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. Author manuscript; available in PMC: 2016 Jun 15.
Published in final edited form as: Respir Physiol Neurobiol. 2015 Oct 20;226:137–146. doi: 10.1016/j.resp.2015.10.001

Fig. 4.

Fig. 4

Schematic illustrating the aging-related functional consequences of diaphragm muscle (DIAm) fiber type specific sarcopenia (atrophy and weakness). In this model, DIAm sarcopenia is predominantly present in the fast-twitch fatigable (type FF) and fast-twitch fatigue intermediate (type FInt) motor units, which in turn are associated with type IIb and IIx DIAm fibers that express the MyHC2B and MyHC2X isoforms, respectively. In contrast, DIAm sarcopenia is less evident in the fast-twitch fatigue resistant (type FR) and slow (type S) motor units, which in turn are associated with type IIa and I DIAm fibers that express the MyHC2A and MyHCSlow isoforms, respectively. The functional consequences of this fiber type specific effect of DIAm sarcopenia is a decrease in the maximum transdiaphragmatic pressure (Pdimax ) the DIAm is capable of generating, and therefore an impaired ability to perform expulsive, high force non-ventilatory behaviors (i.e., coughing and sneezing). However, the Pdi required to perform ventilatory behaviors remains preserved.