Introduction
Chronic obstructive pulmonary disease (COPD) is a
debilitating and progressive disease that primarily affects
the respiratory system. In many patients, it also has
detrimental extra-pulmonary effects, such as weight loss
and skeletal muscle dysfunction/wasting [1]. The pulmonary
and skeletal muscle abnormalities limit the pulmonary
ventilation and enhance the ventilatory requirements
during exercise resulting in exercise-associated symptoms
such as dyspnea and fatigue. These symptoms make
exercise an unpleasant experience, which many patients
try to avoid, and along with a depressive mood status (in
up to 30% of patients), further accelerates the process,
leading to an inactive life-style. Muscle deconditioning,
associated with reduced physical activity, contributes to
further inactivity and as a result patients get trapped in
a vicious cycle of declining physical activity levels and
increasing symptoms with exercise (Figure 1) [1-3].