Muscle function during jumping in frogs. I. Sarcomere length change, EMG pattern, and jumping performance

Area of Science:

• Biomechanics
• Muscle Physiology
• Animal Locomotion

Background:

• Understanding how temperature affects muscle function is crucial for analyzing animal locomotion.
• Frogs utilize powerful muscle contractions for jumping, a key mode of locomotion.

Purpose of the Study:

• To investigate the impact of temperature on frog muscle function during jumping.
• To relate in vivo muscle performance to isolated muscle properties under varying temperatures.

Main Methods:

• Measured maximal jumping performance and semimembranosus (SM) muscle operating conditions in frogs at 25°C and 15°C.
• Related in vivo data to mechanical properties of isolated SM muscle (from accompanying study).
• Analyzed joint excursions, sarcomere shortening, angular velocities, and ground contact time.

Main Results:

• A decrease in temperature from 25°C to 15°C resulted in a 1.75-fold reduction in peak mechanical power and jump distance.
• Joint excursions and sarcomere shortening ranges remained consistent across temperatures.
• Muscle movements were slower at lower temperatures, with reduced angular velocities and increased ground contact time.
• The average shortening velocity of the SM muscle decreased only 1.2-fold at 15°C compared to 25°C.

Conclusions:

• Temperature significantly influences frog jumping performance primarily by altering the speed of muscle contraction.
• Optimal myofilament overlap is maintained, but slower muscle dynamics at lower temperatures limit power output.
• The observed low Q10 for velocity supports models of muscles acting against inertial loads.