Comparison of physiological responses after incremental shuttle walking test and 6-minute walk test in patients with systemic sclerosis

Background The 6-minute walk test (6MWT) is a commonly used to evaluate exercise capacity in patients with systemic sclerosis (SSc), but there was no study using the incremental shuttle walking test (ISWT) for assessing exercise capacity and comparing the patient's cardiorespiratory responses to these tests. The aim was to investigate the usability and determinants of the ISWT in patients with SSc and compare the physiological responses after the ISWT and 6MWT. Methods A total of thirty four female patients with SSc were included. Dyspnea during daily activities and knee extensor muscle strength was assessed, skin fibrosis and disease severity were recorded, and 6MWT and ISWT were carried out for the exercise capacity measurement. Pulmonary function test results were recorded from the individuals' medical records for SSc with interstitial lung disease (SSc-ILD) patients. Results The ISWT distance was significantly correlated with the 6MWT distance (p < 0.001). The 6MWT was correlated with age, modified Rodnan skin score, Medsger severity score, modified British Medical Research Council Questionnaire (mMRC) score, and knee extensor muscle strength (p < 0.05). The 6MWT was correlated with the forced expiratory volume in the first second (FEV1) (lt) and forced vital capacity (FVC) (lt) in patients with SSc-ILD (p < 0.05). The ISWT distance was correlated with age, modified Rodnan skin score, mMRC score, and knee extensor muscle strength (p < 0.05). Age, mMRC, and knee extensor muscle strength explained 33.8% of the variance in 6MWT distance, while age, mMRC, and knee extensor muscle strength explained 51.7% of the variance in the ISWT distance. Conclusion Because of the higher cardiopulmonary responses, and having a more standardized procedure, the ISWT may be preferable for investigating symptom-limited exercise capacity in patients with SSc. Age, dyspnea, and knee extensor muscle strength were the determinants of exercise capacity in patients with SSc.