The total dimensions of the parameter space is 11*18 = 198 for Stage I. For each generation, λ = 120 individuals are sampled from the elites and μ = 40 elites are selected out of the whole population. The values for the parameters for all neuron and muscle units are initialized as: I = 10 mV, Fmax = 1, β = 1.5, ρ = 2.0, ω = 3.0, Vmax = 5.0, cV = −7.0, bV = 0.67, aV = −1.668. The triggering timing of the neuron models are set as Ts = 0,Te = 0.5 for left front, right middle, left back legs, and Ts = 0.5, Te = 1.0 for right front, left middle, right back legs. The success of the optimization is confirmed with the decreasing value of the objective function (Fig. 5). The objective function converges quickly in the first 2000 generations and slowly afterwards.Figure 5Objective function value of best individual from each generation for optimization Stage I (a) and Stage II (b).