The mechanical properties of proteins govern aspects of cell adhesion and muscle function. To elucidate this mechanical behavior, molecular simulations are carried out on the Immunoglobulin 27 domain of the muscle protein titin. Molecular dynamics simulations are carried out both using an implicit solvent model, and with the solvent explicitly modeled. The molecular dynamics simulations are interpreted in terms of the underlying energy landscape. Stretching a protein is shown to produce a dynamic energy landscape in which the energy minima move in configuration space and change in depth; these changes correspond to weakening or strengthening of the hydrogen bonds that control the protein structure. The dynamic energy landscape also involves the creation and destruction of energy minima, such that energy minima with different hydrogen bonding topologies are stable at different elongations. We show how these changes in the energy landscape give rise to the mechanical response and structural changes as the protein is stretched.