The Effect of Speed on Hindlimb Muscle Recruitment during Swimming in the Toad, Bufo marinus
Animals must vary their locomotor behavior to successfully maneuver in their environments, and one parameter that varies widely within the locomotor repertoire of many animals is speed. Changing speed depends on the anatomical and functional properties of muscles that are involved in force production during locomotion. Analysis of the recruitment intensity of such muscles gives insight into how an animal deals with the mechanical demands of increasing speed. In this study simultaneous data on limb movement and muscle activity were collected to address how the toad Bufo marinus changes speed. The muscles analyzed were major extensors and flexors of the knee and hip joints, and I predicted that changes in speed are brought about more by altering the recruitment intensity of hindlimb extensors than flexors. Results show a significant positive relationship between recruitment intensity and speed in both flexors and extensors. These results indicate that toads alter speed by pushing against the water with greater force and retracting their limbs at a greater speed, a pattern unlike what s used during terrestrial locomotion in most tetrapods, where only the propulsive phase appears functionally linked to changes in speed.