The purpose of this study is to investigate the effect of blood flow restriction (BFR) resistance training on vascular function. The investigators aim to compare the effects of different BFR devices (wide-rigid cuffs and narrow elastic bands) on vascular function. The investigators hypothesize that BFR resistance training with wide-rigid cuffs might have a minor negative effect (short-term and reversible) on vascular function, while BFR resistance training with narrow-elastic bands may improve vascular function. Both training methods are equally effective in increasing muscle strength.

Blood flow restriction (BFR) resistance training has been proven to be effective in increasing muscle mass and strength. During BFR training, cuffs (similar to blood pressure cuffs) are placed on the proximal ends of the extremities to partially occlude arterial blood flow to the working muscles and fully restrict venous outflow from the working muscle. The metabolites produced by the working muscle during exercise are trapped in the working muscle, which causes metabolic stress to augment muscle adaptation. Typically, two types of cuffs are used in the BFR training: the narrow-elastic bands and wide-rigid nylon cuffs adapted from surgical tourniquets and blood pressure cuffs.

Currently, the effect of BFR training on vascular function remains unclear. When the cuffs are removed after BFR training, there will be a reactive hyperemic blood flow to wash out all the metabolites produced during exercise. This reactive hyperemic blood flow also will impose shear stress on the arterial vessel wall. The shear stress will lead to an increase in vasodilator factors, which lead to an improvement in vascular function. However, other studies have pointed out that BFR training might cause a negative effect on vascular function when the occlusion pressure was too high. The possible mechanisms of the negative effect might be ischemia-reperfusion injury and retrograde shear stress in the artery. The wide-rigid cuffs are easily available but have the potential to inhibit the expansion of muscle upon increased blood flow accompanying exercise and muscle contraction while the narrow-elastic bands do not prevent the expansion. To the investigators' best knowledge, there is no study directly comparing different BFR cuffs on vascular function. Thus, the aim of the present study is to compare the effects of different BFR cuffs on vascular function (evaluated by flow-mediated dilation, a non-invasive measure of endothelial-derived vasodilation).

Inclusion Criteria:

• Apparently healthy, sedentary or recreationally active young adults aged between 18 - 40 years old and signed the informed consent.

Exclusion Criteria:

• A current COVID-19 diagnosis
• morbid obesity
• hypertension
• smoking
• overt cardiovascular disease
• using any medication that might affect the cardiovascular system
• current participation in resistance training.