Background: Strength training produces acute physiological responses that can influence performance and recovery. However, comparative evidence regarding acute impacts of Complex Strength Training (CST) and Traditional Strength Training (TST) in soccer players remains limited.

Purpose: The study sought to compare the immediate physiological responses elicited by CST and TST among trained soccer players. Methods: Thirty soccer players (male) were randomly allocated into two groups: the Traditional Strength Training Group (TSTG; n = 15) and the Complex Strength Training Group (CSTG; n = 15) following eligibility screening. After a two-week familiarization period, both groups completed a single training session. Pre- and post-intervention assessments included cardiovascular variables (heart rate [HR], systolic blood pressure [SBP], diastolic blood pressure [DBP], and rate pressure product [RPP]), pulmonary variables (respiratory rate [RR], and oxygen saturation [SpO₂]), vital capacity [VC]) and a perceptual variable (rating of perceived exertion [RPE]).

Results: TSTG and CSTG produced significant acute increases in cardiovascular and respiratory parameters (p < 0.05), with elevated RPE and reduced SpO₂. Significant time × group interactions were observed across all key variables, indicating a greater physiological stress response in CSTG. Compared to TSTG, CSTG showed higher increases in SBP (17.8% vs. 13.0%), DBP (11.4% vs. 7.5%), HR (18.52% vs. 13.80%), and RPP (38.8% vs. 30.9%). RR increased more in CSTG (47.99%) than TSTG (30.01%), while VC improved more in CSTG (2.92% vs. 1.57%). Both groups experienced higher RPE (CSTG: 121.57%, TSTG: 103.58%) and reduced SpO₂ (–4.89% vs. –3.74%). Conclusion: CST imposes greater acute cardiovascular, respiratory, and perceptual demands than TST. These findings indicate that CST may function as an effective pre-competition conditioning strategy, but requires careful load management to minimize excessive fatigue.