Acute Systemic Growth Responses To Low Intensity Blood Flow Restricted Resistance Exercise

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Previous research has demonstrated that blood flow restriction during low intensity resistance exercise (BFR-Low) results in a potent muscle growth response in humans. However, it is unclear whether this stimulus is similar to that provoked with free-flow high intensity resistance exercise (FF-HI). PURPOSE: To determine the acute growth hormone (GH) and insulin-like growth factor (IGF-1) responses to BFR-Low and FF-HI in young adults. Additionally, because BFR may induce adverse reactions we evaluated cardiovascular, endothelial inflammation with vascular cell adhesion molecule (VCAM) and blood coagulation (D-dimer) responses. METHODS: Ten healthy subjects aged 20-39 years reported to the laboratory between 7 and 9 AM on two separate occasions in a fasted condition. Knee extension exercise was performed at 20% of maximal strength for the BFR-Low condition in comparison to a FF-HI performed at 80% of maximal strength. Both conditions were performed for 5 sets until task failure. During BFR-Low exercise, a 10 cm wide tourniquet cuff was placed around the upper thigh at 1.5 systolic blood pressure immediately before exercise and remained inflated (∼15 minutes). Blood was sampled every 10 minutes for 150 minutes to assess GH responses and IGF-1 was measured at baseline and 90 minutes post-exercise. RESULTS: Subjects demonstrated a greater mean increase in GH levels with BFR-Low exercise (2.1 ± 2.1 ng/ml) when compared to FF-HI (1.5 ± 2.6 ng/ml), but this difference was not statistically different (p = 0.61). IGF-1 levels demonstrated no change regardless of the exercise condition. Peak heart rate (HR) and systolic blood pressure (BP) showed similar responses to both conditions (HR: BFR-Low: 83.8 ± 12.4; FF-HI: 84.8 ± 6.7 bpm) (SBP: BFR-Low: 148.8 ± -.9 vs. FF-HI: 139.0 ± 15.6 mmHg). Peak diastolic blood pressure was elevated to a greater extent during BFR-Low exercise (BFR-Low: 103 ± 9.7; FF-HI: 92.6 ± 12.4, p=0.05). D-dimer, a degradation product of crosslinked fibrin and VCAM levels showed no change 30 min post exercise for either condition. CONCLUSIONS: Resistance exercise performed at low intensity with BFR has a similar systemic acute growth, blood coagulation and endothelial inflammatory response, but greater cardiovascular demand when compared to resistance exercise performed at a high intensity.