To assess the impact of metabolic stress on blood lactate, muscle damage, inflammatory and hormonal responses following a high-load (70% maximum) strength training session, we compared two methods with a similar number of repetitions but that differed by their metabolic demand: the 3/7 method consisting in two series of five sets of an increasing number of repetitions (3 to 7) with a short inter-set interval (15 s) and the 8 × 6 method that comprises eight sets of six repetitions with a longer inter-set interval (2.5 min). Blood concentrations in lactate, creatine kinase (CK), myoglobin (MB), interleukine-6 (IL-6), leukocytes, growth hormone (GH), insulin-like growth factor-1 (IGF-1) and cortisol were determined before and after each session. Lactate concentration increased more (11.9 vs. 3.1 mmol/L; p < 0.001) for the 3/7 method whereas CK and MB concentrations were augmented similarly (p > 0.05) for both methods. Inflammatory markers (leukocytes and IL-6) increased (p < 0.01) more after the 3/7 method. GH and cortisol concentrations also increased more (p < 0.001) after the 3/7 method with no difference in IGF-1 concentrations between methods. Positive associations were found between the change in lactate and changes in IL-6 (r² = 0.47; p < 0.01), GH (r² = 0.58; p < 0.001) and cortisol (r² = 0.61; p < 0.001) concentrations. In conclusion, the greater lactate accumulation induced by short inter-set intervals during a high-load training session is associated with enhanced inflammatory and hormonal responses, suggesting that metabolic stress might contribute to the greater adaptative response previously observed with this method.

Background/Objectives: Identifying accessible and effective exercise interventions is essential for improving health and physical fitness in individuals with overweight or obesity. Whole-body high-intensity interval training (WB-HIIT) is a time-efficient approach that requires minimal equipment and can be adapted to a wide range of settings and fitness levels. Therefore, this study aimed to investigate the effects of WB-HIIT on cardiorespiratory and musculoskeletal fitness, body composition, and metabolic health markers. Methods: Thirty-six healthy adults with overweight were assigned to either a WB-HIIT group (n = 19; 35 ± 9 years; BMI 30.2 ± 3.1 kg/m²) or a control group (n = 17; 33 ± 11 years; BMI 30.3 ± 3.3 kg/m²). Participants completed pre- and post-intervention assessments including dual-energy X-ray absorptiometry (DXA), blood sampling, maximal cardiopulmonary exercise testing, and measures of muscular strength (3 RM) and functional endurance (1 min sit-to-stand and arm curl). The 10-week supervised WB-HIIT (2–3 sessions per week) included a warm-up, 3–4 sets of 10–12 all-out whole-body exercises (30–40 s) interspersed with 20–30 s recovery, and a cool-down. Results: The control group showed no significant changes in any of the assessed parameters after 10 weeks, except for a modest increase in body fat mass. The WB-HIIT group showed significant improvements in cardiorespiratory fitness, evidenced by increases in VO₂peak (p < 0.05), maximal treadmill incline (p < 0.01), and first ventilatory threshold parameters (p < 0.05). Maximal strength increased significantly in both the leg and bench press (p < 0.001), accompanied by a significant improvement in upper-limb functional endurance (arm curl, p < 0.05). No significant changes were observed in body weight or BMI, but small reductions were found in body fat percentage, trunk fat mass, and waist circumference (p < 0.05). Except for a modest decrease in glycated hemoglobin (p < 0.05), metabolic blood parameters remained unchanged and were already within the normal range at baseline. Conclusions: A 10-week WB-HIIT intervention improved cardiorespiratory fitness, muscular strength, and upper-limb functional endurance, and elicited a modest reduction in trunk fat mass in individuals with overweight or obesity.