Table 1.

Age-Related Alterations in Muscle Mass

	6-Mo	9-Mo	18-Mo	26-Mo	30-Mo
Body weight, g	399 ±19*	512 ± 15	577 ± 25	600 ± 47*	566 ± 76
Soleus
Wet weight, mg	150 ± 8*	202 ± 20	188 ± 3	191 ± 18	167 ± 15*
mg/g BW	0.38 ± 0.01	0.394 ± 0.033	0.32 ± 0.015*	0.32 ± 0.01*	0.30 ± 0.013*
Plantaris
Wet weight, mg	392 ± 23*	486 ± 24	490 ± 25	410 ± 24*	352 ± 28*
mg/g BW	1.35 ± 0.078	1.36 ± 0.112	1.14 ± 0.076*	0.93 ± 0.088*	0.76 ± 0.06*
Medial gastrocnemius
Wet weight, mg	888 ± 45*	1110 ± 53	1036 ± 36	896 ± 81*	731 ± 66*
mg/g BW	2.22 ± 0.076	2.17 ± 0.087	1.81 ± 0.14*	1.49 ± 0.12*	1.30 ± 0.10*
Tibialis anterior
Wet weight, mg	734 ± 41*	931 ± 45	903 ± 22	821 ± 68*	669 ± 47*
mg/g BW	1.84 ± 0.054	1.82 ± 0.06	1.52 ± 0.117*	1.37 ± 0.123*	1.21 ± 0.249*
Extensor digitorum longus
Wet weight, mg	173 ± 8*	221 ± 11	215 ± 7	208 ± 19	170 ± 16*
mg/g BW	0.43 ± 0.006	0.43 ± 0.014	0.36 ± 0.023*	0.35 ± 0.013*	0.30 ± 0.042*

Notes: Body weight (g) and muscle weight for male Fisher 344–Brown Norway F1 hybrid rats at various ages (n = 6–8 per age group). Muscle weight is expressed as a wet weight (mg) and normalized to body weight (mg wet weight/g BW). Data are expressed as mean ± standard deviation.

^*A significant difference (p < .001) from the 9-mo age group.