In diaphragm muscle (DIAm), type I and IIa fibers are recruited to accomplish breathing, while type IIx/IIb fibers are recruited only during expulsive/straining behaviors. Thus, type I and IIa DIAm fibers are much more active (duty cycle of ∼40 %) than type IIx/IIb fibers (duty cycle of <1%), which we hypothesized underlies intrinsic differences in mitochondrial structure and function. MitoTracker Green labeled mitochondria were imaged in 3-D using confocal microscopy. Mitochondrial volume density (MVD, per muscle fiber volume) was higher, and mitochondria were more filamentous in type I and IIa DIAm compared to type IIx/IIb fibers. The maximum velocity of the succinate dehydrogenase reaction (SDH_max), measured using a quantitative histochemical technique was found to be higher in type I and IIa DIAm fibers compared to type IIx/IIb fibers with and without normalizing for MVD. These results are consistent with fiber type differences in the intrinsic structural and functional properties of DIAm fibers and closely match differences in energetic demands.

在膈肌 (DIAm) 中，I 型和 IIa 型纤维被募集以完成呼吸，而 IIx/IIb 型纤维仅在呼气/用力行为期间募集。因此，I 型和 IIa 型 DIAm 纤维比 IIx/IIb 型纤维（占空比 <1%）活跃得多（占空比为 ~40%），我们假设这是线粒体结构和功能的内在差异的基础。MitoTracker Green 标记的线粒体使用共聚焦显微镜进行 3-D 成像。与 IIx/IIb 型纤维相比，线粒体体积密度（MVD，每肌纤维体积）更高，并且线粒体在 I 型和 IIa DIAm 中呈丝状。琥珀酸脱氢酶反应的最大速度（SDH _max), 发现使用定量组织化学技术测量的 I 型和 IIa DIAm 纤维比 IIx/IIb 型纤维更高，有和没有 MVD 标准化。这些结果与 DIAm 纤维固有结构和功能特性的纤维类型差异一致，并且与能量需求的差异密切匹配。