Magnetic twitch assessment of diaphragm and quadriceps weakness in critically ill mechanically ventilated patients

•This study employed magnetic stimulation techniques to assess limb and diaphragm strength in critically ill mechanically ventilated patients.•Leg muscle weakness in acutely ill patients is more severe and pervasive than recognized in previous studies using MRC scoring.•Limb muscle weakness correlates with duration of mechanical ventilation while diaphragm weakness correlates with age and infection.•There is a poor correlation between muscle size and strength and, in particular, muscle size underestimates weakness.•Future trials of anabolic agents in ICU patients should utilize techniques that assess responses by directly measuring muscle function.