Patients with COPD are less physically active, compared with healthy age-matched individuals. It remains unknown whether indices expressing respiratory, central hemodynamic and peripheral muscle oxygenation capacities are related to the reduced levels of daily physical activity (DPA) and whether improvement in physiological indices after pulmonary rehabilitation is associated with improvement in daily physical activity levels.The purpose of this study was to investigate whether: a) activity monitoring reflects variations in biological variables during walking in COPD, b) the intensity of DPA is associated with limitations in respiratory and cardiovascular function as well as in peripheral muscle oxygenation and c) high-intensity interval exercise training-induced biological improvements are associated with improvement in DPA levels.To accomplish the aims three studies were undertaken: a) 42 patients performed an incremental treadmill protocol to the limit of tolerance, b) 19 patients underwent an indoor treadmill test at a speed corresponding to the individual patient’s mean DPA intensity, captured by a triaxial accelerometer during a preceded 7-day period and c) 50 patients were randomly assigned in 2 groups: intervention (n=30) and control (n=20). The intervention group attended a 3-month pulmonary rehabilitation program consisted with high-intensity interval exercise training. Controls did not participate in any regular exercise training.During a) the incremental treadmill protocol strong correlations were found between treadmill walking intensity and oxygen consumption; minute ventilation; cardiac output and arteriovenous oxygen concentration difference b) the indoor treadmill test, the individual patient mean DPA intensity was significantly correlated with changes from baseline in cardiac output recorded by impedance cardiography, systemic vascular conductance, systemic oxygen delivery, arterio-venous oxygen content difference and quadriceps muscle fractional oxygen saturation assessed by near infrared spectrometry. When chest wall volumes, captured by Optoelectronic Plethysmography, were expressed relative to comparable levels of minute ventilation, active patients differed from the less active ones in terms of the lower increase in end-expiratory chest wall volume, the greater expansion in tidal volume and the larger inspiratory reserve chest wall volume (IRVcw). IRVcw, expiratory flow and Borg dyspnoea score emerged as the best contributors accounting for 71.7% of the explained variance in daily movement intensity and c) the course of pulmonary rehabilitation program, improvements in ventilatory and metabolic variables expressing patients’ exercise capacity were associated (0.34<r<0.64) with improvement in daily physical activity levels.Conclusively, in patients with COPD a) activity monitoring reliably reflects variations in central hemodynamic, respiratory and muscle metabolic variations during walking b) besides ventilatory limitations and peripheral muscle weakness, intensity of DPA is associated with both central hemodynamic and peripheral muscle oxygenation capacities. Patients exhibiting greater ability to expand tidal volume and to maintain adequate inspiratory reserve volume tend to be more physically active and c) improvement in physiological variables following high-intensity interval exercise training is associated with improvement in DPA levels.
High-intensity interval exercise training for public health: a big HIT or shall we HIT it on the head?