Figure 1. Experimental protocol and measurement overview. Participants first completed a standardized warm-up followed by a muscle activation assessment. Surface electromyography (sEMG) signals were recorded from the biceps femoris (BF) and rectus femoris (RF) muscles during isometric contractions to determine mean frequency (MF), root mean square (RMS), averaged EMG (aEMG), and integrated EMG (iEMG). Afterward, participants performed an 8 × 1-min small-sided game (SSG) protocol with 1-min passive recovery between bouts. Internal load and respiratory responses were continuously monitored, including training impulse per minute (TRIMP/min), average and peak heart rate (HR_avg, HR_peak), total energy expenditure (EE_total), peak and average oxygen uptake (VO2), average respiratory rate (RespR), and ventilation (VE).