Effect of adult deletion of both Mitofusin (Mfn)1 and Mfn2 on exercise performance: Mfn1 and Mfn2 mRNA expression in various skeletal muscle beds: soleus (SOL), extensor digitorum longus (EDL), tibialis anterior (TA), triceps (TRI), quadriceps (QUAD), gastrocnemius (GAS), and diaphragm (DIA) (A); Mfn1 and Mfn2 protein expression (B); densitometry quantification of Mfn1 and Mfn2 protein expression normalized to tubulin and relative to control in GAS muscle (C; n = 3 per group); longitudinal exercise stress test (D); time to exhaustion (E); total distance run (F); and calculated total work in adult-inducible skeletal muscle-specific Mfn1 and Mfn2 double knockout mice (iMS-MfnDKO) and control littermates (G; n = 7 per group) before deletion and 8 wk after deletion. Data are means ± SE. *P < 0.05; **P < 0.01 compared with control as determined by unpaired t-test.