Résumé
Transcutaneous spinal stimulation (TSS) is a non-invasive neuromodulation technique that activates spinal and supraspinal sensorimotor pathways, supporting functional recovery from motor impairments. Although TSS has tremendous clinical potential, the influence of anatomical and physiological differences, such as sex and body fat percentage, on evoked muscle responses, particularly motor thresholds, remains unclear.
This study investigated the effect of sex and body fat percentage on lower limb motor thresholds elicited by TSS in healthy adults. Seven neurologically healthy adults (4F, 3M; 23.6 ± 4.7 years; body fat: 28.9 ± 7.5%) received TSS. The cathode was positioned between the L1–L2 vertebrae, with stimulation intensities ranging from 10–190 mA. Electromyography (EMG) electrodes were placed over the rectus femoris, biceps femoris, tibialis anterior, medial gastrocnemius, and soleus muscles to measure motor thresholds. Body fat percentage was estimated via skinfold measurements using the Durnin-Womersley equation.
A negligible correlation was observed between body fat percentage and motor threshold across all participants (R = 0.0014). However, subscapular skinfold thickness showed a strong positive correlation with motor threshold (R = 0.6999). Sex-specific analysis revealed a negligible relationship for females (R = 0.0061), whereas males showed a strong positive correlation between body fat percentage and motor threshold (R = 0.9511). These findings suggest that sex and localized adiposity, particularly subscapular fat, can influence the stimulation intensity required to elicit motor responses with TSS. Considering individual anatomical differences may enhance personalized stimulation protocols and aid in establishing normative data for clinical comparisons in populations with neurological disorders.
