To analyze changes on respiratory muscle strength, peripheral and functional capacity of critically ill patients with clinical and surgical etiology, breathing spontaneously and bedridden, within 48 hours of admission to the intensive care unit (ICU) and if there are correlations among these variables. This is an observational study. Respiratory muscle strength will be assessed through the maximum inspiratory pressure (MIP) and maximal expiratory pressure (MEP) and peripheral muscle strength, by the Medical Research Council score (MRC) and hand grip test and functional capacity through the Functional Independence Measure (FIM) and Physical Function ICU Test Score (PFIT-s) in the period between 24h and 48h of hospitalization in the adult ICU. For descriptive purposes, the sample will be stratified according to clinical and surgical characteristics. Correlations will be determined using the Pearson test, with significance level of p <0.05.

Inclusion Criteria:

• Breathing spontaneously
• Length of stay in ICU greater than 24 hours
• Adherence to study

Exclusion Criteria:

• Patients with poor prognosis or palliation;
• Preexisting neuromuscular diseases;
• Immobility or restriction to bed prior to admission;
• Nonunions and amputations;
• Osteomioarticular, cognitive or neurological impairment;
• Non-cooperation;
• Specific contraindications to the application of evaluation methods;
• Hemodynamic or respiratory instability within 48 hours of ICU admission preventing evaluation muscle strength and functional capacity.