Background and Objective: Low-intensity resistance training, when combined with eccentric quasi-isometric (EQI) contractions or blood flow restriction (BFR), can induce significant metabolic and anabolic responses. The aim of this study was to investigate the acute responses of muscle hypertrophy-related markers to EQI, with and without blood flow restriction, in Inactive overweight women.
Materials and Methods: In this semi-experimental study, twenty-seven sedentary women (age range: 25-40 years; BMI: 25-30 kg/m²) were recruited and randomly assigned to three experimental groups: EQI, BFR, and the Combined (Com) protocol. Prior to the intervention, the one-repetition maximum (1RM) was accurately determined for all participants, and arterial occlusion pressure (AOP)—personalized for each individual limb using professional Doppler ultrasound—was established for the BFR groups to ensure standardization. Resistance exercises were performed in two separate training sessions with a 72-hour interval between bouts: leg extension (lower body) and dumbbell biceps curl (upper body). The EQI group performed quasi-isometric eccentric contractions in three sets at 50% of 1RM until reaching voluntary muscle failure. The BFR group performed exercises in three sets at 30% of 1RM with 40% AOP until reaching failure. The Com group performed EQI with BFR in three sets at 50% of 1RM and 40% AOP until failure. The inter-set rest interval was strictly maintained at 120 seconds for all study groups. Venous blood samples for analyzing lactate, growth hormone (GH), and IGF-1 were collected 15 minutes before and immediately after the completion of each exercise session. Data were subsequently analyzed using paired t-tests for within-group analysis and one-way ANOVA for between-group comparisons (P<0.05).
Results: Findings showed that lactate levels significantly increased in all groups (P < 0.05). The greatest increases were observed in the BFR group (lower body: 276%; upper body: 301%), the EQI group (lower body: 161%; upper body: 246%), and the Com group (lower body: 206%; upper body: 218%). Regarding the hormonal response, a significant increase in growth hormone (GH) levels was observed only in the upper body exercise session in the EQI and BFR groups (P < 0.05) (average of 91% in the EQI group and 192.4% in the BFR group). Furthermore, IGF-1 levels did not show significant changes within or between groups in any of the exercise sessions (P > 0.05).
Conclusion: These findings confirm the importance of innovative training models, such as EQI, BFR, or their strategic combination, in inducing effective metabolic responses and activating anabolic pathways without the need for high-intensity external loading, even within a single session. The observed lack of changes in systemic IGF-1 suggests that the anabolic potential of these specific activities is likely mediated through local intracellular signaling pathways, independent of systemic hormonal fluctuations. These results provide new, clinically relevant insights into designing rehabilitation and hypertrophy-based training programs primarily focused on metabolic stress induction in overweight populations.