The influence of training status on mechanisms of rapid vasodilation in healthy humans

Abstract

Rapid vasodilation (ROV) is a feedforward process that increases blood flow to exercising muscles at the onset of exercise, allowing for a quicker increase in oxygen supply in response to an elevated oxygen demand. Whether or not resistance exercise can enhance rapid vasodilation in a healthy, young adult population is unknown. PURPOSE: To investigate the effects of training status on mechanisms of ROV in healthy, young people. METHODS: 6 trained participants (all males) and 6 sedentary participants (all males; sex, age, and height matched with trained participants) completed 2 study visits (1 experimental visit). During the experimental visit, subjects completed 2 trials of 10 different 1-second stimuli, each separated by 2 minutes of rest: 5 intensities of voluntary handgrip contraction (20% and 100% of a subject’s maximal voluntary contraction, 5kg, 10kg, 15kg), 2 intensities of involuntary contraction via ulnar nerve electrical stimulation (5mA and 10mA), 3 intensities of mechanical compression of the forearm (50mmHg, 200mmHg, 300mmHg). The order of stimuli in both trials was randomized separately, and subjects were blinded to the order. Forearm blood flow, (FBF, doppler and echo ultrasound), mean arterial pressure (MAP, finger photoplethysmography), vascular conductance (FVC, FBF/MAP × 100mmHg) were acquired for 30 heart beats immediately before and 30 heartbeats immediately after each stimulus. Absolute changes in FVC (∆FVC) were determined as the difference between FVC at each of 30 heart beats after the stimulus and the average of FVC across 30 heart beats before each respective stimulus. ∆FVCtotal was calculated as the integral of the absolute change in FVC across 30 heart beats after a stimulus; ∆FVCpeak was determined to be the largest ∆FVC value observed within 30 heart beats after a stimulus. RESULTS: Data are mean±SD. Trained subjects displayed greater ∆FVCtotal (ml/100mmHg) and ∆FVCpeak (ml/min/100mmHg) compared to sedentary counterparts in response to relative-intensity voluntary contractions (Total – 20% MVC: 48.25±14.36 vs. 20.58±9.70, p=0.003 d=2.26; 100% MVC: 90.40±40.38 vs. 31.04±12.09, p=0.01 r=0.74) (Peak – 20% MVC: 212.53±63.26 vs. 96.39±41.83, p=0.004 d=2.17; 100% MVC: 347.12±177.44 vs. 154.50±61.04, p=0.01 r=0.74). Trained subjects displayed greater ∆FVCtotal and ∆FVCpeak compared to sedentary counterparts in response to absolute-intensity voluntary contractions (Total – 5kg: 42.30±14.69 vs. 18.80±4.53, p=0.004 d=2.16; 10kg: 50.97±16.10 vs. 24.02±9.83, p=0.006 d=2.02; 15kg: 70.80±21.52 vs. 27.92±8.46, p=0.001 d=2.62) (Peak – 5kg: 188.35±45.43 vs. 99.27±38.45, p=0.01 d=1.76; 10kg: 243.81±68.75 vs. 120.96±45.43, p=0.004 d=2.11; 15kg: 282.66±90.85 vs. 127.67±40.70, p=0.003 d=2.20). Trained subjects also displayed greater ∆FVCtotal compared to sedentary counterparts in response to a 5mA electrically stimulated, involuntary contraction (41.60±15.01 vs. 21.62±9.28, p=0.02 d=1.60) as well as greater ∆FVCpeak compared to sedentary counterparts in response to a 200mmHg mechanical forearm compression (70.36±13.37 vs. 45.72±12.65, p=0.008 d=1.89). CONCLUSION: Our results indicate that trained subjects demonstrated enhanced rapid vasodilation in response to multiple different types of stimuli, compared to sedentary subjects. Thus, at least one of multiple different mechanisms of ROV may respond to exercise training.