Fig. 4.

Fiber type specific microarray analysis revealed fast-twitch MHC IIa muscle fibers of young women are responsive to acute RE in the untrained state with 463 genes altering expression, whereas only 63 genes responded among the MHC IIa muscle fibers of the old women (top). When the fiber type specific gene response of the young and old women is coupled with the muscle fiber CSA adaptations after PRT (bottom) in those women (38), the data support that a substantial gene response after RE is needed to acquire greater physiological adaptations over time. *P < 0.05 from pre- to posttraining.