The value of extra-diaphragmatic inspiratory muscle surface electromyography during postural control tasks in...

Concurrent dysfunctions in postural control and diaphragm are observed in patients with chronic obstructive pulmonary disease (COPD). Measuring diaphragm activation traditionally involves transesophageal diaphragm electromyography (EMG_di), which is costly and relatively invasive. Extra-diaphragmatic inspiratory muscle surface electromyography may serve as a useful physiological marker for EMG_di. This study compared EMG_di amplitude with surface EMG amplitude of other inspiratory muscles, including sternocleidomastoid (sEMG_scm), scalene (sEMG_scal), and parasternal intercostal muscles (sEMG_ic) during postural control tasks in nine patients with COPD (5 males; age: 65 ± 6 years; forced expiratory volume in the first second: 60 ± 27 % predicted). Simultaneous recordings of EMG_di, sEMG_scm, sEMG_scal, and sEMG_ic amplitudes were obtained during six postural control tasks involving upright standing with ballistic arm movements under different conditions of support surface (stable/foam), arm movement frequency (single/repetitive), and breathing modes (normal/breath-hold at end-expiration). EMG amplitudes were normalized to each muscle's maximum voluntary contraction. A linear mixed model with Bonferroni-Holm post-hoc tests and Bland-Altman analyses were performed. There was a significant EMG-by-task interaction (p = 0.0223). The amplitude of EMG_di was significantly lower than sEMG_ic across all tasks (p < 0.0001 to 0.0007), while no significant differences were observed between EMG_di and sEMG_scm or EMG_di and sEMG_scal after Bonferroni-Holm correction (p = 0.019-0.858). Bland-Altman analyses indicated reasonable agreement between EMG_di and both sEMG_scm and sEMG_scal (mean biases: 1.8 % and -3.7 %), while sEMG_ic had a significantly higher overall bias of -20.7 %. These findings suggest that both sEMG_scal and sEMG_scm can serve as useful physiological markers for EMG_di in postural control assessments in patients with COPD. NEW & NOTEWORTHY. This study highlights the potential of extra-diaphragmatic inspiratory muscle surface electromyography as a physiological marker for transesophageal diaphragm electromyography during postural control tasks in patients with COPD, thereby reducing the need for costly and invasive measurements.