Figure 7. Relationship between the inspiratory firing of the parasternal intercostal muscles and their mechanical advantage.

Data for mechanical advantage is derived from De Troyer et al. (1998). Open circles show data for the external intercostals (from De Troyer et al. 2003). Data for the parasternal intercostals are shown as filled circles (current study). The y-axis shows the number of motor unit spikes during inspiration, calculated from the mean group data for each intercostal muscle (see text). The cross shows data for the third parasternal intercostal from the study of De Troyer et al. (2003). Simple linear regressions are shown. There is an increase in inspiratory neural drive to the regions of the intercostal muscles with the higher mechanical advantage.