Acute local and systemic responses to a modulated exercise stimulus using Blood Flow Restriction

Introduction:
Low-intensity (LI) exercise with blood flow restriction (BFR) has become a focus of interest as an alternative to high-intensity training for enhancing physiological adaptations in both athletic populations and rehabilitation [1]. A specific feature of BFR is high metabolic perturbations elicited by relatively low-intensity exercise. However, the physiological mechanisms behind BFR-training are not fully understood and there is limited data on the acute changes that occur at the local and systemic level, especially regarding its similarities and differences to workload-matched high-intensity training. Thus, this randomized cross-over study aimed to compare cardiorespiratory demands and local and systemic metabolic perturbations during LI exercise with and without BFR, as well as high-intensity exercise.
Methods:
Ten healthy young males (26.9±4.6 yrs) underwent three 20-min external workload-matched cycling trials. The cycling trials consisted of LI cycling (at 55%PPO), LI cycling with BFR (LI+BFR, at 50% of the individual arterial occlusion pressure), and high-intensity intermittent cycling (HI, with 10x1min at 90%PPO interspersed with 1-min active recovery at 20%PPO). Cardiorespiratory responses were measured using spirometry. To evaluate metabolic changes at a systemic (blood) and local (skeletal muscle interstitial fluid) level, a venous catheter and a microdialysis probe were inserted into an antecubital vein and vastus lateralis muscle, respectively.
Results:
No significant difference was found in oxygen uptake among the different exercise protocols (p=.39). Average heart rate, pulmonary ventilation, and ventilatory equivalent for CO2 were similar between LI+BFR and HI (p>.67) and higher than LI (p<.01). LI+BFR and HI resulted in higher total energy expenditure compared to LI (p<.05), but a greater proportion of fat utilization was found for LI (p<.05). Venous pH decreased significantly during LI+BFR and HI (p<.05), but remined unchanged during LI (p>.95). Regardless of exercise protocols, blood and interstitial lactate concentration increased during exercise, with significant lower levels found in LI compared to the other protocols (p<.05). In LI+BFR, blood glucose level increased continuously up to 5 minutes post-exercise (post5), whereas no changes occurred in LI and HI, resulting in a significant difference at post5 between LI+BFR vs. LI and HI (p<.05). In contrast, LI+BFR showed a trend towards lower interstitial glucose levels compared to the other protocols.
Conclusion:
Our results indicate that LI+BFR cycling elicits similar cardiorespiratory and metabolic demands as the workload-matched HI protocol. This highlights the effective nature of incorporating BFR in low-intensity exercise to increase energy demand and further modify the metabolic stress in different physiological systems. The potential alterations of glucose metabolism resulting from BFR exercise, both at the local and systemic level, need to be further investigated in terms of its impact on signaling pathways.