One year of home-based daily FES in complete lower motor neuron paraplegia: recovery of tetanic contractility drives the structural improvements of denervated muscle

Objective: Spinal cord injury (SCI) causes muscle atrophy, which is particularly severe, due to inability to perform tetanic contractions, when lower motor neurons (LMN) are involved. We performed a longitudinal study in 25 Europeans suffering from complete conus cauda syndrome from 0.7 to 8.7 years comparing functional and structural thigh muscle properties before and after 2 years of home-based daily training by functional electrical stimulation (FES). The mid-term results after 1 year and preliminary muscle biopsy observations at project end-point from a subset of subjects are here reported. Methods: Muscles were electrically stimulated at home by means of large surface electrodes and a custom-designed stimulator. The poor excitability of the LMN denervated muscles was first improved by twitch-contraction training. Then, tetanic contractions against progressively increased loading were elicited. Finally, standing-up exercises were daily performed. The bulk of thigh muscle was estimated by transverse computer tomography (CT) scan and force measurements. Needle biopsies of vastus lateralis were harvested before and after 2 years of FES. Results: The 1 year home-based daily FES training induced: (1) very similar increases in muscle excitability and contractility in right and left legs; (2) feasibility to elicit tetanic contractions by means of train-stimulation with about ten times improvement of muscle force; (3) increase in the 26% of muscle bulk, as shown by CT scan analyses, improving appearance of limbs and muscle cushioning; (4) myofiber size increase (+94%) in a small series of muscle biopsies obtained after 2 years of FES. None of the subjects that performed 1 year home-based daily FES training (20 persons) had worsened their functional class, while 20% (4/20) improved to functional class 4, that is, the ability to stand. Discussion: The European Union (EU) Project Rise shows that 'home-based daily FES training' is a safe and effective therapy that may maintain life-long physical exercise by active muscle contraction (FES is the only option for denervated muscle) as a procedure to recover the early-lost tetanic contractility of denervated muscle, and to counteract muscle atrophy in order to prevent clinical complications.