**5. Physical activity in COPD**

Using indirect calorimetry techniques like doubly labeled water or metabolic carts, daily physical activity can be reported as an overall metric of active energy expenditure. The duration, frequency, and intensity of physical activity are not quantified by the doubly labeled water approach, despite the fact that it is considered a criteria method [6, 17]. Metabolic cart systems that measure expired O2 and CO2 are, however, not suitable for long-term usage. Physical activity monitors can also be used to directly track physical activity [2].

In general, pedometers, accelerometers, and integrated multi-sensor systems are the three classes of activity monitors that are being utilized more frequently in

#### *Current and Contemporary Developments in Pulmonary Rehabilitation DOI: http://dx.doi.org/10.5772/intechopen.107050*

populations with chronic diseases (like COPD). Pedometers are gadgets that solely measure in the vertical plane mechanically or digitally to quantify the number of steps taken [5]. This is only a small amount of exercise. One, two, or three directions of acceleration can be detected using accelerometers (uni-, bi-, or triaxial accelerometers). These tools enable measurement of movement quality, amount, and intensity [5, 15]. In an effort to improve physical activity assessments, integrated multisensory systems combine accelerometry with various sensors that record physiological reactions to exercise (such as heart rate or skin temperature). Technology has advanced to the point that a variety of activity monitors are now readily available to measure physical activity [18].

Physical activity in patients with COPD is dependent on many factors, including physiological, behavioral, social, environmental, and cultural factors. Only a weak association exists between daily physical activity and post-bronchodilator FEV1. Dynamic hyperinflation, which highly correlates with exertional dyspnea in COPD, and daily physical activity, however, have a strong inverse relationship [19]. Performance on lower-limb muscle function tests and field exercise tests correlates better with physical activity in COPD than resting lung function testing does. Lower levels of physical activity are related to daily COPD symptoms (such as dyspnea and fatigue). In patients with COPD, the relationship between impaired health status and physical activity is minimal to moderate. Interestingly, this link between a drop in physical activity and a decline in health status in COPD patients was validated in a 5-year longitudinal observational study [3, 5, 13].

Levels of physical exercise influence critical outcomes in COPD. Hospitalization due to an exacerbation is connected with lower levels of physical activity. 59 After adjusting for age, FEV1, and prior hospitalizations, a drop in physical activity over time also predicts COPD-related hospitalization in addition to baseline levels of physical activity [20]. Even after accounting for or taking into consideration pertinent confounding factors, people with COPD who engage in less physical activity have a higher chance of dying from any cause. Mortality is also predicted by a decline in physical activity over time. Physical activity has been incorporated as a factor in multidimensional predictive scores for all-cause and respiratory mortality, exacerbations, and COPD-related hospitalization in stable COPD patients, reflecting these substantial relationships [18, 21]. The importance of encouraging physical activity in the early stages of COPD, with a target of more than 2 hours per week, is highlighted by these outcome studies [5, 18].
