S114 Abstracts / Comparative Biochemistry and Physiology, Part A 146 (2007) S107–S127

A6.22Modulation of in vivo muscle power output during

swimming in the African clawed frog (Xenopus laevis)

C. Richards, A. Biewener, (Harvard University, United States)

The goal of this study is to explore how swimming animalsproduce the wide range of performance seen across their naturalbehavior. In vivo recordings of plantaris longus muscle lengthchange were obtained by sonomicrometry. Simultaneous withmuscle length data, force measurements were obtained using anovel tendon buckle force transducer placed on the Achillestendon of Xenopus laevis frogs during brief bursts of swimming.Both within and among individual frogs, the plantaris developedstresses ranging from 33.0 to 189.9 kPa while shortening tostrains ranging from 9.09% to 19.44%. In vivo work loopsrevealed that the plantaris generates a variable amount ofpositive muscle work over a range of swimming cycle durations(from 0.23 to 0.76 s), resulting in a large range of cycle poweroutput (from 2.32 to 74.17 W/kgmuscle), averaged over six frogs.Variation in cycle work (varying mainly as a function of peakcycle stress and, to a lesser extent, strain amplitude) accounts for88% of the variation in cycle power. The remaining 12% ofvariation in cycle power is explained by cycle duration.Additionally, EMG intensity correlated positively with peakmuscle stress (r2 =0.53). These results suggest that relativelyfew parameters (cycle duration, peak cycle stress and strainamplitude) vary to permit a broad range of muscle power outputallowing anurans to swim over a wide range of naturalperformance.

doi:10.1016/j.cbpa.2007.01.196

A6.23Prolonged aestivation causes little change in skeletal musclemorphology or contractile performance in the anuranCyclorana aloboguttata

B. Symonds, C. Franklin, (University of Queensland, Aus-tralia); R. James, (Coventry University, United Kingdom)

Prolonged immobilisation or unloading of skeletal muscle causesmuscle disuse atrophy that is characterised by a reduction inmuscle cross-sectional area and compromised locomotoryfunction. Animals that enter seasonal dormancy, such ashibernators and aestivators, exhibit a decline in metabolic andlocomotor activity that is correlated with seasonal fluctuations intemperature and resource availability. As such, hibernators andaestivators provide a fascinating natural model for investigatingmuscle atrophy associated with disuse (see review byHudson andFranklin, 2002). Previous research has also indicated that aerobicmuscles should bemore susceptible tomuscle disuse atrophy thanglycolyticmuscles as there is a greater change in daily activity.Weinvestigated the effect of aestivation on ileofibularis (relativelyslow twitch) and sartorius (relatively fast twitch) musclemorphology and contractile function in C. alboguttata over a

longer, more ecologically relevant time-frame of ninemonths.Wefound that whole muscle mass, muscle cross-sectional area, fibrenumber and proportions of fibre types remained unchanged afterprolonged disuse. There were significant reductions in ileofibu-laris fibre cross-sectional area (>35%) and sartorius fibre density(44%) and significant slowing of isometric kinetics. However, thework loop power output of both muscles from nine-monthaestivating C. alboguttata were maintained at control levels. Theresults from this study strongly support the supposition that C.alboguttata is able to inhibit the effects of atrophy during disuse inboth sartorius and ileofibularis muscles.

Hudson, N.J. and Franklin, C.E., 2002. JEB 205, 2297–2303.

doi:10.1016/j.cbpa.2007.01.197

A6.24Kinematics and aerodynamics of tethered locust flight

S. Walker, G. Taylor, A. Thomas, (Oxford University, UnitedKingdom)

Most kinematics of insect wings during flight are restricted tolow spatial resolution are often limited to treating the wing asrigid flat plates. For many insects this is an oversimplification astheir wings are deformed due to mechanical and aerodynamiceffects. We filmed locusts (Schistocerca gregaria) duringtethered flight using high-speed digital cameras. Photogram-metry and feature tracking were used to give highly detailed 3Dtopologies of both the fore and hind wings surfaces. The processprovides quantitative measurements of the error and indicatesthat measurements are accurate to within 0.1 mm.These results allow us to look in detail at the changes in shape ofthe locust wings during flight. Initial analysis indicates thatlocusts attempt to maintain constant aerodynamic angle ofattack across the wing during the downstroke, and minimisenegative angle of attack during the upstroke.By combining these measurements with an accurate densitymap of the wing and forces recorded during tethered flight wecan calculate the inertial and aerodynamic forces acting on thewings. These can then be compared to different aerodynamicmodels and smoke visualisation to give further insights into thekinematics and aerodynamics of locust flight. It is also possibleto look at the bending along different parts of the wing toinvestigate the stiffness of different sections of the wings basedon the inertial forces calculated to be acting on the wing duringdifferent parts of the stroke.

doi:10.1016/j.cbpa.2007.01.198

A6.25The steering control of free flight maneuvers in Agrius

H. Wang, N. Ando, R. Kanzaki, (The University of Tokyo,Japan)