Abstract
(1) Background: How variations of the push-up plus (PUP)—particularly changes in the base of support and scapular excursion—affect scapular muscle activation remains unclear. This study compared phase-specific electromyographic (EMG) activity of scapular muscles during four protraction–retraction exercises. (2) Methods: Twenty-six healthy male participants (age: 22.88 ± 1.45 years; height: 1.74 ± 0.05 m; weight: 77.31 ± 8.61 kg; body mass index (BMI): 25.61 ± 2.43 kg/m2) with Pilates experience performed four scapular protraction–retraction exercises under two base-of-support (quadruped vs. single-leg) and two movement-range (PUP vs. STD) conditions. Exercise order was randomized, and sufficient rest intervals were provided to minimize fatigue effects. Surface electromyography was recorded from six scapular muscles and normalized to maximal voluntary isometric contraction. The study was registered on CRIS (KCT0010032). (3) Results: Single-leg PUP showed the greatest serratus anterior (SA) activation, with increases of approximately 30% in protraction, 20–25% in isometric, and 15–20% in retraction. STD variations elicited higher trapezius activation, especially during large scapular excursions. The UT/SA ratio was significantly lower in PUP conditions (η²p = 0.544), reflecting a more favorable stabilization pattern. (4) Conclusions: This experimental repeated-measures study demonstrates that combining single-leg support with traditional PUP meaningfully increases SA recruitment across all phases, whereas increased scapular range enhances trapezius engagement. These findings provide novel phase-specific insights into how PUP variations modulate closed-chain scapular stabilization and may assist clinicians in selecting targeted exercises. Interpretation should be limited to trained healthy males.