## 2 Materials and Methods
### Procedures
#### 2.3.4 Resistance Training Protocol  
The 12-week training program consisted of two weekly sessions, each comprising four upper-body exercises commonly used in powerlifting to improve muscle strength and hypertrophy. Session 1 included the bench press (1 set at a specified intensity with RIR 4), flat dumbbell press (3 sets of 10 repetitions at RIR 1), incline dumbbell press (2 sets of 10 repetitions at RIR 1), and pulley crosses (2 sets of 15 repetitions at RIR 1). Session 2 included the bench press (1 set at a specified intensity with RIR 4), followed by three additional sets of bench press (3 sets of 10 repetitions at RIR 1), incline barbell press (2 sets of 10 repetitions at RIR 1), and dips (2 sets of 15 repetitions at RIR 1). The main difference between the protocols was the load applied to the initial set of the bench press exercise. For the LL-HV group, the first set of Session 1 was performed at 45% of 1 RM, and the first set of Session 2 was performed at 60% of 1 RM. This alternating pattern, sustained throughout the program, aligns with previous research categorizing loads at or below 60% of 1 RM as low-load training [21]. Conversely, the HL-LV group performed the first set of Session 1 at 75% of 1 RM and the first set of Session 2 at 90% of 1 RM, maintaining the same periodization pattern as LL-HV group. This structured plan ensured consistency in the training design while distinctly differentiating the loading strategies for the initial bench press sets, offering a clear comparison of low-load and high-load resistance training protocols. Training sessions were conducted twice weekly, with at least a 72 h recovery period between sessions. This training frequency involved a total of 16 weekly sets primarily targeting the pectoral muscles, with 14 sets being identical between the groups and differing only in a single bench press set per session. This approach aligns with established guidelines for optimizing muscle strength and hypertrophy [27; 39]. Participants exclusively performed the prescribed training protocol, focusing solely on the bench press and the accessory exercises detailed above. No additional exercises targeting other muscle groups were included to ensure that the observed adaptations were solely attributable to the implemented training protocols. Participants were instructed to refrain from any other physical activity that could influence the dependent variables, including additional training for either the upper or lower body. The experimental training protocol was adapted from the methodology developed by [PERSON], European champion in the bench press at the 2017 Arnold's Europe Championshipships and the 2018 European Classic Bench Press Championships. Before each session, participants completed a standardized warm-up comprising general and specific exercises. During this warm-up, the Speed4 Lifts device was attached to the barbell to estimate 1 RM indirectly. Participants performed incremental sets ranging from 50% to 80% of their pre-test 1 RM, while the encoder measured barbell velocity and transmitted the data to a smartphone application (SPEED4 LIFTS, Madrid, Spain) for real-time analysis. This method ensured precise load adjustments by minimizing discrepancies associated with programming solely based on pre-intervention 1 RM values [40]. A 3 min rest period followed the warm-up, in alignment with established research evidence [41; 42]. Participant's existing training regimens were reviewed before the program's commencement to ensure that upper-body training volumes were standardized across groups. The only difference between the groups was in the first set of the bench press exercise, aimed at assessing the effects of a low-load, high-repetition initial set. Both groups trained with the same level of exertion, determined by RIR, a validated method for determining set endpoints [43].