Fig. 3

Schematic of the randomized experimental protocol. Each experiment was divided into two sessions, one involving high-intensity stimulation and the other moderate-intensity stimulation, with the sequence randomized for each subject. A minimum of 48 h was maintained between sessions to prevent residual fatigue. Prior to the first session, SDSS was randomly assigned to one leg, while SES was assigned to the other, and this leg-stimulation arrangement was kept consistent across all sessions. Each session began with determining high and moderate stimulation intensities for the quadriceps (Experiment 1) or vastus lateralis (Experiment 2) muscles using SDSS configuration. Following a 5-minute break, fatigue measurements were conducted using the randomly assigned stimulation configuration (SDSS or SES). The process was then repeated on the opposite leg with the other electrode configuration. The second session mirrored the first, with the stimulation intensities for fatigue measurements being switched while maintaining the same leg-stimulation arrangement