Fig. 5.

Force measured during stance across a range of walking and running speeds (from 1 to 4 m s⁻¹) increases linearly with mean amplitude of EMG (y = 0.58x + 0.42; R² = 0.84). The regression of stance-phase force and EMG has a positive intercept, suggesting that at low forces the relationship may become nonlinear. Both mean force and mean EMG amplitude are lower during swing than during stance. Measurements represent average values averaged over the period of interest. Force and EMG were both averaged over the period from the beginning of stance-phase EMG to the end of stance phase force. Values of both force and EMG were normalized to the values obtained at 2.5 m s⁻¹ for each bird.