Fig. 2. Representative kinematic profiles for three modes of swimming performed by painted turtles, with still images from a high-speed video indicating the position of the limbs (humerus and femur) at specific times during the locomotor sequence. Circles, forelimbs; triangles, hindlimbs; open symbols, right side of the body; closed symbols, left side. A decrease in the angle with midline represents limb protraction and an increase in the angle represents limb retraction. Arrows in the first still image of each sequence indicate the direction of movement during the sequence. (A) Representative kinematic profile of a painted turtle during level rectilinear swimming. Note the synchronous movements of contralateral fore- and hindlimbs and the alternating movements of the ipsilateral fore- and hindlimbs. (B) Representative kinematic profile of a turtle during a forward turn. This 82° turn had an average linear velocity (U_avg) of 1.83 L s^-1, resulting in an R/L of 0.24. The turtle propels itself forward using alternating movements of the hindlimbs. The inboard forelimb (open circle) is held in a protracted position for the entire turn and acts as a pivot. The outboard forelimb (closed circle) moves approximately in phase with the contralateral hindlimb, as in rectilinear swimming. (C) Kinematic profile of a backward turn. This 113° turn had an average linear velocity (U_avg) of 0.86 L s^-1, resulting in an R/L of 0.0091. The turtle used synchronous protraction of the hindlimbs to begin moving backward (not plotted). While moving backward, the right forelimb was retracted while the left hindlimb was protracted. During this time the other set of contralateral limbs were held motionless, after which the outboard hindlimb retracted to accelerate the turn.