Fig. 4. Gait, lateral bending, force, velocity and energy of the COM over one stride (two steps) of a 2.3 g (0.023 N)Hemidactylus garnotii running on the level at 0.50 m s^-1. (A) Tracing of gecko running where a solid black foot represents a foot in contact with the substrate. Minimum lateral trunk bending occurred at midstep. (B) Footfall patterns indicated a trotting gait where a fore- and hindleg couplet hit the ground simultaneously followed by the opposite fore- and hindleg couplet. Solid areas in the bars represent toes down whereas striped bars show the time it takes to attach and detach feet. (C) Whole body GRFs of one stride from the force platform. Red lines, normal forces; blue lines, fore–aft forces. Normal forces fluctuate around body weight. A brief aerial phase was observed midstride. Fore–aft forces decelerate and accelerate the COM in each step similar to that of a forward-bouncing, spring-loaded, inverted pendulum. (D) Integration of fore–aft force yields fore–aft velocity of the COM. Velocity dropped to a minimum during midstep and was at a maximum during midstride. Despite the fluctuating velocity, the gecko maintained a constant average velocity of ±10%. (E) Fore–aft kinetic energy and gravitational potential energy of the COM fluctuated in phase. (F) Total energy of COM.