A) Heart/tibial length (mg/mm) [adult WT, KO, senescent WT, KO; n=9,10,7,4] B) quadriceps mass/tibial length (g/mm) [adult WT, KO, senescent WT, KO; n=5,7,7,4], and C) total body (g) [adult WT, KO, senescent WT, KO; n=9,10,8,4] are shown for male adult and senescent WT and KO mice. Age range: Adult: aged 15-20 weeks; Senescent: aged 27-30 months. Data are presented as mean±SEM. #p<0.01, *p<0.001.