Inspiratory muscle training（IMT）was an rehabilitation therapy for stable patients with chronic obstructive pulmonary disease(COPD). However, its therapeutic effect remains undefined due to unclear of diaphragmatic mobilization during IMT. Diaphragmatic mobilization represented by transdiaphragmatic pressure（Pdi）and neural respiratory drive expressed as corrective root-mean-square(RMS) of diaphragmatic electromyogram(EMGdi) provide vital information to select the proper IMT device and loads in COPD, therefore make curative effect of IMT clarity. Pdi and RMS of diaphragmatic electromyogram (RMSdi%) was respectively measured and compared during inspiratory resistive training and threshold load training in stable patients of COPD.

Subjects：The diagnosis and severity of all participants were measured using the pulmonary function test according to Global Initiative for Chronic Obstructive Lung Disease.

Inclusion criteria: (1)Severe and very severe COPD (postbronchodilator FEV1/FVC under 70% and FEV1 under 50% of the predicted value (GOLD C and D group); (2)Inspiratory muscle weakness（Maximal Inspiratory Pressure under 60cmH2O）; (3) Bronchial dilation test (BDT) negative.

Exclusion criteria: (1) acute exacerbation in the previous 4 weeks; (2) using the oral corticosteroids within4 weeks; (3) history of other respiratory, cardiovascular, neuromuscular, musculoskeletal diseases that could interfere the study.

Study design This was a single-centre, cross-sectional study.

Intervention： Inspiratory resistive training All participants conducted inspiratory resistive training using inspiratory resistive trainer (PFLEX, Respironics Inc, USA). Pdi and EMGdi were recorded synchronously.Inspiratory resistive load was change from low intensity into moderate and high intensity randomly（inspiratory hole diameters was set to 5.3mm, 2.4mm and 1.8mm,respectively）

Inspiratory threshold load training Inspiratory threshold load training was conducted by all participants using the inspiratory threshold load trainer (Threshold Inspiration Muscle Trainer, Respironics Inc, USA) .Inspiratory threshold pressure was set to low, medium and high intensity randomly（threshold pressure was 30%,60% and 80% of MIP, respectively).

Measurements ：transdiaphragmatic pressure and neural respiratory drive

Inclusion Criteria:

1. Severe and very severe COPD (postbronchodilator FEV1/FVC under 70% and FEV1 under 50% of the predicted value (GOLD C and D group);
2. Inspiratory muscle weakness（Maximal Inspiratory Pressure under 60cmH2O）;
3. Bronchial dilation test (BDT) negative

Exclusion Criteria:

1. acute exacerbation in the previous 4 weeks;
2. using the oral corticosteroids within 4 weeks;
3. history of other respiratory, cardiovascular, neuromuscular, musculoskeletal diseases that could interfere the study.