Fig. 8. Contraction properties of longitudinal muscle 214 measured in males less than 5 days old and males more than 18 days old. (A) The length/twitch tension curves of the two groups were comparable. Muscle fibres were not able to tolerate extensions of more than 4 mm (arrows). f_l/f_max, muscle tension at a particular length normalized to maximum tension. (B) Passive tension increased steeply in both groups, starting at 1 mm length, but was consistently higher in mature males (>18 days old), although the difference was not significant (P>0.05; Mann–Whitney rank sum test). (C) The maximum tension generated by muscles from males more than 18 days old exceeded that of muscles of males less than 5 days old. However, the means were not statistically different (P>0.05; Mann–Whitney rank sum test). Values are means ± S.E.M. TW, twitch. (D) No differences were evident with regard to the speed of contraction (see also Table 1) or tetanus fusion frequency.