ABSTRACT Objective The prevalence of asthma is increasing gradually worldwide. The pathophysiological process of asthma causes some alterations in the respiratory system and decreases oxygen-carbon dioxide exchange and respiration volume. These alterations may affect maximal exercise capacity, peripheral muscle strength, sleep quality, and disease-specific quality of life but have yet to be comprehensively investigated. To compare maximal exercise capacity, pulmonary function, peripheral muscle strength, dyspnea, sleep quality, and quality of life in adult patients with asthma, healthy controls were aimed. Methods Forty-one adult stable asthmatic patients (GINA I-III) and 41 healthy subjects were compared. Exercise capacity (cardiopulmonary exercise test [CPET]), pulmonary function (spirometry), peripheral muscle strength (dynamometer), dyspnea (modified Medical Research Council [mMRC] dyspnea scale), quality of life (Asthma Quality of Life Questionnaire [AQLQ]) and sleep quality (Pittsburgh Sleep Quality Index [PSQI]) were evaluated. Results Peak VO2, VO2kg, MET, VE, HR, %VE, %HR, VCO2 parameters of CPET, FVC, FEV1, FEF25-75%, and FEV1/FVC and quadriceps femoris, shoulder abductors, and hand grip muscles strength were significantly decreased in patients with asthma (p < 0.05). MMRC dyspnea scale score was increased, and AQLQ and PSQI scores decreased in asthma patients (p < 0.05). Conclusions Cardiac and pulmonary system responses to peak exercise worsened, and maximal exercise capacity and peripheral muscle strength decreased in adult patients with stable asthma. In addition, dyspnea during daily activities increases, and quality of life and sleep quality are impaired. A variety of exercise training that would benefit asthmatic patients' outcomes should be investigated.