Fig. 3. (A) Strain and (B) electromyogram (EMG) signals recorded from the dl₁ muscle during tethered flight. In the sequence shown, the rest length in the quiescent moth (L_r; upper broken line) is 4% longer than the operational length (L_op; lower broken line). The dl₁ muscles fired a single spike near the onset of muscle shortening in each wing-stroke. The time scale (ordinate) is the same for both traces. The wing-stroke frequency in this sequence was 23 Hz (Table 1, moth 4).