Author(s): MOŠKON, S., ŠINKOVEC, L.1, TOMAŽIN, K.1, AMON, R.2, STROJNIK, V.1, SPUDIC, D.1, Institution: UNIVERSITY OF LJUBLJANA, FACULTY OF SPORTS, Country: SLOVENIA, Abstract-ID: 1253

INTRODUCTION:
Multiple sclerosis (MS) is chronic, autoimmune disease expressed with demyelination of neurons of central nervous system (1), resulting in muscular weakness, spasticity and impaired voluntary muscle activation (2). Strength and aerobic training have beneficial effects for managing the symptoms (3), but people with MS often struggle to reach the intended exercise intensity due to decreased voluntary muscle activation. Potential solution is the submotor electrical stimulation (SES), which stimulates sensory neurons, influencing the alpha motor neurons, thereby enhancing voluntary muscle activation (4). The aim of the study was to determine whether SES of the tibial nerve during isometric ankle plantar flexion (PF) affects the produced torque in the ankle, the amplitude and median frequency (MF) of the electromyogram (EMG) of the soleus muscle in healthy adults and adult patients with MS.
METHODS:
A pilot study included 10 healthy adults and 10 adult patients with MS. Both groups performed 6 repetitions of PF of the ankle at three different levels (20 %, 60 % and 100 %) of maximal isometric voluntary contraction (MVC) with electrical impulses superimposed on the tibial nerve at frequencies of 20 Hz and 80 Hz (train duration one second). Surface EMG electrodes were applied to the soleus. To observe differences in PF torque, amplitude of the EMG and MF before, during and after SES, three-way ANOVAs were performed separately for each intensity of muscle contraction (20 %, 60 % and 100 %).
RESULTS:
Differences in PF torque before, during and after SES were observed (60 %: p < 0,001; 100 %: p < 0,001). However, contrary to expectations, the PF torque decreased, with a more distinct reduction at 80 Hz SES. MF was found to be dependent on the frequency of SES (20 %: p < 0,001; 60 %: p < 0,001; 100 %: p = 0,001). Generally, the increase of MF was more pronounced during 80 Hz SES. SES did not affect the amplitude of the EMG signal. No differences in the effects of SES on PF torque, MF, or EMG amplitude of the soleus muscle were observed between the groups.
CONCLUSION:
The results of the pilot study suggest that SES (1 second, 20 Hz, 80 Hz) has limited potential for acutely increasing ankle PF torque. Most likely and in accordance with previous studies (4, 5), longer SES with higher frequencies would be needed to potentially observe the differences between and within the groups. Due to heterogeneous results in the MS group, further studies are needed to confirm our findings.
REFERENCES:
1) Amatya- et al., Cochrane Database Syst. Rev., 2018
2) Andreu-Carava et al., Physiol. Behav., 2022
3) De Souza-Teixeira et al., Int. J. Sports Med., 2009
4) Alenazy et al., J Electromyogr Kinesiol, 2018
5) Dean et al., Front. in Hum. Neurosci., 2014