The study aims at investigating if time to respiratory muscle fatigue and metabolism are influenced by the pressure wave form mode applied during resistive breathing.

In healthy subjects fitted with a nasogastric double balloon catheter and breathing at a resistance, the investigators will measure time to failure, Borg ratings, VO2, VCO2, flow, esophageal-, gastric- and airway-pressure. This will be done during breathing at either a square wave or triangle wave pressure waveform, in random order and trials separated by >two days. Further respiratory muscle fatigue will be investigated pre and post intervention by maximal esophageal pressure generation (voluntary and with cervical magnetic stimulation).

Inclusion Criteria:

• Healthy men or women
• Age ≥18 and ≤60 years
• BMI ≥ 20 and ≤30

Exclusion Criteria:

• Drug addiction defined as the use of cannabis, opioids or other drugs
• Previous and present neurologic (e.g. ataxia), musculoskeletal (e.g. muscular dystrophy) or mental illnesses (e.g. schizophrenia)
• History of mechanical ventilation, COVID-19 with respiratory complications, lung cancer
• Part of lung resected
• Presence of dyspepsia/heart-burn/abdominal pain
• Presence of esophageal varices
• Presence of liver disease
• Presence of esophageal hernia
• Pregnancy
• Failure to comply with transcranial magnetic stimulation adult safety screen
• History of epilepsy, metal implants in head or jaw
• Acute or chronic lung diseases, e.g. asthma, COPD, bronchitis etc.
• Lack of ability to cooperate