Abstarct: Objective: The aim of this study was to examine the effect of a single session of high-intensity interval training (HIIT) on oxidative stress indices (malondialdehyde [MDA] and total antioxidant capacity [TAC]), heart rate recovery (HRR), and explosive power in overweight men. Methods: In this quasi-experimental study with a pre-test–post-test design and a control group, 20 men aged 30–40 years with overweight (body mass index 25–29.9 kg/m²) from Shahroud city, who had not engaged in regular exercise for at least six months, were purposively selected and randomly assigned to a HIIT group (n=10) or a control group (n=10). The exercise protocol consisted of a 5-minute warm-up at 50–60% of maximum heart rate (HRmax), 8–10 one-minute bouts at 85–90% HRmax interspersed with 1-minute active recovery at 30–40% HRmax, and a 5-minute cool-down. The control group remained seated without any activity for the same duration. Before and immediately after the intervention, 5 ml of blood was drawn from the antecubital vein to measure MDA and TAC using the ELISA method. Additionally, HRR at the first and second minutes (HRR1 and HRR2) and explosive power (via the Sargent vertical jump test) were assessed. Data were analyzed using repeated-measures analysis of variance at a significance level of 0.05. Results: The time × group interaction effect was significant for all study variables. In the HIIT group, mean MDA increased from 0.99 to 5.94 µmol/L (P < 0.001, effect size = 0.759), whereas the increase in the control group was limited to 2.63 µmol/L. TAC in the HIIT group decreased from 1.53 to 0.81 mmol/L, a significantly greater reduction than in the control group (from 0.93 to 0.81) (P = 0.027, effect size = 0.245). HRR1 and HRR2 values in the HIIT group were 19.50 and 37.60 bpm, respectively, compared with 3.50 and 5.00 bpm in the control group (P < 0.001, effect size = 0.955). Explosive power in the HIIT group decreased from 38.60 to 35.90 cm, while the control group showed no noticeable change (P = 0.018, effect size = 0.275). Conclusion: A single session of high-intensity interval training in overweight men simultaneously results in a significant increase in oxidative stress (increased MDA and decreased TAC), a marked improvement in heart rate recovery (increased HRR1 and HRR2), and a temporary decline in explosive power (decreased vertical jump height). These findings indicate that HIIT can act as a potent, multi-faceted physiological stimulus for this population and, provided adequate safety and recovery principles are observed, can serve as a foundation for beneficial long-term adaptations.