Purpose: This study investigated the acute effects of two structured breathwork methods on autonomic recovery following maximal exertion. Materials and Methods: A randomized control trial was conducted with 62 cadets (44 males and 18 females) assigned to three distinct groups: box breathing (BB), cyclic sighing (CS), or spontaneous breathing control. Participants performed a graded exercise test to assess maximal oxygen consumption (VO2). High-frequency heart rate variability (HF-HRV) and heart rate recovery (HRR) were collected to evaluate autonomic recovery and parasympathetic reactivation. HF-HRV was analyzed at three time points: baseline (Pre), 1-3-min postexercise recovery (Post1), and 4-6-min postexercise (Post2). HRR was measured at 1- and 3-min intervals, analyzing reductions from peak heart rate captured at VO2max. All analyses were evaluated using a 3 (group) × 3 (time) mixed-design repeated-measures analysis of variance. Results: All groups were comparable in age, weight, height, and body mass index (21 ± 3 yr; 77.4 ± 15.4 kg; 173.1 ± 9.0 cm; 25.7 ± 4.0 kg·m-2, respectively). HF-HRV revealed significant main effects for time (F(2,118) = 465.01, P < 0.001, Eta2=0.89), group (F(2,59) = 8.20, P < 0.001, Eta2=0.22), and time × group interaction (F(4,118) = 3.54, P = 0.009, Eta2=0.21). Both the CS and BB groups had greater increases in HF-HRV from Post1 to Post2 when compared to spontaneous breathing (P = 0.001). HRR improved across all participants from 1- to 3-min postexercise with n group level differences (F(1,59) = 33.51, P < 0.001, Eta2=0.36). Conclusions: Structured breathwork following maximal exertion significantly accelerated parasympathetic reactivation as reflected by HF-HRV. Both BB and CS offer a simple field-ready intervention aimed to enhance operational readiness for tactical populations through enhancing acute physiological recovery.
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