Comparison Of Blood Flow Characteristics Before, During, And After High-intensity Interval And Moderate-intensity Continuous Exercise

Abstract

PURPOSE: A comparison of blood flow characteristics in the brachial artery during high-intensity interval exercise (HIIE) and moderate-intensity continuous exercise (MOD) has not been conducted. Also, the acute effects of these exercise protocols on measures of vascular reactivity are not fully understood. METHODS: Sixteen healthy males (Age: 23±3 years, BMI: 25.5±3.0) completed HIIE (10, 1 min intervals at 90-95% of HRmax with 1 min of recovery between) and MOD (30 min at 70% of HRmax) on a cycle ergometer. Brachial artery diameter and blood flow measurements were made before, during and after exercise via high-resolution ultrasound. RESULTS: During exercise there were no differences in artery diameter but anterograde velocity (HIIE: 17.96±6.14 cm/sec, MOD: 21.73±8.11 cm/sec, P=0.02) and anterograde shear rate (HIIE: 170.83±55.51 sec-1, MOD: 203.50±76.09 sec-1, P=0.04) were higher during MOD compared to HIIE. Retrograde velocity (HIIE: -7.67±2.79 cm/sec, MOD: -5.50±2.04 cm/sec, P<0.01) and retrograde shear rate (HIIE: -73.82±28.37 sec-1, MOD: -51.48±19.77 sec-1, P<0.01) were of greater magnitude during HIIE compared to MOD. Baseline artery diameter decreased after HIIE (P=0.04), but not after MOD (P=0.19). Peak diameter after occlusion decreased with MOD (P=0.04), but not with HIIE (P=0.80). Minimum diameter during cuff occlusion decreased after HIIE (P=0.02) and marginally decreased after MOD (Pre: P=0.06). No acute changes were seen with flow-mediated dilation (FMD) or low-flow mediated constriction (L-FMC) within either group. The composite end-point of vascular reactivity (COM) increased after HIIE (Pre: 5.64±3.21, Post: 8.57±3.16%, P<0.01) but not MOD (P=0.56). Exercise x time interactions were observed for COM (P=0.02), peak diameter (P=0.05), and a trend for FMD (HIIE-Pre: 5.44±4.11, Post: 7.58±5.99% vs. MOD-Pre: 6.3±2.89, Post: 4.2±5.75%, P=0.09). CONCLUSION: We observed more positive shear stress during MOD and more negative during HIIE. These differences in exercise shear stress during exercise may result in more vascular reactivity after HIIE compared to MOD as well as potentially explain differences observed in the chronic adaptations to these distinct exercise protocols.