Table 2.

Variation in slack lengths and pennations of muscle fascicles from the medial and lateral gastrocnemius muscles

	Within-muscle variance			P
	Medial gastrocnemius	Lateral gastrocnemius	Error variancea	Subject	Muscle	Site
lgs (%)b	42 (31–52)	38 (22–55)	29 (13–44)	<0.001	0.85	0.58
lfs (mm2)c	44 (28–60)	49 (33–65)	34 (7–61)	<0.001	0.26	0.61
2-D pennation (deg)d	24 (17–30)	10 (7–14)	8 (4–12)	<0.001	<0.001	<0.001

Data are variances and P values obtained from data from 10 subjects.

^aCalculated using eqn in the Appendix, assuming that the errors on repeated scans are independent (i.e. assuming ).

^bMuscle–tendon length at which fascicles fall slack, expressed as a percentage of the in vivo range of lengths.

^cFascicle slack length, in mm.

^dTwo-dimensional pennation. Values in parentheses are 95% confidence limits. P values are from a three-way ANOVA (10 subjects × 2 muscles (medial or lateral gastrocnemius) × 14 sites) with repeated measures on the muscle and site factors.