This paper focuses on the contributions of the gluteus maximus, biceps femoris, gastrocnemius and soleus in maintaining the stability of the stance limb in the sagittal plane during the mid-stance phase of gait. In the absence of any one of these muscles, the potential compensatory changes in muscle activation are explored, the aim being to restore stability to the stance limb. The investigation was carried out by integrating musculoskeletal modelling, forward simulation and optimization techniques. We concluded that maintenance of stance limb stability requires a subtle interplay of muscle activations. Weakness in a single muscle is unlikely to be adequately compensated for by increasing or decreasing the activation of one muscle alone.