Maximal inspiratory pressure and exercise-induced inspiratory muscle fatigue in chronic nonspecific low back pain

BACKGROUND: Patients with chronic nonspecific low back pain (CNSLBP) show reduced inspiratory muscle function. However, studies comparing maximal inspiratory pressure (MIP) and exercise-induced inspiratory muscle fatigue (IMF) between CNSLBP and healthy controls (HC) are lacking. OBJECTIVE: To compare MIP and exercise-induced IMF between CNSLBP and HC. DESIGN: Cross-sectional study. METHODS: MIP was recorded in 25 persons with CNSLBP and 15 HC before and immediately, 15 and 30 minutes after a maximal cardiopulmonary exercise test. Inspiratory muscle weakness was defined as a predicted MIP value lower than 80%, and exercise-induced IMF as a =10% reduction in MIP following the exercise test. RESULTS: Baseline MIP was similar between CNSLBP (109±32 cmH2O) and HC (116±32 cmH2O) (p= 0.525). Inspiratory muscle weakness was present in 36% of the CNSLBP group and in 20% of the HC group, with no significant difference between groups (p= 0.777). None of the groups showed significant exercise-induced IMF immediately (CNSLBP: -2.1%, HC: 3.7%), 15 minutes (CNSLBP: -5.4%, HC: -5.2%), and 30 minutes (CNSLBP: -4.7%, HC: -6.6%) after the maximal exercise test (p> 0.05), with no between group differences with regard to magnitude and proportion (CNSLBP: 24%, HC: 33%) (p> 0.05). CONCLUSIONS: This study shows that there is no difference in MIP and the proportion of inspiratory muscle weakness between persons with CNSLBP and HC. Additionally, within both groups, there was no exercise-induced IMF immediately, 15 and 30 minutes after a maximal exercise test. Furthermore, there was no difference in the magnitude and proportion of exercise-induced IMF between both groups.