Muscle strength, symptom intensity, and exercise capacity in patients with cardiorespiratory disorders.

TLDR

The study examined how muscle strength influences symptom intensity and exercise capacity in healthy individuals and those with cardiorespiratory disorders. The authors measured inspiratory/expiratory and leg muscle strengths in 4,617 subjects, had them rate leg effort, dyspnea, and chest pain during graded cycling to capacity, and grouped participants by pulmonary function, cardiac medication, and ischemic chest pain. Patients with cardiorespiratory disorders had markedly lower respiratory and peripheral muscle strengths, and greater muscle strength was linked to lower symptom intensity and higher work capacity, with a two‑fold increase in strength reducing leg effort and dyspnea by 25–30% and boosting capacity 1.4–1.6 times; these results highlight the importance of addressing muscle weakness in managing exercise intolerance.

Abstract

The contribution of muscle strength to symptom intensity and work capacity was examined in normal individuals and patients with cardiorespiratory disorders. Respiratory muscle strengths (maximal inspiratory and expiratory pressures) and peripheral muscle strengths (leg extension, leg flexion, seated bench press, and seated row) were measured in 4,617 subjects referred for clinical exercise testing. Subjects then rated the intensity of leg effort, discomfort with breathing (dyspnea), and chest pain (Borg scale) during an incremental exercise task (100 kpm/min each minute) to capacity on a cycle ergometer. Subjects were classified into groups on the basis of pulmonary function, drug therapy for cardiac disorders, and the presence of chest pain during exercise with electrocardiographic changes indicative of myocardial ischemia. Respiratory and peripheral muscle strengths, normalized for differences in age, sex, and height, were significantly reduced in patients with cardiorespiratory disorders compared with normal individuals. Muscle strength was a significant contributor to symptom intensity and work capacity in both health and disease; a two-fold increase in muscle strength was associated with a 25 to 30% decrease in the intensity of both leg effort and dyspnea and a 1.4- to 1.6-fold increase in work capacity. These results emphasize the need for an integrative approach in the assessment and therapeutic management of exercise intolerance, which considers the contribution of muscle weakness to excessive symptoms and reduced work capacity, in addition to the contribution of ventilatory, gas exchange, and circulatory impairments.