Author(s): GROSPRETRE, S., EON, P.1, CORNEBOIS, M.1, MARUSIC, U.2, MARTIN, A.3, Institution: UNIVERSITY MARIE & LOUIS PASTEUR, Country: FRANCE, Abstract-ID: 859

INTRODUCTION:
Motor imagery (MI) and neuromuscular electrical stimulation (NMES) were shown to limit the decrease of muscle strength during the early stages of limb immobilization (1,2). Recently, a study revealed that corticospinal excitability was enhanced when MI and NMES were combined (MI+NMES), compared with either modality alone (3). These findings raised a pertinent issue regarding the potential impact of MI+NMES during a short-term immobilization. Therefore, the purpose of this study was to evaluate the effect of MI+NMES during a 48-hour arm immobilization on the neuromuscular system. We hypothesized that MI+NMES would attenuate the immobilization-induced strength loss and associated alterations in corticospinal excitability.
METHODS:
Ten healthy participants (age: 25 ± 5 years) completed three experimental conditions, each lasting 48h, performed in a randomized crossover design: control (CON), immobilization (IMMO) and immobilization with intervention (INTER). During IMMO and INTER, participants had their dominant arm immobilized with splints. Additionally, during INTER, participants performed one session of 10 minutes of MI+NMES targeting wrist flexion every two hours. NMES intensity was set at 20% of maximal voluntary contraction (MVC). For each experimental condition, maximal force (MVC) and corticospinal excitability of flexor carpi radialis (FCR) were measured before (PRE), at 24h (POST24) and immediately after each condition (POST48). Corticospinal excitability was assessed at rest by evoking motor evoked potentials (MEP) using transcranial magnetic stimulation applied over contralateral motor region of flexor carpi radialis muscle. MEPs were normalized to the maximal M-wave (Mmax) evoked by median nerve stimulation. Each parameter was recorded on both immobilized and contralateral arm.
RESULTS:
On the immobilized limb, MVC significantly decreased by 15% from PRE to POST24 and from PRE to POST48 (P=0.025 and P=0.008, respectively) only in the IMMO condition. FCR MEP/Mmax significantly decreased from PRE to POST24 (P=0.017) and from PRE to POST48 (P=0.015), only in the IMMO condition. Peripheral measures (Mmax and resting twitches) did not show any significant changes across all conditions. The contralateral limb did not show any significant changes.
CONCLUSION:
These results showed that a short immobilization period (48h) can result in decreased maximal force, accompanied by a decrease in corticospinal excitability targeted to the immobilized limb, while peripheral markers were preserved. This highlights that a decline in motor function, of central origin, already arises at early phases of immobilization. The lack of decline observed in INTER condition shows that NMES+MI combination is a good candidate to mitigate the early decline in nervous system excitability.

REFERENCES :
1. Campbell et al. (2019), Sports Medicine, 49, 981-986
2. Debarnot et al. (2021), Sci Rep, 11:8928
3. Eon et al. (2025), Eur J Appl Physiol, 125(2):561-572