Matthew A. Chatlaong, Lori M. Keys, Daphney M. Stanford, Matthew B. Jessee. University of Mississippi, University, MS.

BACKGROUND: Training with just 1 x 20s cycling sprint does not improve cardiorespiratory fitness (CRF), but 2 sprints does. If the arterial shear stimulus is high enough following just 1 sprint, training may still improve systemic vascular function even without improved CRF. PURPOSE: Compare brachial artery shear rate between 1- and 2- 20s sprints. METHODS: In 1 visit, 40 healthy participants completed 2 20s all-out leg cycling sprints (5 min rest between). Before and after each sprint, participants sat upright with their arm supported. Duplex and B mode ultrasound recordings of the brachial artery were made sequentially (30s duplex for blood velocity, then 5-10s B mode for diameter) at baseline, in minutes 1 (M1), 3 (M3), and 5 (M5) of recovery after sprint 1 (S1) and 2 (S2), then at 10- (M10) and 15- (M15) min post-exercise. For each time point, diameter, shear rate, and blood flow were averaged over video lengths. Peak values were taken from 3s averaging. Bayesian rmANOVA were used to compare all variables between time points. BF10=likelihood of alternative vs. null. Results are mean±SD. RESULTS: After S1, average shear rate (1/s) increased from baseline (70.5±46.8) and did not return until M15 (74.3±41.2,BF10=.2). Comparing sprints, average shear rate was the same for S1M1 (182.5±87.6) vs S2M1 (184.8±104.4) and for S1M3 (108.3±48.9) vs S2M3 (105.1±47.6,BF10 both <.2), but evidence was weak for S1M5 (80.2±37.5) vs S2M5 (94.0±45.2,BF10=1.1). Peak shear rate followed the same pattern. Diameter (mm) decreased from baseline (3.9±0.5) after S1 and did not return until M15 (3.8±0.5,BF10=.2). Comparing sprints, diameter was higher at S1M1 (3.8±0.5) vs all other time points (BF10 all >4.6). Diameter was the same for S1M3 (3.6±0.6), S1M5 (3.6±0.6), S2M1 (3.6±0.6), S2M3 (3.7±0.5), and S2M5 (3.6±0.6, BF10 all <.2). Average blood flow (mL/min) increased from baseline (48.3±32.4) after both sprints, returning toward baseline at S1M5 (46.9±28.0,BF10=.2 ), S2M5 (55.9±36.2,BF10=.4), and 15m (51.5±33.3,BF10=.2). Average blood flow was highest at S1M1 (114.9±57.1) and S2M1 (99.8±58.6), although evidence was weak when comparing them (BF10=1.0). CONCLUSION: While there may be a greater total shear stimulus from doing 2 sprints, the magnitude of the shear stimulus is the same after 1, i.e., it is not augmented after a second sprint. Investigating whether training with 1 sprint can improve vascular function may be warranted.

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