DECREASE IN WORK RATE DURING EXERCISE AT A FIXED HEART RATE: NEW SYSTEMIC BIOMARKER OF EXERCISE (IN)TOLERANCE IN PHYSIOLOGICAL AND PATHOLOGICAL CONDITIONS

Oxidative metabolism constitutes the main determinant of exercise tolerance for everyday life; a functional evaluation of oxidative metabolism is therefore of great importance for health status assessment as well as for the identification of possible preventive and/or therapeutic interventions. The first study presented in this thesis is mainly focused on the identification of “systemic” signs of functional impairment of oxidative metabolism during exercise following 10 days of bed rest (BR). In the present study we proposed a new simple approach to evaluate exercise (in)tolerance to subjects exposed to microgravity, namely the quantification of the work rate (WR) decrease necessary to keep HR constant (at a value slightly higher than corresponding to GET). Previous observations by our group suggested that the phenomenon represents a biomarker of exercise tolerance; moreover, it is a well-accepted concept, that a decreased HR for the same WR is a sign of improved exercise tolerance, thus, a lower WR for the same HR can be considered a sign of impaired exercise tolerance as well. Therefore, we hypothesized a significant more pronounced WR decrease in order to keep HR constant following a 10-day BR. Results of Study 1 confirmed this hypothesis. The decrease in WR necessary to keep HR constant at a value corresponding to GET+20% was significantly aggravated after (~40%) vs. before (~30%) BR, resulting in a shift from the heavy- (>GET) to the moderate-intensity (