Compliance is an important feature of human locomotion, where many studies have focused on the identification of stiffness parameters in order to build new machines, and stiffness is often assumed to be constant. However, it has been shown that during human walking, stiffness profiles are not constant in time and have high modulations in particular when changing walking phases. In order to understand how the constant stiffness assumption influences the walking gait and how much modulation is needed in walking mechanisms to reproduce natural gaits, in this work we focus on the analysis of joint and bi-articular stiffness profiles modulation and the influence of these modulations on the walking motions in different walking environments, i.e. level ground, slope and stairs. The analysis is carried out on periodic steps from motion capture data. mapped on a 14 segments human model with spring damper systems.