Effects of releasing ankle joint during electrically evoked cycling in persons with motor complete spinal cord injury

Abstract

Literature has shown that simulated power production during conventional functional electrical stimulation (FES) cycling was improved by 14% by releasing the ankle joint from a fixed ankle setup and with the stimulation of the tibialis anterior and triceps surae. This study aims to investigate the effect of releasing the ankle joint on the pedal power production during FES cycling in persons with spinal cord injury (SCI). Seven persons with motor complete SCI participated in this study. All participants performed 1 min of fixed-ankle and 1 min of free-ankle FES cycling with two stimulation modes. In mode 1 participants performed FES-evoked cycling with the stimulation of quadriceps and hamstring muscles only (QH stimulation), while Mode 2 had stimulation of quadriceps, hamstring, tibialis anterior, and triceps surae muscles (QHT stimulation). The order of each trial was randomized in each participant. Free-ankle FES cycling offered greater ankle plantar- and dorsiflexion movement at specific slices of 20° crank angle intervals compared to fixed-ankle. There were significant differences in the mean and peak normalized pedal power outputs (POs) [F(1,500) = 14.03, p < 0.01 and F(1,500) = 7.111, p = 0.008, respectively] between fixed- and free-ankle QH stimulation, and fixed- and free-ankle QHT stimulation. Fixed-ankle QHT stimulation elevated the peak normalized pedal PO by 14.5% more than free-ankle QH stimulation. Releasing the ankle joint while providing no stimulation to the triceps surae and tibialis anterior reduces power output. The findings of this study suggest that QHT stimulation is necessary during free-ankle FES cycling to maintain power production as fixed-ankle.

Keywords: Ankle biomechanics; Functional electrical stimulation; Paraplegics; Pedal power; Rehabilitation.

Figure 1

Set up for fixed-ankle FES-evoked cycling. Shown is the placement of markers over the fifth metatarsophalangeal and ankle joints on the solid AFO. Electrodes were placed on the quadriceps, hamstrings, tibialis anterior, and triceps surae muscles.

Figure 2

Two stimulation modes of FES-evoked cycling were used in this study; (a) QH stimulation; (b) QHT stimulation; and (c) stimulation angle. Image adapted from the software 3D Anatomy Learning (Version 3.9, Education Mobile) (open-source project).

Figure 3

The interaction and boxplot of the effect of fixed- and free-ankle FES-evoked cycling with QH and QHT stimulations across each slice of 20° crank angle intervals on (a) mean normalized pedal PO; (b) peak normalized pedal PO; (c) mean ankle ROM; (d) mean knee ROM; and (e) mean hip ROM. *⁰Denotes p < 0.05 between free-ankle QH stimulation compared to the other settings.

Figure 3

The interaction and boxplot of the effect of fixed- and free-ankle FES-evoked cycling with QH and QHT stimulations across each slice of 20° crank angle intervals on (a) mean normalized pedal PO; (b) peak normalized pedal PO; (c) mean ankle ROM; (d) mean knee ROM; and (e) mean hip ROM. *⁰Denotes p < 0.05 between free-ankle QH stimulation compared to the other settings.

Figure 4

The PO and ROM generated during fixed- and free-ankle FES-evoked cycling with QH and QHT stimulations by each slice of 20° crank angle position from 0° to 360°. (a) mean normalized pedal PO; (b) peak normalized pedal PO; (c) mean ankle ROM; (d) mean knee ROM; and (e) mean hip ROM. *¹Denotes p < 0.05 between free-ankle QH stimulation and fixed-ankle QHT stimulation, *²denotes p < 0.05 between free-ankle QHT stimulation and fixed-ankle QH stimulation, *³denotes p < 0.05 between free-ankle QHT stimulation and free-ankle QH stimulation, *⁴denotes p < 0.05 between free-ankle QHT stimulation and fixed-ankle QHT stimulation, and *⁵denotes p < 0.05 between fixed-ankle QHT stimulation and fixed-ankle QH stimulation.