limitations to an SCI individual's pedaling effectiveness and exercise performance. PURPOSE The purpose of this study was to compare joint kinematics and pedal force profiles produced by SCI and able-bodied (AB) individuals during stationary FES-LCE. Joint kinematics and pedal forces were recorded from SCI and AB individuals and compared in order to evaluate pedaling effectiveness during FESLCE. METHODS Six healthy male SCI subjects between ages 20–54 years (mean 32±12 years) participated in FES-LCE. Twelve healthy AB subjects between ages 18–50 years (mean 27±12 years) participated in LCE without FES. Subjects performed progressive resistance leg cycling at a relatively constant cadence of 50 revolutions per minute. During the test, the bike's flywheel resistance was increased 6.1Watts (W) every two minutes up to the maximal tolerated resistance level. Kinematic and pedal force data were collected for 30 seconds at each resistance. A motion analysis system recorded joint kinematics of the right hip, knee, and ankle. A piezoelectric force sensor mounted on the right pedal recorded normal and tangential pedal forces. Joint kinematics and pedal forces were summarized relative to crank position at 0W (submax) and 12W (max) resistance levels for SCI. Group comparisons were made using a student t-test. RESULTS Joint angular displacements were consistent between AB and SCI subjects and did not significantly change with increased resistance levels. However, joint angular accelerations were significantly different between AB and SCI subjects at submax and max resistance levels. Pedal forces increased for AB and SCI subjects with increased resistance from 0W to 12W, but peak pedal forces at the max resistance level were significantly less in SCI than AB subjects (2.8±1.9 vs. 2.3±0.9 pounds (compression); 6.0±2.0 vs. 3.6±1.0 pounds (tension); p<0.05). The corresponding crank positions were also significantly different; p<0.05. CONCLUSIONS Results from this study imply significant differences in joint accelerations and pedal forces between AB and SCI subjects during steady-state LCE. This may be an indication of improper stimulation patterns during FES-LCE, which may limit exercise by SCI individuals. These findings suggest that modifications are needed to the FES-LCE control system to improve its ability to effectively produce pedaling characteristics similar to AB individuals.