Sex differences in skeletal muscle microvascular blood flow in healthy young adults.

This is a cross-sectional study exploring potential sex differences in cardiovascular responses to a single bout of acute maximal exercise. Intervention: single graded exercise test on a treadmill (modified Bruce protocol), to assess cardiorespiratory fitness (VO2peak), skeletal muscle microvascular blood flow, femoral artery blood flow, and cardiac responses to acute maximal exercise. Participants will begin walking at 2.7km/h with increasing speed and/or incline every three minutes until exhaustion (see below). VO2peak is calculated from the highest 10-second rolling average of breath-by-breath respiratory gas analysis (Quark RMR Gas Analyzer, Cosmed, Italy). Maximal effort (i.e., adherence to the intervention) will be determined by one or more of the following criteria: a plateau in VO2, heart rate 90% of age-predicted maximum, rating of perceived exertion (RPE) =17, and/or respiratory exchange ratio =1.1.. Electrocardiography will be recorded throughout, with heart rate, blood pressure, and RPE recorded at the end of each 3-minute stage. The testing session will be supervised by a minimum of two first aid trained research staff at Deakin University, Burwood Campus. Modified Bruce Protocol Stages (3mins each) Stage 1: 2.7km/h; 0% incline Stage 2: 2.7km/h; 5% incline Stage 3: 2.7km/h; 10% incline Stage 4: 4km/h; 12% incline Stage 5: 5.5km/h; 14% incline Stage 6: 6.8km/h; 16% incline Stage 7: 8km/h; 18% incline Stage 8: 8.9km/h; 20% incline Stage 9: 9.7km/h; 22% incline Pre-intervention testing: - Questionnaires to collect general health and medical information, menstrual cycle/oral contraceptive use, dietary habits (24 hour diet recall), and physical activity levels (questionnaire and accelerometer worn for 7 days). Participants will be required to wear the accelerometer for all waking hours, except during water-based activities (swimming/bathing). The questionnaires are one-time assessments, each requiring less than 10 minutes to complete. . - Fasting clinical chemistries (glucose, insulin, total cholesterol, low density lipoprotein, high density lipoprotein, triglycerides, HbA1c, and female sex hormone concentrations). - Body composition (height, weight, and lean/fat mass by DEXA). - Central haemodynamics (systolic and diastolic pressure, pulse pressure, augmentation index, augmentation index at 75bpm, mean arterial pressure) and arterial stiffness assessed via pulse wave analysis and pulse wave velocity.