This study aimed to investigate the effects of caffeine supplementation on heart rate variability (HRV), rate-pressure product (RPP), delayed onset muscle soreness (DOMS), and rating of perceived exertion (RPE) following circuit resistance training. Ten trained male participants (average age: 22.44 ± 0.52 years), each with at least six months of resistance training experience, were involved in a single-blind, counterbalanced crossover design under caffeine and placebo conditions. Participants ingested either 6 mg/kg body weight of caffeine or a placebo after 8 hours of fasting, with a 3–6-day washout period between conditions.

Thirty minutes after ingestion, subjects performed a circuit resistance training protocol including hip thrust, sumo squat, leg extension, hamstring curl, calf raise, and groin exercises, completed in three rounds with short rest intervals. HRV, RPP, DOMS, and RPE were measured before and after the exercise.

Results indicated a significant decrease in HRV parameters RMSSD and HF, and a significant increase in LF and LF/HF ratio in both caffeine and placebo conditions post-exercise (p < 0.05). RPP values differed significantly during all recovery periods (p < 0.05), while RPE and muscle soreness levels decreased significantly post-exercise in both conditions. Additionally, maximum voluntary contraction of the gluteal muscles and pain perception also declined significantly after exercise.

Conclusion: Circuit resistance training independently influences HRV, RPP, RPE, and DOMS values. The ingestion of 6 mg/kg caffeine prior to exercise did not significantly alter these physiological and perceptual responses compared to the placebo condition.