Ventilator-induced diaphragmatic dysfunction appears to contribute to slow weaning from mechanical ventilation. Several trials of inspiratory muscle training to facilitate weaning in intensive care have been performed, with inconsistent results, utilizing different methods of IMT in different populations.

In this study, the investigators want to compare the incidence of 3 inspiratory muscle training programs on inspiratory strength, on difficult to wean patients in intensive care unit.

This is a multi-center randomized trial not blinded with 3 parallels groups:

• Martin's group: a threshold-based IMT is performed like used by Martin in a randomized trial in 2011, in a view of inspiratory strength increase.
• Cader's group: a threshold-based IMT is performed like used by Cader in a randomized trial in 2010 , in a view of inspiratory endurance increase.
• EDRIC's group: a new treshold-based IMT is performed, in a view of both inspiratory strength and endurance increase.

The investigators think that a new threshold-based IMT performed in a view of both inspiratory strength and endurance increase, is more effective and well tolerated than the 2 others protocols.

The main objective of this study is to determinate which IMT program is the most effective on the inspiratory muscle strength and endurance increase. The investigators will be able to study the impact on the weaning time of IMT performed with the best protocol.

The investigators are going to conduct a randomized trial with intention-to-treat analysis. Following 18h of invasive mechanical ventilation in a controlled mode, the failure of the first single breathe trial of 2 hours and the presence of sevrability criterias defined by the European consensus conference in 2007, 88 participants will be included. Participants will be randomizesd to receive one of the 3 protocols of IMT, 2 times per day, 7 days per week, from the inclusion to the extubation.

The ratio of randomization will be 1:1:2 for a better evaluation of EDRIC's group wich propose a new IMT protocol.

Inclusion Criteria:

• Patient ventilated more than 18h in a controlled mode;

• First single breathe trial of 2 hours failure;

• Presence of sevrability criterias definied by the European consensus conference in 2007 an usually used:

  • diminution of the sedfative agents,
  • Patients with spontaneous beath in VAC mode or patient ventilated in a VSAI-PEP mode,
  • PaO2/FiO2 ≥150,
  • Absence d'inotropes ou de vasopresseurs à forte dose ou dose croissante (<1mg/h),
  • SaO2 > 90% with FiO2 ≤ 50%,
  • PEP ≤ 8cmH2O,
  • Corporal température between 36°C and 39°C,
  • Glasgow Score ≥ 8.

Exclusion Criteria:

• Age < 18 years ;
• medically unstable;
• Poor vital pronostic at very short term;
• Cardiac arrest with a poor neurological prognostic;
• Neuromuscular disease ;
• Pneumothorax non drained ;
• Tracheostomy ;
• Current pregnancy ;
• Patients with guardianship or trusteeship.