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

Abstract

Background and aims: To compare maximal inspiratory pressure (MIP) and exercise-induced inspiratory muscle fatigue (IMF) between persons with chronic nonspecific low back pain (CNSLBP) and healthy controls (HC). Methods: MIP was measured pre and 0, 15 and 30min post a maximal cardiopulmonary exercise test (CPET) in 25 persons with CNSLBP and 15 HC. Absolute MIP values were converted to predicted MIP (MIP p red) values using age-, sex-, and BMI­ specific reference equations. Inspiratory muscle weakness was defined as a MIP p red below 80% and IMF as a 2': 10% reduction in MIP p red post-compared to pre-CPET. Correlations between MIP p red and IMF with disability, pain intensity, exercise capac­ity, anxiety, and depression were calculated. Results: There was no difference in age, gender, and BMI be­ tween both groups (p > 0.05). Pre-CPET MIP p red values were similar between persons with CNSLBP (87%±22%) and HC (94%±21%) (p=0.362), and revealed inspiratory muscle weak­ness in 36% of CNSLBP and 20% of HC participants (p = 0. 777). No exercise-induced IMF was observed 0min (CNSLBP:-2%, HC:-4%), 15 min (CNSLBP:-5%, HC:-5%), or 30min (CNSLBP:-5%, HC:-7%) post-CPET (p > 0.05). Higher MIP p red values correlated with better exercise capacity in both groups (CNSLBP: r=0.54, HC: r= 0.55, p < 0.05). In the CNSLBP group, lower MIP p rect cor­ related with higher anxiety (r=-0.49, p = 0.012), and higher IMF correlated with better exercise capacity (r= 0.56, p < 0.05). Conclusions: No significant differences in MIP p red and in­ spiratory muscle weakness were found between persons with CNSBLP and HC. Additionally, no exercise-induced IMF was observed in either group, indicating similar inspiratory muscle fatiguability regardless of CNSLBP status.