ABSTRACT
The strength of skeletal muscles in situ is generally measured as the maximum force these muscles can develop against an external load when the position of the relevant structures and articulations is optimally adjusted. With the exception of some of the neck accessory muscles, the force developed by the respiratory muscles cannot be directly measured. As an alternative, the strength of the respiratory muscles can be defined as the transmural pressure these muscles can develop across the respiratory wall structures when maximally activated. However, the force developed by the respiratory muscles can be estimated from the transmural pressure measurements based on known geometrical features of the chest wall (Fenn, 1963; Rochester et al., 1981; Kikuchi et al., 1982; Loring and Mead, 1982) (see also Chap. 39).
