Does cardiorespiratory fitness influence muscle oxygenation responses to short-term reduced physical activity?

Approximately 30% of adults worldwide do not meet recommended physical activity (PA) guidelines. This high prevalence is concerning as not meeting recommended PA levels (i.e., physical inactivity) is associated with increased risk of cardiovascular and metabolic disease. Studies show that short-term decreases in daily PA of ~60% reduce insulin sensitivity and cardiorespiratory fitness (CRF) and impair vascular function. Limited data have examined the effect of a more modest (~30%) daily PA reduction on measures of vascular function. 

Healthy adults aged 18-40 years will be recruited from Miami University and the surrounding area. Cardiorespiratory fitness (CRF) will be measured at a screening visit, and participants will be stratified into the following groups based on their CRF: high CRF (VO2max ≥75th percentile), low CRF (VO2max ≤25th percentile). Eligible participants will then complete a 3-week protocol. During the first week (day -7 to day 0), participants will maintain their normal daily physical activity level. In the second week (day 0-7), participants will reduce their physical activity level and be provided an electric scooter to facilitate step reduction. Preliminary data from our lab in 12 healthy adults show that access to an electric scooter for 1 week decreased total daily steps by ~3,500 steps/day (~30%). In the third week (day 7-14), participants will resume their normal physical activity level. Physical activity and interstitial glucose will be continuously recorded throughout each week using physical activity monitors (Garmin smart-watches) and continuous glucose monitors, respectively. Participants will attend a single laboratory visit at the end of each week (Days 0, 7, and 14). During these visits, blood glucose responses will be assessed using an oral glucose tolerance test (OGTT). Additionally, PLM-induced changes in near-infrared spectroscopy (NIRS)-based skeletal muscle oxygenation and femoral artery blood flow will be assessed in the right leg as markers of microvascular and macrovascular function, respectively.