Table 1.

Fiber-type composition of gluteus medius and triceps brachii from young and aged American Quarter Horses

	Gluteus Medius		Triceps Brachii
MHC Isoforms	Young	Aged	Young	Aged	Main Effect of Muscle Type, P Value
n	24	9	11	9
MHC-I	3.39 ± 0.35	6.68 ± 0.87‡	10.57 ± 0.99	11.85 ± 0.71	<0.001
MHC-IIA	21.35 ± 0.85	23.18 ± 2.65	33.79 ± 1.22	41.42 ± 4.53*	<0.001
MHC-IIX	75.26 ± 0.92	70.14 ± 2.82†	55.64 ± 1.59	46.73 ± 4.92*	<0.001

Values are means ± SE in %. †P < 0.1, ‡P < 0.001 (young vs. aged within gluteus),

^*P < 0.05 (young vs. aged within triceps).