Table I.

Fiber Type Composition of Muscles from Wild-Type (w.t.) and MyHC-IId Null Mice

(a) Overall Fiber Type Composition
		Tibialis anterior				Diaphragm				Psoas				Masseter
MyHC		w.t.		IId−/−		w.t.		IId−/−		w.t.		IId−/−		w.t.		IId−/−
		%				%				%				%
IIA		9		30		45		82		15		21		<1		100
IIB		73		70		0		0		68		79		43		0
IID		18		0		40		0		17		0		56		0
I		0		0		15		18		0		0		0		0
(b) Fiber Type Composition of Red and White Portions of TA and Psoas Muscles
MyHC		Tibialis anterior								Psoas
		w.t.				IId−/−				w.t.				IId−/−
		red		white		red		white		red		white		red		white
IIA		18		0		63		0		31		0		69		0
IIB		46		100		37		10		34		100		31		100
IID		36		0		0		0		35		0		0		0
I		0		0		0		0		0		0		0		0

Fiber types were determined by counting each type in serial cross sections of muscles stained with antimyosin antibodies as described. Two areas per section of diaphragm and masseter were counted; two areas of each region in TA and psoas muscle were counted. Measurements in TA and psoas were weighted according to the percent of total area of each region (red and white). Numbers reflect averages of three wild-type and three MyHC-IId null mice. Standard deviations from the mean were 4% for all samples.