Near-infrared spectroscopy during low-intensity blood flow restriction resistance exercise

Introduction: Low-intensity resistance exercises with blood flow restriction are known to be effective in promoting muscular strength and hypertrophy; however, there is a paucity of evidence on their acute hemodynamic responses. Objective: To compare the changes in muscular oxyhemoglobin (O2Hb), deoxyhemoglobin (HHb) concentrations, and O2 saturation (StO2) during low load exercise under free blood flow (FreeBF) and blood flow restriction (BFR). Methods: Fifteen healthy males were subjected to bilateral knee extension tests under FreeBF and BFR conditions, in a random order. The knee extension exercise included four sets of 15 repetitions at 20% of one-repetition maximum, with 30s interval between the sets. In the BFR condition, subjects exercised with a cuff positioned on the proximal thigh and inflated to 50% of total occlusion pressure. Changes in the O2Hb, HHb, total hemoglobin (tHb), and StO2 in vastus lateralis muscle were monitored using near-infrared spectroscopy. Results: A two-way repeated-measures ANOVA revealed significant main effects for sets for all variables (P < 0.05). Moreover, the values in StO2 during sets 2, 3, and 4 in BFR conditions were significantly lower than those in freeBF. Significant differences were also seen between the exercise conditions during rest intervals for HHb (rest intervals 2, 3, and 4) and tHb (rest interval 3; P < 0.05). There were no significant interactions between conditions and sets or conditions and intervals for O2Hb. Conclusion: Low-intensity resistance exercise performed with BFR significantly decreased the acute muscle StO2 and increased total muscle hemoglobin.