Effect of acute isometric bilateral leg extension exercise on brachial and common femoral artery flow-mediated dilatation

Introduction:
Flow-mediated dilatation (FMD) is an endothelium-dependant and nitric oxide specific index of endothelial function. The chronic effects of exercise on endothelial function and improvements in FMD have been well established (Tinken et al., 2010). The impact of acute exercise on FMD remains inconclusive. The aim of this study was to investigate the effect of acute isometric bilateral leg extension exercise performed at two different intensities on brachial (BA) and common femoral artery (CFA) FMD.

Method:
11 healthy male participants visited the laboratory for six visits. High intensity, low intensity exercise and control conditions were performed twice at random. High and low exercise intensity were calculated from an Incremental Isometric Exercise Test (Devereux et al., 2011). BA and CFA FMD were measured pre and 5 minutes post exercise for each of the conditions. The absolute change in BA and CFA FMD was expressed as a percentage (%) and raw (mm). Doppler Ultrasound was used to measure FMD. Edge-detection, wall tracking software was used for analysis. During each exercise bout Doppler Ultrasound was used to measure CFA blood flow and artery diameter. Results There was a significant difference in absolute change BA FMD% between high (mean change -4.23%) and low (2.77%) exercise intensities (p=0.033). There was a significant difference in absolute change BA FMD (mm) between high (-0.02mm) and (0.01mm) low intensities (p=0.035). No significant differences existed in absolute change CFA FMD% or FMD (mm) between high and low intensities (p=0.856 and p=0.741) respectively. Blood flow and shear rate were analysed during exercise contractions and upon release. A significant time by intensity interaction was evident (p=0.02 and p=0.014) with significantly higher antegrade blood flow and antegrade shear rate upon release in the high condition. There was no significant main effect or time by intensity interaction evident (p>0.05) with retrograde blood flow and retrograde shear rate. Normalisation of FMD to the shear rate stimulus is ongoing.

Discussion:
Results demonstrate that absolute BA FMD% and FMD (mm) are significantly reduced after a high intensity bout of exercise is performed, which coincides with research utilising alternative modes of acute exercise (Llewellyn et al., 2012). The increases in blood flow and shear rate were greater throughout exercise, when compared to more widely researched exercise modes (Gonzales et al., 2011). This research may provide further insight into how the specific exercise stimulus may cause different acute responses in endothelial function, perhaps promoting isometric exercise training as an efficient alternative to improve resting blood pressure. This research could potentially inform future exercise prescription for training studies which ultimately aim to improve cardiovascular health.