This exploratory study aims to describe and compare the effects of adding FES during PE-assisted overground walking on muscle activation and fatigue in non-disabled individuals, prior to testing in individuals with iSCI.
Following a familiarization session, participants engaged in three walking trials with the Indego® exoskeleton and a walker, during which the PE provided 40% assistance to the knee and hip joints. In the 2nd trial, FES was applied to key muscles involved in walking, delivered at an intensity below the threshold of visible contraction. Electromyographic (EMG) data were collected from the stimulated muscles. The mean amplitude of muscle activity, in specific phases of the gait cycle, and the power spectrum of the median frequency (a muscle fatigue indicator) were calculated for each cycle. Since EMG signals during FES application could not be analyzed due to stimulation artifacts, Wilcoxon tests were performed to compare results before and after FES exposure. Moreover, participants filled out the NASA-TLX questionnaire on subjective workload, after each trial and these data were compared using a Friedman test.
Fifteen participants (8W; median=27 years old [Q1;Q3: 24.5;29.0]) participated in the study. During PE-assisted walking, we observed an extinction of muscle activity in the tibialis anterior and rectus femoris. A visual inspection of EMG signals indicated a notable increase in semitendinosus (ST) and gastrocnemius medialis (MG) activation around toe-off, compared to normative data from overground walking (no PE) at similar speeds.
ST activity between 50 and 70% of the gait cycle significantly decreased immediately post-FES exposure, compared to pre-FES trial (-36%; p0.001). Conversely, MG activation increased (+13%; p=0.008) during the same timeframe post-FES exposure. These differences were sustained over time (ST:p0.001; MG:p=0.041).
No muscle fatigue was observed. However, perceived workload significantly differed between the 1st trial and the others, especially in mental demands (p=0.002), with the first trial being the most demanding (40% assistance, no FES).
The addition of FES during PE-assisted overground walking affected the activation of certain lower limb muscles around toe-off, and these changes persist after FES removal. These effects can be opposite, depending on the muscles involved. Further experiments in individuals with iSCI are necessary to investigate muscle activation and fatigue when adding FES during PE-assisted overground walking.
These studies could ultimately contribute to identifying optimal parameters for overground PE gait training with FES, offering a complementary rehabilitation approach to enhance locomotor recovery.
functional electrical stimulation
muscle activity
