Fig. 2. Contraction properties of longitudinal muscle M214 measured in females less than 5 days old and females more than 18 days old. (A) The length/twitch tension relationship revealed that only muscles from mature females (>18 days old) were able to tolerate extensive lengthening without breakage of fibres. At 8 mm muscle length, the fibres still generated approximately 30 % of maximum tension. The tension generation of muscle fibres from females less than 5 days old declined rapidly after reaching a maximum, and the fibres broke at 4 mm (indicated by an arrow). f_l/f_max, muscle tension at a particular length normalized to maximum tension. (B) Passive tension rose more steeply in muscles from females less than 5 days old than in females more than 18 days old. Above 4.5 mm, passive tension reached a plateau in muscles of females more than 18 days old. (C) A comparison of maximum forces generated by different stimulation frequencies revealed significantly higher tension in muscles from females more than 18 days old compared with muscles from females less than 5 days old (P<0.05). TW, twitch. An asterisk indicates statistical significance (Mann–Whitney rank sum test, P<0.05). Values are means ± S.E.M. (D) Examples of twitch and 5 Hz contractions. Muscles from females less than 5 days old had shorter twitch durations (see also Table 1) and higher tetanus fusion frequencies than muscles from females more than 18 days old.