Rk. Josephson et Cp. Ellington, POWER OUTPUT FROM A FLIGHT-MUSCLE OF THE BUMBLEBEE BOMBUS-TERRESTRIS .1. SOME FEATURES OF THE DORSOVENTRAL FLIGHT-MUSCLE, Journal of Experimental Biology, 200(8), 1997, pp. 1215-1226
1. Isometric contractions from the asynchronous dorso-ventral flight m
uscle of the bumblebee Bombus terrestris were slow and rather weak. Th
e twitch duration (onset to 50% relaxation) was approximately 300 ms a
t 30 degrees C and 170 ms at 40 degrees C. The maximum tetanic tension
was approximately 40 kN m(-2); the ratio of twitch force to tetanic f
orce was approximately 0.2. 2. The unstimulated muscle was quite resis
tant to stretch, with a low-frequency stiffness of 730 kN m(-2) at mus
cle lengths close to that of the muscle in vivo. The length-tension cu
rve for active tetanic tension (that is the increase in tension above
the passive level during stimulation) was very narrow, with a half-wid
th equal to only 17% of the optimal length. 3. The muscle strain durin
g tethered flight was approximately 2% peak-to-peak, occasionally reac
hing 3%. Strain amplitude increased with wing stroke frequency. The th
oracic vibration frequency of escape buzzing, during which the wings a
re not extended but are folded over the abdomen, was approximately twi
ce that of tethered flight but the muscle strain was similar to that o
f flight.